[Intel-gfx] [PATCH 03/14] drm/i915: implement ironlake_wait_for_vblank

[Daniel Vetter]

On Tue, May 08, 2012 at 09:34:18AM -0300, Paulo Zanoni wrote:
> 2012/5/8 Daniel Vetter <daniel at ffwll.ch>:
> > On Fri, May 04, 2012 at 05:18:15PM -0300, Paulo Zanoni wrote:
> >> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> >>
> >> intel_wait_for_vblank uses PIPESTAT, which does not exist on Ironlake
> >> and newer, so now we use PIPEFRAME.
> >>
> >> There's also a check to see if the pipe is stopped.
> >
> > Hm, why do we have this check here? The other wait_for_vblank
> > implementation doesn't bother with this. And if we call wait_for_vblank on
> > a disabled pipe, that's a bug imo.
> > -Daniel
> 
> Because not checking for a stopped pipe adds a useless 50ms delay
> (it's the wait_for() timeout). We're currently calling
> wait_for_vblank() on disabled pipes.
> - Maybe I should add a DRM_DEBUG_KMS message there and then start
> fixing these cases?
> - Maybe I should move the check to intel_wait_for_vblank (including
> the debug message)?

Either is fine, the thing that irked was just that now the semantics of
wait_for_vblank changed depending upon which chipset it runs on:
- for ilk, it will immediately return if the pipe is off
- for pre-ilk, it will time out for 50 ms, complain with a debug message
  and then return.

I'm leaning towards fixing up the callers to not call wait_for_vblank when
the pipe is off (and ditching the check from the ilk wait_for_vblank).
-Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48