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

[Jani Nikula]

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.

>
> thanks,
> -mario
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-- 
Jani Nikula, Intel Open Source Technology Center