Bug#588601: Bug#: 588601, 588602: xpress 200m 5955 => resume from suspend fails with KMS enabled

[Andres Cimmarusti]

I dedicated a large portion of the day to finding a clue to this one.
Following this advice:
http://lxr.linux.no/#linux+v2.6.34.1/Documentation/power/s2ram.txt
I was able to extract a trace from the failed resume process:

Magic number: 0:981:799
hash matches drivers/base/power/main.c:523
pci 0000:01:05.0: hash matches
ec PNP0C09:00: hash matches

The first hash match is none other than my ATI Radeon card as I easily
verified with lspci:

01:05.0 VGA compatible controller: ATI Technologies Inc Radeon XPRESS 200M
5955 (PCIE)

However, the above link says that the likely culprit in the failed resume
process is the last hash match. This corresponds to the EC driver:
http://lxr.free-electrons.com/source/drivers/acpi/ec.c

My card was, till recently, listed under embedded graphics at the AMD/ATI
website. So there appears to be some conflict when using KMS between radeon
and ec that causes the kernel to hang (that explains why I can't ssh into my
computer to get a trace). For this reason I've cloned the original bug and
reported the copy as a kernel bug.
I will try to delve deeper into the matter by activating more verbose
debugging symbols for acpi.

I would appreciate some advice and guidance, since I'm flying half-blind (I
will try to follow the information present here
http://ubuntuforums.org/showthread.php?t=505890)

Cheers,

Andres
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