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

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Do not trigger the pageflip stall check too early
Date: Wed, 17 Dec 2014 23:19:03 +0200	[thread overview]
Message-ID: <20141217211903.GN10649@intel.com> (raw)
In-Reply-To: <20141217205909.GJ2711@phenom.ffwll.local>

On Wed, Dec 17, 2014 at 09:59:09PM +0100, Daniel Vetter wrote:
> 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@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.

It was waiting for test results. Posted now:
http://lists.freedesktop.org/archives/intel-gfx/2014-December/057746.html

-- 
Ville Syrjälä
Intel OTC
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