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

[Marek Szyprowski]

On 20.09.2026 20:21, Dmitry Osipenko wrote:
> On 8/28/26 12:01, oushixiong1025@xxxxxxx wrote:
>> From: Shixiong Ou <oushixiong@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> Signed-off-by: Shixiong Ou <oushixiong@xxxxxxxxxx>
>> ---
>>  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;
>>  }
> Applied to misc-fixes, thanks!


This duplicates commit f2e64f450c16 ("drm/virtio: create blend mode property on cursor
plane") merged a bit earlier, what in turn results in double call to
drm_plane_create_blend_mode_property() what confuses userspace (modetest tool crashes).

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland