[PATCH] drm/blend: Define the direction of Z position values

[Daniel Vetter]

On Fri, Sep 6, 2019 at 4:45 PM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> We forgot that.
>
> Proof is the one igt testcase we have:
>
> https://gitlab.freedesktop.org/drm/igt-gpu-tools/blob/master/tests/kms_atomic.c#L280
>
> While at it also document that we have immutable zpos properties in
> some cases.
>
> Reported-by: Pekka Paalanen <pekka.paalanen at collabora.com>
> Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
> Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.com>
> Cc: Ilia Mirkin <imirkin at alum.mit.edu>
> Acked-by: Ilia Mirkin <imirkin at alum.mit.edu>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>

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

> ---
>  drivers/gpu/drm/drm_blend.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index 37ac168fcb60..d02709dd2d4a 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -130,7 +130,12 @@
>   *     Z position is set up with drm_plane_create_zpos_immutable_property() and
>   *     drm_plane_create_zpos_property(). It controls the visibility of overlapping
>   *     planes. Without this property the primary plane is always below the cursor
> - *     plane, and ordering between all other planes is undefined.
> + *     plane, and ordering between all other planes is undefined. The positive
> + *     Z axis points towards the user, i.e. planes with lower Z position values
> + *     are underneath planes with higher Z position values. Note that the Z
> + *     position value can also be immutable, to inform userspace about the
> + *     hard-coded stacking of overlay planes, see
> + *     drm_plane_create_zpos_immutable_property().
>   *
>   * pixel blend mode:
>   *     Pixel blend mode is set up with drm_plane_create_blend_mode_property().
> --
> 2.23.0
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch