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

[Borah, Chaitanya Kumar]

On 7/15/2026 5:31 PM, Ville Syrjälä wrote:

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.syrj...@linux.intel.com>
Cc: Uma Shankar <uma.shan...@intel.com>
Cc: Leandro Ribeiro <leandro.ribe...@collabora.com>
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16623
Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.bo...@intel.com>

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

Sorry Ville, I missed it. This patch got fast tracked to unblock CI.

==
Chaitanya

---
  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