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path: root/drivers/gpu/drm/drm_blend.c
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Diffstat (limited to 'drivers/gpu/drm/drm_blend.c')
-rw-r--r--drivers/gpu/drm/drm_blend.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
index 37ac168fcb60..121481f6aa71 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. Two planes with the
+ * same Z position value have undefined ordering. Note that the Z position
+ * value can also be immutable, to inform userspace about the hard-coded
+ * stacking of planes, see drm_plane_create_zpos_immutable_property().
*
* pixel blend mode:
* Pixel blend mode is set up with drm_plane_create_blend_mode_property().