[PATCH 3/4] drm/virtio: create blend mode property on cursor plane

[Qinyun Tan <qinyuntan@linux.alibaba.com>]

Since commit 860e748bddcc ("drm: ensure blend mode supported if pixel
format with alpha exposed"), drm_mode_config_validate() warns when a
plane exposes an alpha pixel format but not the "pixel blend mode"
property. The virtio-gpu cursor plane (HOST_ARGB8888) trips this.

The cursor has always blended with pre-multiplied alpha and userspace
assumes that blend mode when the property is not attached. Expose a
"pixel blend mode" property advertising only DRM_MODE_BLEND_PREMULTI
to make the existing semantics explicit and silence the warning. The
primary plane only exposes HOST_XRGB8888, so the call is gated to the
cursor. No functional change.

Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
---
 drivers/gpu/drm/virtio/virtgpu_plane.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
index 1d1b27ece62a7..640815af40980 100644
--- a/drivers/gpu/drm/virtio/virtgpu_plane.c
+++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
@@ -24,6 +24,7 @@
  */
 
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_blend.h>
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_gem_atomic_helper.h>
@@ -609,6 +610,9 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
 
 	if (type == DRM_PLANE_TYPE_PRIMARY)
 		drm_plane_enable_fb_damage_clips(plane);
+	else if (type == DRM_PLANE_TYPE_CURSOR)
+		drm_plane_create_blend_mode_property(plane,
+						     BIT(DRM_MODE_BLEND_PREMULTI));
 
 	return plane;
 }
-- 
2.43.7