[Intel-gfx] [PATCH] drm/i915: Force vblanks around evasion when i915.watermark_test is set.

[Maarten Lankhorst]

Op 13-06-16 om 16:45 schreef Daniel Vetter:
> On Thu, Jun 09, 2016 at 01:36:50PM +0200, Maarten Lankhorst wrote:
>> This will make it more likely that intermediary watermarks cause fifo
>> underruns, which is useful when writing watermark specific tests,
>> to make it more likely to trigger FIFO underruns in intermediary watermarks.
> That's surprising ... with the vblank_wait added you're pretty much
> guaranteed to never hit the evasion case. Note that the vblank evasion
> code also just does a vblank wait if it detects a possible collision.
>
> Given that I'd have assumed that this simply slows down atomic flips,
> which is probably not what we want for testing all. Does this really help?
> Any ideas why?
This is a sanity check on the intermediate watermarks. The vblank test will ensure
that the old plane configuration doesn't cause underruns with watermarks, and that
the intermediate watermarks will work correctly with the new plane configuration too.

I think the latter vblank_wait may be killed, but the former could be really useful,
for example to find correct watervblank values in CHV.

~Maarten