Re: [PATCH] drm/i915/display: expose blend mode on alpha-capable planes

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jul 15, 2026 at 11:12:21AM +0530, Chaitanya Kumar Borah wrote:
> 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 cursor (ARGB8888, all platforms) and the VLV/CHV primary
> and sprite planes trip this.
> 
> Userspace has historically assumed premultiplied blending when the
> property is not attached, so it is safe to assume that planes that
> did not expose the property already blended with fixed pre-multiplied
> alpha in hardware. Therefore, expose a "pixel blend mode" property
> advertising only DRM_MODE_BLEND_PREMULTI to match that assumption and
> silence the warning. The cursor call is unconditional; the primary and
> sprite calls are gated to VLV/CHV, the only platforms whose format lists
> include alpha formats.
> 
> Assisted-by: Claude:claude-opus-4-8
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Uma Shankar <uma.shankar@intel.com>
> Cc: Leandro Ribeiro <leandro.ribeiro@collabora.com>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16623
> Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>

https://lore.kernel.org/intel-gfx/20260522194935.27411-1-ville.syrjala@linux.intel.com/

> ---
>  drivers/gpu/drm/i915/display/i9xx_plane.c   | 4 ++++
>  drivers/gpu/drm/i915/display/intel_cursor.c | 3 +++
>  drivers/gpu/drm/i915/display/intel_sprite.c | 4 ++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/i9xx_plane.c b/drivers/gpu/drm/i915/display/i9xx_plane.c
> index 70734d32a409..490908f59141 100644
> --- a/drivers/gpu/drm/i915/display/i9xx_plane.c
> +++ b/drivers/gpu/drm/i915/display/i9xx_plane.c
> @@ -1108,6 +1108,10 @@ intel_primary_plane_create(struct intel_display *display, enum pipe pipe)
>  						   DRM_MODE_ROTATE_0,
>  						   supported_rotations);
>  
> +	if (display->platform.valleyview || display->platform.cherryview)
> +		drm_plane_create_blend_mode_property(&plane->base,
> +						     BIT(DRM_MODE_BLEND_PREMULTI));
> +
>  	zpos = 0;
>  	drm_plane_create_zpos_immutable_property(&plane->base, zpos);
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_cursor.c b/drivers/gpu/drm/i915/display/intel_cursor.c
> index 88384dea868b..0673f16f6fd0 100644
> --- a/drivers/gpu/drm/i915/display/intel_cursor.c
> +++ b/drivers/gpu/drm/i915/display/intel_cursor.c
> @@ -1078,6 +1078,9 @@ intel_cursor_plane_create(struct intel_display *display,
>  
>  	intel_cursor_add_size_hints_property(cursor);
>  
> +	drm_plane_create_blend_mode_property(&cursor->base,
> +					     BIT(DRM_MODE_BLEND_PREMULTI));
> +
>  	zpos = DISPLAY_RUNTIME_INFO(display)->num_sprites[pipe] + 1;
>  	drm_plane_create_zpos_immutable_property(&cursor->base, zpos);
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_sprite.c b/drivers/gpu/drm/i915/display/intel_sprite.c
> index 6a65f92e8a03..3e38960bbbd8 100644
> --- a/drivers/gpu/drm/i915/display/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/display/intel_sprite.c
> @@ -1722,6 +1722,10 @@ intel_sprite_plane_create(struct intel_display *display,
>  					  DRM_COLOR_YCBCR_BT709,
>  					  DRM_COLOR_YCBCR_LIMITED_RANGE);
>  
> +	if (display->platform.valleyview || display->platform.cherryview)
> +		drm_plane_create_blend_mode_property(&plane->base,
> +						     BIT(DRM_MODE_BLEND_PREMULTI));
> +
>  	zpos = sprite + 1;
>  	drm_plane_create_zpos_immutable_property(&plane->base, zpos);
>  
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel