linux-kernel - [2.6.36-rc2 regression] X201s: resume-from-S2R hangs

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Date:	Mon, 6 Sep 2010 02:05:36 -0700
From:	Andy Isaacson <adi@...apodia.org>
To:	linux-kernel@...r.kernel.org
Cc:	Zou Nan hai <nanhai.zou@...el.com>, Eric Anholt <eric@...olt.net>
Subject: [2.6.36-rc2 regression] X201s: resume-from-S2R hangs

I have a Thinkpad X201s on which suspend-to-RAM was quite reliable until
after 2.6.36-rc1; with problematic kernels, suspend seems to work OK
(the machine goes to sleep with the moon LED steadily lit) but on resume
the LCD never lights up (and it's not just the backlight, the screen
isn't drawing at all) and the keyboard and network are dead.  Nothing
makes it to syslog, either.  The moon LED is turned off though.

There seems to be some timing component to the problem -- some problem
kernels will suspend reliably 25% or 50% of the time and hang the rest.
There also seems to be some per-reboot state involved; one problem
kernel suspended successfully and survived 25 suspends in a row without
triggering a failure.  (But after a reboot, the first suspend hung...)
Other problem kernels fail on 4 out of 4 reboots.

Bisecting is pretty hard under these conditions, but it seems to point
to

commit ce17178094f368d9e3f39b2cb4303da5ed633dd4
Author: Zou Nan hai <nanhai.zou@...el.com>
Date:   Fri Jun 25 13:40:22 2010 +0800

    drm/i915: Enable RC6 on Ironlake.

    RC6 allows the GPU to enter a lower power state when the GPU is idle.

    Signed-off-by: Zou Nan hai <nanhai.zou@...el.com>
    [anholt: Fixed the !renderctx error path to actually not enable RC6.]
    Signed-off-by: Eric Anholt <eric@...olt.net>

Reverting that commit on top of -rc3 seems to fix the problem -- three
reboots so far, no failures yet.

The machine has a "Core(TM) i7 CPU L 640", 4GB of RAM, and BIOS 1.05.
I've attached lspci and dmesg.gz from a successful boot + S2R.

-andy

View attachment "lspci.txt" of type "text/plain" (6189 bytes)

Download attachment "dmesg.gz" of type "application/octet-stream" (16815 bytes)

Download attachment "config.gz" of type "application/octet-stream" (18985 bytes)