Re: [PATCH 1/3] drm: Send pending vblank events before disabling vblank.

From: Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>
To: "Michel Dänzer" <michel@daenzer.net>
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 1/3] drm: Send pending vblank events before disabling vblank.
Date: Wed, 27 Apr 2011 19:17:42 +1000	[thread overview]
Message-ID: <1303895862.15750.18.camel@Ed> (raw)
In-Reply-To: <1303895309.5633.137.camel@thor.local>

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On Wed, 2011-04-27 at 11:08 +0200, Michel Dänzer wrote:
> On Mit, 2011-04-27 at 18:58 +1000, Christopher James Halse Rogers
> wrote: 
> > On Wed, 2011-04-27 at 10:32 +0200, Michel Dänzer wrote:
> > > On Mit, 2011-04-27 at 16:10 +1000, christopher.halse.rogers@canonical.com wrote:
> > > > From: Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>
> > > > 
> > > > This is the least-bad behaviour.  It means that we signal the
> > > > vblank event before it actually happens, but since we're disabling
> > > > vblanks there's no guarantee that it will *ever* happen otherwise.
> > > 
> > > This may indeed be the best we can do for events that are pending when
> > > the CRTC is disabled[0], but I can't see anything that would prevent new
> > > events from getting scheduled (or synchronous vblank waits from timing
> > > out) while the CRTC is disabled?
> > > 
> > > [0] Though it might unnecessarily send events prematurely when the CRTC
> > > is just disabled temporarily, e.g. as part of a modeset.
> > > 
> > > 
> > > Also, this patch won't seem to help at all for other drivers which don't
> > > call drm_vblank_off() directly when disabling a CRTC.
> > 
> > This is true.  On the other hand, the other drivers don't wedge the
> > vblank code into a state where vblanks cannot be re-enabled.  So it's
> > only a problem when disabling one of 2+ monitors on those drivers,
> 
> And with DPMS?
> 

Possibly.  Since vblanks aren't wedged off in this case it's more likely
that the user turning the monitors back on will result in a vblank irq,
which will kick everything back into correct operation.

I've not managed to trigger this on my radeon system in the same way as
my intel systems, but I haven't stressed it as hard either.

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