docs: debugging-via-ohci1394.txt: add it to the core-api book

There is an special chapter inside the core-api book about
some debug infrastructure like tracepoints and debug objects.

It sounded to me that this is the best place to add a chapter
explaining how to use a FireWire controller to do remote
kernel debugging, as explained on this document.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/9b489d36d08ad89d3ad5aefef1f52a0715b29716.1588345503.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 185 deletions

diff --git a/Documentation/debugging-via-ohci1394.txt b/Documentation/debugging-via-ohci1394.txt
deleted file mode 100644
index 981ad4f89fd3..000000000000
--- a/Documentation/debugging-via-ohci1394.txt
+++ /dev/null
@@ -1,185 +0,0 @@
-===========================================================================
-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.
-
-With most FireWire controllers, memory access is limited to the low 4 GB
-of physical address space.  This 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 x86, x86-64 and PowerPC.
-
-At least LSI FW643e and FW643e2 controllers are known to support access to
-physical addresses above 4 GB, but this feature is currently not enabled by
-Linux.
-
-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 firewire-ohci driver in drivers/firewire uses filtered physical
-DMA by default, which is more secure but not suitable for remote debugging.
-Pass the remote_dma=1 parameter to the driver to get unfiltered physical DMA.
-
-Because the firewire-ohci driver depends on the PCI enumeration to be
-completed, an initialization routine which runs pretty early has been
-implemented for x86.  This routine runs long before console_init() can be
-called, i.e. before the printk buffer appears on the console.
-
-To activate it, enable CONFIG_PROVIDE_OHCI1394_DMA_INIT (Kernel hacking menu:
-Remote debugging 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:
-- http://v3.sk/~lkundrak/firescope/
-
-and he implemented fast system dump (alpha version - read README.txt):
-- http://halobates.de/firewire/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:
-- http://halobates.de/firewire/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 firewire-ohci module and check your kernel logs.
-   You should see a line similar to::
-
-     firewire_ohci 0000:15:00.1: added OHCI v1.0 device as card 2, 4 IR + 4 IT
-     ... contexts, quirks 0x11
-
-   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 Windows
-   operating systems.
-
-   The mentioned kernel log message contains the string "physUB" if the
-   controller implements a writable Physical Upper Bound register.  This is
-   required for physical DMA above 4 GB (but not utilized by Linux yet).
-
-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::
-
-     firewire_core 0000:15:00.1: created device fw1: GUID 00061b0020105917, S400
-
-   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, make sure that /dev/fw* is accessible,
-   then start firescope::
-
-	$ firescope
-	Port 0 (/dev/fw1) 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: http://halobates.de/firewire/
-
-FireWire is a trademark of Apple Inc. - for more information please refer to:
-https://en.wikipedia.org/wiki/FireWire