[Intel-gfx] Breakage for Ironlake due to some watermarks changes in Linux 4.0+?

[Mario Kleiner]

On 05/15/2015 11:00 AM, Jani Nikula wrote:
> On Fri, 15 May 2015, Mario Kleiner <mario.kleiner.de at gmail.com> wrote:
>> Hi all,
>>
>> since Linux 4.0 i experience some massive display flicker problem on my
>> Intel HD Ironlake mobile (2010 MacBookPro6,2) under Waylands reference
>> compositor Weston.
>>
>> - Only happens on Linux >= 4.0 on intel-kms with the Intel HD, not under
>> nouveau-kms with the discrete NVidia gpu. Strangely on Linux 4.1-rc it
>> happens all the time, whereas on Linux 4.0 it can work normally for
>> quite a while, but once the problem starts only a reboot can cure it.
>>
>> - Almost only happens on Weston, but only very rarely under the XServer.
>> VT switching from Weston to XOrg makes the problem disappear, switching
>> back to Weston and it starts again immediately.
>>
>> - Only happens if a hardware cursor is displayed - hiding the cursor
>> stops the flicker immediately, showing the cursor starts the flicker.
>>
>> - The drm and desktop is completely idle during this - drm.debug=15
>> shows no activity while this happens.
>>
>> Symptom:
>>
>> Up to the scanline where the cursor is located, the desktop image is
>> displayed, but jumps horizontally left and right by some random number
>> of pixels, maybe in the range 0 - 200 pixels with high frequency, making
>> the content unreadable. Starting with the scanline where scanout of the
>> cursor starts, the display goes blank, as if some display controller
>> fifo would underflow and the controller blanks the display in response.
>> Seems having to scanout the cursor plane in addition to the primary
>> plane is just enough to push it over some limit?
>>
>> I also see cpu and pch pipe a fifo underruns reported by the underflow
>> irq handlers.
>>
>> I saw there were many changes around Linux 4.0 in the kms driver wrt.
>> watermark calculations, so this might be related?
>
> Please try http://patchwork.freedesktop.org/patch/49314 and report back.
>
> BR,
> Jani.
>

The patch fixes my flicker problem nicely. Thanks! If you want, you can 
add a

Tested-by: Mario Kleiner <mario.kleiner.de at gmail.com>

best,
-mario