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

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Date:   Tue, 17 Jul 2018 22:41:20 +1000
From:   Julian Calaby <julian.calaby@...il.com>
To:     paul.kocialkowski@...tlin.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 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.

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/