[PATCH v3 09/15] drm: tilcdc: Replace drm_fb_get_bpp_depth() with drm_format_plane_cpp()

[Ville Syrjälä]

On Fri, Jun 10, 2016 at 03:08:18PM +0300, Tomi Valkeinen wrote:
> On 10/06/16 15:05, Ville Syrjälä wrote:
> 
> >> I'm not sure what's the common way, but tilcdc doesn't support alpha.
> >> ARGB works, of course, by ignoring A, but... If an userspace app creates
> >> ARGB buffer, does the app expect alpha to work?
> > 
> > I think what we decided a while ago (at least for i915, but would be good
> > to use the same convention everywhere) was that ARGB will be assumed to be
> > pre-multiplied and will enable blending using 1.0*sc+(1.0-sa)*dc as the
> > function. There have been some efforts at defining some new properties to
> > control the blend equation, but I guess those got bogged down again.
> 
> Ok, but that's a bit different topic. The question here is, if the HW
> doesn't support alpha (no planes, so nothing to blend), should it accept
> ARGB or not.

What do you mean "no planes"? You have to have a plane if you want
to scanout a framebuffer. And even if you have just one plane with
alpha blending, it should be blended with the background color
(which is black until we get a property to change it).

-- 
Ville Syrjälä
Intel OTC