[Intel-gfx] [PATCH 07/19] drm/i915: Allow mmio updates on all platforms, v2.

[Maarten Lankhorst]

Op 19-04-16 om 14:48 schreef Ville Syrjälä:
> On Tue, Apr 19, 2016 at 09:52:27AM +0200, Maarten Lankhorst wrote:
>> With intel_pipe_update begin/end we ensure that the mmio updates
>> don't run during vblank interrupt, using the hw counter we can
>> be sure that when current vblank count != vblank count at the time
>> of pipe_update_end the mmio update is complete.
> Still seems too racy for my taste.
>
> What should be done is:
>  1. evade vblank
>  2. write regs
>  3. sample vblank counter and allow the irq handler to complete the flip
>     when passing the target vblank count
>  4. check if we just missed the vblank irq, and if so complete the flip immediately
>
> Also I would have started by ridding us of the flip done interrupt
> first, because that means every platform would then follow the same code
> path leading to better testing coverage (and hopefully less bugs). And
> it would allow us to remove the extra vblank wait hacks on BDW.
>
I do set the current vblank counter, only after it advanced to next vblank it would signal vblank done.

I do agree we should get rid of flip handling, but that should be done after removing cs flip support, and can be a cleanup patch after this series.