Re: [PATCH v4 3/3] drm/amd/display: advertise PIXEL_NONE and PREMULTI blend mode for DCE

Reviewed-by: Alex Hung <[email protected]>

On 8/26/26 04:37, Melissa Wen wrote:
> DCE can support PREMULTI and COVERAGE blend mode depending on its
> generation, however current driver implementation either doesn't expose
> more than primary and cursor plane, or doesn't program registers for any
> blend mode other than PIXEL_NONE. To fix the missing-blend-mode-prop
> warning according to current DCE plane caps, create blend mode property
> with PIXEL_NONE and PREMULTI for primary planes. As long as the
> background is black and there is no overlay plane, PIXEL_NONE and
> PREMULTI are equivalent, and PREMULTI has been the mandatory/default
> mode for years, so keep it to avoid regressions.
> 
> Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> Tested-by: Viktor Jägersküpper <[email protected]>
> Tested-by: Dan Wheeler <[email protected]> #v3
> Reviewed-by: Alex Hung <[email protected]> #v3
> Reviewed-by: Leandro Ribeiro <[email protected]> #v2
> Signed-off-by: Melissa Wen <[email protected]>
> 
> ---
> v3:
> - fix indentation (Alex H)
> v4:
> - add PREMULTI to avoid regression (reported by Viktor)
> ---
>   .../amd/display/amdgpu_dm/amdgpu_dm_plane.c   | 24 +++++++++++++------
>   1 file changed, 17 insertions(+), 7 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 ab9bbe8ca333..402f0d333150 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
> @@ -1923,14 +1923,24 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
>   	if (res)
>   		return res;
>   
> -	/* TODO: Check which blend modes are supported in DCE-generation
> -	 * planes, i.e. DC_PLANE_TYPE_DCE_RGB/UNDERLAY and expose blend mode
> -	 * property accordingly.
> +	/* Blend mode support varies on DCE generations according to HW caps
> +	 * and number of planes per CRTC. However, as current driver
> +	 * implementation only creates one primary and one cursor plane per
> +	 * CRTC for DCE (overlay is only created if
> +	 * DC_PLANE_TYPE_DCN_UNIVERSAL), the primary plane blend mode is
> +	 * ignored across DCE versions. Keep PREMULTI to avoid uAPI
> +	 * regressions: it was the default/mandatory mode for many years and,
> +	 * with no overlay plane, primary composes on top of a black
> +	 * background, where PREMULTI and PIXEL_NONE are equivalent.
>   	 */
> -	if ((plane->type == DRM_PLANE_TYPE_OVERLAY ||
> -	     plane->type == DRM_PLANE_TYPE_PRIMARY) &&
> -	    plane_cap && plane_cap->per_pixel_alpha &&
> -	    plane_cap->type == DC_PLANE_TYPE_DCN_UNIVERSAL) {
> +	if (plane_cap && plane_cap->type != DC_PLANE_TYPE_DCN_UNIVERSAL) {
> +		unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> +					  BIT(DRM_MODE_BLEND_PREMULTI);
> +
> +		drm_plane_create_blend_mode_property(plane, blend_caps);
> +	} else if ((plane->type == DRM_PLANE_TYPE_OVERLAY ||
> +		    plane->type == DRM_PLANE_TYPE_PRIMARY) &&
> +		   plane_cap && plane_cap->per_pixel_alpha) {
>   		unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
>   					  BIT(DRM_MODE_BLEND_PREMULTI) |
>   					  BIT(DRM_MODE_BLEND_COVERAGE);