[PATCH] drm: document pre-multiplied assumptions

[Daniel Vetter]

On Wed, Sep 29, 2021 at 04:07:01PM +0300, Pekka Paalanen wrote:
> On Wed, 29 Sep 2021 09:54:14 +0000
> Simon Ser <contact at emersion.fr> wrote:
> 
> > When a plane is missing the "alpha blend mode" property, KMS drivers
> > will use the pre-multiplied mode.
> > 
> > Signed-off-by: Simon Ser <contact at emersion.fr>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Cc: Pekka Paalanen <ppaalanen at gmail.com>
> > ---
> >  drivers/gpu/drm/drm_blend.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> > index ec37cbfabb50..eebb32ba84d7 100644
> > --- a/drivers/gpu/drm/drm_blend.c
> > +++ b/drivers/gpu/drm/drm_blend.c
> > @@ -185,6 +185,9 @@
> >   *		 plane does not expose the "alpha" property, then this is
> >   *		 assumed to be 1.0
> >   *
> > + *	When a plane is missing this property, the plane uses the
> > + *	"Pre-multiplied" equation.
> > + *
> >   * Note that all the property extensions described here apply either to the
> >   * plane or the CRTC (e.g. for the background color, which currently is not
> >   * exposed and assumed to be black).
> 
> Hi Simon,
> 
> thank you! :-D
> 
> I have no idea if that's correct though, but also nothing against it,
> and it does help with what I ranted about in
> https://lists.freedesktop.org/archives/wayland-devel/2021-September/041993.html
> so is it appropriate to offer my
> 
> Acked-by: Pekka Paalanen <pekka.paalanen at collabora.com>

I think if it's not correct we can add an immutable prop like Ville
suggested for that driver.
-Daniel

> 
> ?
> 
> 
> Thanks,
> pq



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