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SubjectRe: [PATCH 06/19] drm/blend: Add a generic alpha property
On Tue, Jan 09, 2018 at 01:32:41PM +0100, Daniel Vetter wrote:
> On Tue, Jan 09, 2018 at 11:56:25AM +0100, Maxime Ripard wrote:
> > Some drivers duplicate the logic to create a property to store a per-plane
> > alpha.
> >
> > Let's create a helper in order to move that to the core.
> >
> > Cc: Boris Brezillon <>
> > Cc: Laurent Pinchart <>
> > Signed-off-by: Maxime Ripard <>
> Do we have userspace for this?

Wayland seems to be on its way to implement this, with ChromeOS using

and more specifically:

> Is encoding a fixed 0-255 range really the best idea?

I don't really know, is there hardware or formats where there is more
than 255? Or did you mean less than that?

> I know other drivers have skimped on the rules here a bit ... But at least
> internally (i.e. within the drm_plane_state) we probably should restrict
> ourselves to u8. And this needs real docs (i.e. the full blend equation
> drivers are supposed to implement).

You mean straight vs premultiplied? Maybe we should implement this as
an additional property in read only depending on how the hardware


Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
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