[Intel-gfx] [RFC] drm/i915: don't wait_for_vblank if the CRTC is disabled

[Daniel Vetter]

On Wed, Mar 18, 2015 at 03:01:22PM -0700, Matt Roper wrote:
> On Wed, Mar 18, 2015 at 04:15:07PM -0300, Paulo Zanoni wrote:
> > From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > 
> > Otherwise we'll get a WARN from drm_wait_one_vblank() saying that
> > vblanks are not available (since they were already disabled in
> > crtc_disable()).
> > 
> > This is certainly a regresison, but QA couldn't bisect it due to
> > other regressions breaking the bisect.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89550
> > Testcase: igt/pm_rpm/legacy-planes
> > Testcase: igt/pm_rpm/legacy-planes-dpms
> > Testcase: igt/pm_rpm/universal-planes
> > Testcase: igt/pm_rpm/universal-planes-dpms
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Matt Roper <matthew.d.roper at intel.com>
> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > 
> > I'm not really sure if this is the best way to fix the regression. Ville and/or
> > Matt should provide some comments here.
> > 
> 
> This will definitely fix the problem (we shouldn't be waiting for vblank
> with a disabled CRTC!), but I think the true bug in our code is that our
> sprite commit function is setting some bits that should have been set
> back in the 'check' phase under the 'if (intel_crtc->active)' branch.
> 
> I'll supply a patch shortly that I think should fix how we got into this
> situation in the first place.  The whole 'wait_for_vblank' flag is
> something we should be able to get rid of completely once I finish the
> atomic watermark work.

Yeah because of runtime PM we shouldn't do anything really for plane
updates when the crtc is off. Unnecessary vblank waits here really smell
like the canary, not the cause.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch