drm/amd/display: Move PRIMARY plane zpos higher

[Why]

Compositors have different ways of assigning surfaces to DRM planes for
render offloading. It may decide between various strategies: overlay,
underlay, or a mix of both (see here for more info:
https://gitlab.freedesktop.org/emersion/libliftoff/-/issues/76)

One way for compositors to implement the underlay strategy is to assign
a higher zpos to the DRM_PRIMARY plane than the DRM_OVERLAY planes,
effectively turning the DRM_OVERLAY plane into an underlay plane.

Today, amdgpu attaches an immutable zpos of 0 to the DRM_PRIMARY plane.
This however, is an arbitrary restriction. DCN pipes are general
purpose, and can be arranged in any z-order. To support compositors
using this allocation scheme, we can set a non-zero immutable zpos for
the PRIMARY, allowing the placement of OVERLAYS (mutable zpos range
0-254) beneath the PRIMARY.

[How]

Assign a zpos = #no of OVERLAY planes to the PRIMARY plane. Then, clean
up any assumptions in the driver of PRIMARY plane having the lowest
zpos.

v2: Fix typo s/decending/descending/

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
index 3e467244ad07..bb534b2b0b71 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
@@ -104,8 +104,6 @@ void amdgpu_dm_plane_fill_blending_from_plane_state(const struct drm_plane_state
 	*global_alpha = false;
 	*global_alpha_value = 0xff;
 
-	if (plane_state->plane->type == DRM_PLANE_TYPE_PRIMARY)
-		return;
 
 	if (plane_state->pixel_blend_mode == DRM_MODE_BLEND_PREMULTI ||
 		plane_state->pixel_blend_mode == DRM_MODE_BLEND_COVERAGE) {
@@ -1701,6 +1699,7 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
 	int res = -EPERM;
 	unsigned int supported_rotations;
 	uint64_t *modifiers = NULL;
+	unsigned int primary_zpos = dm->dc->caps.max_slave_planes;
 
 	num_formats = amdgpu_dm_plane_get_plane_formats(plane, plane_cap, formats,
 							ARRAY_SIZE(formats));
@@ -1730,10 +1729,19 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
 	}
 
 	if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
-		drm_plane_create_zpos_immutable_property(plane, 0);
+		/*
+		 * Allow OVERLAY planes to be used as underlays by assigning an
+		 * immutable zpos = # of OVERLAY planes to the PRIMARY plane.
+		 */
+		drm_plane_create_zpos_immutable_property(plane, primary_zpos);
 	} else if (plane->type == DRM_PLANE_TYPE_OVERLAY) {
-		unsigned int zpos = 1 + drm_plane_index(plane);
-		drm_plane_create_zpos_property(plane, zpos, 1, 254);
+		/*
+		 * OVERLAY planes can be below or above the PRIMARY, but cannot
+		 * be above the CURSOR plane.
+		 */
+		unsigned int zpos = primary_zpos + 1 + drm_plane_index(plane);
+
+		drm_plane_create_zpos_property(plane, zpos, 0, 254);
 	} else if (plane->type == DRM_PLANE_TYPE_CURSOR) {
 		drm_plane_create_zpos_immutable_property(plane, 255);
 	}