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

[Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>]

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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?
> 
> > 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.
> 

Ok.  This appears to be surprisingly difficult.  Particularly, the
vblank code indexes crtcs based on the driver-private numbering, and
there doesn't appear to be a generic interface to grab this number;
Intel uses the DRM_IOCTL_I915_GET_PIPE_FROM_CRTC_ID ioctl, radeon uses
something different.

I'll see what I can come up with, but I don't think I'm sufficiently
familiar with the kms code to quickly come up with a nice API.


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