diff options
| -rw-r--r-- | Documentation/debugging-via-ohci1394.txt | 179 | ||||
| -rw-r--r-- | arch/x86/kernel/setup_32.c | 11 | ||||
| -rw-r--r-- | arch/x86/kernel/setup_64.c | 11 | ||||
| -rw-r--r-- | drivers/Makefile | 2 | ||||
| -rw-r--r-- | drivers/ieee1394/Makefile | 1 | ||||
| -rw-r--r-- | drivers/ieee1394/init_ohci1394_dma.c | 285 | ||||
| -rw-r--r-- | include/asm-x86/fixmap_32.h | 3 | ||||
| -rw-r--r-- | include/asm-x86/fixmap_64.h | 3 | ||||
| -rw-r--r-- | include/linux/init_ohci1394_dma.h | 4 | ||||
| -rw-r--r-- | lib/Kconfig.debug | 28 |
10 files changed, 526 insertions, 1 deletions
diff --git a/Documentation/debugging-via-ohci1394.txt b/Documentation/debugging-via-ohci1394.txt new file mode 100644 index 0000000..de4804e --- /dev/null +++ b/Documentation/debugging-via-ohci1394.txt @@ -0,0 +1,179 @@ + + Using physical DMA provided by OHCI-1394 FireWire controllers for debugging + --------------------------------------------------------------------------- + +Introduction +------------ + +Basically all FireWire controllers which are in use today are compliant +to the OHCI-1394 specification which defines the controller to be a PCI +bus master which uses DMA to offload data transfers from the CPU and has +a "Physical Response Unit" which executes specific requests by employing +PCI-Bus master DMA after applying filters defined by the OHCI-1394 driver. + +Once properly configured, remote machines can send these requests to +ask the OHCI-1394 controller to perform read and write requests on +physical system memory and, for read requests, send the result of +the physical memory read back to the requester. + +With that, it is possible to debug issues by reading interesting memory +locations such as buffers like the printk buffer or the process table. + +Retrieving a full system memory dump is also possible over the FireWire, +using data transfer rates in the order of 10MB/s or more. + +Memory access is currently limited to the low 4G of physical address +space which can be a problem on IA64 machines where memory is located +mostly above that limit, but it is rarely a problem on more common +hardware such as hardware based on x86, x86-64 and PowerPC. + +Together with a early initialization of the OHCI-1394 controller for debugging, +this facility proved most useful for examining long debugs logs in the printk +buffer on to debug early boot problems in areas like ACPI where the system +fails to boot and other means for debugging (serial port) are either not +available (notebooks) or too slow for extensive debug information (like ACPI). + +Drivers +------- + +The OHCI-1394 drivers in drivers/firewire and drivers/ieee1394 initialize +the OHCI-1394 controllers to a working state and can be used to enable +physical DMA. By default you only have to load the driver, and physical +DMA access will be granted to all remote nodes, but it can be turned off +when using the ohci1394 driver. + +Because these drivers depend on the PCI enumeration to be completed, an +initialization routine which can runs pretty early (long before console_init(), +which makes the printk buffer appear on the console can be called) was written. + +To activate it, enable CONFIG_PROVIDE_OHCI1394_DMA_INIT (Kernel hacking menu: +Provide code for enabling DMA over FireWire early on boot) and pass the +parameter "ohci1394_dma=early" to the recompiled kernel on boot. + +Tools +----- + +firescope - Originally developed by Benjamin Herrenschmidt, Andi Kleen ported +it from PowerPC to x86 and x86_64 and added functionality, firescope can now +be used to view the printk buffer of a remote machine, even with live update. + +Bernhard Kaindl enhanced firescope to support accessing 64-bit machines +from 32-bit firescope and vice versa: +- ftp://ftp.suse.de/private/bk/firewire/tools/firescope-0.2.2.tar.bz2 + +and he implemented fast system dump (alpha version - read README.txt): +- ftp://ftp.suse.de/private/bk/firewire/tools/firedump-0.1.tar.bz2 + +There is also a gdb proxy for firewire which allows to use gdb to access +data which can be referenced from symbols found by gdb in vmlinux: +- ftp://ftp.suse.de/private/bk/firewire/tools/fireproxy-0.33.tar.bz2 + +The latest version of this gdb proxy (fireproxy-0.34) can communicate (not +yet stable) with kgdb over an memory-based communication module (kgdbom). + +Getting Started +--------------- + +The OHCI-1394 specification regulates that the OHCI-1394 controller must +disable all physical DMA on each bus reset. + +This means that if you want to debug an issue in a system state where +interrupts are disabled and where no polling of the OHCI-1394 controller +for bus resets takes place, you have to establish any FireWire cable +connections and fully initialize all FireWire hardware __before__ the +system enters such state. + +Step-by-step instructions for using firescope with early OHCI initialization: + +1) Verify that your hardware is supported: + + Load the ohci1394 or the fw-ohci module and check your kernel logs. + You should see a line similar to + + ohci1394: fw-host0: OHCI-1394 1.1 (PCI): IRQ=[18] MMIO=[fe9ff800-fe9fffff] + ... Max Packet=[2048] IR/IT contexts=[4/8] + + when loading the driver. If you have no supported controller, many PCI, + CardBus and even some Express cards which are fully compliant to OHCI-1394 + specification are available. If it requires no driver for Windows operating + systems, it most likely is. Only specialized shops have cards which are not + compliant, they are based on TI PCILynx chips and require drivers for Win- + dows operating systems. + +2) Establish a working FireWire cable connection: + + Any FireWire cable, as long at it provides electrically and mechanically + stable connection and has matching connectors (there are small 4-pin and + large 6-pin FireWire ports) will do. + + If an driver is running on both machines you should see a line like + + ieee1394: Node added: ID:BUS[0-01:1023] GUID[0090270001b84bba] + + on both machines in the kernel log when the cable is plugged in + and connects the two machines. + +3) Test physical DMA using firescope: + + On the debug host, + - load the raw1394 module, + - make sure that /dev/raw1394 is accessible, + then start firescope: + + $ firescope + Port 0 (ohci1394) opened, 2 nodes detected + + FireScope + --------- + Target : <unspecified> + Gen : 1 + [Ctrl-T] choose target + [Ctrl-H] this menu + [Ctrl-Q] quit + + ------> Press Ctrl-T now, the output should be similar to: + + 2 nodes available, local node is: 0 + 0: ffc0, uuid: 00000000 00000000 [LOCAL] + 1: ffc1, uuid: 00279000 ba4bb801 + + Besides the [LOCAL] node, it must show another node without error message. + +4) Prepare for debugging with early OHCI-1394 initialization: + + 4.1) Kernel compilation and installation on debug target + + Compile the kernel to be debugged with CONFIG_PROVIDE_OHCI1394_DMA_INIT + (Kernel hacking: Provide code for enabling DMA over FireWire early on boot) + enabled and install it on the machine to be debugged (debug target). + + 4.2) Transfer the System.map of the debugged kernel to the debug host + + Copy the System.map of the kernel be debugged to the debug host (the host + which is connected to the debugged machine over the FireWire cable). + +5) Retrieving the printk buffer contents: + + With the FireWire cable connected, the OHCI-1394 driver on the debugging + host loaded, reboot the debugged machine, booting the kernel which has + CONFIG_PROVIDE_OHCI1394_DMA_INIT enabled, with the option ohci1394_dma=early. + + Then, on the debugging host, run firescope, for example by using -A: + + firescope -A System.map-of-debug-target-kernel + + Note: -A automatically attaches to the first non-local node. It only works + reliably if only connected two machines are connected using FireWire. + + After having attached to the debug target, press Ctrl-D to view the + complete printk buffer or Ctrl-U to enter auto update mode and get an + updated live view of recent kernel messages logged on the debug target. + + Call "firescope -h" to get more information on firescope's options. + +Notes +----- +Documentation and specifications: ftp://ftp.suse.de/private/bk/firewire/docs + +FireWire is a trademark of Apple Inc. - for more information please refer to: +http://en.wikipedia.org/wiki/FireWire diff --git a/arch/x86/kernel/setup_32.c b/arch/x86/kernel/setup_32.c index 9c0ef49..62adc5f 100644 --- a/arch/x86/kernel/setup_32.c +++ b/arch/x86/kernel/setup_32.c @@ -45,6 +45,7 @@ #include <linux/dmi.h> #include <linux/pfn.h> #include <linux/pci.h> +#include <linux/init_ohci1394_dma.h> #include <video/edid.h> @@ -787,6 +788,16 @@ void __init setup_arch(char **cmdline_p) smp_alloc_memory(); /* AP processor realmode stacks in low memory*/ #endif paging_init(); + + /* + * NOTE: On x86-32, only from this point on, fixmaps are ready for use. + */ + +#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT + if (init_ohci1394_dma_early) + init_ohci1394_dma_on_all_controllers(); +#endif + remapped_pgdat_init(); sparse_init(); zone_sizes_init(); diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c index 697533e..77fb87b 100644 --- a/arch/x86/kernel/setup_64.c +++ b/arch/x86/kernel/setup_64.c @@ -41,6 +41,7 @@ #include <linux/dma-mapping.h> #include <linux/ctype.h> #include <linux/uaccess.h> +#include <linux/init_ohci1394_dma.h> #include <asm/mtrr.h> #include <asm/uaccess.h> @@ -253,6 +254,11 @@ void __attribute__((weak)) __init memory_setup(void) machine_specific_memory_setup(); } +/* + * setup_arch - architecture-specific boot-time initializations + * + * Note: On x86_64, fixmaps are ready for use even before this is called. + */ void __init setup_arch(char **cmdline_p) { unsigned i; @@ -302,6 +308,11 @@ void __init setup_arch(char **cmdline_p) parse_early_param(); +#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT + if (init_ohci1394_dma_early) + init_ohci1394_dma_on_all_controllers(); +#endif + finish_e820_parsing(); early_gart_iommu_check(); diff --git a/drivers/Makefile b/drivers/Makefile index 8cb37e3..d92d4d8 100644 --- a/drivers/Makefile +++ b/drivers/Makefile @@ -38,7 +38,7 @@ obj-$(CONFIG_SCSI) += scsi/ obj-$(CONFIG_ATA) += ata/ obj-$(CONFIG_FUSION) += message/ obj-$(CONFIG_FIREWIRE) += firewire/ -obj-$(CONFIG_IEEE1394) += ieee1394/ +obj-y += ieee1394/ obj-$(CONFIG_UIO) += uio/ obj-y += cdrom/ obj-y += auxdisplay/ diff --git a/drivers/ieee1394/Makefile b/drivers/ieee1394/Makefile index 489c133..1f8153b 100644 --- a/drivers/ieee1394/Makefile +++ b/drivers/ieee1394/Makefile @@ -15,3 +15,4 @@ obj-$(CONFIG_IEEE1394_SBP2) += sbp2.o obj-$(CONFIG_IEEE1394_DV1394) += dv1394.o obj-$(CONFIG_IEEE1394_ETH1394) += eth1394.o +obj-$(CONFIG_PROVIDE_OHCI1394_DMA_INIT) += init_ohci1394_dma.o diff --git a/drivers/ieee1394/init_ohci1394_dma.c b/drivers/ieee1394/init_ohci1394_dma.c new file mode 100644 index 0000000..ddaab6e --- /dev/null +++ b/drivers/ieee1394/init_ohci1394_dma.c @@ -0,0 +1,285 @@ +/* + * init_ohci1394_dma.c - Initializes physical DMA on all OHCI 1394 controllers + * + * Copyright (C) 2006-2007 Bernhard Kaindl <bk@suse.de> + * + * Derived from drivers/ieee1394/ohci1394.c and arch/x86/kernel/early-quirks.c + * this file has functions to: + * - scan the PCI very early on boot for all OHCI 1394-compliant controllers + * - reset and initialize them and make them join the IEEE1394 bus and + * - enable physical DMA on them to allow remote debugging + * + * All code and data is marked as __init and __initdata, respective as + * during boot, all OHCI1394 controllers may be claimed by the firewire + * stack and at this point, this code should not touch them anymore. + * + * To use physical DMA after the initialization of the firewire stack, + * be sure that the stack enables it and (re-)attach after the bus reset + * which may be caused by the firewire stack initialization. + * + * 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/interrupt.h> /* for ohci1394.h */ +#include <linux/delay.h> +#include <linux/pci.h> /* for PCI defines */ +#include <linux/init_ohci1394_dma.h> +#include <asm/pci-direct.h> /* for direct PCI config space access */ +#include <asm/fixmap.h> + +#include "ieee1394_types.h" +#include "ohci1394.h" + +int __initdata init_ohci1394_dma_early; + +/* Reads a PHY register of an OHCI-1394 controller */ +static inline u8 __init get_phy_reg(struct ti_ohci *ohci, u8 addr) +{ + int i; + quadlet_t r; + + reg_write(ohci, OHCI1394_PhyControl, (addr << 8) | 0x00008000); + + for (i = 0; i < OHCI_LOOP_COUNT; i++) { + if (reg_read(ohci, OHCI1394_PhyControl) & 0x80000000) + break; + mdelay(1); + } + r = reg_read(ohci, OHCI1394_PhyControl); + + return (r & 0x00ff0000) >> 16; +} + +/* Writes to a PHY register of an OHCI-1394 controller */ +static inline void __init set_phy_reg(struct ti_ohci *ohci, u8 addr, u8 data) +{ + int i; + + reg_write(ohci, OHCI1394_PhyControl, (addr << 8) | data | 0x00004000); + + for (i = 0; i < OHCI_LOOP_COUNT; i++) { + u32 r = reg_read(ohci, OHCI1394_PhyControl); + if (!(r & 0x00004000)) + break; + mdelay(1); + } +} + +/* Resets an OHCI-1394 controller (for sane state before initialization) */ +static inline void __init init_ohci1394_soft_reset(struct ti_ohci *ohci) { + int i; + + reg_write(ohci, OHCI1394_HCControlSet, OHCI1394_HCControl_softReset); + + for (i = 0; i < OHCI_LOOP_COUNT; i++) { + if (!(reg_read(ohci, OHCI1394_HCControlSet) + & OHCI1394_HCControl_softReset)) + break; + mdelay(1); + } +} + +/* Basic OHCI-1394 register and port inititalization */ +static inline void __init init_ohci1394_initialize(struct ti_ohci *ohci) +{ + quadlet_t bus_options; + int num_ports, i; + + /* Put some defaults to these undefined bus options */ + bus_options = reg_read(ohci, OHCI1394_BusOptions); + bus_options |= 0x60000000; /* Enable CMC and ISC */ + bus_options &= ~0x00ff0000; /* XXX: Set cyc_clk_acc to zero for now */ + bus_options &= ~0x18000000; /* Disable PMC and BMC */ + reg_write(ohci, OHCI1394_BusOptions, bus_options); + + /* Set the bus number */ + reg_write(ohci, OHCI1394_NodeID, 0x0000ffc0); + + /* Enable posted writes */ + reg_write(ohci, OHCI1394_HCControlSet, + OHCI1394_HCControl_postedWriteEnable); + + /* Clear link control register */ + reg_write(ohci, OHCI1394_LinkControlClear, 0xffffffff); + + /* enable phys */ + reg_write(ohci, OHCI1394_LinkControlSet, + OHCI1394_LinkControl_RcvPhyPkt); + + /* Don't accept phy packets into AR request context */ + reg_write(ohci, OHCI1394_LinkControlClear, 0x00000400); + + /* Clear the Isochonouys interrupt masks */ + reg_write(ohci, OHCI1394_IsoRecvIntMaskClear, 0xffffffff); + reg_write(ohci, OHCI1394_IsoRecvIntEventClear, 0xffffffff); + reg_write(ohci, OHCI1394_IsoXmitIntMaskClear, 0xffffffff); + reg_write(ohci, OHCI1394_IsoXmitIntEventClear, 0xffffffff); + + /* Accept asyncronous transfer requests from all nodes for now */ + reg_write(ohci,OHCI1394_AsReqFilterHiSet, 0x80000000); + + /* Specify asyncronous transfer retries */ + reg_write(ohci, OHCI1394_ATRetries, + OHCI1394_MAX_AT_REQ_RETRIES | + (OHCI1394_MAX_AT_RESP_RETRIES<<4) | + (OHCI1394_MAX_PHYS_RESP_RETRIES<<8)); + + /* We don't want hardware swapping */ + reg_write(ohci, OHCI1394_HCControlClear, OHCI1394_HCControl_noByteSwap); + + /* Enable link */ + reg_write(ohci, OHCI1394_HCControlSet, OHCI1394_HCControl_linkEnable); + + /* If anything is connected to a port, make sure it is enabled */ + num_ports = get_phy_reg(ohci, 2) & 0xf; + for (i = 0; i < num_ports; i++) { + unsigned int status; + + set_phy_reg(ohci, 7, i); + status = get_phy_reg(ohci, 8); + + if (status & 0x20) + set_phy_reg(ohci, 8, status & ~1); + } +} + +/** + * init_ohci1394_wait_for_busresets - wait until bus resets are completed + * + * OHCI1394 initialization itself and any device going on- or offline + * and any cable issue cause a IEEE1394 bus reset. The OHCI1394 spec + * specifies that physical DMA is disabled on each bus reset and it + * has to be enabled after each bus reset when needed. We resort + * to polling here because on early boot, we have no interrupts. + */ +static inline void __init init_ohci1394_wait_for_busresets(struct ti_ohci *ohci) +{ + int i, events; + + for (i=0; i < 9; i++) { + mdelay(200); + events = reg_read(ohci, OHCI1394_IntEventSet); + if (events & OHCI1394_busReset) + reg_write(ohci, OHCI1394_IntEventClear, + OHCI1394_busReset); + } +} + +/** + * init_ohci1394_enable_physical_dma - Enable physical DMA for remote debugging + * This enables remote DMA access over IEEE1394 from every host for the low + * 4GB of address space. DMA accesses above 4GB are not available currently. + */ +static inline void __init init_ohci1394_enable_physical_dma(struct ti_ohci *hci) +{ + reg_write(hci, OHCI1394_PhyReqFilterHiSet, 0xffffffff); + reg_write(hci, OHCI1394_PhyReqFilterLoSet, 0xffffffff); + reg_write(hci, OHCI1394_PhyUpperBound, 0xffff0000); +} + +/** + * init_ohci1394_reset_and_init_dma - init controller and enable DMA + * This initializes the given controller and enables physical DMA engine in it. + */ +static inline void __init init_ohci1394_reset_and_init_dma(struct ti_ohci *ohci) +{ + /* Start off with a soft reset, clears everything to a sane state. */ + init_ohci1394_soft_reset(ohci); + + /* Accessing some registers without LPS enabled may cause lock up */ + reg_write(ohci, OHCI1394_HCControlSet, OHCI1394_HCControl_LPS); + + /* Disable and clear interrupts */ + reg_write(ohci, OHCI1394_IntEventClear, 0xffffffff); + reg_write(ohci, OHCI1394_IntMaskClear, 0xffffffff); + + mdelay(50); /* Wait 50msec to make sure we have full link enabled */ + + init_ohci1394_initialize(ohci); + /* + * The initialization causes at least one IEEE1394 bus reset. Enabling + * physical DMA only works *after* *all* bus resets have calmed down: + */ + init_ohci1394_wait_for_busresets(ohci); + + /* We had to wait and do this now if we want to debug early problems */ + init_ohci1394_enable_physical_dma(ohci); +} + +/** + * init_ohci1394_controller - Map the registers of the controller and init DMA + * This maps the registers of the specified controller and initializes it + */ +static inline void __init init_ohci1394_controller(int num, int slot, int func) +{ + unsigned long ohci_base; + struct ti_ohci ohci; + + printk(KERN_INFO "init_ohci1394_dma: initializing OHCI-1394" + " at %02x:%02x.%x\n", num, slot, func); + + ohci_base = read_pci_config(num, slot, func, PCI_BASE_ADDRESS_0+(0<<2)) + & PCI_BASE_ADDRESS_MEM_MASK; + + set_fixmap_nocache(FIX_OHCI1394_BASE, ohci_base); + + ohci.registers = (void *)fix_to_virt(FIX_OHCI1394_BASE); + + init_ohci1394_reset_and_init_dma(&ohci); +} + +/** + * debug_init_ohci1394_dma - scan for OHCI1394 controllers and init DMA on them + * Scans the whole PCI space for OHCI1394 controllers and inits DMA on them + */ +void __init init_ohci1394_dma_on_all_controllers(void) +{ + int num, slot, func; + + if (!early_pci_allowed()) + return; + + /* Poor man's PCI discovery, the only thing we can do at early boot */ + for (num = 0; num < 32; num++) { + for (slot = 0; slot < 32; slot++) { + for (func = 0; func < 8; func++) { + u32 class = read_pci_config(num,slot,func, + PCI_CLASS_REVISION); + if ((class == 0xffffffff)) + continue; /* No device at this func */ + + if (class>>8 != PCI_CLASS_SERIAL_FIREWIRE_OHCI) + continue; /* Not an OHCI-1394 device */ + + init_ohci1394_controller(num, slot, func); + break; /* Assume one controller per device */ + } + } + } + printk(KERN_INFO "init_ohci1394_dma: finished initializing OHCI DMA\n"); +} + +/** + * setup_init_ohci1394_early - enables early OHCI1394 DMA initialization + */ +static int __init setup_ohci1394_dma(char *opt) +{ + if (!strcmp(opt, "early")) + init_ohci1394_dma_early = 1; + return 0; +} + +/* passing ohci1394_dma=early on boot causes early OHCI1394 DMA initialization */ +early_param("ohci1394_dma", setup_ohci1394_dma); diff --git a/include/asm-x86/fixmap_32.h b/include/asm-x86/fixmap_32.h index fde140f..a7404d5 100644 --- a/include/asm-x86/fixmap_32.h +++ b/include/asm-x86/fixmap_32.h @@ -104,6 +104,9 @@ enum fixed_addresses { (__end_of_permanent_fixed_addresses & 511), FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_NESTING - 1, FIX_WP_TEST, +#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT + FIX_OHCI1394_BASE, +#endif __end_of_fixed_addresses }; diff --git a/include/asm-x86/fixmap_64.h b/include/asm-x86/fixmap_64.h index 8f44782..70ddb21 100644 --- a/include/asm-x86/fixmap_64.h +++ b/include/asm-x86/fixmap_64.h @@ -44,6 +44,9 @@ enum fixed_addresses { FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS-1, FIX_EFI_IO_MAP_LAST_PAGE, FIX_EFI_IO_MAP_FIRST_PAGE = FIX_EFI_IO_MAP_LAST_PAGE+MAX_EFI_IO_PAGES-1, +#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT + FIX_OHCI1394_BASE, +#endif __end_of_fixed_addresses }; diff --git a/include/linux/init_ohci1394_dma.h b/include/linux/init_ohci1394_dma.h new file mode 100644 index 0000000..3c03a4b --- /dev/null +++ b/include/linux/init_ohci1394_dma.h @@ -0,0 +1,4 @@ +#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT +extern int __initdata init_ohci1394_dma_early; +extern void __init init_ohci1394_dma_on_all_controllers(void); +#endif diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index aa56e63..89f4035 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -586,5 +586,33 @@ config LATENCYTOP Enable this option if you want to use the LatencyTOP tool to find out which userspace is blocking on what kernel operations. +config PROVIDE_OHCI1394_DMA_INIT + bool "Provide code for enabling DMA over FireWire early on boot" + depends on PCI && X86 + help + If you want to debug problems which hang or crash the kernel early + on boot and the crashing machine has a FireWire port, you can use + this feature to remotely access the memory of the crashed machine + over FireWire. This employs remote DMA as part of the OHCI1394 + specification which is now the standard for FireWire controllers. + + With remote DMA, you can monitor the printk buffer remotely using + firescope and access all memory below 4GB using fireproxy from gdb. + Even controlling a kernel debugger is possible using remote DMA. + + Usage: + + If ohci1394_dma=early is used as boot parameter, it will initialize + all OHCI1394 controllers which are found in the PCI config space. + + As all changes to the FireWire bus such as enabling and disabling + devices cause a bus reset and thereby disable remote DMA for all + devices, be sure to have the cable plugged and FireWire enabled on + the debugging host before booting the debug target for debugging. + + This code (~1k) is freed after boot. By then, the firewire stack + in charge of the OHCI-1394 controllers should be used instead. + + See Documentation/debugging-via-ohci1394.txt for more information. source "samples/Kconfig" |
