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

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Message-ID: <20161022084131.GQ20761@phenom.ffwll.local>
Date:   Sat, 22 Oct 2016 10:41:31 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        Takashi Iwai <tiwai@...e.de>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Noralf Trønnes <noralf@...nnes.org>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH] drm/fb-helper: Don't call dirty callback for untouched
 clips

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
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch