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| author | Simon Ser <contact@emersion.fr> | 2019-10-09 18:10:49 +0300 |
|---|---|---|
| committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2019-10-09 21:04:55 +0300 |
| commit | 8f6ea27b2fefdff58b3a038b5f1b4ed34aed3fd3 (patch) | |
| tree | 403197175f328ddf2a94a018948b4b74248f446f /drivers/gpu/drm/drm_blend.c | |
| parent | f2a4a13ab2ca3605010d72c774b6aab3ba1a09f4 (diff) | |
| download | linux-8f6ea27b2fefdff58b3a038b5f1b4ed34aed3fd3.tar.xz | |
drm: two planes with the same zpos have undefined ordering
Currently the property docs don't specify whether it's okay for two planes to
have the same zpos value and what user-space should expect in this case.
The unspoken, legacy rule used in the past was to make user-space figure
out the zpos from object IDs. However some drivers break this rule,
that's why the ordering is documented as unspecified in case the zpos
property is missing. User-space should rely on the zpos property only.
There are some cases in which user-space might read identical zpos
values for different planes.
For instance, in case the property is mutable, user-space might set two
planes' zpos to the same value. This is necessary to support user-space
using the legacy DRM API where atomic commits are not possible:
user-space needs to update the planes' zpos one by one.
Because of this, user-space should handle multiple planes with the same
zpos.
While at it, remove the assumption that zpos is only for overlay planes.
Additionally, update the drm_plane_state.zpos docs to clarify that zpos
disambiguation via plane object IDs is a recommendation for drivers, not
something user-space can rely on. In other words, when user-space sets
the same zpos on two planes, drivers should rely on the plane object ID.
v2: clarify drm_plane_state.zpos docs (Daniel)
v3: zpos is for all planes (Marius, Daniel)
v4: completely reword the drm_plane_state.zpos docs to make it clear the
recommendation to use plane IDs is for drivers in case user-space uses
duplicate zpos values (Pekka)
v5: reword commit message (Pekka, James)
v6: remove mention of Arm GPUs having planes which can't overlap,
because this isn't uAPI yet (Daniel)
Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Marius Vlad <marius.vlad@collabora.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: James Qian Wang <james.qian.wang@arm.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/T5nHrvXH0GKOp6ONaFHk-j2cwEb4_4C_sBz9rNw8mmPACuut-DQqC74HMAFKZH3_Q15E8a3YnmKCxap-djKA71VVZv_T-tFxaB0he13O7yA=@emersion.fr
Diffstat (limited to 'drivers/gpu/drm/drm_blend.c')
| -rw-r--r-- | drivers/gpu/drm/drm_blend.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c index d02709dd2d4a..121481f6aa71 100644 --- a/drivers/gpu/drm/drm_blend.c +++ b/drivers/gpu/drm/drm_blend.c @@ -132,10 +132,10 @@ * planes. Without this property the primary plane is always below the cursor * 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(). + * 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(). |