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Diffstat (limited to 'Documentation/DocBook')
24 files changed, 13728 insertions, 0 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile new file mode 100644 index 0000000..a221039 --- /dev/null +++ b/Documentation/DocBook/Makefile @@ -0,0 +1,195 @@ +### +# This makefile is used to generate the kernel documentation, +# primarily based on in-line comments in various source files. +# See Documentation/kernel-doc-nano-HOWTO.txt for instruction in how +# to ducument the SRC - and how to read it. +# To add a new book the only step required is to add the book to the +# list of DOCBOOKS. + +DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \ + kernel-hacking.xml kernel-locking.xml via-audio.xml \ + deviceiobook.xml procfs-guide.xml tulip-user.xml \ + writing_usb_driver.xml scsidrivers.xml sis900.xml \ + kernel-api.xml journal-api.xml lsm.xml usb.xml \ + gadget.xml libata.xml mtdnand.xml librs.xml + +### +# The build process is as follows (targets): +# (xmldocs) +# file.tmpl --> file.xml +--> file.ps (psdocs) +# +--> file.pdf (pdfdocs) +# +--> DIR=file (htmldocs) +# +--> man/ (mandocs) + +### +# The targets that may be used. +.PHONY: xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs + +BOOKS := $(addprefix $(obj)/,$(DOCBOOKS)) +xmldocs: $(BOOKS) +sgmldocs: xmldocs + +PS := $(patsubst %.xml, %.ps, $(BOOKS)) +psdocs: $(PS) + +PDF := $(patsubst %.xml, %.pdf, $(BOOKS)) +pdfdocs: $(PDF) + +HTML := $(patsubst %.xml, %.html, $(BOOKS)) +htmldocs: $(HTML) + +MAN := $(patsubst %.xml, %.9, $(BOOKS)) +mandocs: $(MAN) + +installmandocs: mandocs + $(MAKEMAN) install Documentation/DocBook/man + +### +#External programs used +KERNELDOC = scripts/kernel-doc +DOCPROC = scripts/basic/docproc +SPLITMAN = $(PERL) $(srctree)/scripts/split-man +MAKEMAN = $(PERL) $(srctree)/scripts/makeman + +### +# DOCPROC is used for two purposes: +# 1) To generate a dependency list for a .tmpl file +# 2) To preprocess a .tmpl file and call kernel-doc with +# appropriate parameters. +# The following rules are used to generate the .xml documentation +# required to generate the final targets. (ps, pdf, html). +quiet_cmd_docproc = DOCPROC $@ + cmd_docproc = SRCTREE=$(srctree)/ $(DOCPROC) doc $< >$@ +define rule_docproc + set -e; \ + $(if $($(quiet)cmd_$(1)),echo ' $($(quiet)cmd_$(1))';) \ + $(cmd_$(1)); \ + ( \ + echo 'cmd_$@ := $(cmd_$(1))'; \ + echo $@: `SRCTREE=$(srctree) $(DOCPROC) depend $<`; \ + ) > $(dir $@).$(notdir $@).cmd +endef + +%.xml: %.tmpl FORCE + $(call if_changed_rule,docproc) + +### +#Read in all saved dependency files +cmd_files := $(wildcard $(foreach f,$(BOOKS),$(dir $(f)).$(notdir $(f)).cmd)) + +ifneq ($(cmd_files),) + include $(cmd_files) +endif + +### +# Changes in kernel-doc force a rebuild of all documentation +$(BOOKS): $(KERNELDOC) + +### +# procfs guide uses a .c file as example code. +# This requires an explicit dependency +C-procfs-example = procfs_example.xml +C-procfs-example2 = $(addprefix $(obj)/,$(C-procfs-example)) +$(obj)/procfs-guide.xml: $(C-procfs-example2) + +### +# Rules to generate postscript, PDF and HTML +# db2html creates a directory. Generate a html file used for timestamp + +quiet_cmd_db2ps = DB2PS $@ + cmd_db2ps = db2ps -o $(dir $@) $< +%.ps : %.xml + @(which db2ps > /dev/null 2>&1) || \ + (echo "*** You need to install DocBook stylesheets ***"; \ + exit 1) + $(call cmd,db2ps) + +quiet_cmd_db2pdf = DB2PDF $@ + cmd_db2pdf = db2pdf -o $(dir $@) $< +%.pdf : %.xml + @(which db2pdf > /dev/null 2>&1) || \ + (echo "*** You need to install DocBook stylesheets ***"; \ + exit 1) + $(call cmd,db2pdf) + +quiet_cmd_db2html = DB2HTML $@ + cmd_db2html = db2html -o $(patsubst %.html,%,$@) $< && \ + echo '<a HREF="$(patsubst %.html,%,$(notdir $@))/book1.html"> \ + Goto $(patsubst %.html,%,$(notdir $@))</a><p>' > $@ + +%.html: %.xml + @(which db2html > /dev/null 2>&1) || \ + (echo "*** You need to install DocBook stylesheets ***"; \ + exit 1) + @rm -rf $@ $(patsubst %.html,%,$@) + $(call cmd,db2html) + @if [ ! -z "$(PNG-$(basename $(notdir $@)))" ]; then \ + cp $(PNG-$(basename $(notdir $@))) $(patsubst %.html,%,$@); fi + +### +# Rule to generate man files - output is placed in the man subdirectory + +%.9: %.xml +ifneq ($(KBUILD_SRC),) + $(Q)mkdir -p $(objtree)/Documentation/DocBook/man +endif + $(SPLITMAN) $< $(objtree)/Documentation/DocBook/man "$(VERSION).$(PATCHLEVEL).$(SUBLEVEL)" + $(MAKEMAN) convert $(objtree)/Documentation/DocBook/man $< + +### +# Rules to generate postscripts and PNG imgages from .fig format files +quiet_cmd_fig2eps = FIG2EPS $@ + cmd_fig2eps = fig2dev -Leps $< $@ + +%.eps: %.fig + @(which fig2dev > /dev/null 2>&1) || \ + (echo "*** You need to install transfig ***"; \ + exit 1) + $(call cmd,fig2eps) + +quiet_cmd_fig2png = FIG2PNG $@ + cmd_fig2png = fig2dev -Lpng $< $@ + +%.png: %.fig + @(which fig2dev > /dev/null 2>&1) || \ + (echo "*** You need to install transfig ***"; \ + exit 1) + $(call cmd,fig2png) + +### +# Rule to convert a .c file to inline XML documentation +%.xml: %.c + @echo ' GEN $@' + @( \ + echo "<programlisting>"; \ + expand --tabs=8 < $< | \ + sed -e "s/&/\\&/g" \ + -e "s/</\\</g" \ + -e "s/>/\\>/g"; \ + echo "</programlisting>") > $@ + +### +# Help targets as used by the top-level makefile +dochelp: + @echo ' Linux kernel internal documentation in different formats:' + @echo ' xmldocs (XML DocBook), psdocs (Postscript), pdfdocs (PDF)' + @echo ' htmldocs (HTML), mandocs (man pages, use installmandocs to install)' + +### +# Temporary files left by various tools +clean-files := $(DOCBOOKS) \ + $(patsubst %.xml, %.dvi, $(DOCBOOKS)) \ + $(patsubst %.xml, %.aux, $(DOCBOOKS)) \ + $(patsubst %.xml, %.tex, $(DOCBOOKS)) \ + $(patsubst %.xml, %.log, $(DOCBOOKS)) \ + $(patsubst %.xml, %.out, $(DOCBOOKS)) \ + $(patsubst %.xml, %.ps, $(DOCBOOKS)) \ + $(patsubst %.xml, %.pdf, $(DOCBOOKS)) \ + $(patsubst %.xml, %.html, $(DOCBOOKS)) \ + $(patsubst %.xml, %.9, $(DOCBOOKS)) \ + $(C-procfs-example) + +clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS)) + +#man put files in man subdir - traverse down +subdir- := man/ diff --git a/Documentation/DocBook/deviceiobook.tmpl b/Documentation/DocBook/deviceiobook.tmpl new file mode 100644 index 0000000..6f41f2f --- /dev/null +++ b/Documentation/DocBook/deviceiobook.tmpl @@ -0,0 +1,341 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="DoingIO"> + <bookinfo> + <title>Bus-Independent Device Accesses</title> + + <authorgroup> + <author> + <firstname>Matthew</firstname> + <surname>Wilcox</surname> + <affiliation> + <address> + <email>matthew@wil.cx</email> + </address> + </affiliation> + </author> + </authorgroup> + + <authorgroup> + <author> + <firstname>Alan</firstname> + <surname>Cox</surname> + <affiliation> + <address> + <email>alan@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2001</year> + <holder>Matthew Wilcox</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + Linux provides an API which abstracts performing IO across all busses + and devices, allowing device drivers to be written independently of + bus type. + </para> + </chapter> + + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + None. + </para> + </chapter> + + <chapter id="mmio"> + <title>Memory Mapped IO</title> + <sect1> + <title>Getting Access to the Device</title> + <para> + The most widely supported form of IO is memory mapped IO. + That is, a part of the CPU's address space is interpreted + not as accesses to memory, but as accesses to a device. Some + architectures define devices to be at a fixed address, but most + have some method of discovering devices. The PCI bus walk is a + good example of such a scheme. This document does not cover how + to receive such an address, but assumes you are starting with one. + Physical addresses are of type unsigned long. + </para> + + <para> + This address should not be used directly. Instead, to get an + address suitable for passing to the accessor functions described + below, you should call <function>ioremap</function>. + An address suitable for accessing the device will be returned to you. + </para> + + <para> + After you've finished using the device (say, in your module's + exit routine), call <function>iounmap</function> in order to return + the address space to the kernel. Most architectures allocate new + address space each time you call <function>ioremap</function>, and + they can run out unless you call <function>iounmap</function>. + </para> + </sect1> + + <sect1> + <title>Accessing the device</title> + <para> + The part of the interface most used by drivers is reading and + writing memory-mapped registers on the device. Linux provides + interfaces to read and write 8-bit, 16-bit, 32-bit and 64-bit + quantities. Due to a historical accident, these are named byte, + word, long and quad accesses. Both read and write accesses are + supported; there is no prefetch support at this time. + </para> + + <para> + The functions are named <function>readb</function>, + <function>readw</function>, <function>readl</function>, + <function>readq</function>, <function>readb_relaxed</function>, + <function>readw_relaxed</function>, <function>readl_relaxed</function>, + <function>readq_relaxed</function>, <function>writeb</function>, + <function>writew</function>, <function>writel</function> and + <function>writeq</function>. + </para> + + <para> + Some devices (such as framebuffers) would like to use larger + transfers than 8 bytes at a time. For these devices, the + <function>memcpy_toio</function>, <function>memcpy_fromio</function> + and <function>memset_io</function> functions are provided. + Do not use memset or memcpy on IO addresses; they + are not guaranteed to copy data in order. + </para> + + <para> + The read and write functions are defined to be ordered. That is the + compiler is not permitted to reorder the I/O sequence. When the + ordering can be compiler optimised, you can use <function> + __readb</function> and friends to indicate the relaxed ordering. Use + this with care. + </para> + + <para> + While the basic functions are defined to be synchronous with respect + to each other and ordered with respect to each other the busses the + devices sit on may themselves have asynchronicity. In particular many + authors are burned by the fact that PCI bus writes are posted + asynchronously. A driver author must issue a read from the same + device to ensure that writes have occurred in the specific cases the + author cares. This kind of property cannot be hidden from driver + writers in the API. In some cases, the read used to flush the device + may be expected to fail (if the card is resetting, for example). In + that case, the read should be done from config space, which is + guaranteed to soft-fail if the card doesn't respond. + </para> + + <para> + The following is an example of flushing a write to a device when + the driver would like to ensure the write's effects are visible prior + to continuing execution. + </para> + +<programlisting> +static inline void +qla1280_disable_intrs(struct scsi_qla_host *ha) +{ + struct device_reg *reg; + + reg = ha->iobase; + /* disable risc and host interrupts */ + WRT_REG_WORD(&reg->ictrl, 0); + /* + * The following read will ensure that the above write + * has been received by the device before we return from this + * function. + */ + RD_REG_WORD(&reg->ictrl); + ha->flags.ints_enabled = 0; +} +</programlisting> + + <para> + In addition to write posting, on some large multiprocessing systems + (e.g. SGI Challenge, Origin and Altix machines) posted writes won't + be strongly ordered coming from different CPUs. Thus it's important + to properly protect parts of your driver that do memory-mapped writes + with locks and use the <function>mmiowb</function> to make sure they + arrive in the order intended. Issuing a regular <function>readX + </function> will also ensure write ordering, but should only be used + when the driver has to be sure that the write has actually arrived + at the device (not that it's simply ordered with respect to other + writes), since a full <function>readX</function> is a relatively + expensive operation. + </para> + + <para> + Generally, one should use <function>mmiowb</function> prior to + releasing a spinlock that protects regions using <function>writeb + </function> or similar functions that aren't surrounded by <function> + readb</function> calls, which will ensure ordering and flushing. The + following pseudocode illustrates what might occur if write ordering + isn't guaranteed via <function>mmiowb</function> or one of the + <function>readX</function> functions. + </para> + +<programlisting> +CPU A: spin_lock_irqsave(&dev_lock, flags) +CPU A: ... +CPU A: writel(newval, ring_ptr); +CPU A: spin_unlock_irqrestore(&dev_lock, flags) + ... +CPU B: spin_lock_irqsave(&dev_lock, flags) +CPU B: writel(newval2, ring_ptr); +CPU B: ... +CPU B: spin_unlock_irqrestore(&dev_lock, flags) +</programlisting> + + <para> + In the case above, newval2 could be written to ring_ptr before + newval. Fixing it is easy though: + </para> + +<programlisting> +CPU A: spin_lock_irqsave(&dev_lock, flags) +CPU A: ... +CPU A: writel(newval, ring_ptr); +CPU A: mmiowb(); /* ensure no other writes beat us to the device */ +CPU A: spin_unlock_irqrestore(&dev_lock, flags) + ... +CPU B: spin_lock_irqsave(&dev_lock, flags) +CPU B: writel(newval2, ring_ptr); +CPU B: ... +CPU B: mmiowb(); +CPU B: spin_unlock_irqrestore(&dev_lock, flags) +</programlisting> + + <para> + See tg3.c for a real world example of how to use <function>mmiowb + </function> + </para> + + <para> + PCI ordering rules also guarantee that PIO read responses arrive + after any outstanding DMA writes from that bus, since for some devices + the result of a <function>readb</function> call may signal to the + driver that a DMA transaction is complete. In many cases, however, + the driver may want to indicate that the next + <function>readb</function> call has no relation to any previous DMA + writes performed by the device. The driver can use + <function>readb_relaxed</function> for these cases, although only + some platforms will honor the relaxed semantics. Using the relaxed + read functions will provide significant performance benefits on + platforms that support it. The qla2xxx driver provides examples + of how to use <function>readX_relaxed</function>. In many cases, + a majority of the driver's <function>readX</function> calls can + safely be converted to <function>readX_relaxed</function> calls, since + only a few will indicate or depend on DMA completion. + </para> + </sect1> + + <sect1> + <title>ISA legacy functions</title> + <para> + On older kernels (2.2 and earlier) the ISA bus could be read or + written with these functions and without ioremap being used. This is + no longer true in Linux 2.4. A set of equivalent functions exist for + easy legacy driver porting. The functions available are prefixed + with 'isa_' and are <function>isa_readb</function>, + <function>isa_writeb</function>, <function>isa_readw</function>, + <function>isa_writew</function>, <function>isa_readl</function>, + <function>isa_writel</function>, <function>isa_memcpy_fromio</function> + and <function>isa_memcpy_toio</function> + </para> + <para> + These functions should not be used in new drivers, and will + eventually be going away. + </para> + </sect1> + + </chapter> + + <chapter> + <title>Port Space Accesses</title> + <sect1> + <title>Port Space Explained</title> + + <para> + Another form of IO commonly supported is Port Space. This is a + range of addresses separate to the normal memory address space. + Access to these addresses is generally not as fast as accesses + to the memory mapped addresses, and it also has a potentially + smaller address space. + </para> + + <para> + Unlike memory mapped IO, no preparation is required + to access port space. + </para> + + </sect1> + <sect1> + <title>Accessing Port Space</title> + <para> + Accesses to this space are provided through a set of functions + which allow 8-bit, 16-bit and 32-bit accesses; also + known as byte, word and long. These functions are + <function>inb</function>, <function>inw</function>, + <function>inl</function>, <function>outb</function>, + <function>outw</function> and <function>outl</function>. + </para> + + <para> + Some variants are provided for these functions. Some devices + require that accesses to their ports are slowed down. This + functionality is provided by appending a <function>_p</function> + to the end of the function. There are also equivalents to memcpy. + The <function>ins</function> and <function>outs</function> + functions copy bytes, words or longs to the given port. + </para> + </sect1> + + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> +!Einclude/asm-i386/io.h + </chapter> + +</book> diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl new file mode 100644 index 0000000..a344424 --- /dev/null +++ b/Documentation/DocBook/gadget.tmpl @@ -0,0 +1,752 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="USB-Gadget-API"> + <bookinfo> + <title>USB Gadget API for Linux</title> + <date>20 August 2004</date> + <edition>20 August 2004</edition> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + <copyright> + <year>2003-2004</year> + <holder>David Brownell</holder> + </copyright> + + <author> + <firstname>David</firstname> + <surname>Brownell</surname> + <affiliation> + <address><email>dbrownell@users.sourceforge.net</email></address> + </affiliation> + </author> + </bookinfo> + +<toc></toc> + +<chapter><title>Introduction</title> + +<para>This document presents a Linux-USB "Gadget" +kernel mode +API, for use within peripherals and other USB devices +that embed Linux. +It provides an overview of the API structure, +and shows how that fits into a system development project. +This is the first such API released on Linux to address +a number of important problems, including: </para> + +<itemizedlist> + <listitem><para>Supports USB 2.0, for high speed devices which + can stream data at several dozen megabytes per second. + </para></listitem> + <listitem><para>Handles devices with dozens of endpoints just as + well as ones with just two fixed-function ones. Gadget drivers + can be written so they're easy to port to new hardware. + </para></listitem> + <listitem><para>Flexible enough to expose more complex USB device + capabilities such as multiple configurations, multiple interfaces, + composite devices, + and alternate interface settings. + </para></listitem> + <listitem><para>USB "On-The-Go" (OTG) support, in conjunction + with updates to the Linux-USB host side. + </para></listitem> + <listitem><para>Sharing data structures and API models with the + Linux-USB host side API. This helps the OTG support, and + looks forward to more-symmetric frameworks (where the same + I/O model is used by both host and device side drivers). + </para></listitem> + <listitem><para>Minimalist, so it's easier to support new device + controller hardware. I/O processing doesn't imply large + demands for memory or CPU resources. + </para></listitem> +</itemizedlist> + + +<para>Most Linux developers will not be able to use this API, since they +have USB "host" hardware in a PC, workstation, or server. +Linux users with embedded systems are more likely to +have USB peripheral hardware. +To distinguish drivers running inside such hardware from the +more familiar Linux "USB device drivers", +which are host side proxies for the real USB devices, +a different term is used: +the drivers inside the peripherals are "USB gadget drivers". +In USB protocol interactions, the device driver is the master +(or "client driver") +and the gadget driver is the slave (or "function driver"). +</para> + +<para>The gadget API resembles the host side Linux-USB API in that both +use queues of request objects to package I/O buffers, and those requests +may be submitted or canceled. +They share common definitions for the standard USB +<emphasis>Chapter 9</emphasis> messages, structures, and constants. +Also, both APIs bind and unbind drivers to devices. +The APIs differ in detail, since the host side's current +URB framework exposes a number of implementation details +and assumptions that are inappropriate for a gadget API. +While the model for control transfers and configuration +management is necessarily different (one side is a hardware-neutral master, +the other is a hardware-aware slave), the endpoint I/0 API used here +should also be usable for an overhead-reduced host side API. +</para> + +</chapter> + +<chapter id="structure"><title>Structure of Gadget Drivers</title> + +<para>A system running inside a USB peripheral +normally has at least three layers inside the kernel to handle +USB protocol processing, and may have additional layers in +user space code. +The "gadget" API is used by the middle layer to interact +with the lowest level (which directly handles hardware). +</para> + +<para>In Linux, from the bottom up, these layers are: +</para> + +<variablelist> + + <varlistentry> + <term><emphasis>USB Controller Driver</emphasis></term> + + <listitem> + <para>This is the lowest software level. + It is the only layer that talks to hardware, + through registers, fifos, dma, irqs, and the like. + The <filename><linux/usb_gadget.h></filename> API abstracts + the peripheral controller endpoint hardware. + That hardware is exposed through endpoint objects, which accept + streams of IN/OUT buffers, and through callbacks that interact + with gadget drivers. + Since normal USB devices only have one upstream + port, they only have one of these drivers. + The controller driver can support any number of different + gadget drivers, but only one of them can be used at a time. + </para> + + <para>Examples of such controller hardware include + the PCI-based NetChip 2280 USB 2.0 high speed controller, + the SA-11x0 or PXA-25x UDC (found within many PDAs), + and a variety of other products. + </para> + + </listitem></varlistentry> + + <varlistentry> + <term><emphasis>Gadget Driver</emphasis></term> + + <listitem> + <para>The lower boundary of this driver implements hardware-neutral + USB functions, using calls to the controller driver. + Because such hardware varies widely in capabilities and restrictions, + and is used in embedded environments where space is at a premium, + the gadget driver is often configured at compile time + to work with endpoints supported by one particular controller. + Gadget drivers may be portable to several different controllers, + using conditional compilation. + (Recent kernels substantially simplify the work involved in + supporting new hardware, by <emphasis>autoconfiguring</emphasis> + endpoints automatically for many bulk-oriented drivers.) + Gadget driver responsibilities include: + </para> + <itemizedlist> + <listitem><para>handling setup requests (ep0 protocol responses) + possibly including class-specific functionality + </para></listitem> + <listitem><para>returning configuration and string descriptors + </para></listitem> + <listitem><para>(re)setting configurations and interface + altsettings, including enabling and configuring endpoints + </para></listitem> + <listitem><para>handling life cycle events, such as managing + bindings to hardware, + USB suspend/resume, remote wakeup, + and disconnection from the USB host. + </para></listitem> + <listitem><para>managing IN and OUT transfers on all currently + enabled endpoints + </para></listitem> + </itemizedlist> + + <para> + Such drivers may be modules of proprietary code, although + that approach is discouraged in the Linux community. + </para> + </listitem></varlistentry> + + <varlistentry> + <term><emphasis>Upper Level</emphasis></term> + + <listitem> + <para>Most gadget drivers have an upper boundary that connects + to some Linux driver or framework in Linux. + Through that boundary flows the data which the gadget driver + produces and/or consumes through protocol transfers over USB. + Examples include: + </para> + <itemizedlist> + <listitem><para>user mode code, using generic (gadgetfs) + or application specific files in + <filename>/dev</filename> + </para></listitem> + <listitem><para>networking subsystem (for network gadgets, + like the CDC Ethernet Model gadget driver) + </para></listitem> + <listitem><para>data capture drivers, perhaps video4Linux or + a scanner driver; or test and measurement hardware. + </para></listitem> + <listitem><para>input subsystem (for HID gadgets) + </para></listitem> + <listitem><para>sound subsystem (for audio gadgets) + </para></listitem> + <listitem><para>file system (for PTP gadgets) + </para></listitem> + <listitem><para>block i/o subsystem (for usb-storage gadgets) + </para></listitem> + <listitem><para>... and more </para></listitem> + </itemizedlist> + </listitem></varlistentry> + + <varlistentry> + <term><emphasis>Additional Layers</emphasis></term> + + <listitem> + <para>Other layers may exist. + These could include kernel layers, such as network protocol stacks, + as well as user mode applications building on standard POSIX + system call APIs such as + <emphasis>open()</emphasis>, <emphasis>close()</emphasis>, + <emphasis>read()</emphasis> and <emphasis>write()</emphasis>. + On newer systems, POSIX Async I/O calls may be an option. + Such user mode code will not necessarily be subject to + the GNU General Public License (GPL). + </para> + </listitem></varlistentry> + + +</variablelist> + +<para>OTG-capable systems will also need to include a standard Linux-USB +host side stack, +with <emphasis>usbcore</emphasis>, +one or more <emphasis>Host Controller Drivers</emphasis> (HCDs), +<emphasis>USB Device Drivers</emphasis> to support +the OTG "Targeted Peripheral List", +and so forth. +There will also be an <emphasis>OTG Controller Driver</emphasis>, +which is visible to gadget and device driver developers only indirectly. +That helps the host and device side USB controllers implement the +two new OTG protocols (HNP and SRP). +Roles switch (host to peripheral, or vice versa) using HNP +during USB suspend processing, and SRP can be viewed as a +more battery-friendly kind of device wakeup protocol. +</para> + +<para>Over time, reusable utilities are evolving to help make some +gadget driver tasks simpler. +For example, building configuration descriptors from vectors of +descriptors for the configurations interfaces and endpoints is +now automated, and many drivers now use autoconfiguration to +choose hardware endpoints and initialize their descriptors. + +A potential example of particular interest +is code implementing standard USB-IF protocols for +HID, networking, storage, or audio classes. +Some developers are interested in KDB or KGDB hooks, to let +target hardware be remotely debugged. +Most such USB protocol code doesn't need to be hardware-specific, +any more than network protocols like X11, HTTP, or NFS are. +Such gadget-side interface drivers should eventually be combined, +to implement composite devices. +</para> + +</chapter> + + +<chapter id="api"><title>Kernel Mode Gadget API</title> + +<para>Gadget drivers declare themselves through a +<emphasis>struct usb_gadget_driver</emphasis>, which is responsible for +most parts of enumeration for a <emphasis>struct usb_gadget</emphasis>. +The response to a set_configuration usually involves +enabling one or more of the <emphasis>struct usb_ep</emphasis> objects +exposed by the gadget, and submitting one or more +<emphasis>struct usb_request</emphasis> buffers to transfer data. +Understand those four data types, and their operations, and +you will understand how this API works. +</para> + +<note><title>Incomplete Data Type Descriptions</title> + +<para>This documentation was prepared using the standard Linux +kernel <filename>docproc</filename> tool, which turns text +and in-code comments into SGML DocBook and then into usable +formats such as HTML or PDF. +Other than the "Chapter 9" data types, most of the significant +data types and functions are described here. +</para> + +<para>However, docproc does not understand all the C constructs +that are used, so some relevant information is likely omitted from +what you are reading. +One example of such information is endpoint autoconfiguration. +You'll have to read the header file, and use example source +code (such as that for "Gadget Zero"), to fully understand the API. +</para> + +<para>The part of the API implementing some basic +driver capabilities is specific to the version of the +Linux kernel that's in use. +The 2.6 kernel includes a <emphasis>driver model</emphasis> +framework that has no analogue on earlier kernels; +so those parts of the gadget API are not fully portable. +(They are implemented on 2.4 kernels, but in a different way.) +The driver model state is another part of this API that is +ignored by the kerneldoc tools. +</para> +</note> + +<para>The core API does not expose +every possible hardware feature, only the most widely available ones. +There are significant hardware features, such as device-to-device DMA +(without temporary storage in a memory buffer) +that would be added using hardware-specific APIs. +</para> + +<para>This API allows drivers to use conditional compilation to handle +endpoint capabilities of different hardware, but doesn't require that. +Hardware tends to have arbitrary restrictions, relating to +transfer types, addressing, packet sizes, buffering, and availability. +As a rule, such differences only matter for "endpoint zero" logic +that handles device configuration and management. +The API supports limited run-time +detection of capabilities, through naming conventions for endpoints. +Many drivers will be able to at least partially autoconfigure +themselves. +In particular, driver init sections will often have endpoint +autoconfiguration logic that scans the hardware's list of endpoints +to find ones matching the driver requirements +(relying on those conventions), to eliminate some of the most +common reasons for conditional compilation. +</para> + +<para>Like the Linux-USB host side API, this API exposes +the "chunky" nature of USB messages: I/O requests are in terms +of one or more "packets", and packet boundaries are visible to drivers. +Compared to RS-232 serial protocols, USB resembles +synchronous protocols like HDLC +(N bytes per frame, multipoint addressing, host as the primary +station and devices as secondary stations) +more than asynchronous ones +(tty style: 8 data bits per frame, no parity, one stop bit). +So for example the controller drivers won't buffer +two single byte writes into a single two-byte USB IN packet, +although gadget drivers may do so when they implement +protocols where packet boundaries (and "short packets") +are not significant. +</para> + +<sect1 id="lifecycle"><title>Driver Life Cycle</title> + +<para>Gadget drivers make endpoint I/O requests to hardware without +needing to know many details of the hardware, but driver +setup/configuration code needs to handle some differences. +Use the API like this: +</para> + +<orderedlist numeration='arabic'> + +<listitem><para>Register a driver for the particular device side +usb controller hardware, +such as the net2280 on PCI (USB 2.0), +sa11x0 or pxa25x as found in Linux PDAs, +and so on. +At this point the device is logically in the USB ch9 initial state +("attached"), drawing no power and not usable +(since it does not yet support enumeration). +Any host should not see the device, since it's not +activated the data line pullup used by the host to +detect a device, even if VBUS power is available. +</para></listitem> + +<listitem><para>Register a gadget driver that implements some higher level +device function. That will then bind() to a usb_gadget, which +activates the data line pullup sometime after detecting VBUS. +</para></listitem> + +<listitem><para>The hardware driver can now start enumerating. +The steps it handles are to accept USB power and set_address requests. +Other steps are handled by the gadget driver. +If the gadget driver module is unloaded before the host starts to +enumerate, steps before step 7 are skipped. +</para></listitem> + +<listitem><para>The gadget driver's setup() call returns usb descriptors, +based both on what the bus interface hardware provides and on the +functionality being implemented. +That can involve alternate settings or configurations, +unless the hardware prevents such operation. +For OTG devices, each configuration descriptor includes +an OTG descriptor. +</para></listitem> + +<listitem><para>The gadget driver handles the last step of enumeration, +when the USB host issues a set_configuration call. +It enables all endpoints used in that configuration, +with all interfaces in their default settings. +That involves using a list of the hardware's endpoints, enabling each +endpoint according to its descriptor. +It may also involve using <function>usb_gadget_vbus_draw</function> +to let more power be drawn from VBUS, as allowed by that configuration. +For OTG devices, setting a configuration may also involve reporting +HNP capabilities through a user interface. +</para></listitem> + +<listitem><para>Do real work and perform data transfers, possibly involving +changes to interface settings or switching to new configurations, until the +device is disconnect()ed from the host. +Queue any number of transfer requests to each endpoint. +It may be suspended and resumed several times before being disconnected. +On disconnect, the drivers go back to step 3 (above). +</para></listitem> + +<listitem><para>When the gadget driver module is being unloaded, +the driver unbind() callback is issued. That lets the controller +driver be unloaded. +</para></listitem> + +</orderedlist> + +<para>Drivers will normally be arranged so that just loading the +gadget driver module (or statically linking it into a Linux kernel) +allows the peripheral device to be enumerated, but some drivers +will defer enumeration until some higher level component (like +a user mode daemon) enables it. +Note that at this lowest level there are no policies about how +ep0 configuration logic is implemented, +except that it should obey USB specifications. +Such issues are in the domain of gadget drivers, +including knowing about implementation constraints +imposed by some USB controllers +or understanding that composite devices might happen to +be built by integrating reusable components. +</para> + +<para>Note that the lifecycle above can be slightly different +for OTG devices. +Other than providing an additional OTG descriptor in each +configuration, only the HNP-related differences are particularly +visible to driver code. +They involve reporting requirements during the SET_CONFIGURATION +request, and the option to invoke HNP during some suspend callbacks. +Also, SRP changes the semantics of +<function>usb_gadget_wakeup</function> +slightly. +</para> + +</sect1> + +<sect1 id="ch9"><title>USB 2.0 Chapter 9 Types and Constants</title> + +<para>Gadget drivers +rely on common USB structures and constants +defined in the +<filename><linux/usb_ch9.h></filename> +header file, which is standard in Linux 2.6 kernels. +These are the same types and constants used by host +side drivers (and usbcore). +</para> + +!Iinclude/linux/usb_ch9.h +</sect1> + +<sect1 id="core"><title>Core Objects and Methods</title> + +<para>These are declared in +<filename><linux/usb_gadget.h></filename>, +and are used by gadget drivers to interact with +USB peripheral controller drivers. +</para> + + <!-- yeech, this is ugly in nsgmls PDF output. + + the PDF bookmark and refentry output nesting is wrong, + and the member/argument documentation indents ugly. + + plus something (docproc?) adds whitespace before the + descriptive paragraph text, so it can't line up right + unless the explanations are trivial. + --> + +!Iinclude/linux/usb_gadget.h +</sect1> + +<sect1 id="utils"><title>Optional Utilities</title> + +<para>The core API is sufficient for writing a USB Gadget Driver, +but some optional utilities are provided to simplify common tasks. +These utilities include endpoint autoconfiguration. +</para> + +!Edrivers/usb/gadget/usbstring.c +!Edrivers/usb/gadget/config.c +<!-- !Edrivers/usb/gadget/epautoconf.c --> +</sect1> + +</chapter> + +<chapter id="controllers"><title>Peripheral Controller Drivers</title> + +<para>The first hardware supporting this API was the NetChip 2280 +controller, which supports USB 2.0 high speed and is based on PCI. +This is the <filename>net2280</filename> driver module. +The driver supports Linux kernel versions 2.4 and 2.6; +contact NetChip Technologies for development boards and product +information. +</para> + +<para>Other hardware working in the "gadget" framework includes: +Intel's PXA 25x and IXP42x series processors +(<filename>pxa2xx_udc</filename>), +Toshiba TC86c001 "Goku-S" (<filename>goku_udc</filename>), +Renesas SH7705/7727 (<filename>sh_udc</filename>), +MediaQ 11xx (<filename>mq11xx_udc</filename>), +Hynix HMS30C7202 (<filename>h7202_udc</filename>), +National 9303/4 (<filename>n9604_udc</filename>), +Texas Instruments OMAP (<filename>omap_udc</filename>), +Sharp LH7A40x (<filename>lh7a40x_udc</filename>), +and more. +Most of those are full speed controllers. +</para> + +<para>At this writing, there are people at work on drivers in +this framework for several other USB device controllers, +with plans to make many of them be widely available. +</para> + +<!-- !Edrivers/usb/gadget/net2280.c --> + +<para>A partial USB simulator, +the <filename>dummy_hcd</filename> driver, is available. +It can act like a net2280, a pxa25x, or an sa11x0 in terms +of available endpoints and device speeds; and it simulates +control, bulk, and to some extent interrupt transfers. +That lets you develop some parts of a gadget driver on a normal PC, +without any special hardware, and perhaps with the assistance +of tools such as GDB running with User Mode Linux. +At least one person has expressed interest in adapting that +approach, hooking it up to a simulator for a microcontroller. +Such simulators can help debug subsystems where the runtime hardware +is unfriendly to software development, or is not yet available. +</para> + +<para>Support for other controllers is expected to be developed +and contributed +over time, as this driver framework evolves. +</para> + +</chapter> + +<chapter id="gadget"><title>Gadget Drivers</title> + +<para>In addition to <emphasis>Gadget Zero</emphasis> +(used primarily for testing and development with drivers +for usb controller hardware), other gadget drivers exist. +</para> + +<para>There's an <emphasis>ethernet</emphasis> gadget +driver, which implements one of the most useful +<emphasis>Communications Device Class</emphasis> (CDC) models. +One of the standards for cable modem interoperability even +specifies the use of this ethernet model as one of two +mandatory options. +Gadgets using this code look to a USB host as if they're +an Ethernet adapter. +It provides access to a network where the gadget's CPU is one host, +which could easily be bridging, routing, or firewalling +access to other networks. +Since some hardware can't fully implement the CDC Ethernet +requirements, this driver also implements a "good parts only" +subset of CDC Ethernet. +(That subset doesn't advertise itself as CDC Ethernet, +to avoid creating problems.) +</para> + +<para>Support for Microsoft's <emphasis>RNDIS</emphasis> +protocol has been contributed by Pengutronix and Auerswald GmbH. +This is like CDC Ethernet, but it runs on more slightly USB hardware +(but less than the CDC subset). +However, its main claim to fame is being able to connect directly to +recent versions of Windows, using drivers that Microsoft bundles +and supports, making it much simpler to network with Windows. +</para> + +<para>There is also support for user mode gadget drivers, +using <emphasis>gadgetfs</emphasis>. +This provides a <emphasis>User Mode API</emphasis> that presents +each endpoint as a single file descriptor. I/O is done using +normal <emphasis>read()</emphasis> and <emphasis>read()</emphasis> calls. +Familiar tools like GDB and pthreads can be used to +develop and debug user mode drivers, so that once a robust +controller driver is available many applications for it +won't require new kernel mode software. +Linux 2.6 <emphasis>Async I/O (AIO)</emphasis> +support is available, so that user mode software +can stream data with only slightly more overhead +than a kernel driver. +</para> + +<para>There's a USB Mass Storage class driver, which provides +a different solution for interoperability with systems such +as MS-Windows and MacOS. +That <emphasis>File-backed Storage</emphasis> driver uses a +file or block device as backing store for a drive, +like the <filename>loop</filename> driver. +The USB host uses the BBB, CB, or CBI versions of the mass +storage class specification, using transparent SCSI commands +to access the data from the backing store. +</para> + +<para>There's a "serial line" driver, useful for TTY style +operation over USB. +The latest version of that driver supports CDC ACM style +operation, like a USB modem, and so on most hardware it can +interoperate easily with MS-Windows. +One interesting use of that driver is in boot firmware (like a BIOS), +which can sometimes use that model with very small systems without +real serial lines. +</para> + +<para>Support for other kinds of gadget is expected to +be developed and contributed +over time, as this driver framework evolves. +</para> + +</chapter> + +<chapter id="otg"><title>USB On-The-GO (OTG)</title> + +<para>USB OTG support on Linux 2.6 was initially developed +by Texas Instruments for +<ulink url="http://www.omap.com">OMAP</ulink> 16xx and 17xx +series processors. +Other OTG systems should work in similar ways, but the +hardware level details could be very different. +</para> + +<para>Systems need specialized hardware support to implement OTG, +notably including a special <emphasis>Mini-AB</emphasis> jack +and associated transciever to support <emphasis>Dual-Role</emphasis> +operation: +they can act either as a host, using the standard +Linux-USB host side driver stack, +or as a peripheral, using this "gadget" framework. +To do that, the system software relies on small additions +to those programming interfaces, +and on a new internal component (here called an "OTG Controller") +affecting which driver stack connects to the OTG port. +In each role, the system can re-use the existing pool of +hardware-neutral drivers, layered on top of the controller +driver interfaces (<emphasis>usb_bus</emphasis> or +<emphasis>usb_gadget</emphasis>). +Such drivers need at most minor changes, and most of the calls +added to support OTG can also benefit non-OTG products. +</para> + +<itemizedlist> + <listitem><para>Gadget drivers test the <emphasis>is_otg</emphasis> + flag, and use it to determine whether or not to include + an OTG descriptor in each of their configurations. + </para></listitem> + <listitem><para>Gadget drivers may need changes to support the + two new OTG protocols, exposed in new gadget attributes + such as <emphasis>b_hnp_enable</emphasis> flag. + HNP support should be reported through a user interface + (two LEDs could suffice), and is triggered in some cases + when the host suspends the peripheral. + SRP support can be user-initiated just like remote wakeup, + probably by pressing the same button. + </para></listitem> + <listitem><para>On the host side, USB device drivers need + to be taught to trigger HNP at appropriate moments, using + <function>usb_suspend_device()</function>. + That also conserves battery power, which is useful even + for non-OTG configurations. + </para></listitem> + <listitem><para>Also on the host side, a driver must support the + OTG "Targeted Peripheral List". That's just a whitelist, + used to reject peripherals not supported with a given + Linux OTG host. + <emphasis>This whitelist is product-specific; + each product must modify <filename>otg_whitelist.h</filename> + to match its interoperability specification. + </emphasis> + </para> + <para>Non-OTG Linux hosts, like PCs and workstations, + normally have some solution for adding drivers, so that + peripherals that aren't recognized can eventually be supported. + That approach is unreasonable for consumer products that may + never have their firmware upgraded, and where it's usually + unrealistic to expect traditional PC/workstation/server kinds + of support model to work. + For example, it's often impractical to change device firmware + once the product has been distributed, so driver bugs can't + normally be fixed if they're found after shipment. + </para></listitem> +</itemizedlist> + +<para> +Additional changes are needed below those hardware-neutral +<emphasis>usb_bus</emphasis> and <emphasis>usb_gadget</emphasis> +driver interfaces; those aren't discussed here in any detail. +Those affect the hardware-specific code for each USB Host or Peripheral +controller, and how the HCD initializes (since OTG can be active only +on a single port). +They also involve what may be called an <emphasis>OTG Controller +Driver</emphasis>, managing the OTG transceiver and the OTG state +machine logic as well as much of the root hub behavior for the +OTG port. +The OTG controller driver needs to activate and deactivate USB +controllers depending on the relevant device role. +Some related changes were needed inside usbcore, so that it +can identify OTG-capable devices and respond appropriately +to HNP or SRP protocols. +</para> + +</chapter> + +</book> +<!-- + vim:syntax=sgml:sw=4 +--> diff --git a/Documentation/DocBook/journal-api.tmpl b/Documentation/DocBook/journal-api.tmpl new file mode 100644 index 0000000..1ef6f43 --- /dev/null +++ b/Documentation/DocBook/journal-api.tmpl @@ -0,0 +1,333 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="LinuxJBDAPI"> + <bookinfo> + <title>The Linux Journalling API</title> + <authorgroup> + <author> + <firstname>Roger</firstname> + <surname>Gammans</surname> + <affiliation> + <address> + <email>rgammans@computer-surgery.co.uk</email> + </address> + </affiliation> + </author> + </authorgroup> + + <authorgroup> + <author> + <firstname>Stephen</firstname> + <surname>Tweedie</surname> + <affiliation> + <address> + <email>sct@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2002</year> + <holder>Roger Gammans</holder> + </copyright> + +<legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="Overview"> + <title>Overview</title> + <sect1> + <title>Details</title> +<para> +The journalling layer is easy to use. You need to +first of all create a journal_t data structure. There are +two calls to do this dependent on how you decide to allocate the physical +media on which the journal resides. The journal_init_inode() call +is for journals stored in filesystem inodes, or the journal_init_dev() +call can be use for journal stored on a raw device (in a continuous range +of blocks). A journal_t is a typedef for a struct pointer, so when +you are finally finished make sure you call journal_destroy() on it +to free up any used kernel memory. +</para> + +<para> +Once you have got your journal_t object you need to 'mount' or load the journal +file, unless of course you haven't initialised it yet - in which case you +need to call journal_create(). +</para> + +<para> +Most of the time however your journal file will already have been created, but +before you load it you must call journal_wipe() to empty the journal file. +Hang on, you say , what if the filesystem wasn't cleanly umount()'d . Well, it is the +job of the client file system to detect this and skip the call to journal_wipe(). +</para> + +<para> +In either case the next call should be to journal_load() which prepares the +journal file for use. Note that journal_wipe(..,0) calls journal_skip_recovery() +for you if it detects any outstanding transactions in the journal and similarly +journal_load() will call journal_recover() if necessary. +I would advise reading fs/ext3/super.c for examples on this stage. +[RGG: Why is the journal_wipe() call necessary - doesn't this needlessly +complicate the API. Or isn't a good idea for the journal layer to hide +dirty mounts from the client fs] +</para> + +<para> +Now you can go ahead and start modifying the underlying +filesystem. Almost. +</para> + + +<para> + +You still need to actually journal your filesystem changes, this +is done by wrapping them into transactions. Additionally you +also need to wrap the modification of each of the the buffers +with calls to the journal layer, so it knows what the modifications +you are actually making are. To do this use journal_start() which +returns a transaction handle. +</para> + +<para> +journal_start() +and its counterpart journal_stop(), which indicates the end of a transaction +are nestable calls, so you can reenter a transaction if necessary, +but remember you must call journal_stop() the same number of times as +journal_start() before the transaction is completed (or more accurately +leaves the the update phase). Ext3/VFS makes use of this feature to simplify +quota support. +</para> + +<para> +Inside each transaction you need to wrap the modifications to the +individual buffers (blocks). Before you start to modify a buffer you +need to call journal_get_{create,write,undo}_access() as appropriate, +this allows the journalling layer to copy the unmodified data if it +needs to. After all the buffer may be part of a previously uncommitted +transaction. +At this point you are at last ready to modify a buffer, and once +you are have done so you need to call journal_dirty_{meta,}data(). +Or if you've asked for access to a buffer you now know is now longer +required to be pushed back on the device you can call journal_forget() +in much the same way as you might have used bforget() in the past. +</para> + +<para> +A journal_flush() may be called at any time to commit and checkpoint +all your transactions. +</para> + +<para> +Then at umount time , in your put_super() (2.4) or write_super() (2.5) +you can then call journal_destroy() to clean up your in-core journal object. +</para> + + +<para> +Unfortunately there a couple of ways the journal layer can cause a deadlock. +The first thing to note is that each task can only have +a single outstanding transaction at any one time, remember nothing +commits until the outermost journal_stop(). This means +you must complete the transaction at the end of each file/inode/address +etc. operation you perform, so that the journalling system isn't re-entered +on another journal. Since transactions can't be nested/batched +across differing journals, and another filesystem other than +yours (say ext3) may be modified in a later syscall. +</para> + +<para> +The second case to bear in mind is that journal_start() can +block if there isn't enough space in the journal for your transaction +(based on the passed nblocks param) - when it blocks it merely(!) needs to +wait for transactions to complete and be committed from other tasks, +so essentially we are waiting for journal_stop(). So to avoid +deadlocks you must treat journal_start/stop() as if they +were semaphores and include them in your semaphore ordering rules to prevent +deadlocks. Note that journal_extend() has similar blocking behaviour to +journal_start() so you can deadlock here just as easily as on journal_start(). +</para> + +<para> +Try to reserve the right number of blocks the first time. ;-). This will +be the maximum number of blocks you are going to touch in this transaction. +I advise having a look at at least ext3_jbd.h to see the basis on which +ext3 uses to make these decisions. +</para> + +<para> +Another wriggle to watch out for is your on-disk block allocation strategy. +why? Because, if you undo a delete, you need to ensure you haven't reused any +of the freed blocks in a later transaction. One simple way of doing this +is make sure any blocks you allocate only have checkpointed transactions +listed against them. Ext3 does this in ext3_test_allocatable(). +</para> + +<para> +Lock is also providing through journal_{un,}lock_updates(), +ext3 uses this when it wants a window with a clean and stable fs for a moment. +eg. +</para> + +<programlisting> + + journal_lock_updates() //stop new stuff happening.. + journal_flush() // checkpoint everything. + ..do stuff on stable fs + journal_unlock_updates() // carry on with filesystem use. +</programlisting> + +<para> +The opportunities for abuse and DOS attacks with this should be obvious, +if you allow unprivileged userspace to trigger codepaths containing these +calls. +</para> + +<para> +A new feature of jbd since 2.5.25 is commit callbacks with the new +journal_callback_set() function you can now ask the journalling layer +to call you back when the transaction is finally committed to disk, so that +you can do some of your own management. The key to this is the journal_callback +struct, this maintains the internal callback information but you can +extend it like this:- +</para> +<programlisting> + struct myfs_callback_s { + //Data structure element required by jbd.. + struct journal_callback for_jbd; + // Stuff for myfs allocated together. + myfs_inode* i_commited; + + } +</programlisting> + +<para> +this would be useful if you needed to know when data was committed to a +particular inode. +</para> + +</sect1> + +<sect1> +<title>Summary</title> +<para> +Using the journal is a matter of wrapping the different context changes, +being each mount, each modification (transaction) and each changed buffer +to tell the journalling layer about them. +</para> + +<para> +Here is a some pseudo code to give you an idea of how it works, as +an example. +</para> + +<programlisting> + journal_t* my_jnrl = journal_create(); + journal_init_{dev,inode}(jnrl,...) + if (clean) journal_wipe(); + journal_load(); + + foreach(transaction) { /*transactions must be + completed before + a syscall returns to + userspace*/ + + handle_t * xct=journal_start(my_jnrl); + foreach(bh) { + journal_get_{create,write,undo}_access(xact,bh); + if ( myfs_modify(bh) ) { /* returns true + if makes changes */ + journal_dirty_{meta,}data(xact,bh); + } else { + journal_forget(bh); + } + } + journal_stop(xct); + } + journal_destroy(my_jrnl); +</programlisting> +</sect1> + +</chapter> + + <chapter id="adt"> + <title>Data Types</title> + <para> + The journalling layer uses typedefs to 'hide' the concrete definitions + of the structures used. As a client of the JBD layer you can + just rely on the using the pointer as a magic cookie of some sort. + + Obviously the hiding is not enforced as this is 'C'. + </para> + <sect1><title>Structures</title> +!Iinclude/linux/jbd.h + </sect1> +</chapter> + + <chapter id="calls"> + <title>Functions</title> + <para> + The functions here are split into two groups those that + affect a journal as a whole, and those which are used to + manage transactions +</para> + <sect1><title>Journal Level</title> +!Efs/jbd/journal.c +!Efs/jbd/recovery.c + </sect1> + <sect1><title>Transasction Level</title> +!Efs/jbd/transaction.c + </sect1> +</chapter> +<chapter> + <title>See also</title> + <para> + <citation> + <ulink url="ftp://ftp.uk.linux.org/pub/linux/sct/fs/jfs/journal-design.ps.gz"> + Journaling the Linux ext2fs Filesystem,LinuxExpo 98, Stephen Tweedie + </ulink> + </citation> + </para> + <para> + <citation> + <ulink url="http://olstrans.sourceforge.net/release/OLS2000-ext3/OLS2000-ext3.html"> + Ext3 Journalling FileSystem , OLS 2000, Dr. Stephen Tweedie + </ulink> + </citation> + </para> +</chapter> + +</book> diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl new file mode 100644 index 0000000..1bd20c8 --- /dev/null +++ b/Documentation/DocBook/kernel-api.tmpl @@ -0,0 +1,342 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="LinuxKernelAPI"> + <bookinfo> + <title>The Linux Kernel API</title> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="Basics"> + <title>Driver Basics</title> + <sect1><title>Driver Entry and Exit points</title> +!Iinclude/linux/init.h + </sect1> + + <sect1><title>Atomic and pointer manipulation</title> +!Iinclude/asm-i386/atomic.h +!Iinclude/asm-i386/unaligned.h + </sect1> + +<!-- FIXME: + kernel/sched.c has no docs, which stuffs up the sgml. Comment + out until somebody adds docs. KAO + <sect1><title>Delaying, scheduling, and timer routines</title> +X!Ekernel/sched.c + </sect1> +KAO --> + </chapter> + + <chapter id="adt"> + <title>Data Types</title> + <sect1><title>Doubly Linked Lists</title> +!Iinclude/linux/list.h + </sect1> + </chapter> + + <chapter id="libc"> + <title>Basic C Library Functions</title> + + <para> + When writing drivers, you cannot in general use routines which are + from the C Library. Some of the functions have been found generally + useful and they are listed below. The behaviour of these functions + may vary slightly from those defined by ANSI, and these deviations + are noted in the text. + </para> + + <sect1><title>String Conversions</title> +!Ilib/vsprintf.c +!Elib/vsprintf.c + </sect1> + <sect1><title>String Manipulation</title> +!Ilib/string.c +!Elib/string.c + </sect1> + <sect1><title>Bit Operations</title> +!Iinclude/asm-i386/bitops.h + </sect1> + </chapter> + + <chapter id="mm"> + <title>Memory Management in Linux</title> + <sect1><title>The Slab Cache</title> +!Emm/slab.c + </sect1> + <sect1><title>User Space Memory Access</title> +!Iinclude/asm-i386/uaccess.h +!Iarch/i386/lib/usercopy.c + </sect1> + </chapter> + + <chapter id="kfifo"> + <title>FIFO Buffer</title> + <sect1><title>kfifo interface</title> +!Iinclude/linux/kfifo.h +!Ekernel/kfifo.c + </sect1> + </chapter> + + <chapter id="proc"> + <title>The proc filesystem</title> + + <sect1><title>sysctl interface</title> +!Ekernel/sysctl.c + </sect1> + </chapter> + + <chapter id="debugfs"> + <title>The debugfs filesystem</title> + + <sect1><title>debugfs interface</title> +!Efs/debugfs/inode.c +!Efs/debugfs/file.c + </sect1> + </chapter> + + <chapter id="vfs"> + <title>The Linux VFS</title> + <sect1><title>The Directory Cache</title> +!Efs/dcache.c +!Iinclude/linux/dcache.h + </sect1> + <sect1><title>Inode Handling</title> +!Efs/inode.c +!Efs/bad_inode.c + </sect1> + <sect1><title>Registration and Superblocks</title> +!Efs/super.c + </sect1> + <sect1><title>File Locks</title> +!Efs/locks.c +!Ifs/locks.c + </sect1> + </chapter> + + <chapter id="netcore"> + <title>Linux Networking</title> + <sect1><title>Socket Buffer Functions</title> +!Iinclude/linux/skbuff.h +!Enet/core/skbuff.c + </sect1> + <sect1><title>Socket Filter</title> +!Enet/core/filter.c + </sect1> + <sect1><title>Generic Network Statistics</title> +!Iinclude/linux/gen_stats.h +!Enet/core/gen_stats.c +!Enet/core/gen_estimator.c + </sect1> + </chapter> + + <chapter id="netdev"> + <title>Network device support</title> + <sect1><title>Driver Support</title> +!Enet/core/dev.c + </sect1> + <sect1><title>8390 Based Network Cards</title> +!Edrivers/net/8390.c + </sect1> + <sect1><title>Synchronous PPP</title> +!Edrivers/net/wan/syncppp.c + </sect1> + </chapter> + + <chapter id="modload"> + <title>Module Support</title> + <sect1><title>Module Loading</title> +!Ekernel/kmod.c + </sect1> + <sect1><title>Inter Module support</title> + <para> + Refer to the file kernel/module.c for more information. + </para> +<!-- FIXME: Removed for now since no structured comments in source +X!Ekernel/module.c +--> + </sect1> + </chapter> + + <chapter id="hardware"> + <title>Hardware Interfaces</title> + <sect1><title>Interrupt Handling</title> +!Iarch/i386/kernel/irq.c + </sect1> + + <sect1><title>MTRR Handling</title> +!Earch/i386/kernel/cpu/mtrr/main.c + </sect1> + <sect1><title>PCI Support Library</title> +!Edrivers/pci/pci.c + </sect1> + <sect1><title>PCI Hotplug Support Library</title> +!Edrivers/pci/hotplug/pci_hotplug_core.c + </sect1> + <sect1><title>MCA Architecture</title> + <sect2><title>MCA Device Functions</title> + <para> + Refer to the file arch/i386/kernel/mca.c for more information. + </para> +<!-- FIXME: Removed for now since no structured comments in source +X!Earch/i386/kernel/mca.c +--> + </sect2> + <sect2><title>MCA Bus DMA</title> +!Iinclude/asm-i386/mca_dma.h + </sect2> + </sect1> + </chapter> + + <chapter id="devfs"> + <title>The Device File System</title> +!Efs/devfs/base.c + </chapter> + + <chapter id="security"> + <title>Security Framework</title> +!Esecurity/security.c + </chapter> + + <chapter id="pmfuncs"> + <title>Power Management</title> +!Ekernel/power/pm.c + </chapter> + + <chapter id="blkdev"> + <title>Block Devices</title> +!Edrivers/block/ll_rw_blk.c + </chapter> + + <chapter id="miscdev"> + <title>Miscellaneous Devices</title> +!Edrivers/char/misc.c + </chapter> + + <chapter id="viddev"> + <title>Video4Linux</title> +!Edrivers/media/video/videodev.c + </chapter> + + <chapter id="snddev"> + <title>Sound Devices</title> +!Esound/sound_core.c +<!-- FIXME: Removed for now since no structured comments in source +X!Isound/sound_firmware.c +--> + </chapter> + + <chapter id="uart16x50"> + <title>16x50 UART Driver</title> +!Edrivers/serial/serial_core.c +!Edrivers/serial/8250.c + </chapter> + + <chapter id="z85230"> + <title>Z85230 Support Library</title> +!Edrivers/net/wan/z85230.c + </chapter> + + <chapter id="fbdev"> + <title>Frame Buffer Library</title> + + <para> + The frame buffer drivers depend heavily on four data structures. + These structures are declared in include/linux/fb.h. They are + fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs. + The last three can be made available to and from userland. + </para> + + <para> + fb_info defines the current state of a particular video card. + Inside fb_info, there exists a fb_ops structure which is a + collection of needed functions to make fbdev and fbcon work. + fb_info is only visible to the kernel. + </para> + + <para> + fb_var_screeninfo is used to describe the features of a video card + that are user defined. With fb_var_screeninfo, things such as + depth and the resolution may be defined. + </para> + + <para> + The next structure is fb_fix_screeninfo. This defines the + properties of a card that are created when a mode is set and can't + be changed otherwise. A good example of this is the start of the + frame buffer memory. This "locks" the address of the frame buffer + memory, so that it cannot be changed or moved. + </para> + + <para> + The last structure is fb_monospecs. In the old API, there was + little importance for fb_monospecs. This allowed for forbidden things + such as setting a mode of 800x600 on a fix frequency monitor. With + the new API, fb_monospecs prevents such things, and if used + correctly, can prevent a monitor from being cooked. fb_monospecs + will not be useful until kernels 2.5.x. + </para> + + <sect1><title>Frame Buffer Memory</title> +!Edrivers/video/fbmem.c + </sect1> + <sect1><title>Frame Buffer Console</title> +!Edrivers/video/console/fbcon.c + </sect1> + <sect1><title>Frame Buffer Colormap</title> +!Edrivers/video/fbcmap.c + </sect1> +<!-- FIXME: + drivers/video/fbgen.c has no docs, which stuffs up the sgml. Comment + out until somebody adds docs. KAO + <sect1><title>Frame Buffer Generic Functions</title> +X!Idrivers/video/fbgen.c + </sect1> +KAO --> + <sect1><title>Frame Buffer Video Mode Database</title> +!Idrivers/video/modedb.c +!Edrivers/video/modedb.c + </sect1> + <sect1><title>Frame Buffer Macintosh Video Mode Database</title> +!Idrivers/video/macmodes.c + </sect1> + <sect1><title>Frame Buffer Fonts</title> + <para> + Refer to the file drivers/video/console/fonts.c for more information. + </para> +<!-- FIXME: Removed for now since no structured comments in source +X!Idrivers/video/console/fonts.c +--> + </sect1> + </chapter> +</book> diff --git a/Documentation/DocBook/kernel-hacking.tmpl b/Documentation/DocBook/kernel-hacking.tmpl new file mode 100644 index 0000000..49a9ef8 --- /dev/null +++ b/Documentation/DocBook/kernel-hacking.tmpl @@ -0,0 +1,1349 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="lk-hacking-guide"> + <bookinfo> + <title>Unreliable Guide To Hacking The Linux Kernel</title> + + <authorgroup> + <author> + <firstname>Paul</firstname> + <othername>Rusty</othername> + <surname>Russell</surname> + <affiliation> + <address> + <email>rusty@rustcorp.com.au</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2001</year> + <holder>Rusty Russell</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + + <releaseinfo> + This is the first release of this document as part of the kernel tarball. + </releaseinfo> + + </bookinfo> + + <toc></toc> + + <chapter id="introduction"> + <title>Introduction</title> + <para> + Welcome, gentle reader, to Rusty's Unreliable Guide to Linux + Kernel Hacking. This document describes the common routines and + general requirements for kernel code: its goal is to serve as a + primer for Linux kernel development for experienced C + programmers. I avoid implementation details: that's what the + code is for, and I ignore whole tracts of useful routines. + </para> + <para> + Before you read this, please understand that I never wanted to + write this document, being grossly under-qualified, but I always + wanted to read it, and this was the only way. I hope it will + grow into a compendium of best practice, common starting points + and random information. + </para> + </chapter> + + <chapter id="basic-players"> + <title>The Players</title> + + <para> + At any time each of the CPUs in a system can be: + </para> + + <itemizedlist> + <listitem> + <para> + not associated with any process, serving a hardware interrupt; + </para> + </listitem> + + <listitem> + <para> + not associated with any process, serving a softirq, tasklet or bh; + </para> + </listitem> + + <listitem> + <para> + running in kernel space, associated with a process; + </para> + </listitem> + + <listitem> + <para> + running a process in user space. + </para> + </listitem> + </itemizedlist> + + <para> + There is a strict ordering between these: other than the last + category (userspace) each can only be pre-empted by those above. + For example, while a softirq is running on a CPU, no other + softirq will pre-empt it, but a hardware interrupt can. However, + any other CPUs in the system execute independently. + </para> + + <para> + We'll see a number of ways that the user context can block + interrupts, to become truly non-preemptable. + </para> + + <sect1 id="basics-usercontext"> + <title>User Context</title> + + <para> + User context is when you are coming in from a system call or + other trap: you can sleep, and you own the CPU (except for + interrupts) until you call <function>schedule()</function>. + In other words, user context (unlike userspace) is not pre-emptable. + </para> + + <note> + <para> + You are always in user context on module load and unload, + and on operations on the block device layer. + </para> + </note> + + <para> + In user context, the <varname>current</varname> pointer (indicating + the task we are currently executing) is valid, and + <function>in_interrupt()</function> + (<filename>include/linux/interrupt.h</filename>) is <returnvalue>false + </returnvalue>. + </para> + + <caution> + <para> + Beware that if you have interrupts or bottom halves disabled + (see below), <function>in_interrupt()</function> will return a + false positive. + </para> + </caution> + </sect1> + + <sect1 id="basics-hardirqs"> + <title>Hardware Interrupts (Hard IRQs)</title> + + <para> + Timer ticks, <hardware>network cards</hardware> and + <hardware>keyboard</hardware> are examples of real + hardware which produce interrupts at any time. The kernel runs + interrupt handlers, which services the hardware. The kernel + guarantees that this handler is never re-entered: if another + interrupt arrives, it is queued (or dropped). Because it + disables interrupts, this handler has to be fast: frequently it + simply acknowledges the interrupt, marks a `software interrupt' + for execution and exits. + </para> + + <para> + You can tell you are in a hardware interrupt, because + <function>in_irq()</function> returns <returnvalue>true</returnvalue>. + </para> + <caution> + <para> + Beware that this will return a false positive if interrupts are disabled + (see below). + </para> + </caution> + </sect1> + + <sect1 id="basics-softirqs"> + <title>Software Interrupt Context: Bottom Halves, Tasklets, softirqs</title> + + <para> + Whenever a system call is about to return to userspace, or a + hardware interrupt handler exits, any `software interrupts' + which are marked pending (usually by hardware interrupts) are + run (<filename>kernel/softirq.c</filename>). + </para> + + <para> + Much of the real interrupt handling work is done here. Early in + the transition to <acronym>SMP</acronym>, there were only `bottom + halves' (BHs), which didn't take advantage of multiple CPUs. Shortly + after we switched from wind-up computers made of match-sticks and snot, + we abandoned this limitation. + </para> + + <para> + <filename class="headerfile">include/linux/interrupt.h</filename> lists the + different BH's. No matter how many CPUs you have, no two BHs will run at + the same time. This made the transition to SMP simpler, but sucks hard for + scalable performance. A very important bottom half is the timer + BH (<filename class="headerfile">include/linux/timer.h</filename>): you + can register to have it call functions for you in a given length of time. + </para> + + <para> + 2.3.43 introduced softirqs, and re-implemented the (now + deprecated) BHs underneath them. Softirqs are fully-SMP + versions of BHs: they can run on as many CPUs at once as + required. This means they need to deal with any races in shared + data using their own locks. A bitmask is used to keep track of + which are enabled, so the 32 available softirqs should not be + used up lightly. (<emphasis>Yes</emphasis>, people will + notice). + </para> + + <para> + tasklets (<filename class="headerfile">include/linux/interrupt.h</filename>) + are like softirqs, except they are dynamically-registrable (meaning you + can have as many as you want), and they also guarantee that any tasklet + will only run on one CPU at any time, although different tasklets can + run simultaneously (unlike different BHs). + </para> + <caution> + <para> + The name `tasklet' is misleading: they have nothing to do with `tasks', + and probably more to do with some bad vodka Alexey Kuznetsov had at the + time. + </para> + </caution> + + <para> + You can tell you are in a softirq (or bottom half, or tasklet) + using the <function>in_softirq()</function> macro + (<filename class="headerfile">include/linux/interrupt.h</filename>). + </para> + <caution> + <para> + Beware that this will return a false positive if a bh lock (see below) + is held. + </para> + </caution> + </sect1> + </chapter> + + <chapter id="basic-rules"> + <title>Some Basic Rules</title> + + <variablelist> + <varlistentry> + <term>No memory protection</term> + <listitem> + <para> + If you corrupt memory, whether in user context or + interrupt context, the whole machine will crash. Are you + sure you can't do what you want in userspace? + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term>No floating point or <acronym>MMX</acronym></term> + <listitem> + <para> + The <acronym>FPU</acronym> context is not saved; even in user + context the <acronym>FPU</acronym> state probably won't + correspond with the current process: you would mess with some + user process' <acronym>FPU</acronym> state. If you really want + to do this, you would have to explicitly save/restore the full + <acronym>FPU</acronym> state (and avoid context switches). It + is generally a bad idea; use fixed point arithmetic first. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term>A rigid stack limit</term> + <listitem> + <para> + The kernel stack is about 6K in 2.2 (for most + architectures: it's about 14K on the Alpha), and shared + with interrupts so you can't use it all. Avoid deep + recursion and huge local arrays on the stack (allocate + them dynamically instead). + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term>The Linux kernel is portable</term> + <listitem> + <para> + Let's keep it that way. Your code should be 64-bit clean, + and endian-independent. You should also minimize CPU + specific stuff, e.g. inline assembly should be cleanly + encapsulated and minimized to ease porting. Generally it + should be restricted to the architecture-dependent part of + the kernel tree. + </para> + </listitem> + </varlistentry> + </variablelist> + </chapter> + + <chapter id="ioctls"> + <title>ioctls: Not writing a new system call</title> + + <para> + A system call generally looks like this + </para> + + <programlisting> +asmlinkage long sys_mycall(int arg) +{ + return 0; +} + </programlisting> + + <para> + First, in most cases you don't want to create a new system call. + You create a character device and implement an appropriate ioctl + for it. This is much more flexible than system calls, doesn't have + to be entered in every architecture's + <filename class="headerfile">include/asm/unistd.h</filename> and + <filename>arch/kernel/entry.S</filename> file, and is much more + likely to be accepted by Linus. + </para> + + <para> + If all your routine does is read or write some parameter, consider + implementing a <function>sysctl</function> interface instead. + </para> + + <para> + Inside the ioctl you're in user context to a process. When a + error occurs you return a negated errno (see + <filename class="headerfile">include/linux/errno.h</filename>), + otherwise you return <returnvalue>0</returnvalue>. + </para> + + <para> + After you slept you should check if a signal occurred: the + Unix/Linux way of handling signals is to temporarily exit the + system call with the <constant>-ERESTARTSYS</constant> error. The + system call entry code will switch back to user context, process + the signal handler and then your system call will be restarted + (unless the user disabled that). So you should be prepared to + process the restart, e.g. if you're in the middle of manipulating + some data structure. + </para> + + <programlisting> +if (signal_pending()) + return -ERESTARTSYS; + </programlisting> + + <para> + If you're doing longer computations: first think userspace. If you + <emphasis>really</emphasis> want to do it in kernel you should + regularly check if you need to give up the CPU (remember there is + cooperative multitasking per CPU). Idiom: + </para> + + <programlisting> +cond_resched(); /* Will sleep */ + </programlisting> + + <para> + A short note on interface design: the UNIX system call motto is + "Provide mechanism not policy". + </para> + </chapter> + + <chapter id="deadlock-recipes"> + <title>Recipes for Deadlock</title> + + <para> + You cannot call any routines which may sleep, unless: + </para> + <itemizedlist> + <listitem> + <para> + You are in user context. + </para> + </listitem> + + <listitem> + <para> + You do not own any spinlocks. + </para> + </listitem> + + <listitem> + <para> + You have interrupts enabled (actually, Andi Kleen says + that the scheduling code will enable them for you, but + that's probably not what you wanted). + </para> + </listitem> + </itemizedlist> + + <para> + Note that some functions may sleep implicitly: common ones are + the user space access functions (*_user) and memory allocation + functions without <symbol>GFP_ATOMIC</symbol>. + </para> + + <para> + You will eventually lock up your box if you break these rules. + </para> + + <para> + Really. + </para> + </chapter> + + <chapter id="common-routines"> + <title>Common Routines</title> + + <sect1 id="routines-printk"> + <title> + <function>printk()</function> + <filename class="headerfile">include/linux/kernel.h</filename> + </title> + + <para> + <function>printk()</function> feeds kernel messages to the + console, dmesg, and the syslog daemon. It is useful for debugging + and reporting errors, and can be used inside interrupt context, + but use with caution: a machine which has its console flooded with + printk messages is unusable. It uses a format string mostly + compatible with ANSI C printf, and C string concatenation to give + it a first "priority" argument: + </para> + + <programlisting> +printk(KERN_INFO "i = %u\n", i); + </programlisting> + + <para> + See <filename class="headerfile">include/linux/kernel.h</filename>; + for other KERN_ values; these are interpreted by syslog as the + level. Special case: for printing an IP address use + </para> + + <programlisting> +__u32 ipaddress; +printk(KERN_INFO "my ip: %d.%d.%d.%d\n", NIPQUAD(ipaddress)); + </programlisting> + + <para> + <function>printk()</function> internally uses a 1K buffer and does + not catch overruns. Make sure that will be enough. + </para> + + <note> + <para> + You will know when you are a real kernel hacker + when you start typoing printf as printk in your user programs :) + </para> + </note> + + <!--- From the Lions book reader department --> + + <note> + <para> + Another sidenote: the original Unix Version 6 sources had a + comment on top of its printf function: "Printf should not be + used for chit-chat". You should follow that advice. + </para> + </note> + </sect1> + + <sect1 id="routines-copy"> + <title> + <function>copy_[to/from]_user()</function> + / + <function>get_user()</function> + / + <function>put_user()</function> + <filename class="headerfile">include/asm/uaccess.h</filename> + </title> + + <para> + <emphasis>[SLEEPS]</emphasis> + </para> + + <para> + <function>put_user()</function> and <function>get_user()</function> + are used to get and put single values (such as an int, char, or + long) from and to userspace. A pointer into userspace should + never be simply dereferenced: data should be copied using these + routines. Both return <constant>-EFAULT</constant> or 0. + </para> + <para> + <function>copy_to_user()</function> and + <function>copy_from_user()</function> are more general: they copy + an arbitrary amount of data to and from userspace. + <caution> + <para> + Unlike <function>put_user()</function> and + <function>get_user()</function>, they return the amount of + uncopied data (ie. <returnvalue>0</returnvalue> still means + success). + </para> + </caution> + [Yes, this moronic interface makes me cringe. Please submit a + patch and become my hero --RR.] + </para> + <para> + The functions may sleep implicitly. This should never be called + outside user context (it makes no sense), with interrupts + disabled, or a spinlock held. + </para> + </sect1> + + <sect1 id="routines-kmalloc"> + <title><function>kmalloc()</function>/<function>kfree()</function> + <filename class="headerfile">include/linux/slab.h</filename></title> + + <para> + <emphasis>[MAY SLEEP: SEE BELOW]</emphasis> + </para> + + <para> + These routines are used to dynamically request pointer-aligned + chunks of memory, like malloc and free do in userspace, but + <function>kmalloc()</function> takes an extra flag word. + Important values: + </para> + + <variablelist> + <varlistentry> + <term> + <constant> + GFP_KERNEL + </constant> + </term> + <listitem> + <para> + May sleep and swap to free memory. Only allowed in user + context, but is the most reliable way to allocate memory. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <constant> + GFP_ATOMIC + </constant> + </term> + <listitem> + <para> + Don't sleep. Less reliable than <constant>GFP_KERNEL</constant>, + but may be called from interrupt context. You should + <emphasis>really</emphasis> have a good out-of-memory + error-handling strategy. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <constant> + GFP_DMA + </constant> + </term> + <listitem> + <para> + Allocate ISA DMA lower than 16MB. If you don't know what that + is you don't need it. Very unreliable. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + If you see a <errorname>kmem_grow: Called nonatomically from int + </errorname> warning message you called a memory allocation function + from interrupt context without <constant>GFP_ATOMIC</constant>. + You should really fix that. Run, don't walk. + </para> + + <para> + If you are allocating at least <constant>PAGE_SIZE</constant> + (<filename class="headerfile">include/asm/page.h</filename>) bytes, + consider using <function>__get_free_pages()</function> + + (<filename class="headerfile">include/linux/mm.h</filename>). It + takes an order argument (0 for page sized, 1 for double page, 2 + for four pages etc.) and the same memory priority flag word as + above. + </para> + + <para> + If you are allocating more than a page worth of bytes you can use + <function>vmalloc()</function>. It'll allocate virtual memory in + the kernel map. This block is not contiguous in physical memory, + but the <acronym>MMU</acronym> makes it look like it is for you + (so it'll only look contiguous to the CPUs, not to external device + drivers). If you really need large physically contiguous memory + for some weird device, you have a problem: it is poorly supported + in Linux because after some time memory fragmentation in a running + kernel makes it hard. The best way is to allocate the block early + in the boot process via the <function>alloc_bootmem()</function> + routine. + </para> + + <para> + Before inventing your own cache of often-used objects consider + using a slab cache in + <filename class="headerfile">include/linux/slab.h</filename> + </para> + </sect1> + + <sect1 id="routines-current"> + <title><function>current</function> + <filename class="headerfile">include/asm/current.h</filename></title> + + <para> + This global variable (really a macro) contains a pointer to + the current task structure, so is only valid in user context. + For example, when a process makes a system call, this will + point to the task structure of the calling process. It is + <emphasis>not NULL</emphasis> in interrupt context. + </para> + </sect1> + + <sect1 id="routines-udelay"> + <title><function>udelay()</function>/<function>mdelay()</function> + <filename class="headerfile">include/asm/delay.h</filename> + <filename class="headerfile">include/linux/delay.h</filename> + </title> + + <para> + The <function>udelay()</function> function can be used for small pauses. + Do not use large values with <function>udelay()</function> as you risk + overflow - the helper function <function>mdelay()</function> is useful + here, or even consider <function>schedule_timeout()</function>. + </para> + </sect1> + + <sect1 id="routines-endian"> + <title><function>cpu_to_be32()</function>/<function>be32_to_cpu()</function>/<function>cpu_to_le32()</function>/<function>le32_to_cpu()</function> + <filename class="headerfile">include/asm/byteorder.h</filename> + </title> + + <para> + The <function>cpu_to_be32()</function> family (where the "32" can + be replaced by 64 or 16, and the "be" can be replaced by "le") are + the general way to do endian conversions in the kernel: they + return the converted value. All variations supply the reverse as + well: <function>be32_to_cpu()</function>, etc. + </para> + + <para> + There are two major variations of these functions: the pointer + variation, such as <function>cpu_to_be32p()</function>, which take + a pointer to the given type, and return the converted value. The + other variation is the "in-situ" family, such as + <function>cpu_to_be32s()</function>, which convert value referred + to by the pointer, and return void. + </para> + </sect1> + + <sect1 id="routines-local-irqs"> + <title><function>local_irq_save()</function>/<function>local_irq_restore()</function> + <filename class="headerfile">include/asm/system.h</filename> + </title> + + <para> + These routines disable hard interrupts on the local CPU, and + restore them. They are reentrant; saving the previous state in + their one <varname>unsigned long flags</varname> argument. If you + know that interrupts are enabled, you can simply use + <function>local_irq_disable()</function> and + <function>local_irq_enable()</function>. + </para> + </sect1> + + <sect1 id="routines-softirqs"> + <title><function>local_bh_disable()</function>/<function>local_bh_enable()</function> + <filename class="headerfile">include/linux/interrupt.h</filename></title> + + <para> + These routines disable soft interrupts on the local CPU, and + restore them. They are reentrant; if soft interrupts were + disabled before, they will still be disabled after this pair + of functions has been called. They prevent softirqs, tasklets + and bottom halves from running on the current CPU. + </para> + </sect1> + + <sect1 id="routines-processorids"> + <title><function>smp_processor_id</function>() + <filename class="headerfile">include/asm/smp.h</filename></title> + + <para> + <function>smp_processor_id()</function> returns the current + processor number, between 0 and <symbol>NR_CPUS</symbol> (the + maximum number of CPUs supported by Linux, currently 32). These + values are not necessarily continuous. + </para> + </sect1> + + <sect1 id="routines-init"> + <title><type>__init</type>/<type>__exit</type>/<type>__initdata</type> + <filename class="headerfile">include/linux/init.h</filename></title> + + <para> + After boot, the kernel frees up a special section; functions + marked with <type>__init</type> and data structures marked with + <type>__initdata</type> are dropped after boot is complete (within + modules this directive is currently ignored). <type>__exit</type> + is used to declare a function which is only required on exit: the + function will be dropped if this file is not compiled as a module. + See the header file for use. Note that it makes no sense for a function + marked with <type>__init</type> to be exported to modules with + <function>EXPORT_SYMBOL()</function> - this will break. + </para> + <para> + Static data structures marked as <type>__initdata</type> must be initialised + (as opposed to ordinary static data which is zeroed BSS) and cannot be + <type>const</type>. + </para> + + </sect1> + + <sect1 id="routines-init-again"> + <title><function>__initcall()</function>/<function>module_init()</function> + <filename class="headerfile">include/linux/init.h</filename></title> + <para> + Many parts of the kernel are well served as a module + (dynamically-loadable parts of the kernel). Using the + <function>module_init()</function> and + <function>module_exit()</function> macros it is easy to write code + without #ifdefs which can operate both as a module or built into + the kernel. + </para> + + <para> + The <function>module_init()</function> macro defines which + function is to be called at module insertion time (if the file is + compiled as a module), or at boot time: if the file is not + compiled as a module the <function>module_init()</function> macro + becomes equivalent to <function>__initcall()</function>, which + through linker magic ensures that the function is called on boot. + </para> + + <para> + The function can return a negative error number to cause + module loading to fail (unfortunately, this has no effect if + the module is compiled into the kernel). For modules, this is + called in user context, with interrupts enabled, and the + kernel lock held, so it can sleep. + </para> + </sect1> + + <sect1 id="routines-moduleexit"> + <title> <function>module_exit()</function> + <filename class="headerfile">include/linux/init.h</filename> </title> + + <para> + This macro defines the function to be called at module removal + time (or never, in the case of the file compiled into the + kernel). It will only be called if the module usage count has + reached zero. This function can also sleep, but cannot fail: + everything must be cleaned up by the time it returns. + </para> + </sect1> + + <!-- add info on new-style module refcounting here --> + </chapter> + + <chapter id="queues"> + <title>Wait Queues + <filename class="headerfile">include/linux/wait.h</filename> + </title> + <para> + <emphasis>[SLEEPS]</emphasis> + </para> + + <para> + A wait queue is used to wait for someone to wake you up when a + certain condition is true. They must be used carefully to ensure + there is no race condition. You declare a + <type>wait_queue_head_t</type>, and then processes which want to + wait for that condition declare a <type>wait_queue_t</type> + referring to themselves, and place that in the queue. + </para> + + <sect1 id="queue-declaring"> + <title>Declaring</title> + + <para> + You declare a <type>wait_queue_head_t</type> using the + <function>DECLARE_WAIT_QUEUE_HEAD()</function> macro, or using the + <function>init_waitqueue_head()</function> routine in your + initialization code. + </para> + </sect1> + + <sect1 id="queue-waitqueue"> + <title>Queuing</title> + + <para> + Placing yourself in the waitqueue is fairly complex, because you + must put yourself in the queue before checking the condition. + There is a macro to do this: + <function>wait_event_interruptible()</function> + + <filename class="headerfile">include/linux/sched.h</filename> The + first argument is the wait queue head, and the second is an + expression which is evaluated; the macro returns + <returnvalue>0</returnvalue> when this expression is true, or + <returnvalue>-ERESTARTSYS</returnvalue> if a signal is received. + The <function>wait_event()</function> version ignores signals. + </para> + <para> + Do not use the <function>sleep_on()</function> function family - + it is very easy to accidentally introduce races; almost certainly + one of the <function>wait_event()</function> family will do, or a + loop around <function>schedule_timeout()</function>. If you choose + to loop around <function>schedule_timeout()</function> remember + you must set the task state (with + <function>set_current_state()</function>) on each iteration to avoid + busy-looping. + </para> + + </sect1> + + <sect1 id="queue-waking"> + <title>Waking Up Queued Tasks</title> + + <para> + Call <function>wake_up()</function> + + <filename class="headerfile">include/linux/sched.h</filename>;, + which will wake up every process in the queue. The exception is + if one has <constant>TASK_EXCLUSIVE</constant> set, in which case + the remainder of the queue will not be woken. + </para> + </sect1> + </chapter> + + <chapter id="atomic-ops"> + <title>Atomic Operations</title> + + <para> + Certain operations are guaranteed atomic on all platforms. The + first class of operations work on <type>atomic_t</type> + + <filename class="headerfile">include/asm/atomic.h</filename>; this + contains a signed integer (at least 24 bits long), and you must use + these functions to manipulate or read atomic_t variables. + <function>atomic_read()</function> and + <function>atomic_set()</function> get and set the counter, + <function>atomic_add()</function>, + <function>atomic_sub()</function>, + <function>atomic_inc()</function>, + <function>atomic_dec()</function>, and + <function>atomic_dec_and_test()</function> (returns + <returnvalue>true</returnvalue> if it was decremented to zero). + </para> + + <para> + Yes. It returns <returnvalue>true</returnvalue> (i.e. != 0) if the + atomic variable is zero. + </para> + + <para> + Note that these functions are slower than normal arithmetic, and + so should not be used unnecessarily. On some platforms they + are much slower, like 32-bit Sparc where they use a spinlock. + </para> + + <para> + The second class of atomic operations is atomic bit operations on a + <type>long</type>, defined in + + <filename class="headerfile">include/linux/bitops.h</filename>. These + operations generally take a pointer to the bit pattern, and a bit + number: 0 is the least significant bit. + <function>set_bit()</function>, <function>clear_bit()</function> + and <function>change_bit()</function> set, clear, and flip the + given bit. <function>test_and_set_bit()</function>, + <function>test_and_clear_bit()</function> and + <function>test_and_change_bit()</function> do the same thing, + except return true if the bit was previously set; these are + particularly useful for very simple locking. + </para> + + <para> + It is possible to call these operations with bit indices greater + than BITS_PER_LONG. The resulting behavior is strange on big-endian + platforms though so it is a good idea not to do this. + </para> + + <para> + Note that the order of bits depends on the architecture, and in + particular, the bitfield passed to these operations must be at + least as large as a <type>long</type>. + </para> + </chapter> + + <chapter id="symbols"> + <title>Symbols</title> + + <para> + Within the kernel proper, the normal linking rules apply + (ie. unless a symbol is declared to be file scope with the + <type>static</type> keyword, it can be used anywhere in the + kernel). However, for modules, a special exported symbol table is + kept which limits the entry points to the kernel proper. Modules + can also export symbols. + </para> + + <sect1 id="sym-exportsymbols"> + <title><function>EXPORT_SYMBOL()</function> + <filename class="headerfile">include/linux/module.h</filename></title> + + <para> + This is the classic method of exporting a symbol, and it works + for both modules and non-modules. In the kernel all these + declarations are often bundled into a single file to help + genksyms (which searches source files for these declarations). + See the comment on genksyms and Makefiles below. + </para> + </sect1> + + <sect1 id="sym-exportsymbols-gpl"> + <title><function>EXPORT_SYMBOL_GPL()</function> + <filename class="headerfile">include/linux/module.h</filename></title> + + <para> + Similar to <function>EXPORT_SYMBOL()</function> except that the + symbols exported by <function>EXPORT_SYMBOL_GPL()</function> can + only be seen by modules with a + <function>MODULE_LICENSE()</function> that specifies a GPL + compatible license. + </para> + </sect1> + </chapter> + + <chapter id="conventions"> + <title>Routines and Conventions</title> + + <sect1 id="conventions-doublelinkedlist"> + <title>Double-linked lists + <filename class="headerfile">include/linux/list.h</filename></title> + + <para> + There are three sets of linked-list routines in the kernel + headers, but this one seems to be winning out (and Linus has + used it). If you don't have some particular pressing need for + a single list, it's a good choice. In fact, I don't care + whether it's a good choice or not, just use it so we can get + rid of the others. + </para> + </sect1> + + <sect1 id="convention-returns"> + <title>Return Conventions</title> + + <para> + For code called in user context, it's very common to defy C + convention, and return <returnvalue>0</returnvalue> for success, + and a negative error number + (eg. <returnvalue>-EFAULT</returnvalue>) for failure. This can be + unintuitive at first, but it's fairly widespread in the networking + code, for example. + </para> + + <para> + The filesystem code uses <function>ERR_PTR()</function> + + <filename class="headerfile">include/linux/fs.h</filename>; to + encode a negative error number into a pointer, and + <function>IS_ERR()</function> and <function>PTR_ERR()</function> + to get it back out again: avoids a separate pointer parameter for + the error number. Icky, but in a good way. + </para> + </sect1> + + <sect1 id="conventions-borkedcompile"> + <title>Breaking Compilation</title> + + <para> + Linus and the other developers sometimes change function or + structure names in development kernels; this is not done just to + keep everyone on their toes: it reflects a fundamental change + (eg. can no longer be called with interrupts on, or does extra + checks, or doesn't do checks which were caught before). Usually + this is accompanied by a fairly complete note to the linux-kernel + mailing list; search the archive. Simply doing a global replace + on the file usually makes things <emphasis>worse</emphasis>. + </para> + </sect1> + + <sect1 id="conventions-initialising"> + <title>Initializing structure members</title> + + <para> + The preferred method of initializing structures is to use + designated initialisers, as defined by ISO C99, eg: + </para> + <programlisting> +static struct block_device_operations opt_fops = { + .open = opt_open, + .release = opt_release, + .ioctl = opt_ioctl, + .check_media_change = opt_media_change, +}; + </programlisting> + <para> + This makes it easy to grep for, and makes it clear which + structure fields are set. You should do this because it looks + cool. + </para> + </sect1> + + <sect1 id="conventions-gnu-extns"> + <title>GNU Extensions</title> + + <para> + GNU Extensions are explicitly allowed in the Linux kernel. + Note that some of the more complex ones are not very well + supported, due to lack of general use, but the following are + considered standard (see the GCC info page section "C + Extensions" for more details - Yes, really the info page, the + man page is only a short summary of the stuff in info): + </para> + <itemizedlist> + <listitem> + <para> + Inline functions + </para> + </listitem> + <listitem> + <para> + Statement expressions (ie. the ({ and }) constructs). + </para> + </listitem> + <listitem> + <para> + Declaring attributes of a function / variable / type + (__attribute__) + </para> + </listitem> + <listitem> + <para> + typeof + </para> + </listitem> + <listitem> + <para> + Zero length arrays + </para> + </listitem> + <listitem> + <para> + Macro varargs + </para> + </listitem> + <listitem> + <para> + Arithmetic on void pointers + </para> + </listitem> + <listitem> + <para> + Non-Constant initializers + </para> + </listitem> + <listitem> + <para> + Assembler Instructions (not outside arch/ and include/asm/) + </para> + </listitem> + <listitem> + <para> + Function names as strings (__FUNCTION__) + </para> + </listitem> + <listitem> + <para> + __builtin_constant_p() + </para> + </listitem> + </itemizedlist> + + <para> + Be wary when using long long in the kernel, the code gcc generates for + it is horrible and worse: division and multiplication does not work + on i386 because the GCC runtime functions for it are missing from + the kernel environment. + </para> + + <!-- FIXME: add a note about ANSI aliasing cleanness --> + </sect1> + + <sect1 id="conventions-cplusplus"> + <title>C++</title> + + <para> + Using C++ in the kernel is usually a bad idea, because the + kernel does not provide the necessary runtime environment + and the include files are not tested for it. It is still + possible, but not recommended. If you really want to do + this, forget about exceptions at least. + </para> + </sect1> + + <sect1 id="conventions-ifdef"> + <title>#if</title> + + <para> + It is generally considered cleaner to use macros in header files + (or at the top of .c files) to abstract away functions rather than + using `#if' pre-processor statements throughout the source code. + </para> + </sect1> + </chapter> + + <chapter id="submitting"> + <title>Putting Your Stuff in the Kernel</title> + + <para> + In order to get your stuff into shape for official inclusion, or + even to make a neat patch, there's administrative work to be + done: + </para> + <itemizedlist> + <listitem> + <para> + Figure out whose pond you've been pissing in. Look at the top of + the source files, inside the <filename>MAINTAINERS</filename> + file, and last of all in the <filename>CREDITS</filename> file. + You should coordinate with this person to make sure you're not + duplicating effort, or trying something that's already been + rejected. + </para> + + <para> + Make sure you put your name and EMail address at the top of + any files you create or mangle significantly. This is the + first place people will look when they find a bug, or when + <emphasis>they</emphasis> want to make a change. + </para> + </listitem> + + <listitem> + <para> + Usually you want a configuration option for your kernel hack. + Edit <filename>Config.in</filename> in the appropriate directory + (but under <filename>arch/</filename> it's called + <filename>config.in</filename>). The Config Language used is not + bash, even though it looks like bash; the safe way is to use only + the constructs that you already see in + <filename>Config.in</filename> files (see + <filename>Documentation/kbuild/kconfig-language.txt</filename>). + It's good to run "make xconfig" at least once to test (because + it's the only one with a static parser). + </para> + + <para> + Variables which can be Y or N use <type>bool</type> followed by a + tagline and the config define name (which must start with + CONFIG_). The <type>tristate</type> function is the same, but + allows the answer M (which defines + <symbol>CONFIG_foo_MODULE</symbol> in your source, instead of + <symbol>CONFIG_FOO</symbol>) if <symbol>CONFIG_MODULES</symbol> + is enabled. + </para> + + <para> + You may well want to make your CONFIG option only visible if + <symbol>CONFIG_EXPERIMENTAL</symbol> is enabled: this serves as a + warning to users. There many other fancy things you can do: see + the various <filename>Config.in</filename> files for ideas. + </para> + </listitem> + + <listitem> + <para> + Edit the <filename>Makefile</filename>: the CONFIG variables are + exported here so you can conditionalize compilation with `ifeq'. + If your file exports symbols then add the names to + <varname>export-objs</varname> so that genksyms will find them. + <caution> + <para> + There is a restriction on the kernel build system that objects + which export symbols must have globally unique names. + If your object does not have a globally unique name then the + standard fix is to move the + <function>EXPORT_SYMBOL()</function> statements to their own + object with a unique name. + This is why several systems have separate exporting objects, + usually suffixed with ksyms. + </para> + </caution> + </para> + </listitem> + + <listitem> + <para> + Document your option in Documentation/Configure.help. Mention + incompatibilities and issues here. <emphasis> Definitely + </emphasis> end your description with <quote> if in doubt, say N + </quote> (or, occasionally, `Y'); this is for people who have no + idea what you are talking about. + </para> + </listitem> + + <listitem> + <para> + Put yourself in <filename>CREDITS</filename> if you've done + something noteworthy, usually beyond a single file (your name + should be at the top of the source files anyway). + <filename>MAINTAINERS</filename> means you want to be consulted + when changes are made to a subsystem, and hear about bugs; it + implies a more-than-passing commitment to some part of the code. + </para> + </listitem> + + <listitem> + <para> + Finally, don't forget to read <filename>Documentation/SubmittingPatches</filename> + and possibly <filename>Documentation/SubmittingDrivers</filename>. + </para> + </listitem> + </itemizedlist> + </chapter> + + <chapter id="cantrips"> + <title>Kernel Cantrips</title> + + <para> + Some favorites from browsing the source. Feel free to add to this + list. + </para> + + <para> + <filename>include/linux/brlock.h:</filename> + </para> + <programlisting> +extern inline void br_read_lock (enum brlock_indices idx) +{ + /* + * This causes a link-time bug message if an + * invalid index is used: + */ + if (idx >= __BR_END) + __br_lock_usage_bug(); + + read_lock(&__brlock_array[smp_processor_id()][idx]); +} + </programlisting> + + <para> + <filename>include/linux/fs.h</filename>: + </para> + <programlisting> +/* + * Kernel pointers have redundant information, so we can use a + * scheme where we can return either an error code or a dentry + * pointer with the same return value. + * + * This should be a per-architecture thing, to allow different + * error and pointer decisions. + */ + #define ERR_PTR(err) ((void *)((long)(err))) + #define PTR_ERR(ptr) ((long)(ptr)) + #define IS_ERR(ptr) ((unsigned long)(ptr) > (unsigned long)(-1000)) +</programlisting> + + <para> + <filename>include/asm-i386/uaccess.h:</filename> + </para> + + <programlisting> +#define copy_to_user(to,from,n) \ + (__builtin_constant_p(n) ? \ + __constant_copy_to_user((to),(from),(n)) : \ + __generic_copy_to_user((to),(from),(n))) + </programlisting> + + <para> + <filename>arch/sparc/kernel/head.S:</filename> + </para> + + <programlisting> +/* + * Sun people can't spell worth damn. "compatability" indeed. + * At least we *know* we can't spell, and use a spell-checker. + */ + +/* Uh, actually Linus it is I who cannot spell. Too much murky + * Sparc assembly will do this to ya. + */ +C_LABEL(cputypvar): + .asciz "compatability" + +/* Tested on SS-5, SS-10. Probably someone at Sun applied a spell-checker. */ + .align 4 +C_LABEL(cputypvar_sun4m): + .asciz "compatible" + </programlisting> + + <para> + <filename>arch/sparc/lib/checksum.S:</filename> + </para> + + <programlisting> + /* Sun, you just can't beat me, you just can't. Stop trying, + * give up. I'm serious, I am going to kick the living shit + * out of you, game over, lights out. + */ + </programlisting> + </chapter> + + <chapter id="credits"> + <title>Thanks</title> + + <para> + Thanks to Andi Kleen for the idea, answering my questions, fixing + my mistakes, filling content, etc. Philipp Rumpf for more spelling + and clarity fixes, and some excellent non-obvious points. Werner + Almesberger for giving me a great summary of + <function>disable_irq()</function>, and Jes Sorensen and Andrea + Arcangeli added caveats. Michael Elizabeth Chastain for checking + and adding to the Configure section. <!-- Rusty insisted on this + bit; I didn't do it! --> Telsa Gwynne for teaching me DocBook. + </para> + </chapter> +</book> + diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl new file mode 100644 index 0000000..90dc2de --- /dev/null +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -0,0 +1,2088 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="LKLockingGuide"> + <bookinfo> + <title>Unreliable Guide To Locking</title> + + <authorgroup> + <author> + <firstname>Rusty</firstname> + <surname>Russell</surname> + <affiliation> + <address> + <email>rusty@rustcorp.com.au</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2003</year> + <holder>Rusty Russell</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + + <toc></toc> + <chapter id="intro"> + <title>Introduction</title> + <para> + Welcome, to Rusty's Remarkably Unreliable Guide to Kernel + Locking issues. This document describes the locking systems in + the Linux Kernel in 2.6. + </para> + <para> + With the wide availability of HyperThreading, and <firstterm + linkend="gloss-preemption">preemption </firstterm> in the Linux + Kernel, everyone hacking on the kernel needs to know the + fundamentals of concurrency and locking for + <firstterm linkend="gloss-smp"><acronym>SMP</acronym></firstterm>. + </para> + </chapter> + + <chapter id="races"> + <title>The Problem With Concurrency</title> + <para> + (Skip this if you know what a Race Condition is). + </para> + <para> + In a normal program, you can increment a counter like so: + </para> + <programlisting> + very_important_count++; + </programlisting> + + <para> + This is what they would expect to happen: + </para> + + <table> + <title>Expected Results</title> + + <tgroup cols="2" align="left"> + + <thead> + <row> + <entry>Instance 1</entry> + <entry>Instance 2</entry> + </row> + </thead> + + <tbody> + <row> + <entry>read very_important_count (5)</entry> + <entry></entry> + </row> + <row> + <entry>add 1 (6)</entry> + <entry></entry> + </row> + <row> + <entry>write very_important_count (6)</entry> + <entry></entry> + </row> + <row> + <entry></entry> + <entry>read very_important_count (6)</entry> + </row> + <row> + <entry></entry> + <entry>add 1 (7)</entry> + </row> + <row> + <entry></entry> + <entry>write very_important_count (7)</entry> + </row> + </tbody> + + </tgroup> + </table> + + <para> + This is what might happen: + </para> + + <table> + <title>Possible Results</title> + + <tgroup cols="2" align="left"> + <thead> + <row> + <entry>Instance 1</entry> + <entry>Instance 2</entry> + </row> + </thead> + + <tbody> + <row> + <entry>read very_important_count (5)</entry> + <entry></entry> + </row> + <row> + <entry></entry> + <entry>read very_important_count (5)</entry> + </row> + <row> + <entry>add 1 (6)</entry> + <entry></entry> + </row> + <row> + <entry></entry> + <entry>add 1 (6)</entry> + </row> + <row> + <entry>write very_important_count (6)</entry> + <entry></entry> + </row> + <row> + <entry></entry> + <entry>write very_important_count (6)</entry> + </row> + </tbody> + </tgroup> + </table> + + <sect1 id="race-condition"> + <title>Race Conditions and Critical Regions</title> + <para> + This overlap, where the result depends on the + relative timing of multiple tasks, is called a <firstterm>race condition</firstterm>. + The piece of code containing the concurrency issue is called a + <firstterm>critical region</firstterm>. And especially since Linux starting running + on SMP machines, they became one of the major issues in kernel + design and implementation. + </para> + <para> + Preemption can have the same effect, even if there is only one + CPU: by preempting one task during the critical region, we have + exactly the same race condition. In this case the thread which + preempts might run the critical region itself. + </para> + <para> + The solution is to recognize when these simultaneous accesses + occur, and use locks to make sure that only one instance can + enter the critical region at any time. There are many + friendly primitives in the Linux kernel to help you do this. + And then there are the unfriendly primitives, but I'll pretend + they don't exist. + </para> + </sect1> + </chapter> + + <chapter id="locks"> + <title>Locking in the Linux Kernel</title> + + <para> + If I could give you one piece of advice: never sleep with anyone + crazier than yourself. But if I had to give you advice on + locking: <emphasis>keep it simple</emphasis>. + </para> + + <para> + Be reluctant to introduce new locks. + </para> + + <para> + Strangely enough, this last one is the exact reverse of my advice when + you <emphasis>have</emphasis> slept with someone crazier than yourself. + And you should think about getting a big dog. + </para> + + <sect1 id="lock-intro"> + <title>Two Main Types of Kernel Locks: Spinlocks and Semaphores</title> + + <para> + There are two main types of kernel locks. The fundamental type + is the spinlock + (<filename class="headerfile">include/asm/spinlock.h</filename>), + which is a very simple single-holder lock: if you can't get the + spinlock, you keep trying (spinning) until you can. Spinlocks are + very small and fast, and can be used anywhere. + </para> + <para> + The second type is a semaphore + (<filename class="headerfile">include/asm/semaphore.h</filename>): it + can have more than one holder at any time (the number decided at + initialization time), although it is most commonly used as a + single-holder lock (a mutex). If you can't get a semaphore, + your task will put itself on the queue, and be woken up when the + semaphore is released. This means the CPU will do something + else while you are waiting, but there are many cases when you + simply can't sleep (see <xref linkend="sleeping-things"/>), and so + have to use a spinlock instead. + </para> + <para> + Neither type of lock is recursive: see + <xref linkend="deadlock"/>. + </para> + </sect1> + + <sect1 id="uniprocessor"> + <title>Locks and Uniprocessor Kernels</title> + + <para> + For kernels compiled without <symbol>CONFIG_SMP</symbol>, and + without <symbol>CONFIG_PREEMPT</symbol> spinlocks do not exist at + all. This is an excellent design decision: when no-one else can + run at the same time, there is no reason to have a lock. + </para> + + <para> + If the kernel is compiled without <symbol>CONFIG_SMP</symbol>, + but <symbol>CONFIG_PREEMPT</symbol> is set, then spinlocks + simply disable preemption, which is sufficient to prevent any + races. For most purposes, we can think of preemption as + equivalent to SMP, and not worry about it separately. + </para> + + <para> + You should always test your locking code with <symbol>CONFIG_SMP</symbol> + and <symbol>CONFIG_PREEMPT</symbol> enabled, even if you don't have an SMP test box, because it + will still catch some kinds of locking bugs. + </para> + + <para> + Semaphores still exist, because they are required for + synchronization between <firstterm linkend="gloss-usercontext">user + contexts</firstterm>, as we will see below. + </para> + </sect1> + + <sect1 id="usercontextlocking"> + <title>Locking Only In User Context</title> + + <para> + If you have a data structure which is only ever accessed from + user context, then you can use a simple semaphore + (<filename>linux/asm/semaphore.h</filename>) to protect it. This + is the most trivial case: you initialize the semaphore to the number + of resources available (usually 1), and call + <function>down_interruptible()</function> to grab the semaphore, and + <function>up()</function> to release it. There is also a + <function>down()</function>, which should be avoided, because it + will not return if a signal is received. + </para> + + <para> + Example: <filename>linux/net/core/netfilter.c</filename> allows + registration of new <function>setsockopt()</function> and + <function>getsockopt()</function> calls, with + <function>nf_register_sockopt()</function>. Registration and + de-registration are only done on module load and unload (and boot + time, where there is no concurrency), and the list of registrations + is only consulted for an unknown <function>setsockopt()</function> + or <function>getsockopt()</function> system call. The + <varname>nf_sockopt_mutex</varname> is perfect to protect this, + especially since the setsockopt and getsockopt calls may well + sleep. + </para> + </sect1> + + <sect1 id="lock-user-bh"> + <title>Locking Between User Context and Softirqs</title> + + <para> + If a <firstterm linkend="gloss-softirq">softirq</firstterm> shares + data with user context, you have two problems. Firstly, the current + user context can be interrupted by a softirq, and secondly, the + critical region could be entered from another CPU. This is where + <function>spin_lock_bh()</function> + (<filename class="headerfile">include/linux/spinlock.h</filename>) is + used. It disables softirqs on that CPU, then grabs the lock. + <function>spin_unlock_bh()</function> does the reverse. (The + '_bh' suffix is a historical reference to "Bottom Halves", the + old name for software interrupts. It should really be + called spin_lock_softirq()' in a perfect world). + </para> + + <para> + Note that you can also use <function>spin_lock_irq()</function> + or <function>spin_lock_irqsave()</function> here, which stop + hardware interrupts as well: see <xref linkend="hardirq-context"/>. + </para> + + <para> + This works perfectly for <firstterm linkend="gloss-up"><acronym>UP + </acronym></firstterm> as well: the spin lock vanishes, and this macro + simply becomes <function>local_bh_disable()</function> + (<filename class="headerfile">include/linux/interrupt.h</filename>), which + protects you from the softirq being run. + </para> + </sect1> + + <sect1 id="lock-user-tasklet"> + <title>Locking Between User Context and Tasklets</title> + + <para> + This is exactly the same as above, because <firstterm + linkend="gloss-tasklet">tasklets</firstterm> are actually run + from a softirq. + </para> + </sect1> + + <sect1 id="lock-user-timers"> + <title>Locking Between User Context and Timers</title> + + <para> + This, too, is exactly the same as above, because <firstterm + linkend="gloss-timers">timers</firstterm> are actually run from + a softirq. From a locking point of view, tasklets and timers + are identical. + </para> + </sect1> + + <sect1 id="lock-tasklets"> + <title>Locking Between Tasklets/Timers</title> + + <para> + Sometimes a tasklet or timer might want to share data with + another tasklet or timer. + </para> + + <sect2 id="lock-tasklets-same"> + <title>The Same Tasklet/Timer</title> + <para> + Since a tasklet is never run on two CPUs at once, you don't + need to worry about your tasklet being reentrant (running + twice at once), even on SMP. + </para> + </sect2> + + <sect2 id="lock-tasklets-different"> + <title>Different Tasklets/Timers</title> + <para> + If another tasklet/timer wants + to share data with your tasklet or timer , you will both need to use + <function>spin_lock()</function> and + <function>spin_unlock()</function> calls. + <function>spin_lock_bh()</function> is + unnecessary here, as you are already in a tasklet, and + none will be run on the same CPU. + </para> + </sect2> + </sect1> + + <sect1 id="lock-softirqs"> + <title>Locking Between Softirqs</title> + + <para> + Often a softirq might + want to share data with itself or a tasklet/timer. + </para> + + <sect2 id="lock-softirqs-same"> + <title>The Same Softirq</title> + + <para> + The same softirq can run on the other CPUs: you can use a + per-CPU array (see <xref linkend="per-cpu"/>) for better + performance. If you're going so far as to use a softirq, + you probably care about scalable performance enough + to justify the extra complexity. + </para> + + <para> + You'll need to use <function>spin_lock()</function> and + <function>spin_unlock()</function> for shared data. + </para> + </sect2> + + <sect2 id="lock-softirqs-different"> + <title>Different Softirqs</title> + + <para> + You'll need to use <function>spin_lock()</function> and + <function>spin_unlock()</function> for shared data, whether it + be a timer, tasklet, different softirq or the same or another + softirq: any of them could be running on a different CPU. + </para> + </sect2> + </sect1> + </chapter> + + <chapter id="hardirq-context"> + <title>Hard IRQ Context</title> + + <para> + Hardware interrupts usually communicate with a + tasklet or softirq. Frequently this involves putting work in a + queue, which the softirq will take out. + </para> + + <sect1 id="hardirq-softirq"> + <title>Locking Between Hard IRQ and Softirqs/Tasklets</title> + + <para> + If a hardware irq handler shares data with a softirq, you have + two concerns. Firstly, the softirq processing can be + interrupted by a hardware interrupt, and secondly, the + critical region could be entered by a hardware interrupt on + another CPU. This is where <function>spin_lock_irq()</function> is + used. It is defined to disable interrupts on that cpu, then grab + the lock. <function>spin_unlock_irq()</function> does the reverse. + </para> + + <para> + The irq handler does not to use + <function>spin_lock_irq()</function>, because the softirq cannot + run while the irq handler is running: it can use + <function>spin_lock()</function>, which is slightly faster. The + only exception would be if a different hardware irq handler uses + the same lock: <function>spin_lock_irq()</function> will stop + that from interrupting us. + </para> + + <para> + This works perfectly for UP as well: the spin lock vanishes, + and this macro simply becomes <function>local_irq_disable()</function> + (<filename class="headerfile">include/asm/smp.h</filename>), which + protects you from the softirq/tasklet/BH being run. + </para> + + <para> + <function>spin_lock_irqsave()</function> + (<filename>include/linux/spinlock.h</filename>) is a variant + which saves whether interrupts were on or off in a flags word, + which is passed to <function>spin_unlock_irqrestore()</function>. This + means that the same code can be used inside an hard irq handler (where + interrupts are already off) and in softirqs (where the irq + disabling is required). + </para> + + <para> + Note that softirqs (and hence tasklets and timers) are run on + return from hardware interrupts, so + <function>spin_lock_irq()</function> also stops these. In that + sense, <function>spin_lock_irqsave()</function> is the most + general and powerful locking function. + </para> + + </sect1> + <sect1 id="hardirq-hardirq"> + <title>Locking Between Two Hard IRQ Handlers</title> + <para> + It is rare to have to share data between two IRQ handlers, but + if you do, <function>spin_lock_irqsave()</function> should be + used: it is architecture-specific whether all interrupts are + disabled inside irq handlers themselves. + </para> + </sect1> + + </chapter> + + <chapter id="cheatsheet"> + <title>Cheat Sheet For Locking</title> + <para> + Pete Zaitcev gives the following summary: + </para> + <itemizedlist> + <listitem> + <para> + If you are in a process context (any syscall) and want to + lock other process out, use a semaphore. You can take a semaphore + and sleep (<function>copy_from_user*(</function> or + <function>kmalloc(x,GFP_KERNEL)</function>). + </para> + </listitem> + <listitem> + <para> + Otherwise (== data can be touched in an interrupt), use + <function>spin_lock_irqsave()</function> and + <function>spin_unlock_irqrestore()</function>. + </para> + </listitem> + <listitem> + <para> + Avoid holding spinlock for more than 5 lines of code and + across any function call (except accessors like + <function>readb</function>). + </para> + </listitem> + </itemizedlist> + + <sect1 id="minimum-lock-reqirements"> + <title>Table of Minimum Requirements</title> + + <para> The following table lists the <emphasis>minimum</emphasis> + locking requirements between various contexts. In some cases, + the same context can only be running on one CPU at a time, so + no locking is required for that context (eg. a particular + thread can only run on one CPU at a time, but if it needs + shares data with another thread, locking is required). + </para> + <para> + Remember the advice above: you can always use + <function>spin_lock_irqsave()</function>, which is a superset + of all other spinlock primitives. + </para> + <table> +<title>Table of Locking Requirements</title> +<tgroup cols="11"> +<tbody> +<row> +<entry></entry> +<entry>IRQ Handler A</entry> +<entry>IRQ Handler B</entry> +<entry>Softirq A</entry> +<entry>Softirq B</entry> +<entry>Tasklet A</entry> +<entry>Tasklet B</entry> +<entry>Timer A</entry> +<entry>Timer B</entry> +<entry>User Context A</entry> +<entry>User Context B</entry> +</row> + +<row> +<entry>IRQ Handler A</entry> +<entry>None</entry> +</row> + +<row> +<entry>IRQ Handler B</entry> +<entry>spin_lock_irqsave</entry> +<entry>None</entry> +</row> + +<row> +<entry>Softirq A</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock</entry> +</row> + +<row> +<entry>Softirq B</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +</row> + +<row> +<entry>Tasklet A</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>None</entry> +</row> + +<row> +<entry>Tasklet B</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>None</entry> +</row> + +<row> +<entry>Timer A</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>None</entry> +</row> + +<row> +<entry>Timer B</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>spin_lock</entry> +<entry>None</entry> +</row> + +<row> +<entry>User Context A</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>None</entry> +</row> + +<row> +<entry>User Context B</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_irq</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>spin_lock_bh</entry> +<entry>down_interruptible</entry> +<entry>None</entry> +</row> + +</tbody> +</tgroup> +</table> +</sect1> +</chapter> + + <chapter id="Examples"> + <title>Common Examples</title> + <para> +Let's step through a simple example: a cache of number to name +mappings. The cache keeps a count of how often each of the objects is +used, and when it gets full, throws out the least used one. + + </para> + + <sect1 id="examples-usercontext"> + <title>All In User Context</title> + <para> +For our first example, we assume that all operations are in user +context (ie. from system calls), so we can sleep. This means we can +use a semaphore to protect the cache and all the objects within +it. Here's the code: + </para> + + <programlisting> +#include <linux/list.h> +#include <linux/slab.h> +#include <linux/string.h> +#include <asm/semaphore.h> +#include <asm/errno.h> + +struct object +{ + struct list_head list; + int id; + char name[32]; + int popularity; +}; + +/* Protects the cache, cache_num, and the objects within it */ +static DECLARE_MUTEX(cache_lock); +static LIST_HEAD(cache); +static unsigned int cache_num = 0; +#define MAX_CACHE_SIZE 10 + +/* Must be holding cache_lock */ +static struct object *__cache_find(int id) +{ + struct object *i; + + list_for_each_entry(i, &cache, list) + if (i->id == id) { + i->popularity++; + return i; + } + return NULL; +} + +/* Must be holding cache_lock */ +static void __cache_delete(struct object *obj) +{ + BUG_ON(!obj); + list_del(&obj->list); + kfree(obj); + cache_num--; +} + +/* Must be holding cache_lock */ +static void __cache_add(struct object *obj) +{ + list_add(&obj->list, &cache); + if (++cache_num > MAX_CACHE_SIZE) { + struct object *i, *outcast = NULL; + list_for_each_entry(i, &cache, list) { + if (!outcast || i->popularity < outcast->popularity) + outcast = i; + } + __cache_delete(outcast); + } +} + +int cache_add(int id, const char *name) +{ + struct object *obj; + + if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL) + return -ENOMEM; + + strlcpy(obj->name, name, sizeof(obj->name)); + obj->id = id; + obj->popularity = 0; + + down(&cache_lock); + __cache_add(obj); + up(&cache_lock); + return 0; +} + +void cache_delete(int id) +{ + down(&cache_lock); + __cache_delete(__cache_find(id)); + up(&cache_lock); +} + +int cache_find(int id, char *name) +{ + struct object *obj; + int ret = -ENOENT; + + down(&cache_lock); + obj = __cache_find(id); + if (obj) { + ret = 0; + strcpy(name, obj->name); + } + up(&cache_lock); + return ret; +} +</programlisting> + + <para> +Note that we always make sure we have the cache_lock when we add, +delete, or look up the cache: both the cache infrastructure itself and +the contents of the objects are protected by the lock. In this case +it's easy, since we copy the data for the user, and never let them +access the objects directly. + </para> + <para> +There is a slight (and common) optimization here: in +<function>cache_add</function> we set up the fields of the object +before grabbing the lock. This is safe, as no-one else can access it +until we put it in cache. + </para> + </sect1> + + <sect1 id="examples-interrupt"> + <title>Accessing From Interrupt Context</title> + <para> +Now consider the case where <function>cache_find</function> can be +called from interrupt context: either a hardware interrupt or a +softirq. An example would be a timer which deletes object from the +cache. + </para> + <para> +The change is shown below, in standard patch format: the +<symbol>-</symbol> are lines which are taken away, and the +<symbol>+</symbol> are lines which are added. + </para> +<programlisting> +--- cache.c.usercontext 2003-12-09 13:58:54.000000000 +1100 ++++ cache.c.interrupt 2003-12-09 14:07:49.000000000 +1100 +@@ -12,7 +12,7 @@ + int popularity; + }; + +-static DECLARE_MUTEX(cache_lock); ++static spinlock_t cache_lock = SPIN_LOCK_UNLOCKED; + static LIST_HEAD(cache); + static unsigned int cache_num = 0; + #define MAX_CACHE_SIZE 10 +@@ -55,6 +55,7 @@ + int cache_add(int id, const char *name) + { + struct object *obj; ++ unsigned long flags; + + if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL) + return -ENOMEM; +@@ -63,30 +64,33 @@ + obj->id = id; + obj->popularity = 0; + +- down(&cache_lock); ++ spin_lock_irqsave(&cache_lock, flags); + __cache_add(obj); +- up(&cache_lock); ++ spin_unlock_irqrestore(&cache_lock, flags); + return 0; + } + + void cache_delete(int id) + { +- down(&cache_lock); ++ unsigned long flags; ++ ++ spin_lock_irqsave(&cache_lock, flags); + __cache_delete(__cache_find(id)); +- up(&cache_lock); ++ spin_unlock_irqrestore(&cache_lock, flags); + } + + int cache_find(int id, char *name) + { + struct object *obj; + int ret = -ENOENT; ++ unsigned long flags; + +- down(&cache_lock); ++ spin_lock_irqsave(&cache_lock, flags); + obj = __cache_find(id); + if (obj) { + ret = 0; + strcpy(name, obj->name); + } +- up(&cache_lock); ++ spin_unlock_irqrestore(&cache_lock, flags); + return ret; + } +</programlisting> + + <para> +Note that the <function>spin_lock_irqsave</function> will turn off +interrupts if they are on, otherwise does nothing (if we are already +in an interrupt handler), hence these functions are safe to call from +any context. + </para> + <para> +Unfortunately, <function>cache_add</function> calls +<function>kmalloc</function> with the <symbol>GFP_KERNEL</symbol> +flag, which is only legal in user context. I have assumed that +<function>cache_add</function> is still only called in user context, +otherwise this should become a parameter to +<function>cache_add</function>. + </para> + </sect1> + <sect1 id="examples-refcnt"> + <title>Exposing Objects Outside This File</title> + <para> +If our objects contained more information, it might not be sufficient +to copy the information in and out: other parts of the code might want +to keep pointers to these objects, for example, rather than looking up +the id every time. This produces two problems. + </para> + <para> +The first problem is that we use the <symbol>cache_lock</symbol> to +protect objects: we'd need to make this non-static so the rest of the +code can use it. This makes locking trickier, as it is no longer all +in one place. + </para> + <para> +The second problem is the lifetime problem: if another structure keeps +a pointer to an object, it presumably expects that pointer to remain +valid. Unfortunately, this is only guaranteed while you hold the +lock, otherwise someone might call <function>cache_delete</function> +and even worse, add another object, re-using the same address. + </para> + <para> +As there is only one lock, you can't hold it forever: no-one else would +get any work done. + </para> + <para> +The solution to this problem is to use a reference count: everyone who +has a pointer to the object increases it when they first get the +object, and drops the reference count when they're finished with it. +Whoever drops it to zero knows it is unused, and can actually delete it. + </para> + <para> +Here is the code: + </para> + +<programlisting> +--- cache.c.interrupt 2003-12-09 14:25:43.000000000 +1100 ++++ cache.c.refcnt 2003-12-09 14:33:05.000000000 +1100 +@@ -7,6 +7,7 @@ + struct object + { + struct list_head list; ++ unsigned int refcnt; + int id; + char name[32]; + int popularity; +@@ -17,6 +18,35 @@ + static unsigned int cache_num = 0; + #define MAX_CACHE_SIZE 10 + ++static void __object_put(struct object *obj) ++{ ++ if (--obj->refcnt == 0) ++ kfree(obj); ++} ++ ++static void __object_get(struct object *obj) ++{ ++ obj->refcnt++; ++} ++ ++void object_put(struct object *obj) ++{ ++ unsigned long flags; ++ ++ spin_lock_irqsave(&cache_lock, flags); ++ __object_put(obj); ++ spin_unlock_irqrestore(&cache_lock, flags); ++} ++ ++void object_get(struct object *obj) ++{ ++ unsigned long flags; ++ ++ spin_lock_irqsave(&cache_lock, flags); ++ __object_get(obj); ++ spin_unlock_irqrestore(&cache_lock, flags); ++} ++ + /* Must be holding cache_lock */ + static struct object *__cache_find(int id) + { +@@ -35,6 +65,7 @@ + { + BUG_ON(!obj); + list_del(&obj->list); ++ __object_put(obj); + cache_num--; + } + +@@ -63,6 +94,7 @@ + strlcpy(obj->name, name, sizeof(obj->name)); + obj->id = id; + obj->popularity = 0; ++ obj->refcnt = 1; /* The cache holds a reference */ + + spin_lock_irqsave(&cache_lock, flags); + __cache_add(obj); +@@ -79,18 +111,15 @@ + spin_unlock_irqrestore(&cache_lock, flags); + } + +-int cache_find(int id, char *name) ++struct object *cache_find(int id) + { + struct object *obj; +- int ret = -ENOENT; + unsigned long flags; + + spin_lock_irqsave(&cache_lock, flags); + obj = __cache_find(id); +- if (obj) { +- ret = 0; +- strcpy(name, obj->name); +- } ++ if (obj) ++ __object_get(obj); + spin_unlock_irqrestore(&cache_lock, flags); +- return ret; ++ return obj; + } +</programlisting> + +<para> +We encapsulate the reference counting in the standard 'get' and 'put' +functions. Now we can return the object itself from +<function>cache_find</function> which has the advantage that the user +can now sleep holding the object (eg. to +<function>copy_to_user</function> to name to userspace). +</para> +<para> +The other point to note is that I said a reference should be held for +every pointer to the object: thus the reference count is 1 when first +inserted into the cache. In some versions the framework does not hold +a reference count, but they are more complicated. +</para> + + <sect2 id="examples-refcnt-atomic"> + <title>Using Atomic Operations For The Reference Count</title> +<para> +In practice, <type>atomic_t</type> would usually be used for +<structfield>refcnt</structfield>. There are a number of atomic +operations defined in + +<filename class="headerfile">include/asm/atomic.h</filename>: these are +guaranteed to be seen atomically from all CPUs in the system, so no +lock is required. In this case, it is simpler than using spinlocks, +although for anything non-trivial using spinlocks is clearer. The +<function>atomic_inc</function> and +<function>atomic_dec_and_test</function> are used instead of the +standard increment and decrement operators, and the lock is no longer +used to protect the reference count itself. +</para> + +<programlisting> +--- cache.c.refcnt 2003-12-09 15:00:35.000000000 +1100 ++++ cache.c.refcnt-atomic 2003-12-11 15:49:42.000000000 +1100 +@@ -7,7 +7,7 @@ + struct object + { + struct list_head list; +- unsigned int refcnt; ++ atomic_t refcnt; + int id; + char name[32]; + int popularity; +@@ -18,33 +18,15 @@ + static unsigned int cache_num = 0; + #define MAX_CACHE_SIZE 10 + +-static void __object_put(struct object *obj) +-{ +- if (--obj->refcnt == 0) +- kfree(obj); +-} +- +-static void __object_get(struct object *obj) +-{ +- obj->refcnt++; +-} +- + void object_put(struct object *obj) + { +- unsigned long flags; +- +- spin_lock_irqsave(&cache_lock, flags); +- __object_put(obj); +- spin_unlock_irqrestore(&cache_lock, flags); ++ if (atomic_dec_and_test(&obj->refcnt)) ++ kfree(obj); + } + + void object_get(struct object *obj) + { +- unsigned long flags; +- +- spin_lock_irqsave(&cache_lock, flags); +- __object_get(obj); +- spin_unlock_irqrestore(&cache_lock, flags); ++ atomic_inc(&obj->refcnt); + } + + /* Must be holding cache_lock */ +@@ -65,7 +47,7 @@ + { + BUG_ON(!obj); + list_del(&obj->list); +- __object_put(obj); ++ object_put(obj); + cache_num--; + } + +@@ -94,7 +76,7 @@ + strlcpy(obj->name, name, sizeof(obj->name)); + obj->id = id; + obj->popularity = 0; +- obj->refcnt = 1; /* The cache holds a reference */ ++ atomic_set(&obj->refcnt, 1); /* The cache holds a reference */ + + spin_lock_irqsave(&cache_lock, flags); + __cache_add(obj); +@@ -119,7 +101,7 @@ + spin_lock_irqsave(&cache_lock, flags); + obj = __cache_find(id); + if (obj) +- __object_get(obj); ++ object_get(obj); + spin_unlock_irqrestore(&cache_lock, flags); + return obj; + } +</programlisting> +</sect2> +</sect1> + + <sect1 id="examples-lock-per-obj"> + <title>Protecting The Objects Themselves</title> + <para> +In these examples, we assumed that the objects (except the reference +counts) never changed once they are created. If we wanted to allow +the name to change, there are three possibilities: + </para> + <itemizedlist> + <listitem> + <para> +You can make <symbol>cache_lock</symbol> non-static, and tell people +to grab that lock before changing the name in any object. + </para> + </listitem> + <listitem> + <para> +You can provide a <function>cache_obj_rename</function> which grabs +this lock and changes the name for the caller, and tell everyone to +use that function. + </para> + </listitem> + <listitem> + <para> +You can make the <symbol>cache_lock</symbol> protect only the cache +itself, and use another lock to protect the name. + </para> + </listitem> + </itemizedlist> + + <para> +Theoretically, you can make the locks as fine-grained as one lock for +every field, for every object. In practice, the most common variants +are: +</para> + <itemizedlist> + <listitem> + <para> +One lock which protects the infrastructure (the <symbol>cache</symbol> +list in this example) and all the objects. This is what we have done +so far. + </para> + </listitem> + <listitem> + <para> +One lock which protects the infrastructure (including the list +pointers inside the objects), and one lock inside the object which +protects the rest of that object. + </para> + </listitem> + <listitem> + <para> +Multiple locks to protect the infrastructure (eg. one lock per hash +chain), possibly with a separate per-object lock. + </para> + </listitem> + </itemizedlist> + +<para> +Here is the "lock-per-object" implementation: +</para> +<programlisting> +--- cache.c.refcnt-atomic 2003-12-11 15:50:54.000000000 +1100 ++++ cache.c.perobjectlock 2003-12-11 17:15:03.000000000 +1100 +@@ -6,11 +6,17 @@ + + struct object + { ++ /* These two protected by cache_lock. */ + struct list_head list; ++ int popularity; ++ + atomic_t refcnt; ++ ++ /* Doesn't change once created. */ + int id; ++ ++ spinlock_t lock; /* Protects the name */ + char name[32]; +- int popularity; + }; + + static spinlock_t cache_lock = SPIN_LOCK_UNLOCKED; +@@ -77,6 +84,7 @@ + obj->id = id; + obj->popularity = 0; + atomic_set(&obj->refcnt, 1); /* The cache holds a reference */ ++ spin_lock_init(&obj->lock); + + spin_lock_irqsave(&cache_lock, flags); + __cache_add(obj); +</programlisting> + +<para> +Note that I decide that the <structfield>popularity</structfield> +count should be protected by the <symbol>cache_lock</symbol> rather +than the per-object lock: this is because it (like the +<structname>struct list_head</structname> inside the object) is +logically part of the infrastructure. This way, I don't need to grab +the lock of every object in <function>__cache_add</function> when +seeking the least popular. +</para> + +<para> +I also decided that the <structfield>id</structfield> member is +unchangeable, so I don't need to grab each object lock in +<function>__cache_find()</function> to examine the +<structfield>id</structfield>: the object lock is only used by a +caller who wants to read or write the <structfield>name</structfield> +field. +</para> + +<para> +Note also that I added a comment describing what data was protected by +which locks. This is extremely important, as it describes the runtime +behavior of the code, and can be hard to gain from just reading. And +as Alan Cox says, <quote>Lock data, not code</quote>. +</para> +</sect1> +</chapter> + + <chapter id="common-problems"> + <title>Common Problems</title> + <sect1 id="deadlock"> + <title>Deadlock: Simple and Advanced</title> + + <para> + There is a coding bug where a piece of code tries to grab a + spinlock twice: it will spin forever, waiting for the lock to + be released (spinlocks, rwlocks and semaphores are not + recursive in Linux). This is trivial to diagnose: not a + stay-up-five-nights-talk-to-fluffy-code-bunnies kind of + problem. + </para> + + <para> + For a slightly more complex case, imagine you have a region + shared by a softirq and user context. If you use a + <function>spin_lock()</function> call to protect it, it is + possible that the user context will be interrupted by the softirq + while it holds the lock, and the softirq will then spin + forever trying to get the same lock. + </para> + + <para> + Both of these are called deadlock, and as shown above, it can + occur even with a single CPU (although not on UP compiles, + since spinlocks vanish on kernel compiles with + <symbol>CONFIG_SMP</symbol>=n. You'll still get data corruption + in the second example). + </para> + + <para> + This complete lockup is easy to diagnose: on SMP boxes the + watchdog timer or compiling with <symbol>DEBUG_SPINLOCKS</symbol> set + (<filename>include/linux/spinlock.h</filename>) will show this up + immediately when it happens. + </para> + + <para> + A more complex problem is the so-called 'deadly embrace', + involving two or more locks. Say you have a hash table: each + entry in the table is a spinlock, and a chain of hashed + objects. Inside a softirq handler, you sometimes want to + alter an object from one place in the hash to another: you + grab the spinlock of the old hash chain and the spinlock of + the new hash chain, and delete the object from the old one, + and insert it in the new one. + </para> + + <para> + There are two problems here. First, if your code ever + tries to move the object to the same chain, it will deadlock + with itself as it tries to lock it twice. Secondly, if the + same softirq on another CPU is trying to move another object + in the reverse direction, the following could happen: + </para> + + <table> + <title>Consequences</title> + + <tgroup cols="2" align="left"> + + <thead> + <row> + <entry>CPU 1</entry> + <entry>CPU 2</entry> + </row> + </thead> + + <tbody> + <row> + <entry>Grab lock A -> OK</entry> + <entry>Grab lock B -> OK</entry> + </row> + <row> + <entry>Grab lock B -> spin</entry> + <entry>Grab lock A -> spin</entry> + </row> + </tbody> + </tgroup> + </table> + + <para> + The two CPUs will spin forever, waiting for the other to give up + their lock. It will look, smell, and feel like a crash. + </para> + </sect1> + + <sect1 id="techs-deadlock-prevent"> + <title>Preventing Deadlock</title> + + <para> + Textbooks will tell you that if you always lock in the same + order, you will never get this kind of deadlock. Practice + will tell you that this approach doesn't scale: when I + create a new lock, I don't understand enough of the kernel + to figure out where in the 5000 lock hierarchy it will fit. + </para> + + <para> + The best locks are encapsulated: they never get exposed in + headers, and are never held around calls to non-trivial + functions outside the same file. You can read through this + code and see that it will never deadlock, because it never + tries to grab another lock while it has that one. People + using your code don't even need to know you are using a + lock. + </para> + + <para> + A classic problem here is when you provide callbacks or + hooks: if you call these with the lock held, you risk simple + deadlock, or a deadly embrace (who knows what the callback + will do?). Remember, the other programmers are out to get + you, so don't do this. + </para> + + <sect2 id="techs-deadlock-overprevent"> + <title>Overzealous Prevention Of Deadlocks</title> + + <para> + Deadlocks are problematic, but not as bad as data + corruption. Code which grabs a read lock, searches a list, + fails to find what it wants, drops the read lock, grabs a + write lock and inserts the object has a race condition. + </para> + + <para> + If you don't see why, please stay the fuck away from my code. + </para> + </sect2> + </sect1> + + <sect1 id="racing-timers"> + <title>Racing Timers: A Kernel Pastime</title> + + <para> + Timers can produce their own special problems with races. + Consider a collection of objects (list, hash, etc) where each + object has a timer which is due to destroy it. + </para> + + <para> + If you want to destroy the entire collection (say on module + removal), you might do the following: + </para> + + <programlisting> + /* THIS CODE BAD BAD BAD BAD: IF IT WAS ANY WORSE IT WOULD USE + HUNGARIAN NOTATION */ + spin_lock_bh(&list_lock); + + while (list) { + struct foo *next = list->next; + del_timer(&list->timer); + kfree(list); + list = next; + } + + spin_unlock_bh(&list_lock); + </programlisting> + + <para> + Sooner or later, this will crash on SMP, because a timer can + have just gone off before the <function>spin_lock_bh()</function>, + and it will only get the lock after we + <function>spin_unlock_bh()</function>, and then try to free + the element (which has already been freed!). + </para> + + <para> + This can be avoided by checking the result of + <function>del_timer()</function>: if it returns + <returnvalue>1</returnvalue>, the timer has been deleted. + If <returnvalue>0</returnvalue>, it means (in this + case) that it is currently running, so we can do: + </para> + + <programlisting> + retry: + spin_lock_bh(&list_lock); + + while (list) { + struct foo *next = list->next; + if (!del_timer(&list->timer)) { + /* Give timer a chance to delete this */ + spin_unlock_bh(&list_lock); + goto retry; + } + kfree(list); + list = next; + } + + spin_unlock_bh(&list_lock); + </programlisting> + + <para> + Another common problem is deleting timers which restart + themselves (by calling <function>add_timer()</function> at the end + of their timer function). Because this is a fairly common case + which is prone to races, you should use <function>del_timer_sync()</function> + (<filename class="headerfile">include/linux/timer.h</filename>) + to handle this case. It returns the number of times the timer + had to be deleted before we finally stopped it from adding itself back + in. + </para> + </sect1> + + </chapter> + + <chapter id="Efficiency"> + <title>Locking Speed</title> + + <para> +There are three main things to worry about when considering speed of +some code which does locking. First is concurrency: how many things +are going to be waiting while someone else is holding a lock. Second +is the time taken to actually acquire and release an uncontended lock. +Third is using fewer, or smarter locks. I'm assuming that the lock is +used fairly often: otherwise, you wouldn't be concerned about +efficiency. +</para> + <para> +Concurrency depends on how long the lock is usually held: you should +hold the lock for as long as needed, but no longer. In the cache +example, we always create the object without the lock held, and then +grab the lock only when we are ready to insert it in the list. +</para> + <para> +Acquisition times depend on how much damage the lock operations do to +the pipeline (pipeline stalls) and how likely it is that this CPU was +the last one to grab the lock (ie. is the lock cache-hot for this +CPU): on a machine with more CPUs, this likelihood drops fast. +Consider a 700MHz Intel Pentium III: an instruction takes about 0.7ns, +an atomic increment takes about 58ns, a lock which is cache-hot on +this CPU takes 160ns, and a cacheline transfer from another CPU takes +an additional 170 to 360ns. (These figures from Paul McKenney's +<ulink url="http://www.linuxjournal.com/article.php?sid=6993"> Linux +Journal RCU article</ulink>). +</para> + <para> +These two aims conflict: holding a lock for a short time might be done +by splitting locks into parts (such as in our final per-object-lock +example), but this increases the number of lock acquisitions, and the +results are often slower than having a single lock. This is another +reason to advocate locking simplicity. +</para> + <para> +The third concern is addressed below: there are some methods to reduce +the amount of locking which needs to be done. +</para> + + <sect1 id="efficiency-rwlocks"> + <title>Read/Write Lock Variants</title> + + <para> + Both spinlocks and semaphores have read/write variants: + <type>rwlock_t</type> and <structname>struct rw_semaphore</structname>. + These divide users into two classes: the readers and the writers. If + you are only reading the data, you can get a read lock, but to write to + the data you need the write lock. Many people can hold a read lock, + but a writer must be sole holder. + </para> + + <para> + If your code divides neatly along reader/writer lines (as our + cache code does), and the lock is held by readers for + significant lengths of time, using these locks can help. They + are slightly slower than the normal locks though, so in practice + <type>rwlock_t</type> is not usually worthwhile. + </para> + </sect1> + + <sect1 id="efficiency-read-copy-update"> + <title>Avoiding Locks: Read Copy Update</title> + + <para> + There is a special method of read/write locking called Read Copy + Update. Using RCU, the readers can avoid taking a lock + altogether: as we expect our cache to be read more often than + updated (otherwise the cache is a waste of time), it is a + candidate for this optimization. + </para> + + <para> + How do we get rid of read locks? Getting rid of read locks + means that writers may be changing the list underneath the + readers. That is actually quite simple: we can read a linked + list while an element is being added if the writer adds the + element very carefully. For example, adding + <symbol>new</symbol> to a single linked list called + <symbol>list</symbol>: + </para> + + <programlisting> + new->next = list->next; + wmb(); + list->next = new; + </programlisting> + + <para> + The <function>wmb()</function> is a write memory barrier. It + ensures that the first operation (setting the new element's + <symbol>next</symbol> pointer) is complete and will be seen by + all CPUs, before the second operation is (putting the new + element into the list). This is important, since modern + compilers and modern CPUs can both reorder instructions unless + told otherwise: we want a reader to either not see the new + element at all, or see the new element with the + <symbol>next</symbol> pointer correctly pointing at the rest of + the list. + </para> + <para> + Fortunately, there is a function to do this for standard + <structname>struct list_head</structname> lists: + <function>list_add_rcu()</function> + (<filename>include/linux/list.h</filename>). + </para> + <para> + Removing an element from the list is even simpler: we replace + the pointer to the old element with a pointer to its successor, + and readers will either see it, or skip over it. + </para> + <programlisting> + list->next = old->next; + </programlisting> + <para> + There is <function>list_del_rcu()</function> + (<filename>include/linux/list.h</filename>) which does this (the + normal version poisons the old object, which we don't want). + </para> + <para> + The reader must also be careful: some CPUs can look through the + <symbol>next</symbol> pointer to start reading the contents of + the next element early, but don't realize that the pre-fetched + contents is wrong when the <symbol>next</symbol> pointer changes + underneath them. Once again, there is a + <function>list_for_each_entry_rcu()</function> + (<filename>include/linux/list.h</filename>) to help you. Of + course, writers can just use + <function>list_for_each_entry()</function>, since there cannot + be two simultaneous writers. + </para> + <para> + Our final dilemma is this: when can we actually destroy the + removed element? Remember, a reader might be stepping through + this element in the list right now: it we free this element and + the <symbol>next</symbol> pointer changes, the reader will jump + off into garbage and crash. We need to wait until we know that + all the readers who were traversing the list when we deleted the + element are finished. We use <function>call_rcu()</function> to + register a callback which will actually destroy the object once + the readers are finished. + </para> + <para> + But how does Read Copy Update know when the readers are + finished? The method is this: firstly, the readers always + traverse the list inside + <function>rcu_read_lock()</function>/<function>rcu_read_unlock()</function> + pairs: these simply disable preemption so the reader won't go to + sleep while reading the list. + </para> + <para> + RCU then waits until every other CPU has slept at least once: + since readers cannot sleep, we know that any readers which were + traversing the list during the deletion are finished, and the + callback is triggered. The real Read Copy Update code is a + little more optimized than this, but this is the fundamental + idea. + </para> + +<programlisting> +--- cache.c.perobjectlock 2003-12-11 17:15:03.000000000 +1100 ++++ cache.c.rcupdate 2003-12-11 17:55:14.000000000 +1100 +@@ -1,15 +1,18 @@ + #include <linux/list.h> + #include <linux/slab.h> + #include <linux/string.h> ++#include <linux/rcupdate.h> + #include <asm/semaphore.h> + #include <asm/errno.h> + + struct object + { +- /* These two protected by cache_lock. */ ++ /* This is protected by RCU */ + struct list_head list; + int popularity; + ++ struct rcu_head rcu; ++ + atomic_t refcnt; + + /* Doesn't change once created. */ +@@ -40,7 +43,7 @@ + { + struct object *i; + +- list_for_each_entry(i, &cache, list) { ++ list_for_each_entry_rcu(i, &cache, list) { + if (i->id == id) { + i->popularity++; + return i; +@@ -49,19 +52,25 @@ + return NULL; + } + ++/* Final discard done once we know no readers are looking. */ ++static void cache_delete_rcu(void *arg) ++{ ++ object_put(arg); ++} ++ + /* Must be holding cache_lock */ + static void __cache_delete(struct object *obj) + { + BUG_ON(!obj); +- list_del(&obj->list); +- object_put(obj); ++ list_del_rcu(&obj->list); + cache_num--; ++ call_rcu(&obj->rcu, cache_delete_rcu, obj); + } + + /* Must be holding cache_lock */ + static void __cache_add(struct object *obj) + { +- list_add(&obj->list, &cache); ++ list_add_rcu(&obj->list, &cache); + if (++cache_num > MAX_CACHE_SIZE) { + struct object *i, *outcast = NULL; + list_for_each_entry(i, &cache, list) { +@@ -85,6 +94,7 @@ + obj->popularity = 0; + atomic_set(&obj->refcnt, 1); /* The cache holds a reference */ + spin_lock_init(&obj->lock); ++ INIT_RCU_HEAD(&obj->rcu); + + spin_lock_irqsave(&cache_lock, flags); + __cache_add(obj); +@@ -104,12 +114,11 @@ + struct object *cache_find(int id) + { + struct object *obj; +- unsigned long flags; + +- spin_lock_irqsave(&cache_lock, flags); ++ rcu_read_lock(); + obj = __cache_find(id); + if (obj) + object_get(obj); +- spin_unlock_irqrestore(&cache_lock, flags); ++ rcu_read_unlock(); + return obj; + } +</programlisting> + +<para> +Note that the reader will alter the +<structfield>popularity</structfield> member in +<function>__cache_find()</function>, and now it doesn't hold a lock. +One solution would be to make it an <type>atomic_t</type>, but for +this usage, we don't really care about races: an approximate result is +good enough, so I didn't change it. +</para> + +<para> +The result is that <function>cache_find()</function> requires no +synchronization with any other functions, so is almost as fast on SMP +as it would be on UP. +</para> + +<para> +There is a furthur optimization possible here: remember our original +cache code, where there were no reference counts and the caller simply +held the lock whenever using the object? This is still possible: if +you hold the lock, noone can delete the object, so you don't need to +get and put the reference count. +</para> + +<para> +Now, because the 'read lock' in RCU is simply disabling preemption, a +caller which always has preemption disabled between calling +<function>cache_find()</function> and +<function>object_put()</function> does not need to actually get and +put the reference count: we could expose +<function>__cache_find()</function> by making it non-static, and +such callers could simply call that. +</para> +<para> +The benefit here is that the reference count is not written to: the +object is not altered in any way, which is much faster on SMP +machines due to caching. +</para> + </sect1> + + <sect1 id="per-cpu"> + <title>Per-CPU Data</title> + + <para> + Another technique for avoiding locking which is used fairly + widely is to duplicate information for each CPU. For example, + if you wanted to keep a count of a common condition, you could + use a spin lock and a single counter. Nice and simple. + </para> + + <para> + If that was too slow (it's usually not, but if you've got a + really big machine to test on and can show that it is), you + could instead use a counter for each CPU, then none of them need + an exclusive lock. See <function>DEFINE_PER_CPU()</function>, + <function>get_cpu_var()</function> and + <function>put_cpu_var()</function> + (<filename class="headerfile">include/linux/percpu.h</filename>). + </para> + + <para> + Of particular use for simple per-cpu counters is the + <type>local_t</type> type, and the + <function>cpu_local_inc()</function> and related functions, + which are more efficient than simple code on some architectures + (<filename class="headerfile">include/asm/local.h</filename>). + </para> + + <para> + Note that there is no simple, reliable way of getting an exact + value of such a counter, without introducing more locks. This + is not a problem for some uses. + </para> + </sect1> + + <sect1 id="mostly-hardirq"> + <title>Data Which Mostly Used By An IRQ Handler</title> + + <para> + If data is always accessed from within the same IRQ handler, you + don't need a lock at all: the kernel already guarantees that the + irq handler will not run simultaneously on multiple CPUs. + </para> + <para> + Manfred Spraul points out that you can still do this, even if + the data is very occasionally accessed in user context or + softirqs/tasklets. The irq handler doesn't use a lock, and + all other accesses are done as so: + </para> + +<programlisting> + spin_lock(&lock); + disable_irq(irq); + ... + enable_irq(irq); + spin_unlock(&lock); +</programlisting> + <para> + The <function>disable_irq()</function> prevents the irq handler + from running (and waits for it to finish if it's currently + running on other CPUs). The spinlock prevents any other + accesses happening at the same time. Naturally, this is slower + than just a <function>spin_lock_irq()</function> call, so it + only makes sense if this type of access happens extremely + rarely. + </para> + </sect1> + </chapter> + + <chapter id="sleeping-things"> + <title>What Functions Are Safe To Call From Interrupts?</title> + + <para> + Many functions in the kernel sleep (ie. call schedule()) + directly or indirectly: you can never call them while holding a + spinlock, or with preemption disabled. This also means you need + to be in user context: calling them from an interrupt is illegal. + </para> + + <sect1 id="sleeping"> + <title>Some Functions Which Sleep</title> + + <para> + The most common ones are listed below, but you usually have to + read the code to find out if other calls are safe. If everyone + else who calls it can sleep, you probably need to be able to + sleep, too. In particular, registration and deregistration + functions usually expect to be called from user context, and can + sleep. + </para> + + <itemizedlist> + <listitem> + <para> + Accesses to + <firstterm linkend="gloss-userspace">userspace</firstterm>: + </para> + <itemizedlist> + <listitem> + <para> + <function>copy_from_user()</function> + </para> + </listitem> + <listitem> + <para> + <function>copy_to_user()</function> + </para> + </listitem> + <listitem> + <para> + <function>get_user()</function> + </para> + </listitem> + <listitem> + <para> + <function> put_user()</function> + </para> + </listitem> + </itemizedlist> + </listitem> + + <listitem> + <para> + <function>kmalloc(GFP_KERNEL)</function> + </para> + </listitem> + + <listitem> + <para> + <function>down_interruptible()</function> and + <function>down()</function> + </para> + <para> + There is a <function>down_trylock()</function> which can be + used inside interrupt context, as it will not sleep. + <function>up()</function> will also never sleep. + </para> + </listitem> + </itemizedlist> + </sect1> + + <sect1 id="dont-sleep"> + <title>Some Functions Which Don't Sleep</title> + + <para> + Some functions are safe to call from any context, or holding + almost any lock. + </para> + + <itemizedlist> + <listitem> + <para> + <function>printk()</function> + </para> + </listitem> + <listitem> + <para> + <function>kfree()</function> + </para> + </listitem> + <listitem> + <para> + <function>add_timer()</function> and <function>del_timer()</function> + </para> + </listitem> + </itemizedlist> + </sect1> + </chapter> + + <chapter id="references"> + <title>Further reading</title> + + <itemizedlist> + <listitem> + <para> + <filename>Documentation/spinlocks.txt</filename>: + Linus Torvalds' spinlocking tutorial in the kernel sources. + </para> + </listitem> + + <listitem> + <para> + Unix Systems for Modern Architectures: Symmetric + Multiprocessing and Caching for Kernel Programmers: + </para> + + <para> + Curt Schimmel's very good introduction to kernel level + locking (not written for Linux, but nearly everything + applies). The book is expensive, but really worth every + penny to understand SMP locking. [ISBN: 0201633388] + </para> + </listitem> + </itemizedlist> + </chapter> + + <chapter id="thanks"> + <title>Thanks</title> + + <para> + Thanks to Telsa Gwynne for DocBooking, neatening and adding + style. + </para> + + <para> + Thanks to Martin Pool, Philipp Rumpf, Stephen Rothwell, Paul + Mackerras, Ruedi Aschwanden, Alan Cox, Manfred Spraul, Tim + Waugh, Pete Zaitcev, James Morris, Robert Love, Paul McKenney, + John Ashby for proofreading, correcting, flaming, commenting. + </para> + + <para> + Thanks to the cabal for having no influence on this document. + </para> + </chapter> + + <glossary id="glossary"> + <title>Glossary</title> + + <glossentry id="gloss-preemption"> + <glossterm>preemption</glossterm> + <glossdef> + <para> + Prior to 2.5, or when <symbol>CONFIG_PREEMPT</symbol> is + unset, processes in user context inside the kernel would not + preempt each other (ie. you had that CPU until you have it up, + except for interrupts). With the addition of + <symbol>CONFIG_PREEMPT</symbol> in 2.5.4, this changed: when + in user context, higher priority tasks can "cut in": spinlocks + were changed to disable preemption, even on UP. + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-bh"> + <glossterm>bh</glossterm> + <glossdef> + <para> + Bottom Half: for historical reasons, functions with + '_bh' in them often now refer to any software interrupt, e.g. + <function>spin_lock_bh()</function> blocks any software interrupt + on the current CPU. Bottom halves are deprecated, and will + eventually be replaced by tasklets. Only one bottom half will be + running at any time. + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-hwinterrupt"> + <glossterm>Hardware Interrupt / Hardware IRQ</glossterm> + <glossdef> + <para> + Hardware interrupt request. <function>in_irq()</function> returns + <returnvalue>true</returnvalue> in a hardware interrupt handler. + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-interruptcontext"> + <glossterm>Interrupt Context</glossterm> + <glossdef> + <para> + Not user context: processing a hardware irq or software irq. + Indicated by the <function>in_interrupt()</function> macro + returning <returnvalue>true</returnvalue>. + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-smp"> + <glossterm><acronym>SMP</acronym></glossterm> + <glossdef> + <para> + Symmetric Multi-Processor: kernels compiled for multiple-CPU + machines. (CONFIG_SMP=y). + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-softirq"> + <glossterm>Software Interrupt / softirq</glossterm> + <glossdef> + <para> + Software interrupt handler. <function>in_irq()</function> returns + <returnvalue>false</returnvalue>; <function>in_softirq()</function> + returns <returnvalue>true</returnvalue>. Tasklets and softirqs + both fall into the category of 'software interrupts'. + </para> + <para> + Strictly speaking a softirq is one of up to 32 enumerated software + interrupts which can run on multiple CPUs at once. + Sometimes used to refer to tasklets as + well (ie. all software interrupts). + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-tasklet"> + <glossterm>tasklet</glossterm> + <glossdef> + <para> + A dynamically-registrable software interrupt, + which is guaranteed to only run on one CPU at a time. + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-timers"> + <glossterm>timer</glossterm> + <glossdef> + <para> + A dynamically-registrable software interrupt, which is run at + (or close to) a given time. When running, it is just like a + tasklet (in fact, they are called from the TIMER_SOFTIRQ). + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-up"> + <glossterm><acronym>UP</acronym></glossterm> + <glossdef> + <para> + Uni-Processor: Non-SMP. (CONFIG_SMP=n). + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-usercontext"> + <glossterm>User Context</glossterm> + <glossdef> + <para> + The kernel executing on behalf of a particular process (ie. a + system call or trap) or kernel thread. You can tell which + process with the <symbol>current</symbol> macro.) Not to + be confused with userspace. Can be interrupted by software or + hardware interrupts. + </para> + </glossdef> + </glossentry> + + <glossentry id="gloss-userspace"> + <glossterm>Userspace</glossterm> + <glossdef> + <para> + A process executing its own code outside the kernel. + </para> + </glossdef> + </glossentry> + + </glossary> +</book> + diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl new file mode 100644 index 0000000..cf2fce7 --- /dev/null +++ b/Documentation/DocBook/libata.tmpl @@ -0,0 +1,282 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="libataDevGuide"> + <bookinfo> + <title>libATA Developer's Guide</title> + + <authorgroup> + <author> + <firstname>Jeff</firstname> + <surname>Garzik</surname> + </author> + </authorgroup> + + <copyright> + <year>2003</year> + <holder>Jeff Garzik</holder> + </copyright> + + <legalnotice> + <para> + The contents of this file are subject to the Open + Software License version 1.1 that can be found at + <ulink url="http://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein + by reference. + </para> + + <para> + Alternatively, the contents of this file may be used under the terms + of the GNU General Public License version 2 (the "GPL") as distributed + in the kernel source COPYING file, in which case the provisions of + the GPL are applicable instead of the above. If you wish to allow + the use of your version of this file only under the terms of the + GPL and not to allow others to use your version of this file under + the OSL, indicate your decision by deleting the provisions above and + replace them with the notice and other provisions required by the GPL. + If you do not delete the provisions above, a recipient may use your + version of this file under either the OSL or the GPL. + </para> + + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="libataThanks"> + <title>Thanks</title> + <para> + The bulk of the ATA knowledge comes thanks to long conversations with + Andre Hedrick (www.linux-ide.org). + </para> + <para> + Thanks to Alan Cox for pointing out similarities + between SATA and SCSI, and in general for motivation to hack on + libata. + </para> + <para> + libata's device detection + method, ata_pio_devchk, and in general all the early probing was + based on extensive study of Hale Landis's probe/reset code in his + ATADRVR driver (www.ata-atapi.com). + </para> + </chapter> + + <chapter id="libataDriverApi"> + <title>libata Driver API</title> + <sect1> + <title>struct ata_port_operations</title> + + <programlisting> +void (*port_disable) (struct ata_port *); + </programlisting> + + <para> + Called from ata_bus_probe() and ata_bus_reset() error paths, + as well as when unregistering from the SCSI module (rmmod, hot + unplug). + </para> + + <programlisting> +void (*dev_config) (struct ata_port *, struct ata_device *); + </programlisting> + + <para> + Called after IDENTIFY [PACKET] DEVICE is issued to each device + found. Typically used to apply device-specific fixups prior to + issue of SET FEATURES - XFER MODE, and prior to operation. + </para> + + <programlisting> +void (*set_piomode) (struct ata_port *, struct ata_device *); +void (*set_dmamode) (struct ata_port *, struct ata_device *); +void (*post_set_mode) (struct ata_port *ap); + </programlisting> + + <para> + Hooks called prior to the issue of SET FEATURES - XFER MODE + command. dev->pio_mode is guaranteed to be valid when + ->set_piomode() is called, and dev->dma_mode is guaranteed to be + valid when ->set_dmamode() is called. ->post_set_mode() is + called unconditionally, after the SET FEATURES - XFER MODE + command completes successfully. + </para> + + <para> + ->set_piomode() is always called (if present), but + ->set_dma_mode() is only called if DMA is possible. + </para> + + <programlisting> +void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf); +void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf); + </programlisting> + + <para> + ->tf_load() is called to load the given taskfile into hardware + registers / DMA buffers. ->tf_read() is called to read the + hardware registers / DMA buffers, to obtain the current set of + taskfile register values. + </para> + + <programlisting> +void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf); + </programlisting> + + <para> + causes an ATA command, previously loaded with + ->tf_load(), to be initiated in hardware. + </para> + + <programlisting> +u8 (*check_status)(struct ata_port *ap); +void (*dev_select)(struct ata_port *ap, unsigned int device); + </programlisting> + + <para> + Reads the Status ATA shadow register from hardware. On some + hardware, this has the side effect of clearing the interrupt + condition. + </para> + + <programlisting> +void (*dev_select)(struct ata_port *ap, unsigned int device); + </programlisting> + + <para> + Issues the low-level hardware command(s) that causes one of N + hardware devices to be considered 'selected' (active and + available for use) on the ATA bus. + </para> + + <programlisting> +void (*phy_reset) (struct ata_port *ap); + </programlisting> + + <para> + The very first step in the probe phase. Actions vary depending + on the bus type, typically. After waking up the device and probing + for device presence (PATA and SATA), typically a soft reset + (SRST) will be performed. Drivers typically use the helper + functions ata_bus_reset() or sata_phy_reset() for this hook. + </para> + + <programlisting> +void (*bmdma_setup) (struct ata_queued_cmd *qc); +void (*bmdma_start) (struct ata_queued_cmd *qc); + </programlisting> + + <para> + When setting up an IDE BMDMA transaction, these hooks arm + (->bmdma_setup) and fire (->bmdma_start) the hardware's DMA + engine. + </para> + + <programlisting> +void (*qc_prep) (struct ata_queued_cmd *qc); +int (*qc_issue) (struct ata_queued_cmd *qc); + </programlisting> + + <para> + Higher-level hooks, these two hooks can potentially supercede + several of the above taskfile/DMA engine hooks. ->qc_prep is + called after the buffers have been DMA-mapped, and is typically + used to populate the hardware's DMA scatter-gather table. + Most drivers use the standard ata_qc_prep() helper function, but + more advanced drivers roll their own. + </para> + <para> + ->qc_issue is used to make a command active, once the hardware + and S/G tables have been prepared. IDE BMDMA drivers use the + helper function ata_qc_issue_prot() for taskfile protocol-based + dispatch. More advanced drivers roll their own ->qc_issue + implementation, using this as the "issue new ATA command to + hardware" hook. + </para> + + <programlisting> +void (*eng_timeout) (struct ata_port *ap); + </programlisting> + + <para> + This is a high level error handling function, called from the + error handling thread, when a command times out. + </para> + + <programlisting> +irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); +void (*irq_clear) (struct ata_port *); + </programlisting> + + <para> + ->irq_handler is the interrupt handling routine registered with + the system, by libata. ->irq_clear is called during probe just + before the interrupt handler is registered, to be sure hardware + is quiet. + </para> + + <programlisting> +u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg); +void (*scr_write) (struct ata_port *ap, unsigned int sc_reg, + u32 val); + </programlisting> + + <para> + Read and write standard SATA phy registers. Currently only used + if ->phy_reset hook called the sata_phy_reset() helper function. + </para> + + <programlisting> +int (*port_start) (struct ata_port *ap); +void (*port_stop) (struct ata_port *ap); +void (*host_stop) (struct ata_host_set *host_set); + </programlisting> + + <para> + ->port_start() is called just after the data structures for each + port are initialized. Typically this is used to alloc per-port + DMA buffers / tables / rings, enable DMA engines, and similar + tasks. + </para> + <para> + ->host_stop() is called when the rmmod or hot unplug process + begins. The hook must stop all hardware interrupts, DMA + engines, etc. + </para> + <para> + ->port_stop() is called after ->host_stop(). It's sole function + is to release DMA/memory resources, now that they are no longer + actively being used. + </para> + + </sect1> + </chapter> + + <chapter id="libataExt"> + <title>libata Library</title> +!Edrivers/scsi/libata-core.c + </chapter> + + <chapter id="libataInt"> + <title>libata Core Internals</title> +!Idrivers/scsi/libata-core.c + </chapter> + + <chapter id="libataScsiInt"> + <title>libata SCSI translation/emulation</title> +!Edrivers/scsi/libata-scsi.c +!Idrivers/scsi/libata-scsi.c + </chapter> + + <chapter id="PiixInt"> + <title>ata_piix Internals</title> +!Idrivers/scsi/ata_piix.c + </chapter> + + <chapter id="SILInt"> + <title>sata_sil Internals</title> +!Idrivers/scsi/sata_sil.c + </chapter> + +</book> diff --git a/Documentation/DocBook/librs.tmpl b/Documentation/DocBook/librs.tmpl new file mode 100644 index 0000000..3ff39ba --- /dev/null +++ b/Documentation/DocBook/librs.tmpl @@ -0,0 +1,289 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="Reed-Solomon-Library-Guide"> + <bookinfo> + <title>Reed-Solomon Library Programming Interface</title> + + <authorgroup> + <author> + <firstname>Thomas</firstname> + <surname>Gleixner</surname> + <affiliation> + <address> + <email>tglx@linutronix.de</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2004</year> + <holder>Thomas Gleixner</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License version 2 as published by the Free Software Foundation. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The generic Reed-Solomon Library provides encoding, decoding + and error correction functions. + </para> + <para> + Reed-Solomon codes are used in communication and storage + applications to ensure data integrity. + </para> + <para> + This documentation is provided for developers who want to utilize + the functions provided by the library. + </para> + </chapter> + + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + None. + </para> + </chapter> + + <chapter id="usage"> + <title>Usage</title> + <para> + This chapter provides examples how to use the library. + </para> + <sect1> + <title>Initializing</title> + <para> + The init function init_rs returns a pointer to a + rs decoder structure, which holds the necessary + information for encoding, decoding and error correction + with the given polynomial. It either uses an existing + matching decoder or creates a new one. On creation all + the lookup tables for fast en/decoding are created. + The function may take a while, so make sure not to + call it in critical code paths. + </para> + <programlisting> +/* the Reed Solomon control structure */ +static struct rs_control *rs_decoder; + +/* Symbolsize is 10 (bits) + * Primitve polynomial is x^10+x^3+1 + * first consecutive root is 0 + * primitve element to generate roots = 1 + * generator polinomial degree (number of roots) = 6 + */ +rs_decoder = init_rs (10, 0x409, 0, 1, 6); + </programlisting> + </sect1> + <sect1> + <title>Encoding</title> + <para> + The encoder calculates the Reed-Solomon code over + the given data length and stores the result in + the parity buffer. Note that the parity buffer must + be initialized before calling the encoder. + </para> + <para> + The expanded data can be inverted on the fly by + providing a non zero inversion mask. The expanded data is + XOR'ed with the mask. This is used e.g. for FLASH + ECC, where the all 0xFF is inverted to an all 0x00. + The Reed-Solomon code for all 0x00 is all 0x00. The + code is inverted before storing to FLASH so it is 0xFF + too. This prevent's that reading from an erased FLASH + results in ECC errors. + </para> + <para> + The databytes are expanded to the given symbol size + on the fly. There is no support for encoding continuous + bitstreams with a symbol size != 8 at the moment. If + it is necessary it should be not a big deal to implement + such functionality. + </para> + <programlisting> +/* Parity buffer. Size = number of roots */ +uint16_t par[6]; +/* Initialize the parity buffer */ +memset(par, 0, sizeof(par)); +/* Encode 512 byte in data8. Store parity in buffer par */ +encode_rs8 (rs_decoder, data8, 512, par, 0); + </programlisting> + </sect1> + <sect1> + <title>Decoding</title> + <para> + The decoder calculates the syndrome over + the given data length and the received parity symbols + and corrects errors in the data. + </para> + <para> + If a syndrome is available from a hardware decoder + then the syndrome calculation is skipped. + </para> + <para> + The correction of the data buffer can be suppressed + by providing a correction pattern buffer and an error + location buffer to the decoder. The decoder stores the + calculated error location and the correction bitmask + in the given buffers. This is useful for hardware + decoders which use a weird bit ordering scheme. + </para> + <para> + The databytes are expanded to the given symbol size + on the fly. There is no support for decoding continuous + bitstreams with a symbolsize != 8 at the moment. If + it is necessary it should be not a big deal to implement + such functionality. + </para> + + <sect2> + <title> + Decoding with syndrome calculation, direct data correction + </title> + <programlisting> +/* Parity buffer. Size = number of roots */ +uint16_t par[6]; +uint8_t data[512]; +int numerr; +/* Receive data */ +..... +/* Receive parity */ +..... +/* Decode 512 byte in data8.*/ +numerr = decode_rs8 (rs_decoder, data8, par, 512, NULL, 0, NULL, 0, NULL); + </programlisting> + </sect2> + + <sect2> + <title> + Decoding with syndrome given by hardware decoder, direct data correction + </title> + <programlisting> +/* Parity buffer. Size = number of roots */ +uint16_t par[6], syn[6]; +uint8_t data[512]; +int numerr; +/* Receive data */ +..... +/* Receive parity */ +..... +/* Get syndrome from hardware decoder */ +..... +/* Decode 512 byte in data8.*/ +numerr = decode_rs8 (rs_decoder, data8, par, 512, syn, 0, NULL, 0, NULL); + </programlisting> + </sect2> + + <sect2> + <title> + Decoding with syndrome given by hardware decoder, no direct data correction. + </title> + <para> + Note: It's not necessary to give data and received parity to the decoder. + </para> + <programlisting> +/* Parity buffer. Size = number of roots */ +uint16_t par[6], syn[6], corr[8]; +uint8_t data[512]; +int numerr, errpos[8]; +/* Receive data */ +..... +/* Receive parity */ +..... +/* Get syndrome from hardware decoder */ +..... +/* Decode 512 byte in data8.*/ +numerr = decode_rs8 (rs_decoder, NULL, NULL, 512, syn, 0, errpos, 0, corr); +for (i = 0; i < numerr; i++) { + do_error_correction_in_your_buffer(errpos[i], corr[i]); +} + </programlisting> + </sect2> + </sect1> + <sect1> + <title>Cleanup</title> + <para> + The function free_rs frees the allocated resources, + if the caller is the last user of the decoder. + </para> + <programlisting> +/* Release resources */ +free_rs(rs_decoder); + </programlisting> + </sect1> + + </chapter> + + <chapter id="structs"> + <title>Structures</title> + <para> + This chapter contains the autogenerated documentation of the structures which are + used in the Reed-Solomon Library and are relevant for a developer. + </para> +!Iinclude/linux/rslib.h + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> + <para> + This chapter contains the autogenerated documentation of the Reed-Solomon functions + which are exported. + </para> +!Elib/reed_solomon/reed_solomon.c + </chapter> + + <chapter id="credits"> + <title>Credits</title> + <para> + The library code for encoding and decoding was written by Phil Karn. + </para> + <programlisting> + Copyright 2002, Phil Karn, KA9Q + May be used under the terms of the GNU General Public License (GPL) + </programlisting> + <para> + The wrapper functions and interfaces are written by Thomas Gleixner + </para> + <para> + Many users have provided bugfixes, improvements and helping hands for testing. + Thanks a lot. + </para> + <para> + The following people have contributed to this document: + </para> + <para> + Thomas Gleixner<email>tglx@linutronix.de</email> + </para> + </chapter> +</book> diff --git a/Documentation/DocBook/lsm.tmpl b/Documentation/DocBook/lsm.tmpl new file mode 100644 index 0000000..f638221 --- /dev/null +++ b/Documentation/DocBook/lsm.tmpl @@ -0,0 +1,265 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<article class="whitepaper" id="LinuxSecurityModule" lang="en"> + <articleinfo> + <title>Linux Security Modules: General Security Hooks for Linux</title> + <authorgroup> + <author> + <firstname>Stephen</firstname> + <surname>Smalley</surname> + <affiliation> + <orgname>NAI Labs</orgname> + <address><email>ssmalley@nai.com</email></address> + </affiliation> + </author> + <author> + <firstname>Timothy</firstname> + <surname>Fraser</surname> + <affiliation> + <orgname>NAI Labs</orgname> + <address><email>tfraser@nai.com</email></address> + </affiliation> + </author> + <author> + <firstname>Chris</firstname> + <surname>Vance</surname> + <affiliation> + <orgname>NAI Labs</orgname> + <address><email>cvance@nai.com</email></address> + </affiliation> + </author> + </authorgroup> + </articleinfo> + +<sect1><title>Introduction</title> + +<para> +In March 2001, the National Security Agency (NSA) gave a presentation +about Security-Enhanced Linux (SELinux) at the 2.5 Linux Kernel +Summit. SELinux is an implementation of flexible and fine-grained +nondiscretionary access controls in the Linux kernel, originally +implemented as its own particular kernel patch. Several other +security projects (e.g. RSBAC, Medusa) have also developed flexible +access control architectures for the Linux kernel, and various +projects have developed particular access control models for Linux +(e.g. LIDS, DTE, SubDomain). Each project has developed and +maintained its own kernel patch to support its security needs. +</para> + +<para> +In response to the NSA presentation, Linus Torvalds made a set of +remarks that described a security framework he would be willing to +consider for inclusion in the mainstream Linux kernel. He described a +general framework that would provide a set of security hooks to +control operations on kernel objects and a set of opaque security +fields in kernel data structures for maintaining security attributes. +This framework could then be used by loadable kernel modules to +implement any desired model of security. Linus also suggested the +possibility of migrating the Linux capabilities code into such a +module. +</para> + +<para> +The Linux Security Modules (LSM) project was started by WireX to +develop such a framework. LSM is a joint development effort by +several security projects, including Immunix, SELinux, SGI and Janus, +and several individuals, including Greg Kroah-Hartman and James +Morris, to develop a Linux kernel patch that implements this +framework. The patch is currently tracking the 2.4 series and is +targeted for integration into the 2.5 development series. This +technical report provides an overview of the framework and the example +capabilities security module provided by the LSM kernel patch. +</para> + +</sect1> + +<sect1 id="framework"><title>LSM Framework</title> + +<para> +The LSM kernel patch provides a general kernel framework to support +security modules. In particular, the LSM framework is primarily +focused on supporting access control modules, although future +development is likely to address other security needs such as +auditing. By itself, the framework does not provide any additional +security; it merely provides the infrastructure to support security +modules. The LSM kernel patch also moves most of the capabilities +logic into an optional security module, with the system defaulting +to the traditional superuser logic. This capabilities module +is discussed further in <xref linkend="cap"/>. +</para> + +<para> +The LSM kernel patch adds security fields to kernel data structures +and inserts calls to hook functions at critical points in the kernel +code to manage the security fields and to perform access control. It +also adds functions for registering and unregistering security +modules, and adds a general <function>security</function> system call +to support new system calls for security-aware applications. +</para> + +<para> +The LSM security fields are simply <type>void*</type> pointers. For +process and program execution security information, security fields +were added to <structname>struct task_struct</structname> and +<structname>struct linux_binprm</structname>. For filesystem security +information, a security field was added to +<structname>struct super_block</structname>. For pipe, file, and socket +security information, security fields were added to +<structname>struct inode</structname> and +<structname>struct file</structname>. For packet and network device security +information, security fields were added to +<structname>struct sk_buff</structname> and +<structname>struct net_device</structname>. For System V IPC security +information, security fields were added to +<structname>struct kern_ipc_perm</structname> and +<structname>struct msg_msg</structname>; additionally, the definitions +for <structname>struct msg_msg</structname>, <structname>struct +msg_queue</structname>, and <structname>struct +shmid_kernel</structname> were moved to header files +(<filename>include/linux/msg.h</filename> and +<filename>include/linux/shm.h</filename> as appropriate) to allow +the security modules to use these definitions. +</para> + +<para> +Each LSM hook is a function pointer in a global table, +security_ops. This table is a +<structname>security_operations</structname> structure as defined by +<filename>include/linux/security.h</filename>. Detailed documentation +for each hook is included in this header file. At present, this +structure consists of a collection of substructures that group related +hooks based on the kernel object (e.g. task, inode, file, sk_buff, +etc) as well as some top-level hook function pointers for system +operations. This structure is likely to be flattened in the future +for performance. The placement of the hook calls in the kernel code +is described by the "called:" lines in the per-hook documentation in +the header file. The hook calls can also be easily found in the +kernel code by looking for the string "security_ops->". + +</para> + +<para> +Linus mentioned per-process security hooks in his original remarks as a +possible alternative to global security hooks. However, if LSM were +to start from the perspective of per-process hooks, then the base +framework would have to deal with how to handle operations that +involve multiple processes (e.g. kill), since each process might have +its own hook for controlling the operation. This would require a +general mechanism for composing hooks in the base framework. +Additionally, LSM would still need global hooks for operations that +have no process context (e.g. network input operations). +Consequently, LSM provides global security hooks, but a security +module is free to implement per-process hooks (where that makes sense) +by storing a security_ops table in each process' security field and +then invoking these per-process hooks from the global hooks. +The problem of composition is thus deferred to the module. +</para> + +<para> +The global security_ops table is initialized to a set of hook +functions provided by a dummy security module that provides +traditional superuser logic. A <function>register_security</function> +function (in <filename>security/security.c</filename>) is provided to +allow a security module to set security_ops to refer to its own hook +functions, and an <function>unregister_security</function> function is +provided to revert security_ops to the dummy module hooks. This +mechanism is used to set the primary security module, which is +responsible for making the final decision for each hook. +</para> + +<para> +LSM also provides a simple mechanism for stacking additional security +modules with the primary security module. It defines +<function>register_security</function> and +<function>unregister_security</function> hooks in the +<structname>security_operations</structname> structure and provides +<function>mod_reg_security</function> and +<function>mod_unreg_security</function> functions that invoke these +hooks after performing some sanity checking. A security module can +call these functions in order to stack with other modules. However, +the actual details of how this stacking is handled are deferred to the +module, which can implement these hooks in any way it wishes +(including always returning an error if it does not wish to support +stacking). In this manner, LSM again defers the problem of +composition to the module. +</para> + +<para> +Although the LSM hooks are organized into substructures based on +kernel object, all of the hooks can be viewed as falling into two +major categories: hooks that are used to manage the security fields +and hooks that are used to perform access control. Examples of the +first category of hooks include the +<function>alloc_security</function> and +<function>free_security</function> hooks defined for each kernel data +structure that has a security field. These hooks are used to allocate +and free security structures for kernel objects. The first category +of hooks also includes hooks that set information in the security +field after allocation, such as the <function>post_lookup</function> +hook in <structname>struct inode_security_ops</structname>. This hook +is used to set security information for inodes after successful lookup +operations. An example of the second category of hooks is the +<function>permission</function> hook in +<structname>struct inode_security_ops</structname>. This hook checks +permission when accessing an inode. +</para> + +</sect1> + +<sect1 id="cap"><title>LSM Capabilities Module</title> + +<para> +The LSM kernel patch moves most of the existing POSIX.1e capabilities +logic into an optional security module stored in the file +<filename>security/capability.c</filename>. This change allows +users who do not want to use capabilities to omit this code entirely +from their kernel, instead using the dummy module for traditional +superuser logic or any other module that they desire. This change +also allows the developers of the capabilities logic to maintain and +enhance their code more freely, without needing to integrate patches +back into the base kernel. +</para> + +<para> +In addition to moving the capabilities logic, the LSM kernel patch +could move the capability-related fields from the kernel data +structures into the new security fields managed by the security +modules. However, at present, the LSM kernel patch leaves the +capability fields in the kernel data structures. In his original +remarks, Linus suggested that this might be preferable so that other +security modules can be easily stacked with the capabilities module +without needing to chain multiple security structures on the security field. +It also avoids imposing extra overhead on the capabilities module +to manage the security fields. However, the LSM framework could +certainly support such a move if it is determined to be desirable, +with only a few additional changes described below. +</para> + +<para> +At present, the capabilities logic for computing process capabilities +on <function>execve</function> and <function>set*uid</function>, +checking capabilities for a particular process, saving and checking +capabilities for netlink messages, and handling the +<function>capget</function> and <function>capset</function> system +calls have been moved into the capabilities module. There are still a +few locations in the base kernel where capability-related fields are +directly examined or modified, but the current version of the LSM +patch does allow a security module to completely replace the +assignment and testing of capabilities. These few locations would +need to be changed if the capability-related fields were moved into +the security field. The following is a list of known locations that +still perform such direct examination or modification of +capability-related fields: +<itemizedlist> +<listitem><para><filename>fs/open.c</filename>:<function>sys_access</function></para></listitem> +<listitem><para><filename>fs/lockd/host.c</filename>:<function>nlm_bind_host</function></para></listitem> +<listitem><para><filename>fs/nfsd/auth.c</filename>:<function>nfsd_setuser</function></para></listitem> +<listitem><para><filename>fs/proc/array.c</filename>:<function>task_cap</function></para></listitem> +</itemizedlist> +</para> + +</sect1> + +</article> diff --git a/Documentation/DocBook/man/Makefile b/Documentation/DocBook/man/Makefile new file mode 100644 index 0000000..4fb7ea0 --- /dev/null +++ b/Documentation/DocBook/man/Makefile @@ -0,0 +1,3 @@ +# Rules are put in Documentation/DocBook + +clean-files := *.9.gz *.sgml manpage.links manpage.refs diff --git a/Documentation/DocBook/mcabook.tmpl b/Documentation/DocBook/mcabook.tmpl new file mode 100644 index 0000000..4367f46 --- /dev/null +++ b/Documentation/DocBook/mcabook.tmpl @@ -0,0 +1,107 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="MCAGuide"> + <bookinfo> + <title>MCA Driver Programming Interface</title> + + <authorgroup> + <author> + <firstname>Alan</firstname> + <surname>Cox</surname> + <affiliation> + <address> + <email>alan@redhat.com</email> + </address> + </affiliation> + </author> + <author> + <firstname>David</firstname> + <surname>Weinehall</surname> + </author> + <author> + <firstname>Chris</firstname> + <surname>Beauregard</surname> + </author> + </authorgroup> + + <copyright> + <year>2000</year> + <holder>Alan Cox</holder> + <holder>David Weinehall</holder> + <holder>Chris Beauregard</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The MCA bus functions provide a generalised interface to find MCA + bus cards, to claim them for a driver, and to read and manipulate POS + registers without being aware of the motherboard internals or + certain deep magic specific to onboard devices. + </para> + <para> + The basic interface to the MCA bus devices is the slot. Each slot + is numbered and virtual slot numbers are assigned to the internal + devices. Using a pci_dev as other busses do does not really make + sense in the MCA context as the MCA bus resources require card + specific interpretation. + </para> + <para> + Finally the MCA bus functions provide a parallel set of DMA + functions mimicing the ISA bus DMA functions as closely as possible, + although also supporting the additional DMA functionality on the + MCA bus controllers. + </para> + </chapter> + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + None. + </para> + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> +!Earch/i386/kernel/mca.c + </chapter> + + <chapter id="dmafunctions"> + <title>DMA Functions Provided</title> +!Iinclude/asm-i386/mca_dma.h + </chapter> + +</book> diff --git a/Documentation/DocBook/mtdnand.tmpl b/Documentation/DocBook/mtdnand.tmpl new file mode 100644 index 0000000..6e463d0 --- /dev/null +++ b/Documentation/DocBook/mtdnand.tmpl @@ -0,0 +1,1320 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="MTD-NAND-Guide"> + <bookinfo> + <title>MTD NAND Driver Programming Interface</title> + + <authorgroup> + <author> + <firstname>Thomas</firstname> + <surname>Gleixner</surname> + <affiliation> + <address> + <email>tglx@linutronix.de</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2004</year> + <holder>Thomas Gleixner</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License version 2 as published by the Free Software Foundation. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The generic NAND driver supports almost all NAND and AG-AND based + chips and connects them to the Memory Technology Devices (MTD) + subsystem of the Linux Kernel. + </para> + <para> + This documentation is provided for developers who want to implement + board drivers or filesystem drivers suitable for NAND devices. + </para> + </chapter> + + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + None. + </para> + </chapter> + + <chapter id="dochints"> + <title>Documentation hints</title> + <para> + The function and structure docs are autogenerated. Each function and + struct member has a short description which is marked with an [XXX] identifier. + The following chapters explain the meaning of those identifiers. + </para> + <sect1> + <title>Function identifiers [XXX]</title> + <para> + The functions are marked with [XXX] identifiers in the short + comment. The identifiers explain the usage and scope of the + functions. Following identifiers are used: + </para> + <itemizedlist> + <listitem><para> + [MTD Interface]</para><para> + These functions provide the interface to the MTD kernel API. + They are not replacable and provide functionality + which is complete hardware independent. + </para></listitem> + <listitem><para> + [NAND Interface]</para><para> + These functions are exported and provide the interface to the NAND kernel API. + </para></listitem> + <listitem><para> + [GENERIC]</para><para> + Generic functions are not replacable and provide functionality + which is complete hardware independent. + </para></listitem> + <listitem><para> + [DEFAULT]</para><para> + Default functions provide hardware related functionality which is suitable + for most of the implementations. These functions can be replaced by the + board driver if neccecary. Those functions are called via pointers in the + NAND chip description structure. The board driver can set the functions which + should be replaced by board dependend functions before calling nand_scan(). + If the function pointer is NULL on entry to nand_scan() then the pointer + is set to the default function which is suitable for the detected chip type. + </para></listitem> + </itemizedlist> + </sect1> + <sect1> + <title>Struct member identifiers [XXX]</title> + <para> + The struct members are marked with [XXX] identifiers in the + comment. The identifiers explain the usage and scope of the + members. Following identifiers are used: + </para> + <itemizedlist> + <listitem><para> + [INTERN]</para><para> + These members are for NAND driver internal use only and must not be + modified. Most of these values are calculated from the chip geometry + information which is evaluated during nand_scan(). + </para></listitem> + <listitem><para> + [REPLACEABLE]</para><para> + Replaceable members hold hardware related functions which can be + provided by the board driver. The board driver can set the functions which + should be replaced by board dependend functions before calling nand_scan(). + If the function pointer is NULL on entry to nand_scan() then the pointer + is set to the default function which is suitable for the detected chip type. + </para></listitem> + <listitem><para> + [BOARDSPECIFIC]</para><para> + Board specific members hold hardware related information which must + be provided by the board driver. The board driver must set the function + pointers and datafields before calling nand_scan(). + </para></listitem> + <listitem><para> + [OPTIONAL]</para><para> + Optional members can hold information relevant for the board driver. The + generic NAND driver code does not use this information. + </para></listitem> + </itemizedlist> + </sect1> + </chapter> + + <chapter id="basicboarddriver"> + <title>Basic board driver</title> + <para> + For most boards it will be sufficient to provide just the + basic functions and fill out some really board dependend + members in the nand chip description structure. + See drivers/mtd/nand/skeleton for reference. + </para> + <sect1> + <title>Basic defines</title> + <para> + At least you have to provide a mtd structure and + a storage for the ioremap'ed chip address. + You can allocate the mtd structure using kmalloc + or you can allocate it statically. + In case of static allocation you have to allocate + a nand_chip structure too. + </para> + <para> + Kmalloc based example + </para> + <programlisting> +static struct mtd_info *board_mtd; +static unsigned long baseaddr; + </programlisting> + <para> + Static example + </para> + <programlisting> +static struct mtd_info board_mtd; +static struct nand_chip board_chip; +static unsigned long baseaddr; + </programlisting> + </sect1> + <sect1> + <title>Partition defines</title> + <para> + If you want to divide your device into parititions, then + enable the configuration switch CONFIG_MTD_PARITIONS and define + a paritioning scheme suitable to your board. + </para> + <programlisting> +#define NUM_PARTITIONS 2 +static struct mtd_partition partition_info[] = { + { .name = "Flash partition 1", + .offset = 0, + .size = 8 * 1024 * 1024 }, + { .name = "Flash partition 2", + .offset = MTDPART_OFS_NEXT, + .size = MTDPART_SIZ_FULL }, +}; + </programlisting> + </sect1> + <sect1> + <title>Hardware control function</title> + <para> + The hardware control function provides access to the + control pins of the NAND chip(s). + The access can be done by GPIO pins or by address lines. + If you use address lines, make sure that the timing + requirements are met. + </para> + <para> + <emphasis>GPIO based example</emphasis> + </para> + <programlisting> +static void board_hwcontrol(struct mtd_info *mtd, int cmd) +{ + switch(cmd){ + case NAND_CTL_SETCLE: /* Set CLE pin high */ break; + case NAND_CTL_CLRCLE: /* Set CLE pin low */ break; + case NAND_CTL_SETALE: /* Set ALE pin high */ break; + case NAND_CTL_CLRALE: /* Set ALE pin low */ break; + case NAND_CTL_SETNCE: /* Set nCE pin low */ break; + case NAND_CTL_CLRNCE: /* Set nCE pin high */ break; + } +} + </programlisting> + <para> + <emphasis>Address lines based example.</emphasis> It's assumed that the + nCE pin is driven by a chip select decoder. + </para> + <programlisting> +static void board_hwcontrol(struct mtd_info *mtd, int cmd) +{ + struct nand_chip *this = (struct nand_chip *) mtd->priv; + switch(cmd){ + case NAND_CTL_SETCLE: this->IO_ADDR_W |= CLE_ADRR_BIT; break; + case NAND_CTL_CLRCLE: this->IO_ADDR_W &= ~CLE_ADRR_BIT; break; + case NAND_CTL_SETALE: this->IO_ADDR_W |= ALE_ADRR_BIT; break; + case NAND_CTL_CLRALE: this->IO_ADDR_W &= ~ALE_ADRR_BIT; break; + } +} + </programlisting> + </sect1> + <sect1> + <title>Device ready function</title> + <para> + If the hardware interface has the ready busy pin of the NAND chip connected to a + GPIO or other accesible I/O pin, this function is used to read back the state of the + pin. The function has no arguments and should return 0, if the device is busy (R/B pin + is low) and 1, if the device is ready (R/B pin is high). + If the hardware interface does not give access to the ready busy pin, then + the function must not be defined and the function pointer this->dev_ready is set to NULL. + </para> + </sect1> + <sect1> + <title>Init function</title> + <para> + The init function allocates memory and sets up all the board + specific parameters and function pointers. When everything + is set up nand_scan() is called. This function tries to + detect and identify then chip. If a chip is found all the + internal data fields are initialized accordingly. + The structure(s) have to be zeroed out first and then filled with the neccecary + information about the device. + </para> + <programlisting> +int __init board_init (void) +{ + struct nand_chip *this; + int err = 0; + + /* Allocate memory for MTD device structure and private data */ + board_mtd = kmalloc (sizeof(struct mtd_info) + sizeof (struct nand_chip), GFP_KERNEL); + if (!board_mtd) { + printk ("Unable to allocate NAND MTD device structure.\n"); + err = -ENOMEM; + goto out; + } + + /* Initialize structures */ + memset ((char *) board_mtd, 0, sizeof(struct mtd_info) + sizeof(struct nand_chip)); + + /* map physical adress */ + baseaddr = (unsigned long)ioremap(CHIP_PHYSICAL_ADDRESS, 1024); + if(!baseaddr){ + printk("Ioremap to access NAND chip failed\n"); + err = -EIO; + goto out_mtd; + } + + /* Get pointer to private data */ + this = (struct nand_chip *) (); + /* Link the private data with the MTD structure */ + board_mtd->priv = this; + + /* Set address of NAND IO lines */ + this->IO_ADDR_R = baseaddr; + this->IO_ADDR_W = baseaddr; + /* Reference hardware control function */ + this->hwcontrol = board_hwcontrol; + /* Set command delay time, see datasheet for correct value */ + this->chip_delay = CHIP_DEPENDEND_COMMAND_DELAY; + /* Assign the device ready function, if available */ + this->dev_ready = board_dev_ready; + this->eccmode = NAND_ECC_SOFT; + + /* Scan to find existance of the device */ + if (nand_scan (board_mtd, 1)) { + err = -ENXIO; + goto out_ior; + } + + add_mtd_partitions(board_mtd, partition_info, NUM_PARTITIONS); + goto out; + +out_ior: + iounmap((void *)baseaddr); +out_mtd: + kfree (board_mtd); +out: + return err; +} +module_init(board_init); + </programlisting> + </sect1> + <sect1> + <title>Exit function</title> + <para> + The exit function is only neccecary if the driver is + compiled as a module. It releases all resources which + are held by the chip driver and unregisters the partitions + in the MTD layer. + </para> + <programlisting> +#ifdef MODULE +static void __exit board_cleanup (void) +{ + /* Release resources, unregister device */ + nand_release (board_mtd); + + /* unmap physical adress */ + iounmap((void *)baseaddr); + + /* Free the MTD device structure */ + kfree (board_mtd); +} +module_exit(board_cleanup); +#endif + </programlisting> + </sect1> + </chapter> + + <chapter id="boarddriversadvanced"> + <title>Advanced board driver functions</title> + <para> + This chapter describes the advanced functionality of the NAND + driver. For a list of functions which can be overridden by the board + driver see the documentation of the nand_chip structure. + </para> + <sect1> + <title>Multiple chip control</title> + <para> + The nand driver can control chip arrays. Therefor the + board driver must provide an own select_chip function. This + function must (de)select the requested chip. + The function pointer in the nand_chip structure must + be set before calling nand_scan(). The maxchip parameter + of nand_scan() defines the maximum number of chips to + scan for. Make sure that the select_chip function can + handle the requested number of chips. + </para> + <para> + The nand driver concatenates the chips to one virtual + chip and provides this virtual chip to the MTD layer. + </para> + <para> + <emphasis>Note: The driver can only handle linear chip arrays + of equally sized chips. There is no support for + parallel arrays which extend the buswidth.</emphasis> + </para> + <para> + <emphasis>GPIO based example</emphasis> + </para> + <programlisting> +static void board_select_chip (struct mtd_info *mtd, int chip) +{ + /* Deselect all chips, set all nCE pins high */ + GPIO(BOARD_NAND_NCE) |= 0xff; + if (chip >= 0) + GPIO(BOARD_NAND_NCE) &= ~ (1 << chip); +} + </programlisting> + <para> + <emphasis>Address lines based example.</emphasis> + Its assumed that the nCE pins are connected to an + address decoder. + </para> + <programlisting> +static void board_select_chip (struct mtd_info *mtd, int chip) +{ + struct nand_chip *this = (struct nand_chip *) mtd->priv; + + /* Deselect all chips */ + this->IO_ADDR_R &= ~BOARD_NAND_ADDR_MASK; + this->IO_ADDR_W &= ~BOARD_NAND_ADDR_MASK; + switch (chip) { + case 0: + this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIP0; + this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIP0; + break; + .... + case n: + this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIPn; + this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIPn; + break; + } +} + </programlisting> + </sect1> + <sect1> + <title>Hardware ECC support</title> + <sect2> + <title>Functions and constants</title> + <para> + The nand driver supports three different types of + hardware ECC. + <itemizedlist> + <listitem><para>NAND_ECC_HW3_256</para><para> + Hardware ECC generator providing 3 bytes ECC per + 256 byte. + </para> </listitem> + <listitem><para>NAND_ECC_HW3_512</para><para> + Hardware ECC generator providing 3 bytes ECC per + 512 byte. + </para> </listitem> + <listitem><para>NAND_ECC_HW6_512</para><para> + Hardware ECC generator providing 6 bytes ECC per + 512 byte. + </para> </listitem> + <listitem><para>NAND_ECC_HW8_512</para><para> + Hardware ECC generator providing 6 bytes ECC per + 512 byte. + </para> </listitem> + </itemizedlist> + If your hardware generator has a different functionality + add it at the appropriate place in nand_base.c + </para> + <para> + The board driver must provide following functions: + <itemizedlist> + <listitem><para>enable_hwecc</para><para> + This function is called before reading / writing to + the chip. Reset or initialize the hardware generator + in this function. The function is called with an + argument which let you distinguish between read + and write operations. + </para> </listitem> + <listitem><para>calculate_ecc</para><para> + This function is called after read / write from / to + the chip. Transfer the ECC from the hardware to + the buffer. If the option NAND_HWECC_SYNDROME is set + then the function is only called on write. See below. + </para> </listitem> + <listitem><para>correct_data</para><para> + In case of an ECC error this function is called for + error detection and correction. Return 1 respectively 2 + in case the error can be corrected. If the error is + not correctable return -1. If your hardware generator + matches the default algorithm of the nand_ecc software + generator then use the correction function provided + by nand_ecc instead of implementing duplicated code. + </para> </listitem> + </itemizedlist> + </para> + </sect2> + <sect2> + <title>Hardware ECC with syndrome calculation</title> + <para> + Many hardware ECC implementations provide Reed-Solomon + codes and calculate an error syndrome on read. The syndrome + must be converted to a standard Reed-Solomon syndrome + before calling the error correction code in the generic + Reed-Solomon library. + </para> + <para> + The ECC bytes must be placed immidiately after the data + bytes in order to make the syndrome generator work. This + is contrary to the usual layout used by software ECC. The + seperation of data and out of band area is not longer + possible. The nand driver code handles this layout and + the remaining free bytes in the oob area are managed by + the autoplacement code. Provide a matching oob-layout + in this case. See rts_from4.c and diskonchip.c for + implementation reference. In those cases we must also + use bad block tables on FLASH, because the ECC layout is + interferring with the bad block marker positions. + See bad block table support for details. + </para> + </sect2> + </sect1> + <sect1> + <title>Bad block table support</title> + <para> + Most NAND chips mark the bad blocks at a defined + position in the spare area. Those blocks must + not be erased under any circumstances as the bad + block information would be lost. + It is possible to check the bad block mark each + time when the blocks are accessed by reading the + spare area of the first page in the block. This + is time consuming so a bad block table is used. + </para> + <para> + The nand driver supports various types of bad block + tables. + <itemizedlist> + <listitem><para>Per device</para><para> + The bad block table contains all bad block information + of the device which can consist of multiple chips. + </para> </listitem> + <listitem><para>Per chip</para><para> + A bad block table is used per chip and contains the + bad block information for this particular chip. + </para> </listitem> + <listitem><para>Fixed offset</para><para> + The bad block table is located at a fixed offset + in the chip (device). This applies to various + DiskOnChip devices. + </para> </listitem> + <listitem><para>Automatic placed</para><para> + The bad block table is automatically placed and + detected either at the end or at the beginning + of a chip (device) + </para> </listitem> + <listitem><para>Mirrored tables</para><para> + The bad block table is mirrored on the chip (device) to + allow updates of the bad block table without data loss. + </para> </listitem> + </itemizedlist> + </para> + <para> + nand_scan() calls the function nand_default_bbt(). + nand_default_bbt() selects appropriate default + bad block table desriptors depending on the chip information + which was retrieved by nand_scan(). + </para> + <para> + The standard policy is scanning the device for bad + blocks and build a ram based bad block table which + allows faster access than always checking the + bad block information on the flash chip itself. + </para> + <sect2> + <title>Flash based tables</title> + <para> + It may be desired or neccecary to keep a bad block table in FLASH. + For AG-AND chips this is mandatory, as they have no factory marked + bad blocks. They have factory marked good blocks. The marker pattern + is erased when the block is erased to be reused. So in case of + powerloss before writing the pattern back to the chip this block + would be lost and added to the bad blocks. Therefor we scan the + chip(s) when we detect them the first time for good blocks and + store this information in a bad block table before erasing any + of the blocks. + </para> + <para> + The blocks in which the tables are stored are procteted against + accidental access by marking them bad in the memory bad block + table. The bad block table managment functions are allowed + to circumvernt this protection. + </para> + <para> + The simplest way to activate the FLASH based bad block table support + is to set the option NAND_USE_FLASH_BBT in the option field of + the nand chip structure before calling nand_scan(). For AG-AND + chips is this done by default. + This activates the default FLASH based bad block table functionality + of the NAND driver. The default bad block table options are + <itemizedlist> + <listitem><para>Store bad block table per chip</para></listitem> + <listitem><para>Use 2 bits per block</para></listitem> + <listitem><para>Automatic placement at the end of the chip</para></listitem> + <listitem><para>Use mirrored tables with version numbers</para></listitem> + <listitem><para>Reserve 4 blocks at the end of the chip</para></listitem> + </itemizedlist> + </para> + </sect2> + <sect2> + <title>User defined tables</title> + <para> + User defined tables are created by filling out a + nand_bbt_descr structure and storing the pointer in the + nand_chip structure member bbt_td before calling nand_scan(). + If a mirror table is neccecary a second structure must be + created and a pointer to this structure must be stored + in bbt_md inside the nand_chip structure. If the bbt_md + member is set to NULL then only the main table is used + and no scan for the mirrored table is performed. + </para> + <para> + The most important field in the nand_bbt_descr structure + is the options field. The options define most of the + table properties. Use the predefined constants from + nand.h to define the options. + <itemizedlist> + <listitem><para>Number of bits per block</para> + <para>The supported number of bits is 1, 2, 4, 8.</para></listitem> + <listitem><para>Table per chip</para> + <para>Setting the constant NAND_BBT_PERCHIP selects that + a bad block table is managed for each chip in a chip array. + If this option is not set then a per device bad block table + is used.</para></listitem> + <listitem><para>Table location is absolute</para> + <para>Use the option constant NAND_BBT_ABSPAGE and + define the absolute page number where the bad block + table starts in the field pages. If you have selected bad block + tables per chip and you have a multi chip array then the start page + must be given for each chip in the chip array. Note: there is no scan + for a table ident pattern performed, so the fields + pattern, veroffs, offs, len can be left uninitialized</para></listitem> + <listitem><para>Table location is automatically detected</para> + <para>The table can either be located in the first or the last good + blocks of the chip (device). Set NAND_BBT_LASTBLOCK to place + the bad block table at the end of the chip (device). The + bad block tables are marked and identified by a pattern which + is stored in the spare area of the first page in the block which + holds the bad block table. Store a pointer to the pattern + in the pattern field. Further the length of the pattern has to be + stored in len and the offset in the spare area must be given + in the offs member of the nand_bbt_descr stucture. For mirrored + bad block tables different patterns are mandatory.</para></listitem> + <listitem><para>Table creation</para> + <para>Set the option NAND_BBT_CREATE to enable the table creation + if no table can be found during the scan. Usually this is done only + once if a new chip is found. </para></listitem> + <listitem><para>Table write support</para> + <para>Set the option NAND_BBT_WRITE to enable the table write support. + This allows the update of the bad block table(s) in case a block has + to be marked bad due to wear. The MTD interface function block_markbad + is calling the update function of the bad block table. If the write + support is enabled then the table is updated on FLASH.</para> + <para> + Note: Write support should only be enabled for mirrored tables with + version control. + </para></listitem> + <listitem><para>Table version control</para> + <para>Set the option NAND_BBT_VERSION to enable the table version control. + It's highly recommended to enable this for mirrored tables with write + support. It makes sure that the risk of loosing the bad block + table information is reduced to the loss of the information about the + one worn out block which should be marked bad. The version is stored in + 4 consecutive bytes in the spare area of the device. The position of + the version number is defined by the member veroffs in the bad block table + descriptor.</para></listitem> + <listitem><para>Save block contents on write</para> + <para> + In case that the block which holds the bad block table does contain + other useful information, set the option NAND_BBT_SAVECONTENT. When + the bad block table is written then the whole block is read the bad + block table is updated and the block is erased and everything is + written back. If this option is not set only the bad block table + is written and everything else in the block is ignored and erased. + </para></listitem> + <listitem><para>Number of reserved blocks</para> + <para> + For automatic placement some blocks must be reserved for + bad block table storage. The number of reserved blocks is defined + in the maxblocks member of the babd block table description structure. + Reserving 4 blocks for mirrored tables should be a reasonable number. + This also limits the number of blocks which are scanned for the bad + block table ident pattern. + </para></listitem> + </itemizedlist> + </para> + </sect2> + </sect1> + <sect1> + <title>Spare area (auto)placement</title> + <para> + The nand driver implements different possibilities for + placement of filesystem data in the spare area, + <itemizedlist> + <listitem><para>Placement defined by fs driver</para></listitem> + <listitem><para>Automatic placement</para></listitem> + </itemizedlist> + The default placement function is automatic placement. The + nand driver has built in default placement schemes for the + various chiptypes. If due to hardware ECC functionality the + default placement does not fit then the board driver can + provide a own placement scheme. + </para> + <para> + File system drivers can provide a own placement scheme which + is used instead of the default placement scheme. + </para> + <para> + Placement schemes are defined by a nand_oobinfo structure + <programlisting> +struct nand_oobinfo { + int useecc; + int eccbytes; + int eccpos[24]; + int oobfree[8][2]; +}; + </programlisting> + <itemizedlist> + <listitem><para>useecc</para><para> + The useecc member controls the ecc and placement function. The header + file include/mtd/mtd-abi.h contains constants to select ecc and + placement. MTD_NANDECC_OFF switches off the ecc complete. This is + not recommended and available for testing and diagnosis only. + MTD_NANDECC_PLACE selects caller defined placement, MTD_NANDECC_AUTOPLACE + selects automatic placement. + </para></listitem> + <listitem><para>eccbytes</para><para> + The eccbytes member defines the number of ecc bytes per page. + </para></listitem> + <listitem><para>eccpos</para><para> + The eccpos array holds the byte offsets in the spare area where + the ecc codes are placed. + </para></listitem> + <listitem><para>oobfree</para><para> + The oobfree array defines the areas in the spare area which can be + used for automatic placement. The information is given in the format + {offset, size}. offset defines the start of the usable area, size the + length in bytes. More than one area can be defined. The list is terminated + by an {0, 0} entry. + </para></listitem> + </itemizedlist> + </para> + <sect2> + <title>Placement defined by fs driver</title> + <para> + The calling function provides a pointer to a nand_oobinfo + structure which defines the ecc placement. For writes the + caller must provide a spare area buffer along with the + data buffer. The spare area buffer size is (number of pages) * + (size of spare area). For reads the buffer size is + (number of pages) * ((size of spare area) + (number of ecc + steps per page) * sizeof (int)). The driver stores the + result of the ecc check for each tuple in the spare buffer. + The storage sequence is + </para> + <para> + <spare data page 0><ecc result 0>...<ecc result n> + </para> + <para> + ... + </para> + <para> + <spare data page n><ecc result 0>...<ecc result n> + </para> + <para> + This is a legacy mode used by YAFFS1. + </para> + <para> + If the spare area buffer is NULL then only the ECC placement is + done according to the given scheme in the nand_oobinfo structure. + </para> + </sect2> + <sect2> + <title>Automatic placement</title> + <para> + Automatic placement uses the built in defaults to place the + ecc bytes in the spare area. If filesystem data have to be stored / + read into the spare area then the calling function must provide a + buffer. The buffer size per page is determined by the oobfree array in + the nand_oobinfo structure. + </para> + <para> + If the spare area buffer is NULL then only the ECC placement is + done according to the default builtin scheme. + </para> + </sect2> + <sect2> + <title>User space placement selection</title> + <para> + All non ecc functions like mtd->read and mtd->write use an internal + structure, which can be set by an ioctl. This structure is preset + to the autoplacement default. + <programlisting> + ioctl (fd, MEMSETOOBSEL, oobsel); + </programlisting> + oobsel is a pointer to a user supplied structure of type + nand_oobconfig. The contents of this structure must match the + criteria of the filesystem, which will be used. See an example in utils/nandwrite.c. + </para> + </sect2> + </sect1> + <sect1> + <title>Spare area autoplacement default schemes</title> + <sect2> + <title>256 byte pagesize</title> +<informaltable><tgroup cols="3"><tbody> +<row> +<entry>Offset</entry> +<entry>Content</entry> +<entry>Comment</entry> +</row> +<row> +<entry>0x00</entry> +<entry>ECC byte 0</entry> +<entry>Error correction code byte 0</entry> +</row> +<row> +<entry>0x01</entry> +<entry>ECC byte 1</entry> +<entry>Error correction code byte 1</entry> +</row> +<row> +<entry>0x02</entry> +<entry>ECC byte 2</entry> +<entry>Error correction code byte 2</entry> +</row> +<row> +<entry>0x03</entry> +<entry>Autoplace 0</entry> +<entry></entry> +</row> +<row> +<entry>0x04</entry> +<entry>Autoplace 1</entry> +<entry></entry> +</row> +<row> +<entry>0x05</entry> +<entry>Bad block marker</entry> +<entry>If any bit in this byte is zero, then this block is bad. +This applies only to the first page in a block. In the remaining +pages this byte is reserved</entry> +</row> +<row> +<entry>0x06</entry> +<entry>Autoplace 2</entry> +<entry></entry> +</row> +<row> +<entry>0x07</entry> +<entry>Autoplace 3</entry> +<entry></entry> +</row> +</tbody></tgroup></informaltable> + </sect2> + <sect2> + <title>512 byte pagesize</title> +<informaltable><tgroup cols="3"><tbody> +<row> +<entry>Offset</entry> +<entry>Content</entry> +<entry>Comment</entry> +</row> +<row> +<entry>0x00</entry> +<entry>ECC byte 0</entry> +<entry>Error correction code byte 0 of the lower 256 Byte data in +this page</entry> +</row> +<row> +<entry>0x01</entry> +<entry>ECC byte 1</entry> +<entry>Error correction code byte 1 of the lower 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x02</entry> +<entry>ECC byte 2</entry> +<entry>Error correction code byte 2 of the lower 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x03</entry> +<entry>ECC byte 3</entry> +<entry>Error correction code byte 0 of the upper 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x04</entry> +<entry>reserved</entry> +<entry>reserved</entry> +</row> +<row> +<entry>0x05</entry> +<entry>Bad block marker</entry> +<entry>If any bit in this byte is zero, then this block is bad. +This applies only to the first page in a block. In the remaining +pages this byte is reserved</entry> +</row> +<row> +<entry>0x06</entry> +<entry>ECC byte 4</entry> +<entry>Error correction code byte 1 of the upper 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x07</entry> +<entry>ECC byte 5</entry> +<entry>Error correction code byte 2 of the upper 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x08 - 0x0F</entry> +<entry>Autoplace 0 - 7</entry> +<entry></entry> +</row> +</tbody></tgroup></informaltable> + </sect2> + <sect2> + <title>2048 byte pagesize</title> +<informaltable><tgroup cols="3"><tbody> +<row> +<entry>Offset</entry> +<entry>Content</entry> +<entry>Comment</entry> +</row> +<row> +<entry>0x00</entry> +<entry>Bad block marker</entry> +<entry>If any bit in this byte is zero, then this block is bad. +This applies only to the first page in a block. In the remaining +pages this byte is reserved</entry> +</row> +<row> +<entry>0x01</entry> +<entry>Reserved</entry> +<entry>Reserved</entry> +</row> +<row> +<entry>0x02-0x27</entry> +<entry>Autoplace 0 - 37</entry> +<entry></entry> +</row> +<row> +<entry>0x28</entry> +<entry>ECC byte 0</entry> +<entry>Error correction code byte 0 of the first 256 Byte data in +this page</entry> +</row> +<row> +<entry>0x29</entry> +<entry>ECC byte 1</entry> +<entry>Error correction code byte 1 of the first 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x2A</entry> +<entry>ECC byte 2</entry> +<entry>Error correction code byte 2 of the first 256 Bytes data in +this page</entry> +</row> +<row> +<entry>0x2B</entry> +<entry>ECC byte 3</entry> +<entry>Error correction code byte 0 of the second 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x2C</entry> +<entry>ECC byte 4</entry> +<entry>Error correction code byte 1 of the second 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x2D</entry> +<entry>ECC byte 5</entry> +<entry>Error correction code byte 2 of the second 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x2E</entry> +<entry>ECC byte 6</entry> +<entry>Error correction code byte 0 of the third 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x2F</entry> +<entry>ECC byte 7</entry> +<entry>Error correction code byte 1 of the third 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x30</entry> +<entry>ECC byte 8</entry> +<entry>Error correction code byte 2 of the third 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x31</entry> +<entry>ECC byte 9</entry> +<entry>Error correction code byte 0 of the fourth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x32</entry> +<entry>ECC byte 10</entry> +<entry>Error correction code byte 1 of the fourth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x33</entry> +<entry>ECC byte 11</entry> +<entry>Error correction code byte 2 of the fourth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x34</entry> +<entry>ECC byte 12</entry> +<entry>Error correction code byte 0 of the fifth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x35</entry> +<entry>ECC byte 13</entry> +<entry>Error correction code byte 1 of the fifth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x36</entry> +<entry>ECC byte 14</entry> +<entry>Error correction code byte 2 of the fifth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x37</entry> +<entry>ECC byte 15</entry> +<entry>Error correction code byte 0 of the sixt 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x38</entry> +<entry>ECC byte 16</entry> +<entry>Error correction code byte 1 of the sixt 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x39</entry> +<entry>ECC byte 17</entry> +<entry>Error correction code byte 2 of the sixt 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x3A</entry> +<entry>ECC byte 18</entry> +<entry>Error correction code byte 0 of the seventh 256 Bytes of +data in this page</entry> +</row> +<row> +<entry>0x3B</entry> +<entry>ECC byte 19</entry> +<entry>Error correction code byte 1 of the seventh 256 Bytes of +data in this page</entry> +</row> +<row> +<entry>0x3C</entry> +<entry>ECC byte 20</entry> +<entry>Error correction code byte 2 of the seventh 256 Bytes of +data in this page</entry> +</row> +<row> +<entry>0x3D</entry> +<entry>ECC byte 21</entry> +<entry>Error correction code byte 0 of the eigth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x3E</entry> +<entry>ECC byte 22</entry> +<entry>Error correction code byte 1 of the eigth 256 Bytes of data +in this page</entry> +</row> +<row> +<entry>0x3F</entry> +<entry>ECC byte 23</entry> +<entry>Error correction code byte 2 of the eigth 256 Bytes of data +in this page</entry> +</row> +</tbody></tgroup></informaltable> + </sect2> + </sect1> + </chapter> + + <chapter id="filesystems"> + <title>Filesystem support</title> + <para> + The NAND driver provides all neccecary functions for a + filesystem via the MTD interface. + </para> + <para> + Filesystems must be aware of the NAND pecularities and + restrictions. One major restrictions of NAND Flash is, that you cannot + write as often as you want to a page. The consecutive writes to a page, + before erasing it again, are restricted to 1-3 writes, depending on the + manufacturers specifications. This applies similar to the spare area. + </para> + <para> + Therefor NAND aware filesystems must either write in page size chunks + or hold a writebuffer to collect smaller writes until they sum up to + pagesize. Available NAND aware filesystems: JFFS2, YAFFS. + </para> + <para> + The spare area usage to store filesystem data is controlled by + the spare area placement functionality which is described in one + of the earlier chapters. + </para> + </chapter> + <chapter id="tools"> + <title>Tools</title> + <para> + The MTD project provides a couple of helpful tools to handle NAND Flash. + <itemizedlist> + <listitem><para>flasherase, flasheraseall: Erase and format FLASH partitions</para></listitem> + <listitem><para>nandwrite: write filesystem images to NAND FLASH</para></listitem> + <listitem><para>nanddump: dump the contents of a NAND FLASH partitions</para></listitem> + </itemizedlist> + </para> + <para> + These tools are aware of the NAND restrictions. Please use those tools + instead of complaining about errors which are caused by non NAND aware + access methods. + </para> + </chapter> + + <chapter id="defines"> + <title>Constants</title> + <para> + This chapter describes the constants which might be relevant for a driver developer. + </para> + <sect1> + <title>Chip option constants</title> + <sect2> + <title>Constants for chip id table</title> + <para> + These constants are defined in nand.h. They are ored together to describe + the chip functionality. + <programlisting> +/* Chip can not auto increment pages */ +#define NAND_NO_AUTOINCR 0x00000001 +/* Buswitdh is 16 bit */ +#define NAND_BUSWIDTH_16 0x00000002 +/* Device supports partial programming without padding */ +#define NAND_NO_PADDING 0x00000004 +/* Chip has cache program function */ +#define NAND_CACHEPRG 0x00000008 +/* Chip has copy back function */ +#define NAND_COPYBACK 0x00000010 +/* AND Chip which has 4 banks and a confusing page / block + * assignment. See Renesas datasheet for further information */ +#define NAND_IS_AND 0x00000020 +/* Chip has a array of 4 pages which can be read without + * additional ready /busy waits */ +#define NAND_4PAGE_ARRAY 0x00000040 + </programlisting> + </para> + </sect2> + <sect2> + <title>Constants for runtime options</title> + <para> + These constants are defined in nand.h. They are ored together to describe + the functionality. + <programlisting> +/* Use a flash based bad block table. This option is parsed by the + * default bad block table function (nand_default_bbt). */ +#define NAND_USE_FLASH_BBT 0x00010000 +/* The hw ecc generator provides a syndrome instead a ecc value on read + * This can only work if we have the ecc bytes directly behind the + * data bytes. Applies for DOC and AG-AND Renesas HW Reed Solomon generators */ +#define NAND_HWECC_SYNDROME 0x00020000 + </programlisting> + </para> + </sect2> + </sect1> + + <sect1> + <title>ECC selection constants</title> + <para> + Use these constants to select the ECC algorithm. + <programlisting> +/* No ECC. Usage is not recommended ! */ +#define NAND_ECC_NONE 0 +/* Software ECC 3 byte ECC per 256 Byte data */ +#define NAND_ECC_SOFT 1 +/* Hardware ECC 3 byte ECC per 256 Byte data */ +#define NAND_ECC_HW3_256 2 +/* Hardware ECC 3 byte ECC per 512 Byte data */ +#define NAND_ECC_HW3_512 3 +/* Hardware ECC 6 byte ECC per 512 Byte data */ +#define NAND_ECC_HW6_512 4 +/* Hardware ECC 6 byte ECC per 512 Byte data */ +#define NAND_ECC_HW8_512 6 + </programlisting> + </para> + </sect1> + + <sect1> + <title>Hardware control related constants</title> + <para> + These constants describe the requested hardware access function when + the boardspecific hardware control function is called + <programlisting> +/* Select the chip by setting nCE to low */ +#define NAND_CTL_SETNCE 1 +/* Deselect the chip by setting nCE to high */ +#define NAND_CTL_CLRNCE 2 +/* Select the command latch by setting CLE to high */ +#define NAND_CTL_SETCLE 3 +/* Deselect the command latch by setting CLE to low */ +#define NAND_CTL_CLRCLE 4 +/* Select the address latch by setting ALE to high */ +#define NAND_CTL_SETALE 5 +/* Deselect the address latch by setting ALE to low */ +#define NAND_CTL_CLRALE 6 +/* Set write protection by setting WP to high. Not used! */ +#define NAND_CTL_SETWP 7 +/* Clear write protection by setting WP to low. Not used! */ +#define NAND_CTL_CLRWP 8 + </programlisting> + </para> + </sect1> + + <sect1> + <title>Bad block table related constants</title> + <para> + These constants describe the options used for bad block + table descriptors. + <programlisting> +/* Options for the bad block table descriptors */ + +/* The number of bits used per block in the bbt on the device */ +#define NAND_BBT_NRBITS_MSK 0x0000000F +#define NAND_BBT_1BIT 0x00000001 +#define NAND_BBT_2BIT 0x00000002 +#define NAND_BBT_4BIT 0x00000004 +#define NAND_BBT_8BIT 0x00000008 +/* The bad block table is in the last good block of the device */ +#define NAND_BBT_LASTBLOCK 0x00000010 +/* The bbt is at the given page, else we must scan for the bbt */ +#define NAND_BBT_ABSPAGE 0x00000020 +/* The bbt is at the given page, else we must scan for the bbt */ +#define NAND_BBT_SEARCH 0x00000040 +/* bbt is stored per chip on multichip devices */ +#define NAND_BBT_PERCHIP 0x00000080 +/* bbt has a version counter at offset veroffs */ +#define NAND_BBT_VERSION 0x00000100 +/* Create a bbt if none axists */ +#define NAND_BBT_CREATE 0x00000200 +/* Search good / bad pattern through all pages of a block */ +#define NAND_BBT_SCANALLPAGES 0x00000400 +/* Scan block empty during good / bad block scan */ +#define NAND_BBT_SCANEMPTY 0x00000800 +/* Write bbt if neccecary */ +#define NAND_BBT_WRITE 0x00001000 +/* Read and write back block contents when writing bbt */ +#define NAND_BBT_SAVECONTENT 0x00002000 + </programlisting> + </para> + </sect1> + + </chapter> + + <chapter id="structs"> + <title>Structures</title> + <para> + This chapter contains the autogenerated documentation of the structures which are + used in the NAND driver and might be relevant for a driver developer. Each + struct member has a short description which is marked with an [XXX] identifier. + See the chapter "Documentation hints" for an explanation. + </para> +!Iinclude/linux/mtd/nand.h + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> + <para> + This chapter contains the autogenerated documentation of the NAND kernel API functions + which are exported. Each function has a short description which is marked with an [XXX] identifier. + See the chapter "Documentation hints" for an explanation. + </para> +!Edrivers/mtd/nand/nand_base.c +!Edrivers/mtd/nand/nand_bbt.c +!Edrivers/mtd/nand/nand_ecc.c + </chapter> + + <chapter id="intfunctions"> + <title>Internal Functions Provided</title> + <para> + This chapter contains the autogenerated documentation of the NAND driver internal functions. + Each function has a short description which is marked with an [XXX] identifier. + See the chapter "Documentation hints" for an explanation. + The functions marked with [DEFAULT] might be relevant for a board driver developer. + </para> +!Idrivers/mtd/nand/nand_base.c +!Idrivers/mtd/nand/nand_bbt.c +!Idrivers/mtd/nand/nand_ecc.c + </chapter> + + <chapter id="credits"> + <title>Credits</title> + <para> + The following people have contributed to the NAND driver: + <orderedlist> + <listitem><para>Steven J. Hill<email>sjhill@realitydiluted.com</email></para></listitem> + <listitem><para>David Woodhouse<email>dwmw2@infradead.org</email></para></listitem> + <listitem><para>Thomas Gleixner<email>tglx@linutronix.de</email></para></listitem> + </orderedlist> + A lot of users have provided bugfixes, improvements and helping hands for testing. + Thanks a lot. + </para> + <para> + The following people have contributed to this document: + <orderedlist> + <listitem><para>Thomas Gleixner<email>tglx@linutronix.de</email></para></listitem> + </orderedlist> + </para> + </chapter> +</book> diff --git a/Documentation/DocBook/procfs-guide.tmpl b/Documentation/DocBook/procfs-guide.tmpl new file mode 100644 index 0000000..45cad23 --- /dev/null +++ b/Documentation/DocBook/procfs-guide.tmpl @@ -0,0 +1,591 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [ +<!ENTITY procfsexample SYSTEM "procfs_example.xml"> +]> + +<book id="LKProcfsGuide"> + <bookinfo> + <title>Linux Kernel Procfs Guide</title> + + <authorgroup> + <author> + <firstname>Erik</firstname> + <othername>(J.A.K.)</othername> + <surname>Mouw</surname> + <affiliation> + <orgname>Delft University of Technology</orgname> + <orgdiv>Faculty of Information Technology and Systems</orgdiv> + <address> + <email>J.A.K.Mouw@its.tudelft.nl</email> + <pob>PO BOX 5031</pob> + <postcode>2600 GA</postcode> + <city>Delft</city> + <country>The Netherlands</country> + </address> + </affiliation> + </author> + </authorgroup> + + <revhistory> + <revision> + <revnumber>1.0 </revnumber> + <date>May 30, 2001</date> + <revremark>Initial revision posted to linux-kernel</revremark> + </revision> + <revision> + <revnumber>1.1 </revnumber> + <date>June 3, 2001</date> + <revremark>Revised after comments from linux-kernel</revremark> + </revision> + </revhistory> + + <copyright> + <year>2001</year> + <holder>Erik Mouw</holder> + </copyright> + + + <legalnotice> + <para> + This documentation is free software; you can redistribute it + and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This documentation is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR + PURPOSE. See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + + + + + <toc> + </toc> + + + + + <preface> + <title>Preface</title> + + <para> + This guide describes the use of the procfs file system from + within the Linux kernel. The idea to write this guide came up on + the #kernelnewbies IRC channel (see <ulink + url="http://www.kernelnewbies.org/">http://www.kernelnewbies.org/</ulink>), + when Jeff Garzik explained the use of procfs and forwarded me a + message Alexander Viro wrote to the linux-kernel mailing list. I + agreed to write it up nicely, so here it is. + </para> + + <para> + I'd like to thank Jeff Garzik + <email>jgarzik@pobox.com</email> and Alexander Viro + <email>viro@parcelfarce.linux.theplanet.co.uk</email> for their input, + Tim Waugh <email>twaugh@redhat.com</email> for his <ulink + url="http://people.redhat.com/twaugh/docbook/selfdocbook/">Selfdocbook</ulink>, + and Marc Joosen <email>marcj@historia.et.tudelft.nl</email> for + proofreading. + </para> + + <para> + This documentation was written while working on the LART + computing board (<ulink + url="http://www.lart.tudelft.nl/">http://www.lart.tudelft.nl/</ulink>), + which is sponsored by the Mobile Multi-media Communications + (<ulink + url="http://www.mmc.tudelft.nl/">http://www.mmc.tudelft.nl/</ulink>) + and Ubiquitous Communications (<ulink + url="http://www.ubicom.tudelft.nl/">http://www.ubicom.tudelft.nl/</ulink>) + projects. + </para> + + <para> + Erik + </para> + </preface> + + + + + <chapter id="intro"> + <title>Introduction</title> + + <para> + The <filename class="directory">/proc</filename> file system + (procfs) is a special file system in the linux kernel. It's a + virtual file system: it is not associated with a block device + but exists only in memory. The files in the procfs are there to + allow userland programs access to certain information from the + kernel (like process information in <filename + class="directory">/proc/[0-9]+/</filename>), but also for debug + purposes (like <filename>/proc/ksyms</filename>). + </para> + + <para> + This guide describes the use of the procfs file system from + within the Linux kernel. It starts by introducing all relevant + functions to manage the files within the file system. After that + it shows how to communicate with userland, and some tips and + tricks will be pointed out. Finally a complete example will be + shown. + </para> + + <para> + Note that the files in <filename + class="directory">/proc/sys</filename> are sysctl files: they + don't belong to procfs and are governed by a completely + different API described in the Kernel API book. + </para> + </chapter> + + + + + <chapter id="managing"> + <title>Managing procfs entries</title> + + <para> + This chapter describes the functions that various kernel + components use to populate the procfs with files, symlinks, + device nodes, and directories. + </para> + + <para> + A minor note before we start: if you want to use any of the + procfs functions, be sure to include the correct header file! + This should be one of the first lines in your code: + </para> + + <programlisting> +#include <linux/proc_fs.h> + </programlisting> + + + + + <sect1 id="regularfile"> + <title>Creating a regular file</title> + + <funcsynopsis> + <funcprototype> + <funcdef>struct proc_dir_entry* <function>create_proc_entry</function></funcdef> + <paramdef>const char* <parameter>name</parameter></paramdef> + <paramdef>mode_t <parameter>mode</parameter></paramdef> + <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + This function creates a regular file with the name + <parameter>name</parameter>, file mode + <parameter>mode</parameter> in the directory + <parameter>parent</parameter>. To create a file in the root of + the procfs, use <constant>NULL</constant> as + <parameter>parent</parameter> parameter. When successful, the + function will return a pointer to the freshly created + <structname>struct proc_dir_entry</structname>; otherwise it + will return <constant>NULL</constant>. <xref + linkend="userland"/> describes how to do something useful with + regular files. + </para> + + <para> + Note that it is specifically supported that you can pass a + path that spans multiple directories. For example + <function>create_proc_entry</function>(<parameter>"drivers/via0/info"</parameter>) + will create the <filename class="directory">via0</filename> + directory if necessary, with standard + <constant>0755</constant> permissions. + </para> + + <para> + If you only want to be able to read the file, the function + <function>create_proc_read_entry</function> described in <xref + linkend="convenience"/> may be used to create and initialise + the procfs entry in one single call. + </para> + </sect1> + + + + + <sect1> + <title>Creating a symlink</title> + + <funcsynopsis> + <funcprototype> + <funcdef>struct proc_dir_entry* + <function>proc_symlink</function></funcdef> <paramdef>const + char* <parameter>name</parameter></paramdef> + <paramdef>struct proc_dir_entry* + <parameter>parent</parameter></paramdef> <paramdef>const + char* <parameter>dest</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + This creates a symlink in the procfs directory + <parameter>parent</parameter> that points from + <parameter>name</parameter> to + <parameter>dest</parameter>. This translates in userland to + <literal>ln -s</literal> <parameter>dest</parameter> + <parameter>name</parameter>. + </para> + </sect1> + + <sect1> + <title>Creating a directory</title> + + <funcsynopsis> + <funcprototype> + <funcdef>struct proc_dir_entry* <function>proc_mkdir</function></funcdef> + <paramdef>const char* <parameter>name</parameter></paramdef> + <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + Create a directory <parameter>name</parameter> in the procfs + directory <parameter>parent</parameter>. + </para> + </sect1> + + + + + <sect1> + <title>Removing an entry</title> + + <funcsynopsis> + <funcprototype> + <funcdef>void <function>remove_proc_entry</function></funcdef> + <paramdef>const char* <parameter>name</parameter></paramdef> + <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + Removes the entry <parameter>name</parameter> in the directory + <parameter>parent</parameter> from the procfs. Entries are + removed by their <emphasis>name</emphasis>, not by the + <structname>struct proc_dir_entry</structname> returned by the + various create functions. Note that this function doesn't + recursively remove entries. + </para> + + <para> + Be sure to free the <structfield>data</structfield> entry from + the <structname>struct proc_dir_entry</structname> before + <function>remove_proc_entry</function> is called (that is: if + there was some <structfield>data</structfield> allocated, of + course). See <xref linkend="usingdata"/> for more information + on using the <structfield>data</structfield> entry. + </para> + </sect1> + </chapter> + + + + + <chapter id="userland"> + <title>Communicating with userland</title> + + <para> + Instead of reading (or writing) information directly from + kernel memory, procfs works with <emphasis>call back + functions</emphasis> for files: functions that are called when + a specific file is being read or written. Such functions have + to be initialised after the procfs file is created by setting + the <structfield>read_proc</structfield> and/or + <structfield>write_proc</structfield> fields in the + <structname>struct proc_dir_entry*</structname> that the + function <function>create_proc_entry</function> returned: + </para> + + <programlisting> +struct proc_dir_entry* entry; + +entry->read_proc = read_proc_foo; +entry->write_proc = write_proc_foo; + </programlisting> + + <para> + If you only want to use a the + <structfield>read_proc</structfield>, the function + <function>create_proc_read_entry</function> described in <xref + linkend="convenience"/> may be used to create and initialise the + procfs entry in one single call. + </para> + + + + <sect1> + <title>Reading data</title> + + <para> + The read function is a call back function that allows userland + processes to read data from the kernel. The read function + should have the following format: + </para> + + <funcsynopsis> + <funcprototype> + <funcdef>int <function>read_func</function></funcdef> + <paramdef>char* <parameter>page</parameter></paramdef> + <paramdef>char** <parameter>start</parameter></paramdef> + <paramdef>off_t <parameter>off</parameter></paramdef> + <paramdef>int <parameter>count</parameter></paramdef> + <paramdef>int* <parameter>eof</parameter></paramdef> + <paramdef>void* <parameter>data</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + The read function should write its information into the + <parameter>page</parameter>. For proper use, the function + should start writing at an offset of + <parameter>off</parameter> in <parameter>page</parameter> and + write at most <parameter>count</parameter> bytes, but because + most read functions are quite simple and only return a small + amount of information, these two parameters are usually + ignored (it breaks pagers like <literal>more</literal> and + <literal>less</literal>, but <literal>cat</literal> still + works). + </para> + + <para> + If the <parameter>off</parameter> and + <parameter>count</parameter> parameters are properly used, + <parameter>eof</parameter> should be used to signal that the + end of the file has been reached by writing + <literal>1</literal> to the memory location + <parameter>eof</parameter> points to. + </para> + + <para> + The parameter <parameter>start</parameter> doesn't seem to be + used anywhere in the kernel. The <parameter>data</parameter> + parameter can be used to create a single call back function for + several files, see <xref linkend="usingdata"/>. + </para> + + <para> + The <function>read_func</function> function must return the + number of bytes written into the <parameter>page</parameter>. + </para> + + <para> + <xref linkend="example"/> shows how to use a read call back + function. + </para> + </sect1> + + + + + <sect1> + <title>Writing data</title> + + <para> + The write call back function allows a userland process to write + data to the kernel, so it has some kind of control over the + kernel. The write function should have the following format: + </para> + + <funcsynopsis> + <funcprototype> + <funcdef>int <function>write_func</function></funcdef> + <paramdef>struct file* <parameter>file</parameter></paramdef> + <paramdef>const char* <parameter>buffer</parameter></paramdef> + <paramdef>unsigned long <parameter>count</parameter></paramdef> + <paramdef>void* <parameter>data</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + The write function should read <parameter>count</parameter> + bytes at maximum from the <parameter>buffer</parameter>. Note + that the <parameter>buffer</parameter> doesn't live in the + kernel's memory space, so it should first be copied to kernel + space with <function>copy_from_user</function>. The + <parameter>file</parameter> parameter is usually + ignored. <xref linkend="usingdata"/> shows how to use the + <parameter>data</parameter> parameter. + </para> + + <para> + Again, <xref linkend="example"/> shows how to use this call back + function. + </para> + </sect1> + + + + + <sect1 id="usingdata"> + <title>A single call back for many files</title> + + <para> + When a large number of almost identical files is used, it's + quite inconvenient to use a separate call back function for + each file. A better approach is to have a single call back + function that distinguishes between the files by using the + <structfield>data</structfield> field in <structname>struct + proc_dir_entry</structname>. First of all, the + <structfield>data</structfield> field has to be initialised: + </para> + + <programlisting> +struct proc_dir_entry* entry; +struct my_file_data *file_data; + +file_data = kmalloc(sizeof(struct my_file_data), GFP_KERNEL); +entry->data = file_data; + </programlisting> + + <para> + The <structfield>data</structfield> field is a <type>void + *</type>, so it can be initialised with anything. + </para> + + <para> + Now that the <structfield>data</structfield> field is set, the + <function>read_proc</function> and + <function>write_proc</function> can use it to distinguish + between files because they get it passed into their + <parameter>data</parameter> parameter: + </para> + + <programlisting> +int foo_read_func(char *page, char **start, off_t off, + int count, int *eof, void *data) +{ + int len; + + if(data == file_data) { + /* special case for this file */ + } else { + /* normal processing */ + } + + return len; +} + </programlisting> + + <para> + Be sure to free the <structfield>data</structfield> data field + when removing the procfs entry. + </para> + </sect1> + </chapter> + + + + + <chapter id="tips"> + <title>Tips and tricks</title> + + + + + <sect1 id="convenience"> + <title>Convenience functions</title> + + <funcsynopsis> + <funcprototype> + <funcdef>struct proc_dir_entry* <function>create_proc_read_entry</function></funcdef> + <paramdef>const char* <parameter>name</parameter></paramdef> + <paramdef>mode_t <parameter>mode</parameter></paramdef> + <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> + <paramdef>read_proc_t* <parameter>read_proc</parameter></paramdef> + <paramdef>void* <parameter>data</parameter></paramdef> + </funcprototype> + </funcsynopsis> + + <para> + This function creates a regular file in exactly the same way + as <function>create_proc_entry</function> from <xref + linkend="regularfile"/> does, but also allows to set the read + function <parameter>read_proc</parameter> in one call. This + function can set the <parameter>data</parameter> as well, like + explained in <xref linkend="usingdata"/>. + </para> + </sect1> + + + + <sect1> + <title>Modules</title> + + <para> + If procfs is being used from within a module, be sure to set + the <structfield>owner</structfield> field in the + <structname>struct proc_dir_entry</structname> to + <constant>THIS_MODULE</constant>. + </para> + + <programlisting> +struct proc_dir_entry* entry; + +entry->owner = THIS_MODULE; + </programlisting> + </sect1> + + + + + <sect1> + <title>Mode and ownership</title> + + <para> + Sometimes it is useful to change the mode and/or ownership of + a procfs entry. Here is an example that shows how to achieve + that: + </para> + + <programlisting> +struct proc_dir_entry* entry; + +entry->mode = S_IWUSR |S_IRUSR | S_IRGRP | S_IROTH; +entry->uid = 0; +entry->gid = 100; + </programlisting> + + </sect1> + </chapter> + + + + + <chapter id="example"> + <title>Example</title> + + <!-- be careful with the example code: it shouldn't be wider than + approx. 60 columns, or otherwise it won't fit properly on a page + --> + +&procfsexample; + + </chapter> +</book> diff --git a/Documentation/DocBook/procfs_example.c b/Documentation/DocBook/procfs_example.c new file mode 100644 index 0000000..7064084 --- /dev/null +++ b/Documentation/DocBook/procfs_example.c @@ -0,0 +1,224 @@ +/* + * procfs_example.c: an example proc interface + * + * Copyright (C) 2001, Erik Mouw (J.A.K.Mouw@its.tudelft.nl) + * + * This file accompanies the procfs-guide in the Linux kernel + * source. Its main use is to demonstrate the concepts and + * functions described in the guide. + * + * This software has been developed while working on the LART + * computing board (http://www.lart.tudelft.nl/), which is + * sponsored by the Mobile Multi-media Communications + * (http://www.mmc.tudelft.nl/) and Ubiquitous Communications + * (http://www.ubicom.tudelft.nl/) projects. + * + * The author can be reached at: + * + * Erik Mouw + * Information and Communication Theory Group + * Faculty of Information Technology and Systems + * Delft University of Technology + * P.O. Box 5031 + * 2600 GA Delft + * The Netherlands + * + * + * This program is free software; you can redistribute + * it and/or modify it under the terms of the GNU General + * Public License as published by the Free Software + * Foundation; either version 2 of the License, or (at your + * option) any later version. + * + * This program is distributed in the hope that it will be + * useful, but WITHOUT ANY WARRANTY; without even the implied + * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR + * PURPOSE. See the GNU General Public License for more + * details. + * + * You should have received a copy of the GNU General Public + * License along with this program; if not, write to the + * Free Software Foundation, Inc., 59 Temple Place, + * Suite 330, Boston, MA 02111-1307 USA + * + */ + +#include <linux/module.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/proc_fs.h> +#include <linux/jiffies.h> +#include <asm/uaccess.h> + + +#define MODULE_VERS "1.0" +#define MODULE_NAME "procfs_example" + +#define FOOBAR_LEN 8 + +struct fb_data_t { + char name[FOOBAR_LEN + 1]; + char value[FOOBAR_LEN + 1]; +}; + + +static struct proc_dir_entry *example_dir, *foo_file, + *bar_file, *jiffies_file, *symlink; + + +struct fb_data_t foo_data, bar_data; + + +static int proc_read_jiffies(char *page, char **start, + off_t off, int count, + int *eof, void *data) +{ + int len; + + len = sprintf(page, "jiffies = %ld\n", + jiffies); + + return len; +} + + +static int proc_read_foobar(char *page, char **start, + off_t off, int count, + int *eof, void *data) +{ + int len; + struct fb_data_t *fb_data = (struct fb_data_t *)data; + + /* DON'T DO THAT - buffer overruns are bad */ + len = sprintf(page, "%s = '%s'\n", + fb_data->name, fb_data->value); + + return len; +} + + +static int proc_write_foobar(struct file *file, + const char *buffer, + unsigned long count, + void *data) +{ + int len; + struct fb_data_t *fb_data = (struct fb_data_t *)data; + + if(count > FOOBAR_LEN) + len = FOOBAR_LEN; + else + len = count; + + if(copy_from_user(fb_data->value, buffer, len)) + return -EFAULT; + + fb_data->value[len] = '\0'; + + return len; +} + + +static int __init init_procfs_example(void) +{ + int rv = 0; + + /* create directory */ + example_dir = proc_mkdir(MODULE_NAME, NULL); + if(example_dir == NULL) { + rv = -ENOMEM; + goto out; + } + + example_dir->owner = THIS_MODULE; + + /* create jiffies using convenience function */ + jiffies_file = create_proc_read_entry("jiffies", + 0444, example_dir, + proc_read_jiffies, + NULL); + if(jiffies_file == NULL) { + rv = -ENOMEM; + goto no_jiffies; + } + + jiffies_file->owner = THIS_MODULE; + + /* create foo and bar files using same callback + * functions + */ + foo_file = create_proc_entry("foo", 0644, example_dir); + if(foo_file == NULL) { + rv = -ENOMEM; + goto no_foo; + } + + strcpy(foo_data.name, "foo"); + strcpy(foo_data.value, "foo"); + foo_file->data = &foo_data; + foo_file->read_proc = proc_read_foobar; + foo_file->write_proc = proc_write_foobar; + foo_file->owner = THIS_MODULE; + + bar_file = create_proc_entry("bar", 0644, example_dir); + if(bar_file == NULL) { + rv = -ENOMEM; + goto no_bar; + } + + strcpy(bar_data.name, "bar"); + strcpy(bar_data.value, "bar"); + bar_file->data = &bar_data; + bar_file->read_proc = proc_read_foobar; + bar_file->write_proc = proc_write_foobar; + bar_file->owner = THIS_MODULE; + + /* create symlink */ + symlink = proc_symlink("jiffies_too", example_dir, + "jiffies"); + if(symlink == NULL) { + rv = -ENOMEM; + goto no_symlink; + } + + symlink->owner = THIS_MODULE; + + /* everything OK */ + printk(KERN_INFO "%s %s initialised\n", + MODULE_NAME, MODULE_VERS); + return 0; + +no_symlink: + remove_proc_entry("tty", example_dir); +no_tty: + remove_proc_entry("bar", example_dir); +no_bar: + remove_proc_entry("foo", example_dir); +no_foo: + remove_proc_entry("jiffies", example_dir); +no_jiffies: + remove_proc_entry(MODULE_NAME, NULL); +out: + return rv; +} + + +static void __exit cleanup_procfs_example(void) +{ + remove_proc_entry("jiffies_too", example_dir); + remove_proc_entry("tty", example_dir); + remove_proc_entry("bar", example_dir); + remove_proc_entry("foo", example_dir); + remove_proc_entry("jiffies", example_dir); + remove_proc_entry(MODULE_NAME, NULL); + + printk(KERN_INFO "%s %s removed\n", + MODULE_NAME, MODULE_VERS); +} + + +module_init(init_procfs_example); +module_exit(cleanup_procfs_example); + +MODULE_AUTHOR("Erik Mouw"); +MODULE_DESCRIPTION("procfs examples"); diff --git a/Documentation/DocBook/scsidrivers.tmpl b/Documentation/DocBook/scsidrivers.tmpl new file mode 100644 index 0000000..d058e65 --- /dev/null +++ b/Documentation/DocBook/scsidrivers.tmpl @@ -0,0 +1,193 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="scsidrivers"> + <bookinfo> + <title>SCSI Subsystem Interfaces</title> + + <authorgroup> + <author> + <firstname>Douglas</firstname> + <surname>Gilbert</surname> + <affiliation> + <address> + <email>dgilbert@interlog.com</email> + </address> + </affiliation> + </author> + </authorgroup> + <pubdate>2003-08-11</pubdate> + + <copyright> + <year>2002</year> + <year>2003</year> + <holder>Douglas Gilbert</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> +This document outlines the interface between the Linux scsi mid level +and lower level drivers. Lower level drivers are variously called HBA +(host bus adapter) drivers, host drivers (HD) or pseudo adapter drivers. +The latter alludes to the fact that a lower level driver may be a +bridge to another IO subsystem (and the "ide-scsi" driver is an example +of this). There can be many lower level drivers active in a running +system, but only one per hardware type. For example, the aic7xxx driver +controls adaptec controllers based on the 7xxx chip series. Most lower +level drivers can control one or more scsi hosts (a.k.a. scsi initiators). + </para> +<para> +This document can been found in an ASCII text file in the linux kernel +source: <filename>Documentation/scsi/scsi_mid_low_api.txt</filename> . +It currently hold a little more information than this document. The +<filename>drivers/scsi/hosts.h</filename> and <filename> +drivers/scsi/scsi.h</filename> headers contain descriptions of members +of important structures for the scsi subsystem. +</para> + </chapter> + + <chapter id="driver-struct"> + <title>Driver structure</title> + <para> +Traditionally a lower level driver for the scsi subsystem has been +at least two files in the drivers/scsi directory. For example, a +driver called "xyz" has a header file "xyz.h" and a source file +"xyz.c". [Actually there is no good reason why this couldn't all +be in one file.] Some drivers that have been ported to several operating +systems (e.g. aic7xxx which has separate files for generic and +OS-specific code) have more than two files. Such drivers tend to have +their own directory under the drivers/scsi directory. + </para> + <para> +scsi_module.c is normally included at the end of a lower +level driver. For it to work a declaration like this is needed before +it is included: +<programlisting> + static Scsi_Host_Template driver_template = DRIVER_TEMPLATE; + /* DRIVER_TEMPLATE should contain pointers to supported interface + functions. Scsi_Host_Template is defined hosts.h */ + #include "scsi_module.c" +</programlisting> + </para> + <para> +The scsi_module.c assumes the name "driver_template" is appropriately +defined. It contains 2 functions: +<orderedlist> +<listitem><para> + init_this_scsi_driver() called during builtin and module driver + initialization: invokes mid level's scsi_register_host() +</para></listitem> +<listitem><para> + exit_this_scsi_driver() called during closedown: invokes + mid level's scsi_unregister_host() +</para></listitem> +</orderedlist> + </para> +<para> +When a new, lower level driver is being added to Linux, the following +files (all found in the drivers/scsi directory) will need some attention: +Makefile, Config.help and Config.in . It is probably best to look at what +an existing lower level driver does in this regard. +</para> + </chapter> + + <chapter id="intfunctions"> + <title>Interface Functions</title> +!EDocumentation/scsi/scsi_mid_low_api.txt + </chapter> + + <chapter id="locks"> + <title>Locks</title> +<para> +Each Scsi_Host instance has a spin_lock called Scsi_Host::default_lock +which is initialized in scsi_register() [found in hosts.c]. Within the +same function the Scsi_Host::host_lock pointer is initialized to point +at default_lock with the scsi_assign_lock() function. Thereafter +lock and unlock operations performed by the mid level use the +Scsi_Host::host_lock pointer. +</para> +<para> +Lower level drivers can override the use of Scsi_Host::default_lock by +using scsi_assign_lock(). The earliest opportunity to do this would +be in the detect() function after it has invoked scsi_register(). It +could be replaced by a coarser grain lock (e.g. per driver) or a +lock of equal granularity (i.e. per host). Using finer grain locks +(e.g. per scsi device) may be possible by juggling locks in +queuecommand(). +</para> + </chapter> + + <chapter id="changes"> + <title>Changes since lk 2.4 series</title> +<para> +io_request_lock has been replaced by several finer grained locks. The lock +relevant to lower level drivers is Scsi_Host::host_lock and there is one +per scsi host. +</para> +<para> +The older error handling mechanism has been removed. This means the +lower level interface functions abort() and reset() have been removed. +</para> +<para> +In the 2.4 series the scsi subsystem configuration descriptions were +aggregated with the configuration descriptions from all other Linux +subsystems in the Documentation/Configure.help file. In the 2.5 series, +the scsi subsystem now has its own (much smaller) drivers/scsi/Config.help +file. +</para> + </chapter> + + <chapter id="credits"> + <title>Credits</title> +<para> +The following people have contributed to this document: +<orderedlist> +<listitem><para> +Mike Anderson <email>andmike@us.ibm.com</email> +</para></listitem> +<listitem><para> +James Bottomley <email>James.Bottomley@steeleye.com</email> +</para></listitem> +<listitem><para> +Patrick Mansfield <email>patmans@us.ibm.com</email> +</para></listitem> +</orderedlist> +</para> + </chapter> + +</book> diff --git a/Documentation/DocBook/sis900.tmpl b/Documentation/DocBook/sis900.tmpl new file mode 100644 index 0000000..6c2cbac --- /dev/null +++ b/Documentation/DocBook/sis900.tmpl @@ -0,0 +1,585 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="SiS900Guide"> + +<bookinfo> + +<title>SiS 900/7016 Fast Ethernet Device Driver</title> + +<authorgroup> +<author> +<firstname>Ollie</firstname> +<surname>Lho</surname> +</author> + +<author> +<firstname>Lei Chun</firstname> +<surname>Chang</surname> +</author> +</authorgroup> + +<edition>Document Revision: 0.3 for SiS900 driver v1.06 & v1.07</edition> +<pubdate>November 16, 2000</pubdate> + +<copyright> + <year>1999</year> + <holder>Silicon Integrated System Corp.</holder> +</copyright> + +<legalnotice> + <para> + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + </para> + + <para> + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + </para> +</legalnotice> + +<abstract> +<para> +This document gives some information on installation and usage of SiS 900/7016 +device driver under Linux. +</para> +</abstract> + +</bookinfo> + +<toc></toc> + +<chapter id="intro"> + <title>Introduction</title> + +<para> +This document describes the revision 1.06 and 1.07 of SiS 900/7016 Fast Ethernet +device driver under Linux. The driver is developed by Silicon Integrated +System Corp. and distributed freely under the GNU General Public License (GPL). +The driver can be compiled as a loadable module and used under Linux kernel +version 2.2.x. (rev. 1.06) +With minimal changes, the driver can also be used under 2.3.x and 2.4.x kernel +(rev. 1.07), please see +<xref linkend="install"/>. If you are intended to +use the driver for earlier kernels, you are on your own. +</para> + +<para> +The driver is tested with usual TCP/IP applications including +FTP, Telnet, Netscape etc. and is used constantly by the developers. +</para> + +<para> +Please send all comments/fixes/questions to +<ulink url="mailto:lcchang@sis.com.tw">Lei-Chun Chang</ulink>. +</para> +</chapter> + +<chapter id="changes"> + <title>Changes</title> + +<para> +Changes made in Revision 1.07 + +<orderedlist> +<listitem> +<para> +Separation of sis900.c and sis900.h in order to move most +constant definition to sis900.h (many of those constants were +corrected) +</para> +</listitem> + +<listitem> +<para> +Clean up PCI detection, the pci-scan from Donald Becker were not used, +just simple pci_find_*. +</para> +</listitem> + +<listitem> +<para> +MII detection is modified to support multiple mii transceiver. +</para> +</listitem> + +<listitem> +<para> +Bugs in read_eeprom, mdio_* were removed. +</para> +</listitem> + +<listitem> +<para> +Lot of sis900 irrelevant comments were removed/changed and +more comments were added to reflect the real situation. +</para> +</listitem> + +<listitem> +<para> +Clean up of physical/virtual address space mess in buffer +descriptors. +</para> +</listitem> + +<listitem> +<para> +Better transmit/receive error handling. +</para> +</listitem> + +<listitem> +<para> +The driver now uses zero-copy single buffer management +scheme to improve performance. +</para> +</listitem> + +<listitem> +<para> +Names of variables were changed to be more consistent. +</para> +</listitem> + +<listitem> +<para> +Clean up of auo-negotiation and timer code. +</para> +</listitem> + +<listitem> +<para> +Automatic detection and change of PHY on the fly. +</para> +</listitem> + +<listitem> +<para> +Bug in mac probing fixed. +</para> +</listitem> + +<listitem> +<para> +Fix 630E equalier problem by modifying the equalizer workaround rule. +</para> +</listitem> + +<listitem> +<para> +Support for ICS1893 10/100 Interated PHYceiver. +</para> +</listitem> + +<listitem> +<para> +Support for media select by ifconfig. +</para> +</listitem> + +<listitem> +<para> +Added kernel-doc extratable documentation. +</para> +</listitem> + +</orderedlist> +</para> +</chapter> + +<chapter id="tested"> + <title>Tested Environment</title> + +<para> +This driver is developed on the following hardware + +<itemizedlist> +<listitem> + +<para> +Intel Celeron 500 with SiS 630 (rev 02) chipset +</para> +</listitem> +<listitem> + +<para> +SiS 900 (rev 01) and SiS 7016/7014 Fast Ethernet Card +</para> +</listitem> + +</itemizedlist> + +and tested with these software environments + +<itemizedlist> +<listitem> + +<para> +Red Hat Linux version 6.2 +</para> +</listitem> +<listitem> + +<para> +Linux kernel version 2.4.0 +</para> +</listitem> +<listitem> + +<para> +Netscape version 4.6 +</para> +</listitem> +<listitem> + +<para> +NcFTP 3.0.0 beta 18 +</para> +</listitem> +<listitem> + +<para> +Samba version 2.0.3 +</para> +</listitem> + +</itemizedlist> + +</para> + +</chapter> + +<chapter id="files"> +<title>Files in This Package</title> + +<para> +In the package you can find these files: +</para> + +<para> +<variablelist> + +<varlistentry> +<term>sis900.c</term> +<listitem> +<para> +Driver source file in C +</para> +</listitem> +</varlistentry> + +<varlistentry> +<term>sis900.h</term> +<listitem> +<para> +Header file for sis900.c +</para> +</listitem> +</varlistentry> + +<varlistentry> +<term>sis900.sgml</term> +<listitem> +<para> +DocBook SGML source of the document +</para> +</listitem> +</varlistentry> + +<varlistentry> +<term>sis900.txt</term> +<listitem> +<para> +Driver document in plain text +</para> +</listitem> +</varlistentry> + +</variablelist> +</para> +</chapter> + +<chapter id="install"> + <title>Installation</title> + +<para> +Silicon Integrated System Corp. is cooperating closely with core Linux Kernel +developers. The revisions of SiS 900 driver are distributed by the usuall channels +for kernel tar files and patches. Those kernel tar files for official kernel and +patches for kernel pre-release can be download at +<ulink url="http://ftp.kernel.org/pub/linux/kernel/">official kernel ftp site</ulink> +and its mirrors. +The 1.06 revision can be found in kernel version later than 2.3.15 and pre-2.2.14, +and 1.07 revision can be found in kernel version 2.4.0. +If you have no prior experience in networking under Linux, please read +<ulink url="http://www.tldp.org/">Ethernet HOWTO</ulink> and +<ulink url="http://www.tldp.org/">Networking HOWTO</ulink> available from +Linux Documentation Project (LDP). +</para> + +<para> +The driver is bundled in release later than 2.2.11 and 2.3.15 so this +is the most easy case. +Be sure you have the appropriate packages for compiling kernel source. +Those packages are listed in Document/Changes in kernel source +distribution. If you have to install the driver other than those bundled +in kernel release, you should have your driver file +<filename>sis900.c</filename> and <filename>sis900.h</filename> +copied into <filename class="directory">/usr/src/linux/drivers/net/</filename> first. +There are two alternative ways to install the driver +</para> + +<sect1> +<title>Building the driver as loadable module</title> + +<para> +To build the driver as a loadable kernel module you have to reconfigure +the kernel to activate network support by +</para> + +<para><screen> +make menuconfig +</screen></para> + +<para> +Choose <quote>Loadable module support ---></quote>, +then select <quote>Enable loadable module support</quote>. +</para> + +<para> +Choose <quote>Network Device Support ---></quote>, select +<quote>Ethernet (10 or 100Mbit)</quote>. +Then select <quote>EISA, VLB, PCI and on board controllers</quote>, +and choose <quote>SiS 900/7016 PCI Fast Ethernet Adapter support</quote> +to <quote>M</quote>. +</para> + +<para> +After reconfiguring the kernel, you can make the driver module by +</para> + +<para><screen> +make modules +</screen></para> + +<para> +The driver should be compiled with no errors. After compiling the driver, +the driver can be installed to proper place by +</para> + +<para><screen> +make modules_install +</screen></para> + +<para> +Load the driver into kernel by +</para> + +<para><screen> +insmod sis900 +</screen></para> + +<para> +When loading the driver into memory, some information message can be view by +</para> + +<para> +<screen> +dmesg +</screen> + +or + +<screen> +cat /var/log/message +</screen> +</para> + +<para> +If the driver is loaded properly you will have messages similar to this: +</para> + +<para><screen> +sis900.c: v1.07.06 11/07/2000 +eth0: SiS 900 PCI Fast Ethernet at 0xd000, IRQ 10, 00:00:e8:83:7f:a4. +eth0: SiS 900 Internal MII PHY transceiver found at address 1. +eth0: Using SiS 900 Internal MII PHY as default +</screen></para> + +<para> +showing the version of the driver and the results of probing routine. +</para> + +<para> +Once the driver is loaded, network can be brought up by +</para> + +<para><screen> +/sbin/ifconfig eth0 IPADDR broadcast BROADCAST netmask NETMASK media TYPE +</screen></para> + +<para> +where IPADDR, BROADCAST, NETMASK are your IP address, broadcast address and +netmask respectively. TYPE is used to set medium type used by the device. +Typical values are "10baseT"(twisted-pair 10Mbps Ethernet) or "100baseT" +(twisted-pair 100Mbps Ethernet). For more information on how to configure +network interface, please refer to +<ulink url="http://www.tldp.org/">Networking HOWTO</ulink>. +</para> + +<para> +The link status is also shown by kernel messages. For example, after the +network interface is activated, you may have the message: +</para> + +<para><screen> +eth0: Media Link On 100mbps full-duplex +</screen></para> + +<para> +If you try to unplug the twist pair (TP) cable you will get +</para> + +<para><screen> +eth0: Media Link Off +</screen></para> + +<para> +indicating that the link is failed. +</para> +</sect1> + +<sect1> +<title>Building the driver into kernel</title> + +<para> +If you want to make the driver into kernel, choose <quote>Y</quote> +rather than <quote>M</quote> on +<quote>SiS 900/7016 PCI Fast Ethernet Adapter support</quote> +when configuring the kernel. Build the kernel image in the usual way +</para> + +<para><screen> +make clean + +make bzlilo +</screen></para> + +<para> +Next time the system reboot, you have the driver in memory. +</para> + +</sect1> +</chapter> + +<chapter id="problems"> + <title>Known Problems and Bugs</title> + +<para> +There are some known problems and bugs. If you find any other bugs please +mail to <ulink url="mailto:lcchang@sis.com.tw">lcchang@sis.com.tw</ulink> + +<orderedlist> + +<listitem> +<para> +AM79C901 HomePNA PHY is not thoroughly tested, there may be some +bugs in the <quote>on the fly</quote> change of transceiver. +</para> +</listitem> + +<listitem> +<para> +A bug is hidden somewhere in the receive buffer management code, +the bug causes NULL pointer reference in the kernel. This fault is +caught before bad things happen and reported with the message: + +<computeroutput> +eth0: NULL pointer encountered in Rx ring, skipping +</computeroutput> + +which can be viewed with <literal remap="tt">dmesg</literal> or +<literal remap="tt">cat /var/log/message</literal>. +</para> +</listitem> + +<listitem> +<para> +The media type change from 10Mbps to 100Mbps twisted-pair ethernet +by ifconfig causes the media link down. +</para> +</listitem> + +</orderedlist> +</para> +</chapter> + +<chapter id="RHistory"> + <title>Revision History</title> + +<para> +<itemizedlist> + +<listitem> +<para> +November 13, 2000, Revision 1.07, seventh release, 630E problem fixed +and further clean up. +</para> +</listitem> + +<listitem> +<para> +November 4, 1999, Revision 1.06, Second release, lots of clean up +and optimization. +</para> +</listitem> + +<listitem> +<para> +August 8, 1999, Revision 1.05, Initial Public Release +</para> +</listitem> + +</itemizedlist> +</para> +</chapter> + +<chapter id="acknowledgements"> + <title>Acknowledgements</title> + +<para> +This driver was originally derived form +<ulink url="mailto:becker@cesdis1.gsfc.nasa.gov">Donald Becker</ulink>'s +<ulink url="ftp://cesdis.gsfc.nasa.gov/pub/linux/drivers/kern-2.3/pci-skeleton.c" +>pci-skeleton</ulink> and +<ulink url="ftp://cesdis.gsfc.nasa.gov/pub/linux/drivers/kern-2.3/rtl8139.c" +>rtl8139</ulink> drivers. Donald also provided various suggestion +regarded with improvements made in revision 1.06. +</para> + +<para> +The 1.05 revision was created by +<ulink url="mailto:cmhuang@sis.com.tw">Jim Huang</ulink>, AMD 79c901 +support was added by <ulink url="mailto:lcs@sis.com.tw">Chin-Shan Li</ulink>. +</para> +</chapter> + +<chapter id="functions"> +<title>List of Functions</title> +!Idrivers/net/sis900.c +</chapter> + +</book> diff --git a/Documentation/DocBook/tulip-user.tmpl b/Documentation/DocBook/tulip-user.tmpl new file mode 100644 index 0000000..6520d7a --- /dev/null +++ b/Documentation/DocBook/tulip-user.tmpl @@ -0,0 +1,327 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="TulipUserGuide"> + <bookinfo> + <title>Tulip Driver User's Guide</title> + + <authorgroup> + <author> + <firstname>Jeff</firstname> + <surname>Garzik</surname> + <affiliation> + <address> + <email>jgarzik@pobox.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2001</year> + <holder>Jeff Garzik</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + + <toc></toc> + + <chapter id="intro"> + <title>Introduction</title> +<para> +The Tulip Ethernet Card Driver +is maintained by Jeff Garzik (<email>jgarzik@pobox.com</email>). +</para> + +<para> +The Tulip driver was developed by Donald Becker and changed by +Jeff Garzik, Takashi Manabe and a cast of thousands. +</para> + +<para> +For 2.4.x and later kernels, the Linux Tulip driver is available at +<ulink url="http://sourceforge.net/projects/tulip/">http://sourceforge.net/projects/tulip/</ulink> +</para> + +<para> + This driver is for the Digital "Tulip" Ethernet adapter interface. + It should work with most DEC 21*4*-based chips/ethercards, as well as + with work-alike chips from Lite-On (PNIC) and Macronix (MXIC) and ASIX. +</para> + +<para> + The original author may be reached as becker@scyld.com, or C/O + Scyld Computing Corporation, + 410 Severn Ave., Suite 210, + Annapolis MD 21403 +</para> + +<para> + Additional information on Donald Becker's tulip.c + is available at <ulink url="http://www.scyld.com/network/tulip.html">http://www.scyld.com/network/tulip.html</ulink> +</para> + + </chapter> + + <chapter id="drvr-compat"> + <title>Driver Compatibility</title> + +<para> +This device driver is designed for the DECchip "Tulip", Digital's +single-chip ethernet controllers for PCI (now owned by Intel). +Supported members of the family +are the 21040, 21041, 21140, 21140A, 21142, and 21143. Similar work-alike +chips from Lite-On, Macronics, ASIX, Compex and other listed below are also +supported. +</para> + +<para> +These chips are used on at least 140 unique PCI board designs. The great +number of chips and board designs supported is the reason for the +driver size and complexity. Almost of the increasing complexity is in the +board configuration and media selection code. There is very little +increasing in the operational critical path length. +</para> + </chapter> + + <chapter id="board-settings"> + <title>Board-specific Settings</title> + +<para> +PCI bus devices are configured by the system at boot time, so no jumpers +need to be set on the board. The system BIOS preferably should assign the +PCI INTA signal to an otherwise unused system IRQ line. +</para> + +<para> +Some boards have EEPROMs tables with default media entry. The factory default +is usually "autoselect". This should only be overridden when using +transceiver connections without link beat e.g. 10base2 or AUI, or (rarely!) +for forcing full-duplex when used with old link partners that do not do +autonegotiation. +</para> + </chapter> + + <chapter id="driver-operation"> + <title>Driver Operation</title> + +<sect1><title>Ring buffers</title> + +<para> +The Tulip can use either ring buffers or lists of Tx and Rx descriptors. +This driver uses statically allocated rings of Rx and Tx descriptors, set at +compile time by RX/TX_RING_SIZE. This version of the driver allocates skbuffs +for the Rx ring buffers at open() time and passes the skb->data field to the +Tulip as receive data buffers. When an incoming frame is less than +RX_COPYBREAK bytes long, a fresh skbuff is allocated and the frame is +copied to the new skbuff. When the incoming frame is larger, the skbuff is +passed directly up the protocol stack and replaced by a newly allocated +skbuff. +</para> + +<para> +The RX_COPYBREAK value is chosen to trade-off the memory wasted by +using a full-sized skbuff for small frames vs. the copying costs of larger +frames. For small frames the copying cost is negligible (esp. considering +that we are pre-loading the cache with immediately useful header +information). For large frames the copying cost is non-trivial, and the +larger copy might flush the cache of useful data. A subtle aspect of this +choice is that the Tulip only receives into longword aligned buffers, thus +the IP header at offset 14 isn't longword aligned for further processing. +Copied frames are put into the new skbuff at an offset of "+2", thus copying +has the beneficial effect of aligning the IP header and preloading the +cache. +</para> + +</sect1> + +<sect1><title>Synchronization</title> +<para> +The driver runs as two independent, single-threaded flows of control. One +is the send-packet routine, which enforces single-threaded use by the +dev->tbusy flag. The other thread is the interrupt handler, which is single +threaded by the hardware and other software. +</para> + +<para> +The send packet thread has partial control over the Tx ring and 'dev->tbusy' +flag. It sets the tbusy flag whenever it's queuing a Tx packet. If the next +queue slot is empty, it clears the tbusy flag when finished otherwise it sets +the 'tp->tx_full' flag. +</para> + +<para> +The interrupt handler has exclusive control over the Rx ring and records stats +from the Tx ring. (The Tx-done interrupt can't be selectively turned off, so +we can't avoid the interrupt overhead by having the Tx routine reap the Tx +stats.) After reaping the stats, it marks the queue entry as empty by setting +the 'base' to zero. Iff the 'tp->tx_full' flag is set, it clears both the +tx_full and tbusy flags. +</para> + +</sect1> + + </chapter> + + <chapter id="errata"> + <title>Errata</title> + +<para> +The old DEC databooks were light on details. +The 21040 databook claims that CSR13, CSR14, and CSR15 should each be the last +register of the set CSR12-15 written. Hmmm, now how is that possible? +</para> + +<para> +The DEC SROM format is very badly designed not precisely defined, leading to +part of the media selection junkheap below. Some boards do not have EEPROM +media tables and need to be patched up. Worse, other boards use the DEC +design kit media table when it isn't correct for their board. +</para> + +<para> +We cannot use MII interrupts because there is no defined GPIO pin to attach +them. The MII transceiver status is polled using an kernel timer. +</para> + </chapter> + + <chapter id="changelog"> + <title>Driver Change History</title> + + <sect1><title>Version 0.9.14 (February 20, 2001)</title> + <itemizedlist> + <listitem><para>Fix PNIC problems (Manfred Spraul)</para></listitem> + <listitem><para>Add new PCI id for Accton comet</para></listitem> + <listitem><para>Support Davicom tulips</para></listitem> + <listitem><para>Fix oops in eeprom parsing</para></listitem> + <listitem><para>Enable workarounds for early PCI chipsets</para></listitem> + <listitem><para>IA64, hppa csr0 support</para></listitem> + <listitem><para>Support media types 5, 6</para></listitem> + <listitem><para>Interpret a bit more of the 21142 SROM extended media type 3</para></listitem> + <listitem><para>Add missing delay in eeprom reading</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.11 (November 3, 2000)</title> + <itemizedlist> + <listitem><para>Eliminate extra bus accesses when sharing interrupts (prumpf)</para></listitem> + <listitem><para>Barrier following ownership descriptor bit flip (prumpf)</para></listitem> + <listitem><para>Endianness fixes for >14 addresses in setup frames (prumpf)</para></listitem> + <listitem><para>Report link beat to kernel/userspace via netif_carrier_*. (kuznet)</para></listitem> + <listitem><para>Better spinlocking in set_rx_mode.</para></listitem> + <listitem><para>Fix I/O resource request failure error messages (DaveM catch)</para></listitem> + <listitem><para>Handle DMA allocation failure.</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.10 (September 6, 2000)</title> + <itemizedlist> + <listitem><para>Simple interrupt mitigation (via jamal)</para></listitem> + <listitem><para>More PCI ids</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.9 (August 11, 2000)</title> + <itemizedlist> + <listitem><para>More PCI ids</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.8 (July 13, 2000)</title> + <itemizedlist> + <listitem><para>Correct signed/unsigned comparison for dummy frame index</para></listitem> + <listitem><para>Remove outdated references to struct enet_statistics</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.7 (June 17, 2000)</title> + <itemizedlist> + <listitem><para>Timer cleanups (Andrew Morton)</para></listitem> + <listitem><para>Alpha compile fix (somebody?)</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.6 (May 31, 2000)</title> + <itemizedlist> + <listitem><para>Revert 21143-related support flag patch</para></listitem> + <listitem><para>Add HPPA/media-table debugging printk</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.5 (May 30, 2000)</title> + <itemizedlist> + <listitem><para>HPPA support (willy@puffingroup)</para></listitem> + <listitem><para>CSR6 bits and tulip.h cleanup (Chris Smith)</para></listitem> + <listitem><para>Improve debugging messages a bit</para></listitem> + <listitem><para>Add delay after CSR13 write in t21142_start_nway</para></listitem> + <listitem><para>Remove unused ETHER_STATS code</para></listitem> + <listitem><para>Convert 'extern inline' to 'static inline' in tulip.h (Chris Smith)</para></listitem> + <listitem><para>Update DS21143 support flags in tulip_chip_info[]</para></listitem> + <listitem><para>Use spin_lock_irq, not _irqsave/restore, in tulip_start_xmit()</para></listitem> + <listitem><para>Add locking to set_rx_mode()</para></listitem> + <listitem><para>Fix race with chip setting DescOwned bit (Hal Murray)</para></listitem> + <listitem><para>Request 100% of PIO and MMIO resource space assigned to card</para></listitem> + <listitem><para>Remove error message from pci_enable_device failure</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.4.3 (April 14, 2000)</title> + <itemizedlist> + <listitem><para>mod_timer fix (Hal Murray)</para></listitem> + <listitem><para>PNIC2 resuscitation (Chris Smith)</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.4.2 (March 21, 2000)</title> + <itemizedlist> + <listitem><para>Fix 21041 CSR7, CSR13/14/15 handling</para></listitem> + <listitem><para>Merge some PCI ids from tulip 0.91x</para></listitem> + <listitem><para>Merge some HAS_xxx flags and flag settings from tulip 0.91x</para></listitem> + <listitem><para>asm/io.h fix (submitted by many) and cleanup</para></listitem> + <listitem><para>s/HAS_NWAY143/HAS_NWAY/</para></listitem> + <listitem><para>Cleanup 21041 mode reporting</para></listitem> + <listitem><para>Small code cleanups</para></listitem> + </itemizedlist> + </sect1> + + <sect1><title>Version 0.9.4.1 (March 18, 2000)</title> + <itemizedlist> + <listitem><para>Finish PCI DMA conversion (davem)</para></listitem> + <listitem><para>Do not netif_start_queue() at end of tulip_tx_timeout() (kuznet)</para></listitem> + <listitem><para>PCI DMA fix (kuznet)</para></listitem> + <listitem><para>eeprom.c code cleanup</para></listitem> + <listitem><para>Remove Xircom Tulip crud</para></listitem> + </itemizedlist> + </sect1> + </chapter> + +</book> diff --git a/Documentation/DocBook/usb.tmpl b/Documentation/DocBook/usb.tmpl new file mode 100644 index 0000000..f3ef0bf --- /dev/null +++ b/Documentation/DocBook/usb.tmpl @@ -0,0 +1,979 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="Linux-USB-API"> + <bookinfo> + <title>The Linux-USB Host Side API</title> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + +<chapter id="intro"> + <title>Introduction to USB on Linux</title> + + <para>A Universal Serial Bus (USB) is used to connect a host, + such as a PC or workstation, to a number of peripheral + devices. USB uses a tree structure, with the host at the + root (the system's master), hubs as interior nodes, and + peripheral devices as leaves (and slaves). + Modern PCs support several such trees of USB devices, usually + one USB 2.0 tree (480 Mbit/sec each) with + a few USB 1.1 trees (12 Mbit/sec each) that are used when you + connect a USB 1.1 device directly to the machine's "root hub". + </para> + + <para>That master/slave asymmetry was designed in part for + ease of use. It is not physically possible to assemble + (legal) USB cables incorrectly: all upstream "to-the-host" + connectors are the rectangular type, matching the sockets on + root hubs, and the downstream type are the squarish type + (or they are built in to the peripheral). + Software doesn't need to deal with distributed autoconfiguration + since the pre-designated master node manages all that. + At the electrical level, bus protocol overhead is reduced by + eliminating arbitration and moving scheduling into host software. + </para> + + <para>USB 1.0 was announced in January 1996, and was revised + as USB 1.1 (with improvements in hub specification and + support for interrupt-out transfers) in September 1998. + USB 2.0 was released in April 2000, including high speed + transfers and transaction translating hubs (used for USB 1.1 + and 1.0 backward compatibility). + </para> + + <para>USB support was added to Linux early in the 2.2 kernel series + shortly before the 2.3 development forked off. Updates + from 2.3 were regularly folded back into 2.2 releases, bringing + new features such as <filename>/sbin/hotplug</filename> support, + more drivers, and more robustness. + The 2.5 kernel series continued such improvements, and also + worked on USB 2.0 support, + higher performance, + better consistency between host controller drivers, + API simplification (to make bugs less likely), + and providing internal "kerneldoc" documentation. + </para> + + <para>Linux can run inside USB devices as well as on + the hosts that control the devices. + Because the Linux 2.x USB support evolved to support mass market + platforms such as Apple Macintosh or PC-compatible systems, + it didn't address design concerns for those types of USB systems. + So it can't be used inside mass-market PDAs, or other peripherals. + USB device drivers running inside those Linux peripherals + don't do the same things as the ones running inside hosts, + and so they've been given a different name: + they're called <emphasis>gadget drivers</emphasis>. + This document does not present gadget drivers. + </para> + + </chapter> + +<chapter id="host"> + <title>USB Host-Side API Model</title> + + <para>Within the kernel, + host-side drivers for USB devices talk to the "usbcore" APIs. + There are two types of public "usbcore" APIs, targetted at two different + layers of USB driver. Those are + <emphasis>general purpose</emphasis> drivers, exposed through + driver frameworks such as block, character, or network devices; + and drivers that are <emphasis>part of the core</emphasis>, + which are involved in managing a USB bus. + Such core drivers include the <emphasis>hub</emphasis> driver, + which manages trees of USB devices, and several different kinds + of <emphasis>host controller driver (HCD)</emphasis>, + which control individual busses. + </para> + + <para>The device model seen by USB drivers is relatively complex. + </para> + + <itemizedlist> + + <listitem><para>USB supports four kinds of data transfer + (control, bulk, interrupt, and isochronous). Two transfer + types use bandwidth as it's available (control and bulk), + while the other two types of transfer (interrupt and isochronous) + are scheduled to provide guaranteed bandwidth. + </para></listitem> + + <listitem><para>The device description model includes one or more + "configurations" per device, only one of which is active at a time. + Devices that are capable of high speed operation must also support + full speed configurations, along with a way to ask about the + "other speed" configurations that might be used. + </para></listitem> + + <listitem><para>Configurations have one or more "interface", each + of which may have "alternate settings". Interfaces may be + standardized by USB "Class" specifications, or may be specific to + a vendor or device.</para> + + <para>USB device drivers actually bind to interfaces, not devices. + Think of them as "interface drivers", though you + may not see many devices where the distinction is important. + <emphasis>Most USB devices are simple, with only one configuration, + one interface, and one alternate setting.</emphasis> + </para></listitem> + + <listitem><para>Interfaces have one or more "endpoints", each of + which supports one type and direction of data transfer such as + "bulk out" or "interrupt in". The entire configuration may have + up to sixteen endpoints in each direction, allocated as needed + among all the interfaces. + </para></listitem> + + <listitem><para>Data transfer on USB is packetized; each endpoint + has a maximum packet size. + Drivers must often be aware of conventions such as flagging the end + of bulk transfers using "short" (including zero length) packets. + </para></listitem> + + <listitem><para>The Linux USB API supports synchronous calls for + control and bulk messaging. + It also supports asynchnous calls for all kinds of data transfer, + using request structures called "URBs" (USB Request Blocks). + </para></listitem> + + </itemizedlist> + + <para>Accordingly, the USB Core API exposed to device drivers + covers quite a lot of territory. You'll probably need to consult + the USB 2.0 specification, available online from www.usb.org at + no cost, as well as class or device specifications. + </para> + + <para>The only host-side drivers that actually touch hardware + (reading/writing registers, handling IRQs, and so on) are the HCDs. + In theory, all HCDs provide the same functionality through the same + API. In practice, that's becoming more true on the 2.5 kernels, + but there are still differences that crop up especially with + fault handling. Different controllers don't necessarily report + the same aspects of failures, and recovery from faults (including + software-induced ones like unlinking an URB) isn't yet fully + consistent. + Device driver authors should make a point of doing disconnect + testing (while the device is active) with each different host + controller driver, to make sure drivers don't have bugs of + their own as well as to make sure they aren't relying on some + HCD-specific behavior. + (You will need external USB 1.1 and/or + USB 2.0 hubs to perform all those tests.) + </para> + + </chapter> + +<chapter><title>USB-Standard Types</title> + + <para>In <filename><linux/usb_ch9.h></filename> you will find + the USB data types defined in chapter 9 of the USB specification. + These data types are used throughout USB, and in APIs including + this host side API, gadget APIs, and usbfs. + </para> + +!Iinclude/linux/usb_ch9.h + + </chapter> + +<chapter><title>Host-Side Data Types and Macros</title> + + <para>The host side API exposes several layers to drivers, some of + which are more necessary than others. + These support lifecycle models for host side drivers + and devices, and support passing buffers through usbcore to + some HCD that performs the I/O for the device driver. + </para> + + +!Iinclude/linux/usb.h + + </chapter> + + <chapter><title>USB Core APIs</title> + + <para>There are two basic I/O models in the USB API. + The most elemental one is asynchronous: drivers submit requests + in the form of an URB, and the URB's completion callback + handle the next step. + All USB transfer types support that model, although there + are special cases for control URBs (which always have setup + and status stages, but may not have a data stage) and + isochronous URBs (which allow large packets and include + per-packet fault reports). + Built on top of that is synchronous API support, where a + driver calls a routine that allocates one or more URBs, + submits them, and waits until they complete. + There are synchronous wrappers for single-buffer control + and bulk transfers (which are awkward to use in some + driver disconnect scenarios), and for scatterlist based + streaming i/o (bulk or interrupt). + </para> + + <para>USB drivers need to provide buffers that can be + used for DMA, although they don't necessarily need to + provide the DMA mapping themselves. + There are APIs to use used when allocating DMA buffers, + which can prevent use of bounce buffers on some systems. + In some cases, drivers may be able to rely on 64bit DMA + to eliminate another kind of bounce buffer. + </para> + +!Edrivers/usb/core/urb.c +!Edrivers/usb/core/message.c +!Edrivers/usb/core/file.c +!Edrivers/usb/core/usb.c +!Edrivers/usb/core/hub.c + </chapter> + + <chapter><title>Host Controller APIs</title> + + <para>These APIs are only for use by host controller drivers, + most of which implement standard register interfaces such as + EHCI, OHCI, or UHCI. + UHCI was one of the first interfaces, designed by Intel and + also used by VIA; it doesn't do much in hardware. + OHCI was designed later, to have the hardware do more work + (bigger transfers, tracking protocol state, and so on). + EHCI was designed with USB 2.0; its design has features that + resemble OHCI (hardware does much more work) as well as + UHCI (some parts of ISO support, TD list processing). + </para> + + <para>There are host controllers other than the "big three", + although most PCI based controllers (and a few non-PCI based + ones) use one of those interfaces. + Not all host controllers use DMA; some use PIO, and there + is also a simulator. + </para> + + <para>The same basic APIs are available to drivers for all + those controllers. + For historical reasons they are in two layers: + <structname>struct usb_bus</structname> is a rather thin + layer that became available in the 2.2 kernels, while + <structname>struct usb_hcd</structname> is a more featureful + layer (available in later 2.4 kernels and in 2.5) that + lets HCDs share common code, to shrink driver size + and significantly reduce hcd-specific behaviors. + </para> + +!Edrivers/usb/core/hcd.c +!Edrivers/usb/core/hcd-pci.c +!Edrivers/usb/core/buffer.c + </chapter> + + <chapter> + <title>The USB Filesystem (usbfs)</title> + + <para>This chapter presents the Linux <emphasis>usbfs</emphasis>. + You may prefer to avoid writing new kernel code for your + USB driver; that's the problem that usbfs set out to solve. + User mode device drivers are usually packaged as applications + or libraries, and may use usbfs through some programming library + that wraps it. Such libraries include + <ulink url="http://libusb.sourceforge.net">libusb</ulink> + for C/C++, and + <ulink url="http://jUSB.sourceforge.net">jUSB</ulink> for Java. + </para> + + <note><title>Unfinished</title> + <para>This particular documentation is incomplete, + especially with respect to the asynchronous mode. + As of kernel 2.5.66 the code and this (new) documentation + need to be cross-reviewed. + </para> + </note> + + <para>Configure usbfs into Linux kernels by enabling the + <emphasis>USB filesystem</emphasis> option (CONFIG_USB_DEVICEFS), + and you get basic support for user mode USB device drivers. + Until relatively recently it was often (confusingly) called + <emphasis>usbdevfs</emphasis> although it wasn't solving what + <emphasis>devfs</emphasis> was. + Every USB device will appear in usbfs, regardless of whether or + not it has a kernel driver; but only devices with kernel drivers + show up in devfs. + </para> + + <sect1> + <title>What files are in "usbfs"?</title> + + <para>Conventionally mounted at + <filename>/proc/bus/usb</filename>, usbfs + features include: + <itemizedlist> + <listitem><para><filename>/proc/bus/usb/devices</filename> + ... a text file + showing each of the USB devices on known to the kernel, + and their configuration descriptors. + You can also poll() this to learn about new devices. + </para></listitem> + <listitem><para><filename>/proc/bus/usb/BBB/DDD</filename> + ... magic files + exposing the each device's configuration descriptors, and + supporting a series of ioctls for making device requests, + including I/O to devices. (Purely for access by programs.) + </para></listitem> + </itemizedlist> + </para> + + <para> Each bus is given a number (BBB) based on when it was + enumerated; within each bus, each device is given a similar + number (DDD). + Those BBB/DDD paths are not "stable" identifiers; + expect them to change even if you always leave the devices + plugged in to the same hub port. + <emphasis>Don't even think of saving these in application + configuration files.</emphasis> + Stable identifiers are available, for user mode applications + that want to use them. HID and networking devices expose + these stable IDs, so that for example you can be sure that + you told the right UPS to power down its second server. + "usbfs" doesn't (yet) expose those IDs. + </para> + + </sect1> + + <sect1> + <title>Mounting and Access Control</title> + + <para>There are a number of mount options for usbfs, which will + be of most interest to you if you need to override the default + access control policy. + That policy is that only root may read or write device files + (<filename>/proc/bus/BBB/DDD</filename>) although anyone may read + the <filename>devices</filename> + or <filename>drivers</filename> files. + I/O requests to the device also need the CAP_SYS_RAWIO capability, + </para> + + <para>The significance of that is that by default, all user mode + device drivers need super-user privileges. + You can change modes or ownership in a driver setup + when the device hotplugs, or maye just start the + driver right then, as a privileged server (or some activity + within one). + That's the most secure approach for multi-user systems, + but for single user systems ("trusted" by that user) + it's more convenient just to grant everyone all access + (using the <emphasis>devmode=0666</emphasis> option) + so the driver can start whenever it's needed. + </para> + + <para>The mount options for usbfs, usable in /etc/fstab or + in command line invocations of <emphasis>mount</emphasis>, are: + + <variablelist> + <varlistentry> + <term><emphasis>busgid</emphasis>=NNNNN</term> + <listitem><para>Controls the GID used for the + /proc/bus/usb/BBB + directories. (Default: 0)</para></listitem></varlistentry> + <varlistentry><term><emphasis>busmode</emphasis>=MMM</term> + <listitem><para>Controls the file mode used for the + /proc/bus/usb/BBB + directories. (Default: 0555) + </para></listitem></varlistentry> + <varlistentry><term><emphasis>busuid</emphasis>=NNNNN</term> + <listitem><para>Controls the UID used for the + /proc/bus/usb/BBB + directories. (Default: 0)</para></listitem></varlistentry> + + <varlistentry><term><emphasis>devgid</emphasis>=NNNNN</term> + <listitem><para>Controls the GID used for the + /proc/bus/usb/BBB/DDD + files. (Default: 0)</para></listitem></varlistentry> + <varlistentry><term><emphasis>devmode</emphasis>=MMM</term> + <listitem><para>Controls the file mode used for the + /proc/bus/usb/BBB/DDD + files. (Default: 0644)</para></listitem></varlistentry> + <varlistentry><term><emphasis>devuid</emphasis>=NNNNN</term> + <listitem><para>Controls the UID used for the + /proc/bus/usb/BBB/DDD + files. (Default: 0)</para></listitem></varlistentry> + + <varlistentry><term><emphasis>listgid</emphasis>=NNNNN</term> + <listitem><para>Controls the GID used for the + /proc/bus/usb/devices and drivers files. + (Default: 0)</para></listitem></varlistentry> + <varlistentry><term><emphasis>listmode</emphasis>=MMM</term> + <listitem><para>Controls the file mode used for the + /proc/bus/usb/devices and drivers files. + (Default: 0444)</para></listitem></varlistentry> + <varlistentry><term><emphasis>listuid</emphasis>=NNNNN</term> + <listitem><para>Controls the UID used for the + /proc/bus/usb/devices and drivers files. + (Default: 0)</para></listitem></varlistentry> + </variablelist> + + </para> + + <para>Note that many Linux distributions hard-wire the mount options + for usbfs in their init scripts, such as + <filename>/etc/rc.d/rc.sysinit</filename>, + rather than making it easy to set this per-system + policy in <filename>/etc/fstab</filename>. + </para> + + </sect1> + + <sect1> + <title>/proc/bus/usb/devices</title> + + <para>This file is handy for status viewing tools in user + mode, which can scan the text format and ignore most of it. + More detailed device status (including class and vendor + status) is available from device-specific files. + For information about the current format of this file, + see the + <filename>Documentation/usb/proc_usb_info.txt</filename> + file in your Linux kernel sources. + </para> + + <para>Otherwise the main use for this file from programs + is to poll() it to get notifications of usb devices + as they're plugged or unplugged. + To see what changed, you'd need to read the file and + compare "before" and "after" contents, scan the filesystem, + or see its hotplug event. + </para> + + </sect1> + + <sect1> + <title>/proc/bus/usb/BBB/DDD</title> + + <para>Use these files in one of these basic ways: + </para> + + <para><emphasis>They can be read,</emphasis> + producing first the device descriptor + (18 bytes) and then the descriptors for the current configuration. + See the USB 2.0 spec for details about those binary data formats. + You'll need to convert most multibyte values from little endian + format to your native host byte order, although a few of the + fields in the device descriptor (both of the BCD-encoded fields, + and the vendor and product IDs) will be byteswapped for you. + Note that configuration descriptors include descriptors for + interfaces, altsettings, endpoints, and maybe additional + class descriptors. + </para> + + <para><emphasis>Perform USB operations</emphasis> using + <emphasis>ioctl()</emphasis> requests to make endpoint I/O + requests (synchronously or asynchronously) or manage + the device. + These requests need the CAP_SYS_RAWIO capability, + as well as filesystem access permissions. + Only one ioctl request can be made on one of these + device files at a time. + This means that if you are synchronously reading an endpoint + from one thread, you won't be able to write to a different + endpoint from another thread until the read completes. + This works for <emphasis>half duplex</emphasis> protocols, + but otherwise you'd use asynchronous i/o requests. + </para> + + </sect1> + + + <sect1> + <title>Life Cycle of User Mode Drivers</title> + + <para>Such a driver first needs to find a device file + for a device it knows how to handle. + Maybe it was told about it because a + <filename>/sbin/hotplug</filename> event handling agent + chose that driver to handle the new device. + Or maybe it's an application that scans all the + /proc/bus/usb device files, and ignores most devices. + In either case, it should <function>read()</function> all + the descriptors from the device file, + and check them against what it knows how to handle. + It might just reject everything except a particular + vendor and product ID, or need a more complex policy. + </para> + + <para>Never assume there will only be one such device + on the system at a time! + If your code can't handle more than one device at + a time, at least detect when there's more than one, and + have your users choose which device to use. + </para> + + <para>Once your user mode driver knows what device to use, + it interacts with it in either of two styles. + The simple style is to make only control requests; some + devices don't need more complex interactions than those. + (An example might be software using vendor-specific control + requests for some initialization or configuration tasks, + with a kernel driver for the rest.) + </para> + + <para>More likely, you need a more complex style driver: + one using non-control endpoints, reading or writing data + and claiming exclusive use of an interface. + <emphasis>Bulk</emphasis> transfers are easiest to use, + but only their sibling <emphasis>interrupt</emphasis> transfers + work with low speed devices. + Both interrupt and <emphasis>isochronous</emphasis> transfers + offer service guarantees because their bandwidth is reserved. + Such "periodic" transfers are awkward to use through usbfs, + unless you're using the asynchronous calls. However, interrupt + transfers can also be used in a synchronous "one shot" style. + </para> + + <para>Your user-mode driver should never need to worry + about cleaning up request state when the device is + disconnected, although it should close its open file + descriptors as soon as it starts seeing the ENODEV + errors. + </para> + + </sect1> + + <sect1><title>The ioctl() Requests</title> + + <para>To use these ioctls, you need to include the following + headers in your userspace program: +<programlisting>#include <linux/usb.h> +#include <linux/usbdevice_fs.h> +#include <asm/byteorder.h></programlisting> + The standard USB device model requests, from "Chapter 9" of + the USB 2.0 specification, are automatically included from + the <filename><linux/usb_ch9.h></filename> header. + </para> + + <para>Unless noted otherwise, the ioctl requests + described here will + update the modification time on the usbfs file to which + they are applied (unless they fail). + A return of zero indicates success; otherwise, a + standard USB error code is returned. (These are + documented in + <filename>Documentation/usb/error-codes.txt</filename> + in your kernel sources.) + </para> + + <para>Each of these files multiplexes access to several + I/O streams, one per endpoint. + Each device has one control endpoint (endpoint zero) + which supports a limited RPC style RPC access. + Devices are configured + by khubd (in the kernel) setting a device-wide + <emphasis>configuration</emphasis> that affects things + like power consumption and basic functionality. + The endpoints are part of USB <emphasis>interfaces</emphasis>, + which may have <emphasis>altsettings</emphasis> + affecting things like which endpoints are available. + Many devices only have a single configuration and interface, + so drivers for them will ignore configurations and altsettings. + </para> + + + <sect2> + <title>Management/Status Requests</title> + + <para>A number of usbfs requests don't deal very directly + with device I/O. + They mostly relate to device management and status. + These are all synchronous requests. + </para> + + <variablelist> + + <varlistentry><term>USBDEVFS_CLAIMINTERFACE</term> + <listitem><para>This is used to force usbfs to + claim a specific interface, + which has not previously been claimed by usbfs or any other + kernel driver. + The ioctl parameter is an integer holding the number of + the interface (bInterfaceNumber from descriptor). + </para><para> + Note that if your driver doesn't claim an interface + before trying to use one of its endpoints, and no + other driver has bound to it, then the interface is + automatically claimed by usbfs. + </para><para> + This claim will be released by a RELEASEINTERFACE ioctl, + or by closing the file descriptor. + File modification time is not updated by this request. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_CONNECTINFO</term> + <listitem><para>Says whether the device is lowspeed. + The ioctl parameter points to a structure like this: +<programlisting>struct usbdevfs_connectinfo { + unsigned int devnum; + unsigned char slow; +}; </programlisting> + File modification time is not updated by this request. + </para><para> + <emphasis>You can't tell whether a "not slow" + device is connected at high speed (480 MBit/sec) + or just full speed (12 MBit/sec).</emphasis> + You should know the devnum value already, + it's the DDD value of the device file name. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_GETDRIVER</term> + <listitem><para>Returns the name of the kernel driver + bound to a given interface (a string). Parameter + is a pointer to this structure, which is modified: +<programlisting>struct usbdevfs_getdriver { + unsigned int interface; + char driver[USBDEVFS_MAXDRIVERNAME + 1]; +};</programlisting> + File modification time is not updated by this request. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_IOCTL</term> + <listitem><para>Passes a request from userspace through + to a kernel driver that has an ioctl entry in the + <emphasis>struct usb_driver</emphasis> it registered. +<programlisting>struct usbdevfs_ioctl { + int ifno; + int ioctl_code; + void *data; +}; + +/* user mode call looks like this. + * 'request' becomes the driver->ioctl() 'code' parameter. + * the size of 'param' is encoded in 'request', and that data + * is copied to or from the driver->ioctl() 'buf' parameter. + */ +static int +usbdev_ioctl (int fd, int ifno, unsigned request, void *param) +{ + struct usbdevfs_ioctl wrapper; + + wrapper.ifno = ifno; + wrapper.ioctl_code = request; + wrapper.data = param; + + return ioctl (fd, USBDEVFS_IOCTL, &wrapper); +} </programlisting> + File modification time is not updated by this request. + </para><para> + This request lets kernel drivers talk to user mode code + through filesystem operations even when they don't create + a charactor or block special device. + It's also been used to do things like ask devices what + device special file should be used. + Two pre-defined ioctls are used + to disconnect and reconnect kernel drivers, so + that user mode code can completely manage binding + and configuration of devices. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_RELEASEINTERFACE</term> + <listitem><para>This is used to release the claim usbfs + made on interface, either implicitly or because of a + USBDEVFS_CLAIMINTERFACE call, before the file + descriptor is closed. + The ioctl parameter is an integer holding the number of + the interface (bInterfaceNumber from descriptor); + File modification time is not updated by this request. + </para><warning><para> + <emphasis>No security check is made to ensure + that the task which made the claim is the one + which is releasing it. + This means that user mode driver may interfere + other ones. </emphasis> + </para></warning></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_RESETEP</term> + <listitem><para>Resets the data toggle value for an endpoint + (bulk or interrupt) to DATA0. + The ioctl parameter is an integer endpoint number + (1 to 15, as identified in the endpoint descriptor), + with USB_DIR_IN added if the device's endpoint sends + data to the host. + </para><warning><para> + <emphasis>Avoid using this request. + It should probably be removed.</emphasis> + Using it typically means the device and driver will lose + toggle synchronization. If you really lost synchronization, + you likely need to completely handshake with the device, + using a request like CLEAR_HALT + or SET_INTERFACE. + </para></warning></listitem></varlistentry> + + </variablelist> + + </sect2> + + <sect2> + <title>Synchronous I/O Support</title> + + <para>Synchronous requests involve the kernel blocking + until until the user mode request completes, either by + finishing successfully or by reporting an error. + In most cases this is the simplest way to use usbfs, + although as noted above it does prevent performing I/O + to more than one endpoint at a time. + </para> + + <variablelist> + + <varlistentry><term>USBDEVFS_BULK</term> + <listitem><para>Issues a bulk read or write request to the + device. + The ioctl parameter is a pointer to this structure: +<programlisting>struct usbdevfs_bulktransfer { + unsigned int ep; + unsigned int len; + unsigned int timeout; /* in milliseconds */ + void *data; +};</programlisting> + </para><para>The "ep" value identifies a + bulk endpoint number (1 to 15, as identified in an endpoint + descriptor), + masked with USB_DIR_IN when referring to an endpoint which + sends data to the host from the device. + The length of the data buffer is identified by "len"; + Recent kernels support requests up to about 128KBytes. + <emphasis>FIXME say how read length is returned, + and how short reads are handled.</emphasis>. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_CLEAR_HALT</term> + <listitem><para>Clears endpoint halt (stall) and + resets the endpoint toggle. This is only + meaningful for bulk or interrupt endpoints. + The ioctl parameter is an integer endpoint number + (1 to 15, as identified in an endpoint descriptor), + masked with USB_DIR_IN when referring to an endpoint which + sends data to the host from the device. + </para><para> + Use this on bulk or interrupt endpoints which have + stalled, returning <emphasis>-EPIPE</emphasis> status + to a data transfer request. + Do not issue the control request directly, since + that could invalidate the host's record of the + data toggle. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_CONTROL</term> + <listitem><para>Issues a control request to the device. + The ioctl parameter points to a structure like this: +<programlisting>struct usbdevfs_ctrltransfer { + __u8 bRequestType; + __u8 bRequest; + __u16 wValue; + __u16 wIndex; + __u16 wLength; + __u32 timeout; /* in milliseconds */ + void *data; +};</programlisting> + </para><para> + The first eight bytes of this structure are the contents + of the SETUP packet to be sent to the device; see the + USB 2.0 specification for details. + The bRequestType value is composed by combining a + USB_TYPE_* value, a USB_DIR_* value, and a + USB_RECIP_* value (from + <emphasis><linux/usb.h></emphasis>). + If wLength is nonzero, it describes the length of the data + buffer, which is either written to the device + (USB_DIR_OUT) or read from the device (USB_DIR_IN). + </para><para> + At this writing, you can't transfer more than 4 KBytes + of data to or from a device; usbfs has a limit, and + some host controller drivers have a limit. + (That's not usually a problem.) + <emphasis>Also</emphasis> there's no way to say it's + not OK to get a short read back from the device. + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_RESET</term> + <listitem><para>Does a USB level device reset. + The ioctl parameter is ignored. + After the reset, this rebinds all device interfaces. + File modification time is not updated by this request. + </para><warning><para> + <emphasis>Avoid using this call</emphasis> + until some usbcore bugs get fixed, + since it does not fully synchronize device, interface, + and driver (not just usbfs) state. + </para></warning></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_SETINTERFACE</term> + <listitem><para>Sets the alternate setting for an + interface. The ioctl parameter is a pointer to a + structure like this: +<programlisting>struct usbdevfs_setinterface { + unsigned int interface; + unsigned int altsetting; +}; </programlisting> + File modification time is not updated by this request. + </para><para> + Those struct members are from some interface descriptor + applying to the the current configuration. + The interface number is the bInterfaceNumber value, and + the altsetting number is the bAlternateSetting value. + (This resets each endpoint in the interface.) + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_SETCONFIGURATION</term> + <listitem><para>Issues the + <function>usb_set_configuration</function> call + for the device. + The parameter is an integer holding the number of + a configuration (bConfigurationValue from descriptor). + File modification time is not updated by this request. + </para><warning><para> + <emphasis>Avoid using this call</emphasis> + until some usbcore bugs get fixed, + since it does not fully synchronize device, interface, + and driver (not just usbfs) state. + </para></warning></listitem></varlistentry> + + </variablelist> + </sect2> + + <sect2> + <title>Asynchronous I/O Support</title> + + <para>As mentioned above, there are situations where it may be + important to initiate concurrent operations from user mode code. + This is particularly important for periodic transfers + (interrupt and isochronous), but it can be used for other + kinds of USB requests too. + In such cases, the asynchronous requests described here + are essential. Rather than submitting one request and having + the kernel block until it completes, the blocking is separate. + </para> + + <para>These requests are packaged into a structure that + resembles the URB used by kernel device drivers. + (No POSIX Async I/O support here, sorry.) + It identifies the endpoint type (USBDEVFS_URB_TYPE_*), + endpoint (number, masked with USB_DIR_IN as appropriate), + buffer and length, and a user "context" value serving to + uniquely identify each request. + (It's usually a pointer to per-request data.) + Flags can modify requests (not as many as supported for + kernel drivers). + </para> + + <para>Each request can specify a realtime signal number + (between SIGRTMIN and SIGRTMAX, inclusive) to request a + signal be sent when the request completes. + </para> + + <para>When usbfs returns these urbs, the status value + is updated, and the buffer may have been modified. + Except for isochronous transfers, the actual_length is + updated to say how many bytes were transferred; if the + USBDEVFS_URB_DISABLE_SPD flag is set + ("short packets are not OK"), if fewer bytes were read + than were requested then you get an error report. + </para> + +<programlisting>struct usbdevfs_iso_packet_desc { + unsigned int length; + unsigned int actual_length; + unsigned int status; +}; + +struct usbdevfs_urb { + unsigned char type; + unsigned char endpoint; + int status; + unsigned int flags; + void *buffer; + int buffer_length; + int actual_length; + int start_frame; + int number_of_packets; + int error_count; + unsigned int signr; + void *usercontext; + struct usbdevfs_iso_packet_desc iso_frame_desc[]; +};</programlisting> + + <para> For these asynchronous requests, the file modification + time reflects when the request was initiated. + This contrasts with their use with the synchronous requests, + where it reflects when requests complete. + </para> + + <variablelist> + + <varlistentry><term>USBDEVFS_DISCARDURB</term> + <listitem><para> + <emphasis>TBS</emphasis> + File modification time is not updated by this request. + </para><para> + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_DISCSIGNAL</term> + <listitem><para> + <emphasis>TBS</emphasis> + File modification time is not updated by this request. + </para><para> + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_REAPURB</term> + <listitem><para> + <emphasis>TBS</emphasis> + File modification time is not updated by this request. + </para><para> + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_REAPURBNDELAY</term> + <listitem><para> + <emphasis>TBS</emphasis> + File modification time is not updated by this request. + </para><para> + </para></listitem></varlistentry> + + <varlistentry><term>USBDEVFS_SUBMITURB</term> + <listitem><para> + <emphasis>TBS</emphasis> + </para><para> + </para></listitem></varlistentry> + + </variablelist> + </sect2> + + </sect1> + + </chapter> + +</book> +<!-- vim:syntax=sgml:sw=4 +--> diff --git a/Documentation/DocBook/via-audio.tmpl b/Documentation/DocBook/via-audio.tmpl new file mode 100644 index 0000000..36e6421 --- /dev/null +++ b/Documentation/DocBook/via-audio.tmpl @@ -0,0 +1,597 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="ViaAudioGuide"> + <bookinfo> + <title>Via 686 Audio Driver for Linux</title> + + <authorgroup> + <author> + <firstname>Jeff</firstname> + <surname>Garzik</surname> + </author> + </authorgroup> + + <copyright> + <year>1999-2001</year> + <holder>Jeff Garzik</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The Via VT82C686A "super southbridge" chips contain + AC97-compatible audio logic which features dual 16-bit stereo + PCM sound channels (full duplex), plus a third PCM channel intended for use + in hardware-assisted FM synthesis. + </para> + <para> + The current Linux kernel audio driver for this family of chips + supports audio playback and recording, but hardware-assisted + FM features, and hardware buffer direct-access (mmap) + support are not yet available. + </para> + <para> + This driver supports any Linux kernel version after 2.4.10. + </para> + <para> + Please send bug reports to the mailing list <email>linux-via@gtf.org</email>. + To subscribe, e-mail <email>majordomo@gtf.org</email> with + </para> + <programlisting> + subscribe linux-via + </programlisting> + <para> + in the body of the message. + </para> + </chapter> + + <chapter id="install"> + <title>Driver Installation</title> + <para> + To use this audio driver, select the + CONFIG_SOUND_VIA82CXXX option in the section Sound during kernel configuration. + Follow the usual kernel procedures for rebuilding the kernel, + or building and installing driver modules. + </para> + <para> + To make this driver the default audio driver, you can add the + following to your /etc/conf.modules file: + </para> + <programlisting> + alias sound via82cxxx_audio + </programlisting> + <para> + Note that soundcore and ac97_codec support modules + are also required for working audio, in addition to + the via82cxxx_audio module itself. + </para> + </chapter> + + <chapter id="reportbug"> + <title>Submitting a bug report</title> + <sect1 id="bugrepdesc"><title>Description of problem</title> + <para> + Describe the application you were using to play/record sound, and how + to reproduce the problem. + </para> + </sect1> + <sect1 id="bugrepdiag"><title>Diagnostic output</title> + <para> + Obtain the via-audio-diag diagnostics program from + http://sf.net/projects/gkernel/ and provide a dump of the + audio chip's registers while the problem is occurring. Sample command line: + </para> + <programlisting> + ./via-audio-diag -aps > diag-output.txt + </programlisting> + </sect1> + <sect1 id="bugrepdebug"><title>Driver debug output</title> + <para> + Define <constant>VIA_DEBUG</constant> at the beginning of the driver, then capture and email + the kernel log output. This can be viewed in the system kernel log (if + enabled), or via the dmesg program. Sample command line: + </para> + <programlisting> + dmesg > /tmp/dmesg-output.txt + </programlisting> + </sect1> + <sect1 id="bugrepprintk"><title>Bigger kernel message buffer</title> + <para> + If you wish to increase the size of the buffer displayed by dmesg, then + change the <constant>LOG_BUF_LEN</constant> macro at the top of linux/kernel/printk.c, recompile + your kernel, and pass the <constant>LOG_BUF_LEN</constant> value to dmesg. Sample command line with + <constant>LOG_BUF_LEN</constant> == 32768: + </para> + <programlisting> + dmesg -s 32768 > /tmp/dmesg-output.txt + </programlisting> + </sect1> + </chapter> + + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + <variablelist> + <varlistentry><term>Low volume</term> + <listitem> + <para> + Volume too low on many systems. Workaround: use mixer program + such as xmixer to increase volume. + </para> + </listitem></varlistentry> + + </variablelist> + + </para> + </chapter> + + <chapter id="thanks"> + <title>Thanks</title> + <para> + Via for providing e-mail support, specs, and NDA'd source code. + </para> + <para> + MandrakeSoft for providing hacking time. + </para> + <para> + AC97 mixer interface fixes and debugging by Ron Cemer <email>roncemer@gte.net</email>. + </para> + <para> + Rui Sousa <email>rui.sousa@conexant.com</email>, for bugfixing + MMAP support, and several other notable fixes that resulted from + his hard work and testing. + </para> + <para> + Adrian Cox <email>adrian@humboldt.co.uk</email>, for bugfixing + MMAP support, and several other notable fixes that resulted from + his hard work and testing. + </para> + <para> + Thomas Sailer for further bugfixes. + </para> + </chapter> + + <chapter id="notes"> + <title>Random Notes</title> + <para> + Two /proc pseudo-files provide diagnostic information. This is generally + not useful to most users. Power users can disable CONFIG_SOUND_VIA82CXXX_PROCFS, + and remove the /proc support code. Once + version 2.0.0 is released, the /proc support code will be disabled by + default. Available /proc pseudo-files: + </para> + <programlisting> + /proc/driver/via/0/info + /proc/driver/via/0/ac97 + </programlisting> + <para> + This driver by default supports all PCI audio devices which report + a vendor id of 0x1106, and a device id of 0x3058. Subsystem vendor + and device ids are not examined. + </para> + <para> + GNU indent formatting options: + <programlisting> +-kr -i8 -ts8 -br -ce -bap -sob -l80 -pcs -cs -ss -bs -di1 -nbc -lp -psl + </programlisting> + </para> + <para> + Via has graciously donated e-mail support and source code to help further + the development of this driver. Their assistance has been invaluable + in the design and coding of the next major version of this driver. + </para> + <para> + The Via audio chip apparently provides a second PCM scatter-gather + DMA channel just for FM data, but does not have a full hardware MIDI + processor. I haven't put much thought towards a solution here, but it + might involve using SoftOSS midi wave table, or simply disabling MIDI + support altogether and using the FM PCM channel as a second (input? output?) + </para> + </chapter> + + <chapter id="changelog"> + <title>Driver ChangeLog</title> + +<sect1 id="version191"><title> +Version 1.9.1 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + DSP read/write bugfixes from Thomas Sailer. + </para> + </listitem> + + <listitem> + <para> + Add new PCI id for single-channel use of Via 8233. + </para> + </listitem> + + <listitem> + <para> + Other bug fixes, tweaks, new ioctls. + </para> + </listitem> + + </itemizedlist> +</sect1> + +<sect1 id="version1115"><title> +Version 1.1.15 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Support for variable fragment size and variable fragment number (Rui + Sousa) + </para> + </listitem> + + <listitem> + <para> + Fixes for the SPEED, STEREO, CHANNELS, FMT ioctls when in read & + write mode (Rui Sousa) + </para> + </listitem> + + <listitem> + <para> + Mmaped sound is now fully functional. (Rui Sousa) + </para> + </listitem> + + <listitem> + <para> + Make sure to enable PCI device before reading any of its PCI + config information. (fixes potential hotplug problems) + </para> + </listitem> + + <listitem> + <para> + Clean up code a bit and add more internal function documentation. + </para> + </listitem> + + <listitem> + <para> + AC97 codec access fixes (Adrian Cox) + </para> + </listitem> + + <listitem> + <para> + Big endian fixes (Adrian Cox) + </para> + </listitem> + + <listitem> + <para> + MIDI support (Adrian Cox) + </para> + </listitem> + + <listitem> + <para> + Detect and report locked-rate AC97 codecs. If your hardware only + supports 48Khz (locked rate), then your recording/playback software + must upsample or downsample accordingly. The hardware cannot do it. + </para> + </listitem> + + <listitem> + <para> + Use new pci_request_regions and pci_disable_device functions in + kernel 2.4.6. + </para> + </listitem> + + </itemizedlist> +</sect1> + +<sect1 id="version1114"><title> +Version 1.1.14 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Use VM_RESERVE when available, to eliminate unnecessary page faults. + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version1112"><title> +Version 1.1.12 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + mmap bug fixes from Linus. + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version1111"><title> +Version 1.1.11 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Many more bug fixes. mmap enabled by default, but may still be buggy. + </para> + </listitem> + + <listitem> + <para> + Uses new and spiffy method of mmap'ing the DMA buffer, based + on a suggestion from Linus. + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version1110"><title> +Version 1.1.10 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Many bug fixes. mmap enabled by default, but may still be buggy. + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version119"><title> +Version 1.1.9 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Redesign and rewrite audio playback implementation. (faster and smaller, hopefully) + </para> + </listitem> + + <listitem> + <para> + Implement recording and full duplex (DSP_CAP_DUPLEX) support. + </para> + </listitem> + + <listitem> + <para> + Make procfs support optional. + </para> + </listitem> + + <listitem> + <para> + Quick interrupt status check, to lessen overhead in interrupt + sharing situations. + </para> + </listitem> + + <listitem> + <para> + Add mmap(2) support. Disabled for now, it is still buggy and experimental. + </para> + </listitem> + + <listitem> + <para> + Surround all syscalls with a semaphore for cheap and easy SMP protection. + </para> + </listitem> + + <listitem> + <para> + Fix bug in channel shutdown (hardware channel reset) code. + </para> + </listitem> + + <listitem> + <para> + Remove unnecessary spinlocks (better performance). + </para> + </listitem> + + <listitem> + <para> + Eliminate "unknown AFMT" message by using a different method + of selecting the best AFMT_xxx sound sample format for use. + </para> + </listitem> + + <listitem> + <para> + Support for realtime hardware pointer position reporting + (DSP_CAP_REALTIME, SNDCTL_DSP_GETxPTR ioctls) + </para> + </listitem> + + <listitem> + <para> + Support for capture/playback triggering + (DSP_CAP_TRIGGER, SNDCTL_DSP_SETTRIGGER ioctls) + </para> + </listitem> + + <listitem> + <para> + SNDCTL_DSP_SETDUPLEX and SNDCTL_DSP_POST ioctls now handled. + </para> + </listitem> + + <listitem> + <para> + Rewrite open(2) and close(2) logic to allow only one user at + a time. All other open(2) attempts will sleep until they succeed. + FIXME: open(O_RDONLY) and open(O_WRONLY) should be allowed to succeed. + </para> + </listitem> + + <listitem> + <para> + Reviewed code to ensure that SMP and multiple audio devices + are fully supported. + </para> + </listitem> + + </itemizedlist> +</sect1> + +<sect1 id="version118"><title> +Version 1.1.8 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Clean up interrupt handler output. Fixes the following kernel error message: + </para> + <programlisting> + unhandled interrupt ... + </programlisting> + </listitem> + + <listitem> + <para> + Convert documentation to DocBook, so that PDF, HTML and PostScript (.ps) output is readily + available. + </para> + </listitem> + + </itemizedlist> +</sect1> + +<sect1 id="version117"><title> +Version 1.1.7 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Fix module unload bug where mixer device left registered + after driver exit + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version116"><title> +Version 1.1.6 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Rewrite via_set_rate to mimic ALSA basic AC97 rate setting + </para> + </listitem> + <listitem> + <para> + Remove much dead code + </para> + </listitem> + <listitem> + <para> + Complete spin_lock_irqsave -> spin_lock_irq conversion in via_dsp_ioctl + </para> + </listitem> + <listitem> + <para> + Fix build problem in via_dsp_ioctl + </para> + </listitem> + <listitem> + <para> + Optimize included headers to eliminate headers found in linux/sound + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version115"><title> +Version 1.1.5 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Disable some overly-verbose debugging code + </para> + </listitem> + <listitem> + <para> + Remove unnecessary sound locks + </para> + </listitem> + <listitem> + <para> + Fix some ioctls for better time resolution + </para> + </listitem> + <listitem> + <para> + Begin spin_lock_irqsave -> spin_lock_irq conversion in via_dsp_ioctl + </para> + </listitem> + </itemizedlist> +</sect1> + +<sect1 id="version114"><title> +Version 1.1.4 +</title> + <itemizedlist spacing="compact"> + <listitem> + <para> + Completed rewrite of driver. Eliminated SoundBlaster compatibility + completely, and now uses the much-faster scatter-gather DMA engine. + </para> + </listitem> + </itemizedlist> +</sect1> + + </chapter> + + <chapter id="intfunctions"> + <title>Internal Functions</title> +!Isound/oss/via82cxxx_audio.c + </chapter> + +</book> + + diff --git a/Documentation/DocBook/videobook.tmpl b/Documentation/DocBook/videobook.tmpl new file mode 100644 index 0000000..3ec6c87 --- /dev/null +++ b/Documentation/DocBook/videobook.tmpl @@ -0,0 +1,1663 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="V4LGuide"> + <bookinfo> + <title>Video4Linux Programming</title> + + <authorgroup> + <author> + <firstname>Alan</firstname> + <surname>Cox</surname> + <affiliation> + <address> + <email>alan@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2000</year> + <holder>Alan Cox</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + Parts of this document first appeared in Linux Magazine under a + ninety day exclusivity. + </para> + <para> + Video4Linux is intended to provide a common programming interface + for the many TV and capture cards now on the market, as well as + parallel port and USB video cameras. Radio, teletext decoders and + vertical blanking data interfaces are also provided. + </para> + </chapter> + <chapter id="radio"> + <title>Radio Devices</title> + <para> + There are a wide variety of radio interfaces available for PC's, and these + are generally very simple to program. The biggest problem with supporting + such devices is normally extracting documentation from the vendor. + </para> + <para> + The radio interface supports a simple set of control ioctls standardised + across all radio and tv interfaces. It does not support read or write, which + are used for video streams. The reason radio cards do not allow you to read + the audio stream into an application is that without exception they provide + a connection on to a soundcard. Soundcards can be used to read the radio + data just fine. + </para> + <sect1 id="registerradio"> + <title>Registering Radio Devices</title> + <para> + The Video4linux core provides an interface for registering devices. The + first step in writing our radio card driver is to register it. + </para> + <programlisting> + + +static struct video_device my_radio +{ + "My radio", + VID_TYPE_TUNER, + VID_HARDWARE_MYRADIO, + radio_open. + radio_close, + NULL, /* no read */ + NULL, /* no write */ + NULL, /* no poll */ + radio_ioctl, + NULL, /* no special init function */ + NULL /* no private data */ +}; + + + </programlisting> + <para> + This declares our video4linux device driver interface. The VID_TYPE_ value + defines what kind of an interface we are, and defines basic capabilities. + </para> + <para> + The only defined value relevant for a radio card is VID_TYPE_TUNER which + indicates that the device can be tuned. Clearly our radio is going to have some + way to change channel so it is tuneable. + </para> + <para> + The VID_HARDWARE_ types are unique to each device. Numbers are assigned by + <email>alan@redhat.com</email> when device drivers are going to be released. Until then you + can pull a suitably large number out of your hat and use it. 10000 should be + safe for a very long time even allowing for the huge number of vendors + making new and different radio cards at the moment. + </para> + <para> + We declare an open and close routine, but we do not need read or write, + which are used to read and write video data to or from the card itself. As + we have no read or write there is no poll function. + </para> + <para> + The private initialise function is run when the device is registered. In + this driver we've already done all the work needed. The final pointer is a + private data pointer that can be used by the device driver to attach and + retrieve private data structures. We set this field "priv" to NULL for + the moment. + </para> + <para> + Having the structure defined is all very well but we now need to register it + with the kernel. + </para> + <programlisting> + + +static int io = 0x320; + +int __init myradio_init(struct video_init *v) +{ + if(!request_region(io, MY_IO_SIZE, "myradio")) + { + printk(KERN_ERR + "myradio: port 0x%03X is in use.\n", io); + return -EBUSY; + } + + if(video_device_register(&my_radio, VFL_TYPE_RADIO)==-1) { + release_region(io, MY_IO_SIZE); + return -EINVAL; + } + return 0; +} + + </programlisting> + <para> + The first stage of the initialisation, as is normally the case, is to check + that the I/O space we are about to fiddle with doesn't belong to some other + driver. If it is we leave well alone. If the user gives the address of the + wrong device then we will spot this. These policies will generally avoid + crashing the machine. + </para> + <para> + Now we ask the Video4Linux layer to register the device for us. We hand it + our carefully designed video_device structure and also tell it which group + of devices we want it registered with. In this case VFL_TYPE_RADIO. + </para> + <para> + The types available are + </para> + <table frame="all"><title>Device Types</title> + <tgroup cols="3" align="left"> + <tbody> + <row> + <entry>VFL_TYPE_RADIO</entry><entry>/dev/radio{n}</entry><entry> + + Radio devices are assigned in this block. As with all of these + selections the actual number assignment is done by the video layer + accordijng to what is free.</entry> + </row><row> + <entry>VFL_TYPE_GRABBER</entry><entry>/dev/video{n}</entry><entry> + Video capture devices and also -- counter-intuitively for the name -- + hardware video playback devices such as MPEG2 cards.</entry> + </row><row> + <entry>VFL_TYPE_VBI</entry><entry>/dev/vbi{n}</entry><entry> + The VBI devices capture the hidden lines on a television picture + that carry further information like closed caption data, teletext + (primarily in Europe) and now Intercast and the ATVEC internet + television encodings.</entry> + </row><row> + <entry>VFL_TYPE_VTX</entry><entry>/dev/vtx[n}</entry><entry> + VTX is 'Videotext' also known as 'Teletext'. This is a system for + sending numbered, 40x25, mostly textual page images over the hidden + lines. Unlike the /dev/vbi interfaces, this is for 'smart' decoder + chips. (The use of the word smart here has to be taken in context, + the smartest teletext chips are fairly dumb pieces of technology). + </entry> + </row> + </tbody> + </tgroup> + </table> + <para> + We are most definitely a radio. + </para> + <para> + Finally we allocate our I/O space so that nobody treads on us and return 0 + to signify general happiness with the state of the universe. + </para> + </sect1> + <sect1 id="openradio"> + <title>Opening And Closing The Radio</title> + + <para> + The functions we declared in our video_device are mostly very simple. + Firstly we can drop in what is basically standard code for open and close. + </para> + <programlisting> + + +static int users = 0; + +static int radio_open(stuct video_device *dev, int flags) +{ + if(users) + return -EBUSY; + users++; + return 0; +} + + </programlisting> + <para> + At open time we need to do nothing but check if someone else is also using + the radio card. If nobody is using it we make a note that we are using it, + then we ensure that nobody unloads our driver on us. + </para> + <programlisting> + + +static int radio_close(struct video_device *dev) +{ + users--; +} + + </programlisting> + <para> + At close time we simply need to reduce the user count and allow the module + to become unloadable. + </para> + <para> + If you are sharp you will have noticed neither the open nor the close + routines attempt to reset or change the radio settings. This is intentional. + It allows an application to set up the radio and exit. It avoids a user + having to leave an application running all the time just to listen to the + radio. + </para> + </sect1> + <sect1 id="ioctlradio"> + <title>The Ioctl Interface</title> + <para> + This leaves the ioctl routine, without which the driver will not be + terribly useful to anyone. + </para> + <programlisting> + + +static int radio_ioctl(struct video_device *dev, unsigned int cmd, void *arg) +{ + switch(cmd) + { + case VIDIOCGCAP: + { + struct video_capability v; + v.type = VID_TYPE_TUNER; + v.channels = 1; + v.audios = 1; + v.maxwidth = 0; + v.minwidth = 0; + v.maxheight = 0; + v.minheight = 0; + strcpy(v.name, "My Radio"); + if(copy_to_user(arg, &v, sizeof(v))) + return -EFAULT; + return 0; + } + + </programlisting> + <para> + VIDIOCGCAP is the first ioctl all video4linux devices must support. It + allows the applications to find out what sort of a card they have found and + to figure out what they want to do about it. The fields in the structure are + </para> + <table frame="all"><title>struct video_capability fields</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>name</entry><entry>The device text name. This is intended for the user.</entry> + </row><row> + <entry>channels</entry><entry>The number of different channels you can tune on + this card. It could even by zero for a card that has + no tuning capability. For our simple FM radio it is 1. + An AM/FM radio would report 2.</entry> + </row><row> + <entry>audios</entry><entry>The number of audio inputs on this device. For our + radio there is only one audio input.</entry> + </row><row> + <entry>minwidth,minheight</entry><entry>The smallest size the card is capable of capturing + images in. We set these to zero. Radios do not + capture pictures</entry> + </row><row> + <entry>maxwidth,maxheight</entry><entry>The largest image size the card is capable of + capturing. For our radio we report 0. + </entry> + </row><row> + <entry>type</entry><entry>This reports the capabilities of the device, and + matches the field we filled in in the struct + video_device when registering.</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + Having filled in the fields, we use copy_to_user to copy the structure into + the users buffer. If the copy fails we return an EFAULT to the application + so that it knows it tried to feed us garbage. + </para> + <para> + The next pair of ioctl operations select which tuner is to be used and let + the application find the tuner properties. We have only a single FM band + tuner in our example device. + </para> + <programlisting> + + + case VIDIOCGTUNER: + { + struct video_tuner v; + if(copy_from_user(&v, arg, sizeof(v))!=0) + return -EFAULT; + if(v.tuner) + return -EINVAL; + v.rangelow=(87*16000); + v.rangehigh=(108*16000); + v.flags = VIDEO_TUNER_LOW; + v.mode = VIDEO_MODE_AUTO; + v.signal = 0xFFFF; + strcpy(v.name, "FM"); + if(copy_to_user(&v, arg, sizeof(v))!=0) + return -EFAULT; + return 0; + } + + </programlisting> + <para> + The VIDIOCGTUNER ioctl allows applications to query a tuner. The application + sets the tuner field to the tuner number it wishes to query. The query does + not change the tuner that is being used, it merely enquires about the tuner + in question. + </para> + <para> + We have exactly one tuner so after copying the user buffer to our temporary + structure we complain if they asked for a tuner other than tuner 0. + </para> + <para> + The video_tuner structure has the following fields + </para> + <table frame="all"><title>struct video_tuner fields</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>int tuner</entry><entry>The number of the tuner in question</entry> + </row><row> + <entry>char name[32]</entry><entry>A text description of this tuner. "FM" will do fine. + This is intended for the application.</entry> + </row><row> + <entry>u32 flags</entry> + <entry>Tuner capability flags</entry> + </row> + <row> + <entry>u16 mode</entry><entry>The current reception mode</entry> + + </row><row> + <entry>u16 signal</entry><entry>The signal strength scaled between 0 and 65535. If + a device cannot tell the signal strength it should + report 65535. Many simple cards contain only a + signal/no signal bit. Such cards will report either + 0 or 65535.</entry> + + </row><row> + <entry>u32 rangelow, rangehigh</entry><entry> + The range of frequencies supported by the radio + or TV. It is scaled according to the VIDEO_TUNER_LOW + flag.</entry> + + </row> + </tbody> + </tgroup> + </table> + + <table frame="all"><title>struct video_tuner flags</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_TUNER_PAL</entry><entry>A PAL TV tuner</entry> + </row><row> + <entry>VIDEO_TUNER_NTSC</entry><entry>An NTSC (US) TV tuner</entry> + </row><row> + <entry>VIDEO_TUNER_SECAM</entry><entry>A SECAM (French) TV tuner</entry> + </row><row> + <entry>VIDEO_TUNER_LOW</entry><entry> + The tuner frequency is scaled in 1/16th of a KHz + steps. If not it is in 1/16th of a MHz steps + </entry> + </row><row> + <entry>VIDEO_TUNER_NORM</entry><entry>The tuner can set its format</entry> + </row><row> + <entry>VIDEO_TUNER_STEREO_ON</entry><entry>The tuner is currently receiving a stereo signal</entry> + </row> + </tbody> + </tgroup> + </table> + + <table frame="all"><title>struct video_tuner modes</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_MODE_PAL</entry><entry>PAL Format</entry> + </row><row> + <entry>VIDEO_MODE_NTSC</entry><entry>NTSC Format (USA)</entry> + </row><row> + <entry>VIDEO_MODE_SECAM</entry><entry>French Format</entry> + </row><row> + <entry>VIDEO_MODE_AUTO</entry><entry>A device that does not need to do + TV format switching</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + The settings for the radio card are thus fairly simple. We report that we + are a tuner called "FM" for FM radio. In order to get the best tuning + resolution we report VIDEO_TUNER_LOW and select tuning to 1/16th of KHz. Its + unlikely our card can do that resolution but it is a fair bet the card can + do better than 1/16th of a MHz. VIDEO_TUNER_LOW is appropriate to almost all + radio usage. + </para> + <para> + We report that the tuner automatically handles deciding what format it is + receiving - true enough as it only handles FM radio. Our example card is + also incapable of detecting stereo or signal strengths so it reports a + strength of 0xFFFF (maximum) and no stereo detected. + </para> + <para> + To finish off we set the range that can be tuned to be 87-108Mhz, the normal + FM broadcast radio range. It is important to find out what the card is + actually capable of tuning. It is easy enough to simply use the FM broadcast + range. Unfortunately if you do this you will discover the FM broadcast + ranges in the USA, Europe and Japan are all subtly different and some users + cannot receive all the stations they wish. + </para> + <para> + The application also needs to be able to set the tuner it wishes to use. In + our case, with a single tuner this is rather simple to arrange. + </para> + <programlisting> + + case VIDIOCSTUNER: + { + struct video_tuner v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.tuner != 0) + return -EINVAL; + return 0; + } + + </programlisting> + <para> + We copy the user supplied structure into kernel memory so we can examine it. + If the user has selected a tuner other than zero we reject the request. If + they wanted tuner 0 then, surprisingly enough, that is the current tuner already. + </para> + <para> + The next two ioctls we need to provide are to get and set the frequency of + the radio. These both use an unsigned long argument which is the frequency. + The scale of the frequency depends on the VIDEO_TUNER_LOW flag as I + mentioned earlier on. Since we have VIDEO_TUNER_LOW set this will be in + 1/16ths of a KHz. + </para> + <programlisting> + +static unsigned long current_freq; + + + + case VIDIOCGFREQ: + if(copy_to_user(arg, &current_freq, + sizeof(unsigned long)) + return -EFAULT; + return 0; + + </programlisting> + <para> + Querying the frequency in our case is relatively simple. Our radio card is + too dumb to let us query the signal strength so we remember our setting if + we know it. All we have to do is copy it to the user. + </para> + <programlisting> + + + case VIDIOCSFREQ: + { + u32 freq; + if(copy_from_user(arg, &freq, + sizeof(unsigned long))!=0) + return -EFAULT; + if(hardware_set_freq(freq)<0) + return -EINVAL; + current_freq = freq; + return 0; + } + + </programlisting> + <para> + Setting the frequency is a little more complex. We begin by copying the + desired frequency into kernel space. Next we call a hardware specific routine + to set the radio up. This might be as simple as some scaling and a few + writes to an I/O port. For most radio cards it turns out a good deal more + complicated and may involve programming things like a phase locked loop on + the card. This is what documentation is for. + </para> + <para> + The final set of operations we need to provide for our radio are the + volume controls. Not all radio cards can even do volume control. After all + there is a perfectly good volume control on the sound card. We will assume + our radio card has a simple 4 step volume control. + </para> + <para> + There are two ioctls with audio we need to support + </para> + <programlisting> + +static int current_volume=0; + + case VIDIOCGAUDIO: + { + struct video_audio v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.audio != 0) + return -EINVAL; + v.volume = 16384*current_volume; + v.step = 16384; + strcpy(v.name, "Radio"); + v.mode = VIDEO_SOUND_MONO; + v.balance = 0; + v.base = 0; + v.treble = 0; + + if(copy_to_user(arg. &v, sizeof(v))) + return -EFAULT; + return 0; + } + + </programlisting> + <para> + Much like the tuner we start by copying the user structure into kernel + space. Again we check if the user has asked for a valid audio input. We have + only input 0 and we punt if they ask for another input. + </para> + <para> + Then we fill in the video_audio structure. This has the following format + </para> + <table frame="all"><title>struct video_audio fields</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>audio</entry><entry>The input the user wishes to query</entry> + </row><row> + <entry>volume</entry><entry>The volume setting on a scale of 0-65535</entry> + </row><row> + <entry>base</entry><entry>The base level on a scale of 0-65535</entry> + </row><row> + <entry>treble</entry><entry>The treble level on a scale of 0-65535</entry> + </row><row> + <entry>flags</entry><entry>The features this audio device supports + </entry> + </row><row> + <entry>name</entry><entry>A text name to display to the user. We picked + "Radio" as it explains things quite nicely.</entry> + </row><row> + <entry>mode</entry><entry>The current reception mode for the audio + + We report MONO because our card is too stupid to know if it is in + mono or stereo. + </entry> + </row><row> + <entry>balance</entry><entry>The stereo balance on a scale of 0-65535, 32768 is + middle.</entry> + </row><row> + <entry>step</entry><entry>The step by which the volume control jumps. This is + used to help make it easy for applications to set + slider behaviour.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table frame="all"><title>struct video_audio flags</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_AUDIO_MUTE</entry><entry>The audio is currently muted. We + could fake this in our driver but we + choose not to bother.</entry> + </row><row> + <entry>VIDEO_AUDIO_MUTABLE</entry><entry>The input has a mute option</entry> + </row><row> + <entry>VIDEO_AUDIO_TREBLE</entry><entry>The input has a treble control</entry> + </row><row> + <entry>VIDEO_AUDIO_BASS</entry><entry>The input has a base control</entry> + </row> + </tbody> + </tgroup> + </table> + + <table frame="all"><title>struct video_audio modes</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_SOUND_MONO</entry><entry>Mono sound</entry> + </row><row> + <entry>VIDEO_SOUND_STEREO</entry><entry>Stereo sound</entry> + </row><row> + <entry>VIDEO_SOUND_LANG1</entry><entry>Alternative language 1 (TV specific)</entry> + </row><row> + <entry>VIDEO_SOUND_LANG2</entry><entry>Alternative language 2 (TV specific)</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + Having filled in the structure we copy it back to user space. + </para> + <para> + The VIDIOCSAUDIO ioctl allows the user to set the audio parameters in the + video_audio structure. The driver does its best to honour the request. + </para> + <programlisting> + + case VIDIOCSAUDIO: + { + struct video_audio v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.audio) + return -EINVAL; + current_volume = v/16384; + hardware_set_volume(current_volume); + return 0; + } + + </programlisting> + <para> + In our case there is very little that the user can set. The volume is + basically the limit. Note that we could pretend to have a mute feature + by rewriting this to + </para> + <programlisting> + + case VIDIOCSAUDIO: + { + struct video_audio v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.audio) + return -EINVAL; + current_volume = v/16384; + if(v.flags&VIDEO_AUDIO_MUTE) + hardware_set_volume(0); + else + hardware_set_volume(current_volume); + current_muted = v.flags & + VIDEO_AUDIO_MUTE; + return 0; + } + + </programlisting> + <para> + This with the corresponding changes to the VIDIOCGAUDIO code to report the + state of the mute flag we save and to report the card has a mute function, + will allow applications to use a mute facility with this card. It is + questionable whether this is a good idea however. User applications can already + fake this themselves and kernel space is precious. + </para> + <para> + We now have a working radio ioctl handler. So we just wrap up the function + </para> + <programlisting> + + + } + return -ENOIOCTLCMD; +} + + </programlisting> + <para> + and pass the Video4Linux layer back an error so that it knows we did not + understand the request we got passed. + </para> + </sect1> + <sect1 id="modradio"> + <title>Module Wrapper</title> + <para> + Finally we add in the usual module wrapping and the driver is done. + </para> + <programlisting> + +#ifndef MODULE + +static int io = 0x300; + +#else + +static int io = -1; + +#endif + +MODULE_AUTHOR("Alan Cox"); +MODULE_DESCRIPTION("A driver for an imaginary radio card."); +module_param(io, int, 0444); +MODULE_PARM_DESC(io, "I/O address of the card."); + +static int __init init(void) +{ + if(io==-1) + { + printk(KERN_ERR + "You must set an I/O address with io=0x???\n"); + return -EINVAL; + } + return myradio_init(NULL); +} + +static void __exit cleanup(void) +{ + video_unregister_device(&my_radio); + release_region(io, MY_IO_SIZE); +} + +module_init(init); +module_exit(cleanup); + + </programlisting> + <para> + In this example we set the IO base by default if the driver is compiled into + the kernel: you can still set it using "my_radio.irq" if this file is called <filename>my_radio.c</filename>. For the module we require the + user sets the parameter. We set io to a nonsense port (-1) so that we can + tell if the user supplied an io parameter or not. + </para> + <para> + We use MODULE_ defines to give an author for the card driver and a + description. We also use them to declare that io is an integer and it is the + address of the card, and can be read by anyone from sysfs. + </para> + <para> + The clean-up routine unregisters the video_device we registered, and frees + up the I/O space. Note that the unregister takes the actual video_device + structure as its argument. Unlike the file operations structure which can be + shared by all instances of a device a video_device structure as an actual + instance of the device. If you are registering multiple radio devices you + need to fill in one structure per device (most likely by setting up a + template and copying it to each of the actual device structures). + </para> + </sect1> + </chapter> + <chapter> + <title>Video Capture Devices</title> + <sect1 id="introvid"> + <title>Video Capture Device Types</title> + <para> + The video capture devices share the same interfaces as radio devices. In + order to explain the video capture interface I will use the example of a + camera that has no tuners or audio input. This keeps the example relatively + clean. To get both combine the two driver examples. + </para> + <para> + Video capture devices divide into four categories. A little technology + backgrounder. Full motion video even at television resolution (which is + actually fairly low) is pretty resource-intensive. You are continually + passing megabytes of data every second from the capture card to the display. + several alternative approaches have emerged because copying this through the + processor and the user program is a particularly bad idea . + </para> + <para> + The first is to add the television image onto the video output directly. + This is also how some 3D cards work. These basic cards can generally drop the + video into any chosen rectangle of the display. Cards like this, which + include most mpeg1 cards that used the feature connector, aren't very + friendly in a windowing environment. They don't understand windows or + clipping. The video window is always on the top of the display. + </para> + <para> + Chroma keying is a technique used by cards to get around this. It is an old + television mixing trick where you mark all the areas you wish to replace + with a single clear colour that isn't used in the image - TV people use an + incredibly bright blue while computing people often use a particularly + virulent purple. Bright blue occurs on the desktop. Anyone with virulent + purple windows has another problem besides their TV overlay. + </para> + <para> + The third approach is to copy the data from the capture card to the video + card, but to do it directly across the PCI bus. This relieves the processor + from doing the work but does require some smartness on the part of the video + capture chip, as well as a suitable video card. Programming this kind of + card and more so debugging it can be extremely tricky. There are some quite + complicated interactions with the display and you may also have to cope with + various chipset bugs that show up when PCI cards start talking to each + other. + </para> + <para> + To keep our example fairly simple we will assume a card that supports + overlaying a flat rectangular image onto the frame buffer output, and which + can also capture stuff into processor memory. + </para> + </sect1> + <sect1 id="regvid"> + <title>Registering Video Capture Devices</title> + <para> + This time we need to add more functions for our camera device. + </para> + <programlisting> +static struct video_device my_camera +{ + "My Camera", + VID_TYPE_OVERLAY|VID_TYPE_SCALES|\ + VID_TYPE_CAPTURE|VID_TYPE_CHROMAKEY, + VID_HARDWARE_MYCAMERA, + camera_open. + camera_close, + camera_read, /* no read */ + NULL, /* no write */ + camera_poll, /* no poll */ + camera_ioctl, + NULL, /* no special init function */ + NULL /* no private data */ +}; + </programlisting> + <para> + We need a read() function which is used for capturing data from + the card, and we need a poll function so that a driver can wait for the next + frame to be captured. + </para> + <para> + We use the extra video capability flags that did not apply to the + radio interface. The video related flags are + </para> + <table frame="all"><title>Capture Capabilities</title> + <tgroup cols="2" align="left"> + <tbody> + <row> +<entry>VID_TYPE_CAPTURE</entry><entry>We support image capture</entry> +</row><row> +<entry>VID_TYPE_TELETEXT</entry><entry>A teletext capture device (vbi{n])</entry> +</row><row> +<entry>VID_TYPE_OVERLAY</entry><entry>The image can be directly overlaid onto the + frame buffer</entry> +</row><row> +<entry>VID_TYPE_CHROMAKEY</entry><entry>Chromakey can be used to select which parts + of the image to display</entry> +</row><row> +<entry>VID_TYPE_CLIPPING</entry><entry>It is possible to give the board a list of + rectangles to draw around. </entry> +</row><row> +<entry>VID_TYPE_FRAMERAM</entry><entry>The video capture goes into the video memory + and actually changes it. Applications need + to know this so they can clean up after the + card</entry> +</row><row> +<entry>VID_TYPE_SCALES</entry><entry>The image can be scaled to various sizes, + rather than being a single fixed size.</entry> +</row><row> +<entry>VID_TYPE_MONOCHROME</entry><entry>The capture will be monochrome. This isn't a + complete answer to the question since a mono + camera on a colour capture card will still + produce mono output.</entry> +</row><row> +<entry>VID_TYPE_SUBCAPTURE</entry><entry>The card allows only part of its field of + view to be captured. This enables + applications to avoid copying all of a large + image into memory when only some section is + relevant.</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + We set VID_TYPE_CAPTURE so that we are seen as a capture card, + VID_TYPE_CHROMAKEY so the application knows it is time to draw in virulent + purple, and VID_TYPE_SCALES because we can be resized. + </para> + <para> + Our setup is fairly similar. This time we also want an interrupt line + for the 'frame captured' signal. Not all cards have this so some of them + cannot handle poll(). + </para> + <programlisting> + + +static int io = 0x320; +static int irq = 11; + +int __init mycamera_init(struct video_init *v) +{ + if(!request_region(io, MY_IO_SIZE, "mycamera")) + { + printk(KERN_ERR + "mycamera: port 0x%03X is in use.\n", io); + return -EBUSY; + } + + if(video_device_register(&my_camera, + VFL_TYPE_GRABBER)==-1) { + release_region(io, MY_IO_SIZE); + return -EINVAL; + } + return 0; +} + + </programlisting> + <para> + This is little changed from the needs of the radio card. We specify + VFL_TYPE_GRABBER this time as we want to be allocated a /dev/video name. + </para> + </sect1> + <sect1 id="opvid"> + <title>Opening And Closing The Capture Device</title> + <programlisting> + + +static int users = 0; + +static int camera_open(stuct video_device *dev, int flags) +{ + if(users) + return -EBUSY; + if(request_irq(irq, camera_irq, 0, "camera", dev)<0) + return -EBUSY; + users++; + return 0; +} + + +static int camera_close(struct video_device *dev) +{ + users--; + free_irq(irq, dev); +} + </programlisting> + <para> + The open and close routines are also quite similar. The only real change is + that we now request an interrupt for the camera device interrupt line. If we + cannot get the interrupt we report EBUSY to the application and give up. + </para> + </sect1> + <sect1 id="irqvid"> + <title>Interrupt Handling</title> + <para> + Our example handler is for an ISA bus device. If it was PCI you would be + able to share the interrupt and would have set SA_SHIRQ to indicate a + shared IRQ. We pass the device pointer as the interrupt routine argument. We + don't need to since we only support one card but doing this will make it + easier to upgrade the driver for multiple devices in the future. + </para> + <para> + Our interrupt routine needs to do little if we assume the card can simply + queue one frame to be read after it captures it. + </para> + <programlisting> + + +static struct wait_queue *capture_wait; +static int capture_ready = 0; + +static void camera_irq(int irq, void *dev_id, + struct pt_regs *regs) +{ + capture_ready=1; + wake_up_interruptible(&capture_wait); +} + </programlisting> + <para> + The interrupt handler is nice and simple for this card as we are assuming + the card is buffering the frame for us. This means we have little to do but + wake up anybody interested. We also set a capture_ready flag, as we may + capture a frame before an application needs it. In this case we need to know + that a frame is ready. If we had to collect the frame on the interrupt life + would be more complex. + </para> + <para> + The two new routines we need to supply are camera_read which returns a + frame, and camera_poll which waits for a frame to become ready. + </para> + <programlisting> + + +static int camera_poll(struct video_device *dev, + struct file *file, struct poll_table *wait) +{ + poll_wait(file, &capture_wait, wait); + if(capture_read) + return POLLIN|POLLRDNORM; + return 0; +} + + </programlisting> + <para> + Our wait queue for polling is the capture_wait queue. This will cause the + task to be woken up by our camera_irq routine. We check capture_read to see + if there is an image present and if so report that it is readable. + </para> + </sect1> + <sect1 id="rdvid"> + <title>Reading The Video Image</title> + <programlisting> + + +static long camera_read(struct video_device *dev, char *buf, + unsigned long count) +{ + struct wait_queue wait = { current, NULL }; + u8 *ptr; + int len; + int i; + + add_wait_queue(&capture_wait, &wait); + + while(!capture_ready) + { + if(file->flags&O_NDELAY) + { + remove_wait_queue(&capture_wait, &wait); + current->state = TASK_RUNNING; + return -EWOULDBLOCK; + } + if(signal_pending(current)) + { + remove_wait_queue(&capture_wait, &wait); + current->state = TASK_RUNNING; + return -ERESTARTSYS; + } + schedule(); + current->state = TASK_INTERRUPTIBLE; + } + remove_wait_queue(&capture_wait, &wait); + current->state = TASK_RUNNING; + + </programlisting> + <para> + The first thing we have to do is to ensure that the application waits until + the next frame is ready. The code here is almost identical to the mouse code + we used earlier in this chapter. It is one of the common building blocks of + Linux device driver code and probably one which you will find occurs in any + drivers you write. + </para> + <para> + We wait for a frame to be ready, or for a signal to interrupt our waiting. If a + signal occurs we need to return from the system call so that the signal can + be sent to the application itself. We also check to see if the user actually + wanted to avoid waiting - ie if they are using non-blocking I/O and have other things + to get on with. + </para> + <para> + Next we copy the data from the card to the user application. This is rarely + as easy as our example makes out. We will add capture_w, and capture_h here + to hold the width and height of the captured image. We assume the card only + supports 24bit RGB for now. + </para> + <programlisting> + + + + capture_ready = 0; + + ptr=(u8 *)buf; + len = capture_w * 3 * capture_h; /* 24bit RGB */ + + if(len>count) + len=count; /* Doesn't all fit */ + + for(i=0; i<len; i++) + { + put_user(inb(io+IMAGE_DATA), ptr); + ptr++; + } + + hardware_restart_capture(); + + return i; +} + + </programlisting> + <para> + For a real hardware device you would try to avoid the loop with put_user(). + Each call to put_user() has a time overhead checking whether the accesses to user + space are allowed. It would be better to read a line into a temporary buffer + then copy this to user space in one go. + </para> + <para> + Having captured the image and put it into user space we can kick the card to + get the next frame acquired. + </para> + </sect1> + <sect1 id="iocvid"> + <title>Video Ioctl Handling</title> + <para> + As with the radio driver the major control interface is via the ioctl() + function. Video capture devices support the same tuner calls as a radio + device and also support additional calls to control how the video functions + are handled. In this simple example the card has no tuners to avoid making + the code complex. + </para> + <programlisting> + + + +static int camera_ioctl(struct video_device *dev, unsigned int cmd, void *arg) +{ + switch(cmd) + { + case VIDIOCGCAP: + { + struct video_capability v; + v.type = VID_TYPE_CAPTURE|\ + VID_TYPE_CHROMAKEY|\ + VID_TYPE_SCALES|\ + VID_TYPE_OVERLAY; + v.channels = 1; + v.audios = 0; + v.maxwidth = 640; + v.minwidth = 16; + v.maxheight = 480; + v.minheight = 16; + strcpy(v.name, "My Camera"); + if(copy_to_user(arg, &v, sizeof(v))) + return -EFAULT; + return 0; + } + + + </programlisting> + <para> + The first ioctl we must support and which all video capture and radio + devices are required to support is VIDIOCGCAP. This behaves exactly the same + as with a radio device. This time, however, we report the extra capabilities + we outlined earlier on when defining our video_dev structure. + </para> + <para> + We now set the video flags saying that we support overlay, capture, + scaling and chromakey. We also report size limits - our smallest image is + 16x16 pixels, our largest is 640x480. + </para> + <para> + To keep things simple we report no audio and no tuning capabilities at all. + </para> + <programlisting> + + case VIDIOCGCHAN: + { + struct video_channel v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.channel != 0) + return -EINVAL; + v.flags = 0; + v.tuners = 0; + v.type = VIDEO_TYPE_CAMERA; + v.norm = VIDEO_MODE_AUTO; + strcpy(v.name, "Camera Input");break; + if(copy_to_user(&v, arg, sizeof(v))) + return -EFAULT; + return 0; + } + + + </programlisting> + <para> + This follows what is very much the standard way an ioctl handler looks + in Linux. We copy the data into a kernel space variable and we check that the + request is valid (in this case that the input is 0). Finally we copy the + camera info back to the user. + </para> + <para> + The VIDIOCGCHAN ioctl allows a user to ask about video channels (that is + inputs to the video card). Our example card has a single camera input. The + fields in the structure are + </para> + <table frame="all"><title>struct video_channel fields</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + + <entry>channel</entry><entry>The channel number we are selecting</entry> + </row><row> + <entry>name</entry><entry>The name for this channel. This is intended + to describe the port to the user. + Appropriate names are therefore things like + "Camera" "SCART input"</entry> + </row><row> + <entry>flags</entry><entry>Channel properties</entry> + </row><row> + <entry>type</entry><entry>Input type</entry> + </row><row> + <entry>norm</entry><entry>The current television encoding being used + if relevant for this channel. + </entry> + </row> + </tbody> + </tgroup> + </table> + <table frame="all"><title>struct video_channel flags</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_VC_TUNER</entry><entry>Channel has a tuner.</entry> + </row><row> + <entry>VIDEO_VC_AUDIO</entry><entry>Channel has audio.</entry> + </row> + </tbody> + </tgroup> + </table> + <table frame="all"><title>struct video_channel types</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_TYPE_TV</entry><entry>Television input.</entry> + </row><row> + <entry>VIDEO_TYPE_CAMERA</entry><entry>Fixed camera input.</entry> + </row><row> + <entry>0</entry><entry>Type is unknown.</entry> + </row> + </tbody> + </tgroup> + </table> + <table frame="all"><title>struct video_channel norms</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>VIDEO_MODE_PAL</entry><entry>PAL encoded Television</entry> + </row><row> + <entry>VIDEO_MODE_NTSC</entry><entry>NTSC (US) encoded Television</entry> + </row><row> + <entry>VIDEO_MODE_SECAM</entry><entry>SECAM (French) Television </entry> + </row><row> + <entry>VIDEO_MODE_AUTO</entry><entry>Automatic switching, or format does not + matter</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + The corresponding VIDIOCSCHAN ioctl allows a user to change channel and to + request the norm is changed - for example to switch between a PAL or an NTSC + format camera. + </para> + <programlisting> + + + case VIDIOCSCHAN: + { + struct video_channel v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.channel != 0) + return -EINVAL; + if(v.norm != VIDEO_MODE_AUTO) + return -EINVAL; + return 0; + } + + + </programlisting> + <para> + The implementation of this call in our driver is remarkably easy. Because we + are assuming fixed format hardware we need only check that the user has not + tried to change anything. + </para> + <para> + The user also needs to be able to configure and adjust the picture they are + seeing. This is much like adjusting a television set. A user application + also needs to know the palette being used so that it knows how to display + the image that has been captured. The VIDIOCGPICT and VIDIOCSPICT ioctl + calls provide this information. + </para> + <programlisting> + + + case VIDIOCGPICT + { + struct video_picture v; + v.brightness = hardware_brightness(); + v.hue = hardware_hue(); + v.colour = hardware_saturation(); + v.contrast = hardware_brightness(); + /* Not settable */ + v.whiteness = 32768; + v.depth = 24; /* 24bit */ + v.palette = VIDEO_PALETTE_RGB24; + if(copy_to_user(&v, arg, + sizeof(v))) + return -EFAULT; + return 0; + } + + + </programlisting> + <para> + The brightness, hue, color, and contrast provide the picture controls that + are akin to a conventional television. Whiteness provides additional + control for greyscale images. All of these values are scaled between 0-65535 + and have 32768 as the mid point setting. The scaling means that applications + do not have to worry about the capability range of the hardware but can let + it make a best effort attempt. + </para> + <para> + Our depth is 24, as this is in bits. We will be returning RGB24 format. This + has one byte of red, then one of green, then one of blue. This then repeats + for every other pixel in the image. The other common formats the interface + defines are + </para> + <table frame="all"><title>Framebuffer Encodings</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>GREY</entry><entry>Linear greyscale. This is for simple cameras and the + like</entry> + </row><row> + <entry>RGB565</entry><entry>The top 5 bits hold 32 red levels, the next six bits + hold green and the low 5 bits hold blue. </entry> + </row><row> + <entry>RGB555</entry><entry>The top bit is clear. The red green and blue levels + each occupy five bits.</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + Additional modes are support for YUV capture formats. These are common for + TV and video conferencing applications. + </para> + <para> + The VIDIOCSPICT ioctl allows a user to set some of the picture parameters. + Exactly which ones are supported depends heavily on the card itself. It is + possible to support many modes and effects in software. In general doing + this in the kernel is a bad idea. Video capture is a performance-sensitive + application and the programs can often do better if they aren't being + 'helped' by an overkeen driver writer. Thus for our device we will report + RGB24 only and refuse to allow a change. + </para> + <programlisting> + + + case VIDIOCSPICT: + { + struct video_picture v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.depth!=24 || + v.palette != VIDEO_PALETTE_RGB24) + return -EINVAL; + set_hardware_brightness(v.brightness); + set_hardware_hue(v.hue); + set_hardware_saturation(v.colour); + set_hardware_brightness(v.contrast); + return 0; + } + + + </programlisting> + <para> + We check the user has not tried to change the palette or the depth. We do + not want to carry out some of the changes and then return an error. This may + confuse the application which will be assuming no change occurred. + </para> + <para> + In much the same way as you need to be able to set the picture controls to + get the right capture images, many cards need to know what they are + displaying onto when generating overlay output. In some cases getting this + wrong even makes a nasty mess or may crash the computer. For that reason + the VIDIOCSBUF ioctl used to set up the frame buffer information may well + only be usable by root. + </para> + <para> + We will assume our card is one of the old ISA devices with feature connector + and only supports a couple of standard video modes. Very common for older + cards although the PCI devices are way smarter than this. + </para> + <programlisting> + + +static struct video_buffer capture_fb; + + case VIDIOCGFBUF: + { + if(copy_to_user(arg, &capture_fb, + sizeof(capture_fb))) + return -EFAULT; + return 0; + + } + + + </programlisting> + <para> + We keep the frame buffer information in the format the ioctl uses. This + makes it nice and easy to work with in the ioctl calls. + </para> + <programlisting> + + case VIDIOCSFBUF: + { + struct video_buffer v; + + if(!capable(CAP_SYS_ADMIN)) + return -EPERM; + + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.width!=320 && v.width!=640) + return -EINVAL; + if(v.height!=200 && v.height!=240 + && v.height!=400 + && v.height !=480) + return -EINVAL; + memcpy(&capture_fb, &v, sizeof(v)); + hardware_set_fb(&v); + return 0; + } + + + + </programlisting> + <para> + The capable() function checks a user has the required capability. The Linux + operating system has a set of about 30 capabilities indicating privileged + access to services. The default set up gives the superuser (uid 0) all of + them and nobody else has any. + </para> + <para> + We check that the user has the SYS_ADMIN capability, that is they are + allowed to operate as the machine administrator. We don't want anyone but + the administrator making a mess of the display. + </para> + <para> + Next we check for standard PC video modes (320 or 640 wide with either + EGA or VGA depths). If the mode is not a standard video mode we reject it as + not supported by our card. If the mode is acceptable we save it so that + VIDIOCFBUF will give the right answer next time it is called. The + hardware_set_fb() function is some undescribed card specific function to + program the card for the desired mode. + </para> + <para> + Before the driver can display an overlay window it needs to know where the + window should be placed, and also how large it should be. If the card + supports clipping it needs to know which rectangles to omit from the + display. The video_window structure is used to describe the way the image + should be displayed. + </para> + <table frame="all"><title>struct video_window fields</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>width</entry><entry>The width in pixels of the desired image. The card + may use a smaller size if this size is not available</entry> + </row><row> + <entry>height</entry><entry>The height of the image. The card may use a smaller + size if this size is not available.</entry> + </row><row> + <entry>x</entry><entry> The X position of the top left of the window. This + is in pixels relative to the left hand edge of the + picture. Not all cards can display images aligned on + any pixel boundary. If the position is unsuitable + the card adjusts the image right and reduces the + width.</entry> + </row><row> + <entry>y</entry><entry> The Y position of the top left of the window. This + is counted in pixels relative to the top edge of the + picture. As with the width if the card cannot + display starting on this line it will adjust the + values.</entry> + </row><row> + <entry>chromakey</entry><entry>The colour (expressed in RGB32 format) for the + chromakey colour if chroma keying is being used. </entry> + </row><row> + <entry>clips</entry><entry>An array of rectangles that must not be drawn + over.</entry> + </row><row> + <entry>clipcount</entry><entry>The number of clips in this array.</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + Each clip is a struct video_clip which has the following fields + </para> + <table frame="all"><title>video_clip fields</title> + <tgroup cols="2" align="left"> + <tbody> + <row> + <entry>x, y</entry><entry>Co-ordinates relative to the display</entry> + </row><row> + <entry>width, height</entry><entry>Width and height in pixels</entry> + </row><row> + <entry>next</entry><entry>A spare field for the application to use</entry> + </row> + </tbody> + </tgroup> + </table> + <para> + The driver is required to ensure it always draws in the area requested or a smaller area, and that it never draws in any of the areas that are clipped. + This may well mean it has to leave alone. small areas the application wished to be + drawn. + </para> + <para> + Our example card uses chromakey so does not have to address most of the + clipping. We will add a video_window structure to our global variables to + remember our parameters, as we did with the frame buffer. + </para> + <programlisting> + + + case VIDIOCGWIN: + { + if(copy_to_user(arg, &capture_win, + sizeof(capture_win))) + return -EFAULT; + return 0; + } + + + case VIDIOCSWIN: + { + struct video_window v; + if(copy_from_user(&v, arg, sizeof(v))) + return -EFAULT; + if(v.width > 640 || v.height > 480) + return -EINVAL; + if(v.width < 16 || v.height < 16) + return -EINVAL; + hardware_set_key(v.chromakey); + hardware_set_window(v); + memcpy(&capture_win, &v, sizeof(v)); + capture_w = v.width; + capture_h = v.height; + return 0; + } + + + </programlisting> + <para> + Because we are using Chromakey our setup is fairly simple. Mostly we have to + check the values are sane and load them into the capture card. + </para> + <para> + With all the setup done we can now turn on the actual capture/overlay. This + is done with the VIDIOCCAPTURE ioctl. This takes a single integer argument + where 0 is on and 1 is off. + </para> + <programlisting> + + + case VIDIOCCAPTURE: + { + int v; + if(get_user(v, (int *)arg)) + return -EFAULT; + if(v==0) + hardware_capture_off(); + else + { + if(capture_fb.width == 0 + || capture_w == 0) + return -EINVAL; + hardware_capture_on(); + } + return 0; + } + + + </programlisting> + <para> + We grab the flag from user space and either enable or disable according to + its value. There is one small corner case we have to consider here. Suppose + that the capture was requested before the video window or the frame buffer + had been set up. In those cases there will be unconfigured fields in our + card data, as well as unconfigured hardware settings. We check for this case and + return an error if the frame buffer or the capture window width is zero. + </para> + <programlisting> + + + default: + return -ENOIOCTLCMD; + } +} + </programlisting> + <para> + + We don't need to support any other ioctls, so if we get this far, it is time + to tell the video layer that we don't now what the user is talking about. + </para> + </sect1> + <sect1 id="endvid"> + <title>Other Functionality</title> + <para> + The Video4Linux layer supports additional features, including a high + performance mmap() based capture mode and capturing part of the image. + These features are out of the scope of the book. You should however have enough + example code to implement most simple video4linux devices for radio and TV + cards. + </para> + </sect1> + </chapter> + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + <variablelist> + <varlistentry><term>Multiple Opens</term> + <listitem> + <para> + The driver assumes multiple opens should not be allowed. A driver + can work around this but not cleanly. + </para> + </listitem></varlistentry> + + <varlistentry><term>API Deficiencies</term> + <listitem> + <para> + The existing API poorly reflects compression capable devices. There + are plans afoot to merge V4L, V4L2 and some other ideas into a + better interface. + </para> + </listitem></varlistentry> + </variablelist> + + </para> + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> +!Edrivers/media/video/videodev.c + </chapter> + +</book> diff --git a/Documentation/DocBook/wanbook.tmpl b/Documentation/DocBook/wanbook.tmpl new file mode 100644 index 0000000..9eebcc3 --- /dev/null +++ b/Documentation/DocBook/wanbook.tmpl @@ -0,0 +1,99 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="WANGuide"> + <bookinfo> + <title>Synchronous PPP and Cisco HDLC Programming Guide</title> + + <authorgroup> + <author> + <firstname>Alan</firstname> + <surname>Cox</surname> + <affiliation> + <address> + <email>alan@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2000</year> + <holder>Alan Cox</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The syncppp drivers in Linux provide a fairly complete + implementation of Cisco HDLC and a minimal implementation of + PPP. The longer term goal is to switch the PPP layer to the + generic PPP interface that is new in Linux 2.3.x. The API should + remain unchanged when this is done, but support will then be + available for IPX, compression and other PPP features + </para> + </chapter> + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + <variablelist> + <varlistentry><term>PPP is minimal</term> + <listitem> + <para> + The current PPP implementation is very basic, although sufficient + for most wan usages. + </para> + </listitem></varlistentry> + + <varlistentry><term>Cisco HDLC Quirks</term> + <listitem> + <para> + Currently we do not end all packets with the correct Cisco multicast + or unicast flags. Nothing appears to mind too much but this should + be corrected. + </para> + </listitem></varlistentry> + </variablelist> + + </para> + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> +!Edrivers/net/wan/syncppp.c + </chapter> + +</book> diff --git a/Documentation/DocBook/writing_usb_driver.tmpl b/Documentation/DocBook/writing_usb_driver.tmpl new file mode 100644 index 0000000..51f3bfb --- /dev/null +++ b/Documentation/DocBook/writing_usb_driver.tmpl @@ -0,0 +1,419 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="USBDeviceDriver"> + <bookinfo> + <title>Writing USB Device Drivers</title> + + <authorgroup> + <author> + <firstname>Greg</firstname> + <surname>Kroah-Hartman</surname> + <affiliation> + <address> + <email>greg@kroah.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2001-2002</year> + <holder>Greg Kroah-Hartman</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + + <para> + This documentation is based on an article published in + Linux Journal Magazine, October 2001, Issue 90. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The Linux USB subsystem has grown from supporting only two different + types of devices in the 2.2.7 kernel (mice and keyboards), to over 20 + different types of devices in the 2.4 kernel. Linux currently supports + almost all USB class devices (standard types of devices like keyboards, + mice, modems, printers and speakers) and an ever-growing number of + vendor-specific devices (such as USB to serial converters, digital + cameras, Ethernet devices and MP3 players). For a full list of the + different USB devices currently supported, see Resources. + </para> + <para> + The remaining kinds of USB devices that do not have support on Linux are + almost all vendor-specific devices. Each vendor decides to implement a + custom protocol to talk to their device, so a custom driver usually needs + to be created. Some vendors are open with their USB protocols and help + with the creation of Linux drivers, while others do not publish them, and + developers are forced to reverse-engineer. See Resources for some links + to handy reverse-engineering tools. + </para> + <para> + Because each different protocol causes a new driver to be created, I have + written a generic USB driver skeleton, modeled after the pci-skeleton.c + file in the kernel source tree upon which many PCI network drivers have + been based. This USB skeleton can be found at drivers/usb/usb-skeleton.c + in the kernel source tree. In this article I will walk through the basics + of the skeleton driver, explaining the different pieces and what needs to + be done to customize it to your specific device. + </para> + </chapter> + + <chapter id="basics"> + <title>Linux USB Basics</title> + <para> + If you are going to write a Linux USB driver, please become familiar with + the USB protocol specification. It can be found, along with many other + useful documents, at the USB home page (see Resources). An excellent + introduction to the Linux USB subsystem can be found at the USB Working + Devices List (see Resources). It explains how the Linux USB subsystem is + structured and introduces the reader to the concept of USB urbs, which + are essential to USB drivers. + </para> + <para> + The first thing a Linux USB driver needs to do is register itself with + the Linux USB subsystem, giving it some information about which devices + the driver supports and which functions to call when a device supported + by the driver is inserted or removed from the system. All of this + information is passed to the USB subsystem in the usb_driver structure. + The skeleton driver declares a usb_driver as: + </para> + <programlisting> +static struct usb_driver skel_driver = { + .name = "skeleton", + .probe = skel_probe, + .disconnect = skel_disconnect, + .fops = &skel_fops, + .minor = USB_SKEL_MINOR_BASE, + .id_table = skel_table, +}; + </programlisting> + <para> + The variable name is a string that describes the driver. It is used in + informational messages printed to the system log. The probe and + disconnect function pointers are called when a device that matches the + information provided in the id_table variable is either seen or removed. + </para> + <para> + The fops and minor variables are optional. Most USB drivers hook into + another kernel subsystem, such as the SCSI, network or TTY subsystem. + These types of drivers register themselves with the other kernel + subsystem, and any user-space interactions are provided through that + interface. But for drivers that do not have a matching kernel subsystem, + such as MP3 players or scanners, a method of interacting with user space + is needed. The USB subsystem provides a way to register a minor device + number and a set of file_operations function pointers that enable this + user-space interaction. The skeleton driver needs this kind of interface, + so it provides a minor starting number and a pointer to its + file_operations functions. + </para> + <para> + The USB driver is then registered with a call to usb_register, usually in + the driver's init function, as shown here: + </para> + <programlisting> +static int __init usb_skel_init(void) +{ + int result; + + /* register this driver with the USB subsystem */ + result = usb_register(&skel_driver); + if (result < 0) { + err("usb_register failed for the "__FILE__ "driver." + "Error number %d", result); + return -1; + } + + return 0; +} +module_init(usb_skel_init); + </programlisting> + <para> + When the driver is unloaded from the system, it needs to unregister + itself with the USB subsystem. This is done with the usb_unregister + function: + </para> + <programlisting> +static void __exit usb_skel_exit(void) +{ + /* deregister this driver with the USB subsystem */ + usb_deregister(&skel_driver); +} +module_exit(usb_skel_exit); + </programlisting> + <para> + To enable the linux-hotplug system to load the driver automatically when + the device is plugged in, you need to create a MODULE_DEVICE_TABLE. The + following code tells the hotplug scripts that this module supports a + single device with a specific vendor and product ID: + </para> + <programlisting> +/* table of devices that work with this driver */ +static struct usb_device_id skel_table [] = { + { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) }, + { } /* Terminating entry */ +}; +MODULE_DEVICE_TABLE (usb, skel_table); + </programlisting> + <para> + There are other macros that can be used in describing a usb_device_id for + drivers that support a whole class of USB drivers. See usb.h for more + information on this. + </para> + </chapter> + + <chapter id="device"> + <title>Device operation</title> + <para> + When a device is plugged into the USB bus that matches the device ID + pattern that your driver registered with the USB core, the probe function + is called. The usb_device structure, interface number and the interface ID + are passed to the function: + </para> + <programlisting> +static int skel_probe(struct usb_interface *interface, + const struct usb_device_id *id) + </programlisting> + <para> + The driver now needs to verify that this device is actually one that it + can accept. If so, it returns 0. + If not, or if any error occurs during initialization, an errorcode + (such as <literal>-ENOMEM</literal> or <literal>-ENODEV</literal>) + is returned from the probe function. + </para> + <para> + In the skeleton driver, we determine what end points are marked as bulk-in + and bulk-out. We create buffers to hold the data that will be sent and + received from the device, and a USB urb to write data to the device is + initialized. + </para> + <para> + Conversely, when the device is removed from the USB bus, the disconnect + function is called with the device pointer. The driver needs to clean any + private data that has been allocated at this time and to shut down any + pending urbs that are in the USB system. The driver also unregisters + itself from the devfs subsystem with the call: + </para> + <programlisting> +/* remove our devfs node */ +devfs_unregister(skel->devfs); + </programlisting> + <para> + Now that the device is plugged into the system and the driver is bound to + the device, any of the functions in the file_operations structure that + were passed to the USB subsystem will be called from a user program trying + to talk to the device. The first function called will be open, as the + program tries to open the device for I/O. We increment our private usage + count and save off a pointer to our internal structure in the file + structure. This is done so that future calls to file operations will + enable the driver to determine which device the user is addressing. All + of this is done with the following code: + </para> + <programlisting> +/* increment our usage count for the module */ +++skel->open_count; + +/* save our object in the file's private structure */ +file->private_data = dev; + </programlisting> + <para> + After the open function is called, the read and write functions are called + to receive and send data to the device. In the skel_write function, we + receive a pointer to some data that the user wants to send to the device + and the size of the data. The function determines how much data it can + send to the device based on the size of the write urb it has created (this + size depends on the size of the bulk out end point that the device has). + Then it copies the data from user space to kernel space, points the urb to + the data and submits the urb to the USB subsystem. This can be shown in + he following code: + </para> + <programlisting> +/* we can only write as much as 1 urb will hold */ +bytes_written = (count > skel->bulk_out_size) ? skel->bulk_out_size : count; + +/* copy the data from user space into our urb */ +copy_from_user(skel->write_urb->transfer_buffer, buffer, bytes_written); + +/* set up our urb */ +usb_fill_bulk_urb(skel->write_urb, + skel->dev, + usb_sndbulkpipe(skel->dev, skel->bulk_out_endpointAddr), + skel->write_urb->transfer_buffer, + bytes_written, + skel_write_bulk_callback, + skel); + +/* send the data out the bulk port */ +result = usb_submit_urb(skel->write_urb); +if (result) { + err("Failed submitting write urb, error %d", result); +} + </programlisting> + <para> + When the write urb is filled up with the proper information using the + usb_fill_bulk_urb function, we point the urb's completion callback to call our + own skel_write_bulk_callback function. This function is called when the + urb is finished by the USB subsystem. The callback function is called in + interrupt context, so caution must be taken not to do very much processing + at that time. Our implementation of skel_write_bulk_callback merely + reports if the urb was completed successfully or not and then returns. + </para> + <para> + The read function works a bit differently from the write function in that + we do not use an urb to transfer data from the device to the driver. + Instead we call the usb_bulk_msg function, which can be used to send or + receive data from a device without having to create urbs and handle + urb completion callback functions. We call the usb_bulk_msg function, + giving it a buffer into which to place any data received from the device + and a timeout value. If the timeout period expires without receiving any + data from the device, the function will fail and return an error message. + This can be shown with the following code: + </para> + <programlisting> +/* do an immediate bulk read to get data from the device */ +retval = usb_bulk_msg (skel->dev, + usb_rcvbulkpipe (skel->dev, + skel->bulk_in_endpointAddr), + skel->bulk_in_buffer, + skel->bulk_in_size, + &count, HZ*10); +/* if the read was successful, copy the data to user space */ +if (!retval) { + if (copy_to_user (buffer, skel->bulk_in_buffer, count)) + retval = -EFAULT; + else + retval = count; +} + </programlisting> + <para> + The usb_bulk_msg function can be very useful for doing single reads or + writes to a device; however, if you need to read or write constantly to a + device, it is recommended to set up your own urbs and submit them to the + USB subsystem. + </para> + <para> + When the user program releases the file handle that it has been using to + talk to the device, the release function in the driver is called. In this + function we decrement our private usage count and wait for possible + pending writes: + </para> + <programlisting> +/* decrement our usage count for the device */ +--skel->open_count; + </programlisting> + <para> + One of the more difficult problems that USB drivers must be able to handle + smoothly is the fact that the USB device may be removed from the system at + any point in time, even if a program is currently talking to it. It needs + to be able to shut down any current reads and writes and notify the + user-space programs that the device is no longer there. The following + code (function <function>skel_delete</function>) + is an example of how to do this: </para> + <programlisting> +static inline void skel_delete (struct usb_skel *dev) +{ + if (dev->bulk_in_buffer != NULL) + kfree (dev->bulk_in_buffer); + if (dev->bulk_out_buffer != NULL) + usb_buffer_free (dev->udev, dev->bulk_out_size, + dev->bulk_out_buffer, + dev->write_urb->transfer_dma); + if (dev->write_urb != NULL) + usb_free_urb (dev->write_urb); + kfree (dev); +} + </programlisting> + <para> + If a program currently has an open handle to the device, we reset the flag + <literal>device_present</literal>. For + every read, write, release and other functions that expect a device to be + present, the driver first checks this flag to see if the device is + still present. If not, it releases that the device has disappeared, and a + -ENODEV error is returned to the user-space program. When the release + function is eventually called, it determines if there is no device + and if not, it does the cleanup that the skel_disconnect + function normally does if there are no open files on the device (see + Listing 5). + </para> + </chapter> + + <chapter id="iso"> + <title>Isochronous Data</title> + <para> + This usb-skeleton driver does not have any examples of interrupt or + isochronous data being sent to or from the device. Interrupt data is sent + almost exactly as bulk data is, with a few minor exceptions. Isochronous + data works differently with continuous streams of data being sent to or + from the device. The audio and video camera drivers are very good examples + of drivers that handle isochronous data and will be useful if you also + need to do this. + </para> + </chapter> + + <chapter id="Conclusion"> + <title>Conclusion</title> + <para> + Writing Linux USB device drivers is not a difficult task as the + usb-skeleton driver shows. This driver, combined with the other current + USB drivers, should provide enough examples to help a beginning author + create a working driver in a minimal amount of time. The linux-usb-devel + mailing list archives also contain a lot of helpful information. + </para> + </chapter> + + <chapter id="resources"> + <title>Resources</title> + <para> + The Linux USB Project: <ulink url="http://www.linux-usb.org">http://www.linux-usb.org/</ulink> + </para> + <para> + Linux Hotplug Project: <ulink url="http://linux-hotplug.sourceforge.net">http://linux-hotplug.sourceforge.net/</ulink> + </para> + <para> + Linux USB Working Devices List: <ulink url="http://www.qbik.ch/usb/devices">http://www.qbik.ch/usb/devices/</ulink> + </para> + <para> + linux-usb-devel Mailing List Archives: <ulink url="http://marc.theaimsgroup.com/?l=linux-usb-devel">http://marc.theaimsgroup.com/?l=linux-usb-devel</ulink> + </para> + <para> + Programming Guide for Linux USB Device Drivers: <ulink url="http://usb.cs.tum.edu/usbdoc">http://usb.cs.tum.edu/usbdoc</ulink> + </para> + <para> + USB Home Page: <ulink url="http://www.usb.org">http://www.usb.org</ulink> + </para> + </chapter> + +</book> diff --git a/Documentation/DocBook/z8530book.tmpl b/Documentation/DocBook/z8530book.tmpl new file mode 100644 index 0000000..a507876 --- /dev/null +++ b/Documentation/DocBook/z8530book.tmpl @@ -0,0 +1,385 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="Z85230Guide"> + <bookinfo> + <title>Z8530 Programming Guide</title> + + <authorgroup> + <author> + <firstname>Alan</firstname> + <surname>Cox</surname> + <affiliation> + <address> + <email>alan@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2000</year> + <holder>Alan Cox</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="intro"> + <title>Introduction</title> + <para> + The Z85x30 family synchronous/asynchronous controller chips are + used on a large number of cheap network interface cards. The + kernel provides a core interface layer that is designed to make + it easy to provide WAN services using this chip. + </para> + <para> + The current driver only support synchronous operation. Merging the + asynchronous driver support into this code to allow any Z85x30 + device to be used as both a tty interface and as a synchronous + controller is a project for Linux post the 2.4 release + </para> + <para> + The support code handles most common card configurations and + supports running both Cisco HDLC and Synchronous PPP. With extra + glue the frame relay and X.25 protocols can also be used with this + driver. + </para> + </chapter> + + <chapter> + <title>Driver Modes</title> + <para> + The Z85230 driver layer can drive Z8530, Z85C30 and Z85230 devices + in three different modes. Each mode can be applied to an individual + channel on the chip (each chip has two channels). + </para> + <para> + The PIO synchronous mode supports the most common Z8530 wiring. Here + the chip is interface to the I/O and interrupt facilities of the + host machine but not to the DMA subsystem. When running PIO the + Z8530 has extremely tight timing requirements. Doing high speeds, + even with a Z85230 will be tricky. Typically you should expect to + achieve at best 9600 baud with a Z8C530 and 64Kbits with a Z85230. + </para> + <para> + The DMA mode supports the chip when it is configured to use dual DMA + channels on an ISA bus. The better cards tend to support this mode + of operation for a single channel. With DMA running the Z85230 tops + out when it starts to hit ISA DMA constraints at about 512Kbits. It + is worth noting here that many PC machines hang or crash when the + chip is driven fast enough to hold the ISA bus solid. + </para> + <para> + Transmit DMA mode uses a single DMA channel. The DMA channel is used + for transmission as the transmit FIFO is smaller than the receive + FIFO. it gives better performance than pure PIO mode but is nowhere + near as ideal as pure DMA mode. + </para> + </chapter> + + <chapter> + <title>Using the Z85230 driver</title> + <para> + The Z85230 driver provides the back end interface to your board. To + configure a Z8530 interface you need to detect the board and to + identify its ports and interrupt resources. It is also your problem + to verify the resources are available. + </para> + <para> + Having identified the chip you need to fill in a struct z8530_dev, + which describes each chip. This object must exist until you finally + shutdown the board. Firstly zero the active field. This ensures + nothing goes off without you intending it. The irq field should + be set to the interrupt number of the chip. (Each chip has a single + interrupt source rather than each channel). You are responsible + for allocating the interrupt line. The interrupt handler should be + set to <function>z8530_interrupt</function>. The device id should + be set to the z8530_dev structure pointer. Whether the interrupt can + be shared or not is board dependent, and up to you to initialise. + </para> + <para> + The structure holds two channel structures. + Initialise chanA.ctrlio and chanA.dataio with the address of the + control and data ports. You can or this with Z8530_PORT_SLEEP to + indicate your interface needs the 5uS delay for chip settling done + in software. The PORT_SLEEP option is architecture specific. Other + flags may become available on future platforms, eg for MMIO. + Initialise the chanA.irqs to &z8530_nop to start the chip up + as disabled and discarding interrupt events. This ensures that + stray interrupts will be mopped up and not hang the bus. Set + chanA.dev to point to the device structure itself. The + private and name field you may use as you wish. The private field + is unused by the Z85230 layer. The name is used for error reporting + and it may thus make sense to make it match the network name. + </para> + <para> + Repeat the same operation with the B channel if your chip has + both channels wired to something useful. This isn't always the + case. If it is not wired then the I/O values do not matter, but + you must initialise chanB.dev. + </para> + <para> + If your board has DMA facilities then initialise the txdma and + rxdma fields for the relevant channels. You must also allocate the + ISA DMA channels and do any necessary board level initialisation + to configure them. The low level driver will do the Z8530 and + DMA controller programming but not board specific magic. + </para> + <para> + Having initialised the device you can then call + <function>z8530_init</function>. This will probe the chip and + reset it into a known state. An identification sequence is then + run to identify the chip type. If the checks fail to pass the + function returns a non zero error code. Typically this indicates + that the port given is not valid. After this call the + type field of the z8530_dev structure is initialised to either + Z8530, Z85C30 or Z85230 according to the chip found. + </para> + <para> + Once you have called z8530_init you can also make use of the utility + function <function>z8530_describe</function>. This provides a + consistent reporting format for the Z8530 devices, and allows all + the drivers to provide consistent reporting. + </para> + </chapter> + + <chapter> + <title>Attaching Network Interfaces</title> + <para> + If you wish to use the network interface facilities of the driver, + then you need to attach a network device to each channel that is + present and in use. In addition to use the SyncPPP and Cisco HDLC + you need to follow some additional plumbing rules. They may seem + complex but a look at the example hostess_sv11 driver should + reassure you. + </para> + <para> + The network device used for each channel should be pointed to by + the netdevice field of each channel. The dev-> priv field of the + network device points to your private data - you will need to be + able to find your ppp device from this. In addition to use the + sync ppp layer the private data must start with a void * pointer + to the syncppp structures. + </para> + <para> + The way most drivers approach this particular problem is to + create a structure holding the Z8530 device definition and + put that and the syncppp pointer into the private field of + the network device. The network device fields of the channels + then point back to the network devices. The ppp_device can also + be put in the private structure conveniently. + </para> + <para> + If you wish to use the synchronous ppp then you need to attach + the syncppp layer to the network device. You should do this before + you register the network device. The + <function>sppp_attach</function> requires that the first void * + pointer in your private data is pointing to an empty struct + ppp_device. The function fills in the initial data for the + ppp/hdlc layer. + </para> + <para> + Before you register your network device you will also need to + provide suitable handlers for most of the network device callbacks. + See the network device documentation for more details on this. + </para> + </chapter> + + <chapter> + <title>Configuring And Activating The Port</title> + <para> + The Z85230 driver provides helper functions and tables to load the + port registers on the Z8530 chips. When programming the register + settings for a channel be aware that the documentation recommends + initialisation orders. Strange things happen when these are not + followed. + </para> + <para> + <function>z8530_channel_load</function> takes an array of + pairs of initialisation values in an array of u8 type. The first + value is the Z8530 register number. Add 16 to indicate the alternate + register bank on the later chips. The array is terminated by a 255. + </para> + <para> + The driver provides a pair of public tables. The + z8530_hdlc_kilostream table is for the UK 'Kilostream' service and + also happens to cover most other end host configurations. The + z8530_hdlc_kilostream_85230 table is the same configuration using + the enhancements of the 85230 chip. The configuration loaded is + standard NRZ encoded synchronous data with HDLC bitstuffing. All + of the timing is taken from the other end of the link. + </para> + <para> + When writing your own tables be aware that the driver internally + tracks register values. It may need to reload values. You should + therefore be sure to set registers 1-7, 9-11, 14 and 15 in all + configurations. Where the register settings depend on DMA selection + the driver will update the bits itself when you open or close. + Loading a new table with the interface open is not recommended. + </para> + <para> + There are three standard configurations supported by the core + code. In PIO mode the interface is programmed up to use + interrupt driven PIO. This places high demands on the host processor + to avoid latency. The driver is written to take account of latency + issues but it cannot avoid latencies caused by other drivers, + notably IDE in PIO mode. Because the drivers allocate buffers you + must also prevent MTU changes while the port is open. + </para> + <para> + Once the port is open it will call the rx_function of each channel + whenever a completed packet arrived. This is invoked from + interrupt context and passes you the channel and a network + buffer (struct sk_buff) holding the data. The data includes + the CRC bytes so most users will want to trim the last two + bytes before processing the data. This function is very timing + critical. When you wish to simply discard data the support + code provides the function <function>z8530_null_rx</function> + to discard the data. + </para> + <para> + To active PIO mode sending and receiving the <function> + z8530_sync_open</function> is called. This expects to be passed + the network device and the channel. Typically this is called from + your network device open callback. On a failure a non zero error + status is returned. The <function>z8530_sync_close</function> + function shuts down a PIO channel. This must be done before the + channel is opened again and before the driver shuts down + and unloads. + </para> + <para> + The ideal mode of operation is dual channel DMA mode. Here the + kernel driver will configure the board for DMA in both directions. + The driver also handles ISA DMA issues such as controller + programming and the memory range limit for you. This mode is + activated by calling the <function>z8530_sync_dma_open</function> + function. On failure a non zero error value is returned. + Once this mode is activated it can be shut down by calling the + <function>z8530_sync_dma_close</function>. You must call the close + function matching the open mode you used. + </para> + <para> + The final supported mode uses a single DMA channel to drive the + transmit side. As the Z85C30 has a larger FIFO on the receive + channel this tends to increase the maximum speed a little. + This is activated by calling the <function>z8530_sync_txdma_open + </function>. This returns a non zero error code on failure. The + <function>z8530_sync_txdma_close</function> function closes down + the Z8530 interface from this mode. + </para> + </chapter> + + <chapter> + <title>Network Layer Functions</title> + <para> + The Z8530 layer provides functions to queue packets for + transmission. The driver internally buffers the frame currently + being transmitted and one further frame (in order to keep back + to back transmission running). Any further buffering is up to + the caller. + </para> + <para> + The function <function>z8530_queue_xmit</function> takes a network + buffer in sk_buff format and queues it for transmission. The + caller must provide the entire packet with the exception of the + bitstuffing and CRC. This is normally done by the caller via + the syncppp interface layer. It returns 0 if the buffer has been + queued and non zero values for queue full. If the function accepts + the buffer it becomes property of the Z8530 layer and the caller + should not free it. + </para> + <para> + The function <function>z8530_get_stats</function> returns a pointer + to an internally maintained per interface statistics block. This + provides most of the interface code needed to implement the network + layer get_stats callback. + </para> + </chapter> + + <chapter> + <title>Porting The Z8530 Driver</title> + <para> + The Z8530 driver is written to be portable. In DMA mode it makes + assumptions about the use of ISA DMA. These are probably warranted + in most cases as the Z85230 in particular was designed to glue to PC + type machines. The PIO mode makes no real assumptions. + </para> + <para> + Should you need to retarget the Z8530 driver to another architecture + the only code that should need changing are the port I/O functions. + At the moment these assume PC I/O port accesses. This may not be + appropriate for all platforms. Replacing + <function>z8530_read_port</function> and <function>z8530_write_port + </function> is intended to be all that is required to port this + driver layer. + </para> + </chapter> + + <chapter id="bugs"> + <title>Known Bugs And Assumptions</title> + <para> + <variablelist> + <varlistentry><term>Interrupt Locking</term> + <listitem> + <para> + The locking in the driver is done via the global cli/sti lock. This + makes for relatively poor SMP performance. Switching this to use a + per device spin lock would probably materially improve performance. + </para> + </listitem></varlistentry> + + <varlistentry><term>Occasional Failures</term> + <listitem> + <para> + We have reports of occasional failures when run for very long + periods of time and the driver starts to receive junk frames. At + the moment the cause of this is not clear. + </para> + </listitem></varlistentry> + </variablelist> + + </para> + </chapter> + + <chapter id="pubfunctions"> + <title>Public Functions Provided</title> +!Edrivers/net/wan/z85230.c + </chapter> + + <chapter id="intfunctions"> + <title>Internal Functions</title> +!Idrivers/net/wan/z85230.c + </chapter> + +</book> |
