usb gadget: use new serial core

Teach "gadget serial" to use the new abstracted (and bugfixed) TTY glue,
and remove all the orignal tangled-up code.  Update the documentation
accordingly.  This is a net object code shrink and cleanup; it should
make it a lot easier to see how the TTY glue should accomodate updates
to the TTY layer, be bugfixed, etc.

Notable behavior changes include:  it can now support getty even when
there's no USB connection; it fits properly into the mdev/udev world;
and RX handling is better (throttling works, and low latency).

Configurations with scripts setting up the /dev/ttygserial device node
(with "experimental" major number) may want to change that to be a
symlink pointing to the /dev/ttyGS0 file, as a migration aid; else,
just switch entirely over to mdev/udev.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 26 insertions, 9 deletions

diff --git a/Documentation/usb/gadget_serial.txt b/Documentation/usb/gadget_serial.txt
index 815f5c2..9b22bd1 100644
--- a/Documentation/usb/gadget_serial.txt
+++ b/Documentation/usb/gadget_serial.txt
@@ -1,6 +1,7 @@
 
                  Linux Gadget Serial Driver v2.0
                            11/20/2004
+                  (updated 8-May-2008 for v2.3)
 
 
 License and Disclaimer
@@ -31,7 +32,7 @@ Prerequisites
 -------------
 Versions of the gadget serial driver are available for the
 2.4 Linux kernels, but this document assumes you are using
-version 2.0 or later of the gadget serial driver in a 2.6
+version 2.3 or later of the gadget serial driver in a 2.6
 Linux kernel.
 
 This document assumes that you are familiar with Linux and
@@ -40,6 +41,12 @@ standard utilities, use minicom and HyperTerminal, and work with
 USB and serial devices.  It also assumes you configure the Linux
 gadget and usb drivers as modules.
 
+With version 2.3 of the driver, major and minor device nodes are
+no longer statically defined.  Your Linux based system should mount
+sysfs in /sys, and use "mdev" (in Busybox) or "udev" to make the
+/dev nodes matching the sysfs /sys/class/tty files.
+
+
 
 Overview
 --------
@@ -104,15 +111,8 @@ driver.  All this are listed under "USB Gadget Support" when
 configuring the kernel.  Then rebuild and install the kernel or
 modules.
 
-The gadget serial driver uses major number 127, for now.  So you
-will need to create a device node for it, like this:
-
-  mknod /dev/ttygserial c 127 0
-
-You only need to do this once.
-
 Then you must load the gadget serial driver.  To load it as an
-ACM device, do this:
+ACM device (recommended for interoperability), do this:
 
   modprobe g_serial use_acm=1
 
@@ -125,6 +125,23 @@ controller driver.  This must be done each time you reboot the gadget
 side Linux system.  You can add this to the start up scripts, if
 desired.
 
+Your system should use mdev (from busybox) or udev to make the
+device nodes.  After this gadget driver has been set up you should
+then see a /dev/ttyGS0 node:
+
+  # ls -l /dev/ttyGS0 | cat
+  crw-rw----    1 root     root     253,   0 May  8 14:10 /dev/ttyGS0
+  #
+
+Note that the major number (253, above) is system-specific.  If
+you need to create /dev nodes by hand, the right numbers to use
+will be in the /sys/class/tty/ttyGS0/dev file.
+
+When you link this gadget driver early, perhaps even statically,
+you may want to set up an /etc/inittab entry to run "getty" on it.
+The /dev/ttyGS0 line should work like most any other serial port.
+
+
 If gadget serial is loaded as an ACM device you will want to use
 either the Windows or Linux ACM driver on the host side.  If gadget
 serial is loaded as a bulk in/out device, you will want to use the