linux-kernel - Re: [linux-sunxi] [PATCH 2/2] drm/sun4i: sun4i: Introduce a quirk for lowest plane alpha support

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Date:   Wed, 18 Jul 2018 09:21:17 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Julian Calaby <julian.calaby@...il.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        "Mailing List, Arm" <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        thomas.petazzoni@...tlin.com,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH 2/2] drm/sun4i: sun4i: Introduce a quirk
 for lowest plane alpha support

Hi,

On Tue, 2018-07-17 at 22:41 +1000, Julian Calaby wrote:
> Hi Paul,
> 
> On Tue, Jul 17, 2018 at 6:53 PM Paul Kocialkowski
> <paul.kocialkowski@...tlin.com> wrote:
> > 
> > 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.
> > 
> > In particular, the A13 is known to have this limitation. However, it was
> > recently discovered that the A20 and A33 are capable of having alpha on
> > their lowest plane.
> > 
> > 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.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun4i_backend.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/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,
> >         }
> > 
> >         /* We can't have an alpha plane at the lowest position */
> > -       if (plane_states[0]->fb->format->has_alpha ||
> > -           (plane_states[0]->alpha != DRM_BLEND_ALPHA_OPAQUE))
> > +       if ((plane_states[0]->fb->format->has_alpha ||
> > +           (plane_states[0]->alpha != DRM_BLEND_ALPHA_OPAQUE)) &&
> > +           !backend->quirks->supports_lowest_plane_alpha)
> 
> 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!

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

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