Re: [PATCH] drm/i915: Do not trigger the pageflip stall check too early

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Dec 17, 2014 at 04:48:19PM +0000, Chris Wilson wrote:
> On Wed, Dec 17, 2014 at 04:41:42PM +0000, Chris Wilson wrote:
> > On gen2-4, we have a separate pageflip prepare/finish phase. The intent
> > of the stall check is to detect when we have incurred a delay,
> > potentially indefinite, after the pageflip is submitted and before the
> > flip is processed by the hardware. However, our notion of
> > INTEL_FLIP_PENDING/INTEL_FLIP_COMPLETE do not tally with how we set the
> > values during prepare/finish and the current stall check erroneously
> > assumes that when the pending value >= COMPLETE, the driver has seen the
> > hardware completion flag. But what the driver actually means, is that it
> > has seen the acknowlegement that the flip is queued and is now pending
> > the completion event.
> 
> Bah, otoh, as we don't mark the flip as pending before completion on
> gen5+, we know don't detect when the flip is wedged there after applying
> this patch.
> 
> It is quite possible that the work->pending check is entirely bogus.
> Back to the drawing board.

We just apply my fix. And then we can even get rid of the whole
prepare/finish mess.

-- 
Ville Syrjälä
Intel OTC
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