[PATCH] drm: rcar-du: Create immutable zpos property for primary planes

[Daniel Stone]

On Thu, 2 Apr 2020 at 11:40, Laurent Pinchart
<laurent.pinchart+renesas at ideasonboard.com> wrote:
> The R-Car DU driver creates a zpos property, ranging from 1 to 7, for
> all the overlay planes, but leaves the primary plane without a zpos
> property. The DRM/KMS API doesn't clearly specify if this is acceptable,
> of it the property is mandatory for all planes when exposed for some of
> the planes. Nonetheless, weston v8.0 has been reported to have trouble
> handling this situation.

Yeah. It didn't even occur to me/us that someone would do that, to be
honest. We need to have zpos information for all planes that we're
using in order for zpos to be at all meaningful, and we can't exactly
avoid using the primary plane. Without knowing the primary plane's
zpos, we can't know if the overlays are actually overlays or in fact
underlays.

> The DRM core offers support for immutable zpos properties. Creating an
> immutable zpos property set to 0 for the primary planes seems to be a
> good way forward, as it shouldn't introduce any regression, and can fix
> the issue. Do so.

Perfect. We support immutable properties entirely well, we just need
to know about them.

> Reported-by: Kuninori Morimoto <kuninori.morimoto.gx at renesas.com>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>

Reviewed-by: Daniel Stone <daniels at collabora.com>

Cheers,
Daniel