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Message-ID: <cdd9c0632d495aedb6cc709033c983ce19f59e48.camel@bootlin.com>
Subject: Re: [linux-sunxi] [PATCH 2/2] drm/sun4i: sun4i: Introduce a quirk
 for lowest plane alpha support
From:   Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To:     Julian Calaby <julian.calaby@gmail.com>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        "Mailing List, Arm" <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        David Airlie <airlied@linux.ie>, Chen-Yu Tsai <wens@csie.org>,
        thomas.petazzoni@bootlin.com,
        linux-sunxi <linux-sunxi@googlegroups.com>
Date:   Wed, 18 Jul 2018 09:21:17 +0200
In-Reply-To: <CAGRGNgX27bbJz2qe3FOb4eP5WKgDYFUNxoz7SkUbN_QDF25pAg@mail.gmail.com>
References: <20180717085230.17472-1-paul.kocialkowski@bootlin.com>
         <20180717085230.17472-2-paul.kocialkowski@bootlin.com>
         <CAGRGNgX27bbJz2qe3FOb4eP5WKgDYFUNxoz7SkUbN_QDF25pAg@mail.gmail.com>
Organization: Bootlin
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Hi,

On Tue, 2018-07-17 at 22:41 +1000, Julian Calaby wrote:
> Hi Paul,
>=20
> On Tue, Jul 17, 2018 at 6:53 PM Paul Kocialkowski
> <paul.kocialkowski@bootlin.com> wrote:
> >=20
> > Not all sunxi platforms with the first version of the Display Engine
> > support an alpha component on the plane with the lowest z position
> > (as in: lowest z-pos), that gets blended with the background color.
> >=20
> > In particular, the A13 is known to have this limitation. However, it wa=
s
> > recently discovered that the A20 and A33 are capable of having alpha on
> > their lowest plane.
> >=20
> > Thus, this introduces a specific quirk to indicate such support,
> > per-platform. Since this was not tested on sun4i and sun6i platforms, a
> > conservative approach is kept and this feature is not supported.
> >=20
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun4i_backend.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >=20
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/su=
n4i/sun4i_backend.c
> > index a3cc398d4d80..cdc4a8a91ea2 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > @@ -584,8 +587,9 @@ static int sun4i_backend_atomic_check(struct sunxi_=
engine *engine,
> >         }
> >=20
> >         /* We can't have an alpha plane at the lowest position */
> > -       if (plane_states[0]->fb->format->has_alpha ||
> > -           (plane_states[0]->alpha !=3D DRM_BLEND_ALPHA_OPAQUE))
> > +       if ((plane_states[0]->fb->format->has_alpha ||
> > +           (plane_states[0]->alpha !=3D DRM_BLEND_ALPHA_OPAQUE)) &&
> > +           !backend->quirks->supports_lowest_plane_alpha)
>=20
> From a readability perspective, it'd be fractionally nicer if the
> quirk check was before the alpha checks.

Agreed, I will do that in v2.

Thanks!

--=20
Paul Kocialkowski, Bootlin (formerly Free Electrons)
Embedded Linux and kernel engineering
https://bootlin.com

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