Undo a feature introduced in v3.14 by commit fcd46b34
"firewire: Enable remote DMA above 4 GB".  That change raised the
minimum address at which protocol drivers and user programs can register
for request reception from 0x0001'0000'0000 to 0x8000'0000'0000.
It turned out that at least one vendor-specific protocol exists which
uses lower addresses:  https://bugzilla.kernel.org/show_bug.cgi?id=76921

For the time being, revert most of commit fcd46b34 so that affected
protocols work like with kernel v3.13 and before.  Just keep the valid
documentation parts from the regressing commit, and the ability to
identify controllers which could be programmed to accept >32 bit
physical DMA addresses.  The rest of fcd46b34 should probably be
brought back as an optional instead of default feature.
Reported-by: NFabien Spindler <fabien.spindler@inria.fr>
Cc: <stable@vger.kernel.org> # 3.14+
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

This makes all of a machine's memory accessible to remote debugging via
FireWire, using the physical response unit (i.e. RDMA) of OHCI-1394 link
layer controllers.

This requires actual support by the controller.  The only ones currently
known to support it are Agere/LSI FW643.  Most if not all other OHCI-1394
controllers do not implement the optional Physical Upper Bound register.
With them, RDMA will continue to be limited to the lowermost 4 GB.

firewire-ohci's startup message in the kernel log is augmented to tell
whether the controller does expose more than 4 GB to RDMA.

While OHCI-1394 allows for a maximum Physical Upper Bound of
0xffff'0000'0000 (near 256 TB), this implementation sets it to
0x8000'0000'0000 (128 TB) in order to avoid interference with applications
that require interrupt-served asynchronous request reception at
respectively low addresses.

Note, this change does not switch remote DMA on.  It only increases the
range of remote access to all memory (instead of just 4 GB) whenever
remote DMA was switched on by other means.  The latter is achieved by
setting firewire-ohci's remote_dma parameter, or if the physical DMA
filter is opened through firewire-sbp2.

Derived from patch "firewire: Enable physical DMA above 4GB" by
Peter Hurley <peter@hurleysoftware.com> from March 27, 2013.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

This makes it possible to debug kernel over FireWire without the need to
recompile it.

[Stefan R: changed description from "...0" to "...N"]

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: NLubomir Rintel <lkundrak@v3.sk>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

The old firewire stack is long dead now and a new version firescope has
been released with support for current kernels.
Signed-off-by: NLubomir Rintel <lkundrak@v3.sk>
Cc: Rob Landley <rob@landley.net>
Cc: Justin P. Mattock <justinmattock@gmail.com>
Cc: Bernhard Kaindl <bk@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

Update URLs of the userspace tools to use ohci1394_dma=early for
debugging.

Seems the address ftp://ftp.suse.de/private/bk/firewire/tools/* is not
very helpful.  After a quick search, seems this was talked about:
http://www.mail-archive.com/kgdb-bugreport@lists.sourceforge.net/msg02761.html
(can't find the original thread).
Signed-off-by: NJustin P. Mattock <justinmattock@gmail.com>
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

This way firewire-ohci can be used for remote debugging like ohci1394.
Version with amendment from Fri, 11 Apr 2008 00:08:08 +0200.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: NBernhard Kaindl <bk@suse.de>

Rectify a factoid about firewire-ohci.
Acked-by: NIngo Molnar <mingo@elte.hu>

Also fix a typo spotted by Bernhard Kaindl.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>

This patch adds a new configuration option, which adds support for a new
early_param which gets checked in arch/x86/kernel/setup_{32,64}.c:setup_arch()
to decide wether OHCI-1394 FireWire controllers should be initialized and
enabled for physical DMA access to allow remote debugging of early problems
like issues ACPI or other subsystems which are executed very early.

If the config option is not enabled, no code is changed, and if the boot
paramenter is not given, no new code is executed, and independent of that,
all new code is freed after boot, so the config option can be even enabled
in standard, non-debug kernels.

With specialized tools, it is then possible to get debugging information
from machines which have no serial ports (notebooks) such as the printk
buffer contents, or any data which can be referenced from global pointers,
if it is stored below the 4GB limit and even memory dumps of of the physical
RAM region below the 4GB limit can be taken without any cooperation from the
CPU of the host, so the machine can be crashed early, it does not matter.

In the extreme, even kernel debuggers can be accessed in this way. I wrote
a small kgdb module and an accompanying gdb stub for FireWire which allows
to gdb to talk to kgdb using remote remory reads and writes over FireWire.

An version of the gdb stub fore FireWire is able to read all global data
from a system which is running a a normal kernel without any kernel debugger,
without any interruption or support of the system's CPU. That way, e.g. the
task struct and so on can be read and even manipulated when the physical DMA
access is granted.

A HOWTO is included in this patch, in Documentation/debugging-via-ohci1394.txt
and I've put a copy online at
ftp://ftp.suse.de/private/bk/firewire/docs/debugging-via-ohci1394.txt

It also has links to all the tools which are available to make use of it
another copy of it is online at:
ftp://ftp.suse.de/private/bk/firewire/kernel/ohci1394_dma_early-v2.diffSigned-Off-By: NBernhard Kaindl <bk@suse.de>
Tested-By: NThomas Renninger <trenn@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>