[Intel-gfx] [PATCH] drm/i915: Fix frontbuffer false positve.

[Matt Roper]

On Tue, Feb 03, 2015 at 12:57:31PM +0100, Daniel Vetter wrote:
> On Mon, Feb 02, 2015 at 03:38:16PM -0800, Rodrigo Vivi wrote:
> > frontbuffer bits must be updated during commit times not on atomica prepare
> > one, otherwise we have a risk of false positive.
> >
> > Cc Daniel Vetter <daniel.vetter at ffwll.ch>
> > Cc: Sonika Jindal <sonika.jindal at intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> 
> atomic.fb_bits isn't used at all right now, instead the
> begin_crtc_commit function recomputes them. That looks wrong. 

We build up the collection of bits in atomic.fb_bits while going through
the atomic pipeline for each plane, then do a single call to

        intel_frontbuffer_flip(dev, intel_crtc->atomic.fb_bits);

in intel_finish_crtc_commit to flush them all out together (and if
check/prepare fail, we never actually get to that flush).

> Also for async commits we need
> to do the proper 2-stage flip stuff that current page_flip code does using
> frontbuffer_flip_prepare/complete.

I need to look at the frontbuffer stuff again...maybe we don't need
atomic.fb_bits at all and should just use intel_frontbuffer_flip_prepare
in the places we set the bits now and intel_frontbuffer_flip_complete
where we're calling the flip mentioned above?


Matt

> 
> This patch here should have 0 effect (presuming I'm reading code
> correctly), so what kinf of bug exactly are you seeing?
> 
> Adding Matt&Ander.
> -Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795