Re: [PATCH v2 3/4] drm/virtio: create blend mode property on cursor plane

[Thomas Zimmermann <tzimmermann@suse.de>]

Am 01.09.26 um 10:32 schrieb Qinyun Tan:
> 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 virtio-gpu specification does not define the cursor alpha
> semantics. The host forwards the cursor pixels verbatim to its display
> frontends, and the remote cursor protocols among them (SPICE alpha
> cursors, the VNC "Cursor With Alpha" encoding) both define
> pre-multiplied alpha, matching what userspace has always assumed when
> the property is not attached. Expose a "pixel blend mode" property
> advertising only DRM_MODE_BLEND_PREMULTI to make these 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>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

> ---
> v2: no code change; explain the protocol-level justification for
> PREMULTI in the commit message.
>
>   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;
>   }

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)