linux-kernel - Re: [PATCH 06/19] drm/blend: Add a generic alpha property

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Message-ID: <20180109135322.7lb3snbxfcezobhz@flea>
Date:   Tue, 9 Jan 2018 14:53:22 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-arm-kernel@...ts.infradead.org, thomas@...sch.nl
Subject: Re: [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 <boris.brezillon@...e-electrons.com>
> > Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> 
> Do we have userspace for this?

Wayland seems to be on its way to implement this, with ChromeOS using
it:
https://lists.freedesktop.org/archives/wayland-devel/2017-August/034741.html

and more specifically:
https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml#118

> 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
behaves?

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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