[Intel-gfx] i915 / 3.15 intermittently boots into blank screeen

[Daniel Vetter]

On Tue, Jul 29, 2014 at 11:09 PM, Jan Niggemann <jn at hz6.de> wrote:
> Am 18.07.2014 18:25, schrieb Daniel Vetter:
>>
>> On Fri, Jul 18, 2014 at 4:49 PM, Jan Niggemann <jn at hz6.de> wrote:
>>
>>>
>>> Am 18.07.2014 15:27, schrieb Daniel Vetter:
>>>>
>>>>
>>>> On Thu, Jul 17, 2014 at 10:31:30PM +0200, Jan Niggemann wrote:
>>>>>
>>>>>
>>>>> I'm experiencing an issue with 3.15.5 on my Lenovo T400:
>>>>> Since 3.15 (or 3.14, can't say for sure), the boot starts normally, but
>>>>> the
>>>>> first mode change doesn't occur, resulting in a black screen with
>>>>> backlight
>>>>> on. The system is entirely unresponsive and I can only press the power
>>>>> button until to switch it off.
>>>>
>>>>
>>>> I think the only way to move forward here is to double-check that 3.14
>>>>
>>>> works and 3.15 is broken by recompiling with the same .config
>>>> (occasionally config changes cause regressions). And then do a full git
>>>> bisect to find the offending commit.
>>>
>>>
>>> thank you for the feedback.
>>> I still have all my custom built kernels, I will test 3.14.0 through
>>> 3.14.8
>>> to make sure those were OK and report back.
>>
>>
>> You only need to test 3.14.0, since the backported fixes only contain
>> a very small subset of all patches for 3.15. So it's more efficient to
>> then switch to git bisect between 3.14 and 3.15 directly (after you've
>> confirmed that 3.15.0 is indeed busted).
>
> I familiarized with git bisect, that was something I had never used before.
>
> I started it with "git bisect start v3.15 v3.14 -- drivers/gpu/drm/i915"
>
> This lead me to this:
>
> cfa7c862982b431add7f2b362526bf31372fc7b0 is the first bad commit
> commit cfa7c862982b431add7f2b362526bf31372fc7b0
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date:   Tue Apr 29 11:53:58 2014 +0200
>
>     drm/i915: Sanitize the enable_ppgtt module option once
>
>     Otherwise we'll end up spamming dmesg on every context creation on snb
>     with vt-d enabled. This regression was introduced in
>
>     commit 246cbfb5fb9a1ca0997fbb135464c1ff5bb9c549
>     Author: Ben Widawsky <benjamin.widawsky at intel.com>
>     Date:   Fri Dec 6 14:11:14 2013 -0800
>
>         drm/i915: Reorganize intel_enable_ppgtt
>
>     As the i915.enable_ppgtt is read-only it cannot be changed after the
>     module is loaded and so we can perform an early sanitization of the
>     values.
>
>     v2:
>     - Add comment and pimp commit message (Chris)
>     - Use the param consistently (Jani)
>
>     v3:
>     - Fix init sequence on pre-gen6 by moving the sanitize_ppgtt call to
>       gtt_init. Fixes boot hangs on pre-gen6.
>     - Add a debug output for the sanitize ppgtt mode.
>
>     References: https://lkml.org/lkml/2014/4/17/599
>     Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77916
>     Cc: Alessandro Suardi <alessandro.suardi at gmail.com>
>     Cc: Ben Widawsky <ben at bwidawsk.net>
>     Cc: Chris Wilson <chris at chris-wilson.co.uk>
>     Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
>     Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>     Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>
> :040000 040000 5488e397a1aaa28dca4a252452e9463b0a8f8d10
> 214c8e98b3c72844e48ab7aef02cba7daf139fab M      drivers
>
> I realized that the issue does always show, contrary to the subject
> initially chosen.
>
> Unfortunately I can't say anything else, but maybe this will help you
> experts spot the issue.
> If I can help more, be it with testing or anything else, just let me know.

Hm, I'm not aware of this breaking any gm45 machines, mine here is
still happy. Can you please make sure that you don't have any i915
module options set anywhere, either on the kernel cmdline, modeprobe
config files in /etc or anywhere else?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch