Date:	Fri, 26 Nov 2010 14:34:39 +0100
From:	Zdenek Kabelac <zkabelac@...hat.com>
To:	Florian Mickler <florian@...kler.org>
CC:	Chris Vine <chris@...ne.freeserve.co.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Chris Wilson <chris@...is-wilson.co.uk>
Subject: Re: kernel 2.6.37-rc2 breaks i915 graphics

Dne 26.11.2010 10:23, Florian Mickler napsal(a):
> On Sun, 21 Nov 2010 18:34:23 +0000
> Chris Vine <chris@...ne.freeserve.co.uk> wrote:
> 
>> On Sun, 21 Nov 2010 10:30:43 +0000
>> Chris Wilson <chris@...is-wilson.co.uk> wrote:
>>
>>> On Sun, 21 Nov 2010 10:23:44 +0000, Chris Vine
>>> <chris@...ne.freeserve.co.uk> wrote:
>>>> Hi,
>>>>
>>>> With kernel 2.6.37-rc2, i915 graphics usually fails on boot-up after
>>>> modesetting with my Lenovo S12 netbook which uses the Intel 945GME
>>>> Express Integrated Graphics Controller.  It displays up to the
>>>> point at which modesetting takes place and then usually goes blank.
>>>>
>>>> There may be some kind of race at work here: first, sometimes
>>>> (maybe 1 times in 4) graphics comes up correctly on a first cold
>>>> boot, but I have never managed to get it to come up on a warm
>>>> reboot. Secondly, graphics can be restored when I know (but cannot
>>>> see) that boot-up has concluded, simply by suspending the laptop
>>>> and then resuming.  Resuming the laptop after a suspend always
>>>> brings up the graphics correctly.
>>>
>>> Add drm.debug=0xe to your boot commandline and compare if there is any
>>> difference between a successful cold boot, a broken cold boot and a
>>> warm boot. Similarly, comparing the output of intel_reg_dumper after
>>> each should yield a few clues as to what stage in the boot process we
>>> fail. -Chris
>>
>> First an additional datum point: 2.6.37-rc1 works normally, so the bug
>> is something introduced between 2.6.37-rc1 and 2.6.37-rc2 (to that
>> extent it may be related to this bug which reports a similar phenomenon:
>> http://lkml.org/lkml/2010/11/21/23 ).
>>
>> Attached is the dmesg output from a successful cold boot with
>> 2.6.37-rc2, an unsuccessful cold boot and an unsuccessful warm boot,
>> each with drm.debug=0xe.
>>
> 
> I trimmed the failure boot logs to the stuff before suspending, in
> order to only compare the boot sequence. 
> 
> Looks like only in failure case there are "pipe b
> underrun" reported...
> In success case, no "pipe b underrun" is reported. 
> 
> Also in success case connectors are probed much more often:
> 
> $ grep drm:drm_helper_probe_single_connector_modes dmesg-2.6.37-rc2.succeed  | wc -l
> 76
> $ grep drm:drm_helper_probe_single_connector_modes dmesg-2.6.37-rc2.*.fail  | wc -l
> 32
> $ grep drm:drm_helper_probe_single_connector_modes dmesg-2.6.37-rc2.cold.fail  | wc -l
> 16
> 
> 
> I could not spot any other differences both failure modes have in common against the success case.
> 
> If Chris (Wilson) doesn't yet know what could be the bug a bisection 
> between 2.6.37-rc1 and rc2 might be helpful. 
> 
>  
>> I can't provide the output of intel_reg_dumper:  I can't compile the
>> latest intel-gpu-tools from git (missing declaration/definition of
>> I915_EXE_BLT).  Probably something in a relevant library is too old.
>>

Reminds me - I need to keep drm_kms_helper disabled for reliable
resume on T61:

https://bugzilla.kernel.org/show_bug.cgi?id=19052
https://bugzilla.redhat.com/show_bug.cgi?id=617809

Zdenek

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