Re: [PATCH] drm/fb-helper: Don't call dirty callback for untouched clips

From: Daniel Vetter
Date: Sat Oct 22 2016 - 04:42:00 EST

On Fri, Oct 21, 2016 at 09:02:27PM +0100, Chris Wilson wrote:
> On Fri, Oct 21, 2016 at 08:19:03PM +0200, Daniel Vetter wrote:
> > On Fri, Oct 21, 2016 at 01:57:28PM +0100, Chris Wilson wrote:
> > > I think of a use for sending an empty clip: where you don't want to
> > > push any new pixel data, but you do want to be sure that the pipeline
> > > has been flushed.
> >
> > What exactly should an empty rectangle flush out? It's a bit unclear, but
> > for speed I guess drivers should be allowed to make dirty async ...
> No idea! I'm just speculating that I can see a use for a dirtyfb barrier
> even with an empty cliprect. Empty clips are a useful distinction
> elsewhere that I would suggest not forbidding them outright but defining
> their behaviour.

In general I prefer clarifying unused and undefined cases to "reject
them". We can always add a cap later on when we want to give them some
real meaning.
Daniel Vetter
Software Engineer, Intel Corporation