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

[Daniel Vetter]

On Wed, Dec 17, 2014 at 06:35:04PM +0000, Chris Wilson wrote:
> On Wed, Dec 17, 2014 at 08:19:00PM +0200, Ville Syrjälä wrote:
> > 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.
> 
> I concur. I was trying to see if there was any value in trusting IIR but
> not ISR for gen2/3, but that's silly. So with the current flip interrupt
> handling we really do not have the two phases anymore.
> 
> https://bugs.freedesktop.org/attachment.cgi?id=110912
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Jani can you please pick this on up directly? It doesn't seem to have ever
reached intel-gfx unfortunately, at least google doesn't find it.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch