[git pull] drm for v4.8

[Daniel Vetter]

On Tue, Aug 2, 2016 at 4:26 AM, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
> On Mon, Aug 1, 2016 at 9:32 PM, Dave Airlie <airlied at linux.ie> wrote:
>>
>> This is the main drm pull request for 4.8, I'm down with a cold at the moment
>> so hopefully this isn't in too bad a state, I finished pulling stuff last
>> week mostly (nouveau fixes just went in today), so only this message should
>> be influenced by illness. Apologies to anyone who's major feature I missed :-)
>>
>> i915:
>>         BXT support enabled by default
>>         GVT-g infrastructure
>>         GuC command submission and fixes
>>         BXT workarounds
>>         SKL/BKL workarounds
>>         Demidlayering device registration
>>         Thundering herd fixes
>>         Missing pci ids
>>         Atomic updates
>
> Hmm. I did the merge and pushed it out, but testing it on my laptop
> shows some very annoying flickering problem.
>
> The screen goes dark for a very short while (one frame? Who knows?
> Seems longer occasionally). I have no idea what triggers it, but it
> happens quite a lot when it happens. Like once every second or two.
> And it seems to happen most of the time, although right now it happens
> to be behaving nicely, so sometimes it goes for a while without the
> flickering.
>
> Things *work*, but the flickering is nasty enough to make the end
> result painful to use.
>
> The only thing I see in dmesg that looks bad is
>
>    [drm:intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR*
> uncleared fifo underrun on pipe A
>    [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A
> FIFO underrun
>
> but I've seen that before, and it happens a couple of times during
> boot. Not once per second.
>
> This is my old Vaio 11 Pro, now running Fedora 24 (up-to-date as of today).
>
> So it's bog-standard intel graphics (i5-4200U - Haswell ULT).
>
> Suggestions to try?

psr or fbc are the likely culprits. More likely fbc if the underruns
correlate with the flicker (but note that by default we only report
them once per modest, needs to be reset with a dpms or
suspend/resume). Driver should even pick up the new module option
settings at runtime (but again you need to force a modeset, just
suspend/resume quickly), so fast to test.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch