We forgot that.
Proof is the one igt testcase we have:
https://gitlab.freedesktop.org/drm/igt-gpu-tools/blob/master/tests/kms_atomi...
While at it also document that we have immutable zpos properties in some cases.
Reported-by: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pekka Paalanen pekka.paalanen@collabora.com Reviewed-by: Pekka Paalanen pekka.paalanen@collabora.com Cc: Ilia Mirkin imirkin@alum.mit.edu Acked-by: Ilia Mirkin imirkin@alum.mit.edu Signed-off-by: Daniel Vetter daniel.vetter@intel.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().