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

[Michel Dänzer]

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 at canonical.com wrote:
> > > From: Christopher James Halse Rogers <christopher.halse.rogers at 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?

> whereas it's easily triggerable on single monitor systems on intel. 

Anyway, this patch is probably good at least as a preliminary fix for
the inconsistent vblank state with the intel driver.


> > Maybe it would be possible to move those calls to core code, and/or only
> > force sending out events when the CRTC isn't just getting disabled
> > temporarily.
> > 
> 
> As in: have the core modesetting code call drm_vblank_off before making
> the driver-specific calls when disabling a crtc?  I'll look into it -
> that would appear to be a more general solution.

Yeah, something like that, thanks.


-- 
Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer