[PATCH] drm/virtio: Add pixel blend mode property to cursor plane

[oushixiong1025@163.com]

From: Shixiong Ou <oushixiong@kylinos.cn>

The cursor plane exposes a format with an alpha channel
(DRM_FORMAT_ARGB8888) without a pixel blend mode property. Since
commit 860e748bddcc ("drm: ensure blend mode supported if pixel
format with alpha exposed") this triggers a warning during
drm_mode_config_validate():

[    0.649020] ------------[ cut here ]------------
[    0.649040] [PLANE:36:plane-1] pixel format with alpha exposed but blend mode not setup
[    0.649081] WARNING: drivers/gpu/drm/drm_mode_config.c:872 at drm_mode_config_validate
......
[    0.649761] Call trace:
[    0.649764]  drm_mode_config_validate+0x398/0x558 [drm] (P)
[    0.649912]  drm_dev_register+0x1cc/0x2a0 [drm]
[    0.650058]  virtio_gpu_probe+0xd4/0x1c0 [virtio_gpu]
[    0.650088]  virtio_dev_probe+0x1c8/0x310
......
[    0.650261] ---[ end trace 0000000000000000 ]---


Create the property with the only supported blend mode,
DRM_MODE_BLEND_PREMULTI, which is also the property's default and
matches what userspace had to assume before the property existed.

Reported-by: Ye Liu <liuye@kylinos.cn>
Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
---
 drivers/gpu/drm/virtio/virtgpu_plane.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
index 1d1b27ece62a..11771c943ea6 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>
@@ -588,6 +589,7 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
 	struct drm_plane *plane;
 	const uint32_t *formats;
 	int nformats;
+	int ret;
 
 	if (type == DRM_PLANE_TYPE_CURSOR) {
 		formats = virtio_gpu_cursor_formats;
@@ -610,5 +612,17 @@ 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);
 
+	if (type == DRM_PLANE_TYPE_CURSOR) {
+		/*
+		 * The cursor plane exposes a format with an alpha channel,
+		 * which requires a blend mode property. The host blends
+		 * premultiplied alpha, matching the property's default.
+		 */
+		ret = drm_plane_create_blend_mode_property(plane,
+							   BIT(DRM_MODE_BLEND_PREMULTI));
+		if (ret)
+			return ERR_PTR(ret);
+	}
+
 	return plane;
 }
-- 
2.25.1

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