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

[Jani Nikula]

On Tue, 19 May 2015, Mario Kleiner <mario.kleiner.de at gmail.com> wrote:
> 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>

Thanks for testing, I've pushed the fix to drm-intel-fixes, headed to
-rc5.

BR,
Jani.


>
> best,
> -mario

-- 
Jani Nikula, Intel Open Source Technology Center