From 9813e158d13d51d20d9257879bf79da7abcc9107 Mon Sep 17 00:00:00 2001 From: Leandro Ribeiro Date: Tue, 26 May 2026 15:16:59 -0300 Subject: [PATCH] drm/drm_blend: allow blend mode property without PREMULTI Some hardware only supports the COVERAGE blend mode and lacks PREMULTI support entirely. DRM currently requires that PREMULTI is present when creating a blend mode property, which prevents such drivers from being properly upstreamed. Remove this restriction and allow drivers to create a blend mode property without PREMULTI, enabling support for hardware that implements only COVERAGE blend mode. This does not introduce a regression, as no existing upstream drivers expose only COVERAGE. However, userspace that wants to support such kind of hardware in the future will have to check the supported blend modes instead of assuming PREMULTI is always supported. Signed-off-by: Leandro Ribeiro Acked-by: Pekka Paalanen Reviewed-by: Daniel Stone Link: https://patch.msgid.link/20260526181700.25310-2-leandro.ribeiro@collabora.com Signed-off-by: Daniel Stone --- drivers/gpu/drm/drm_blend.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c index 2f0d1ba285be..d17ae964fb21 100644 --- a/drivers/gpu/drm/drm_blend.c +++ b/drivers/gpu/drm/drm_blend.c @@ -563,10 +563,10 @@ EXPORT_SYMBOL(drm_atomic_normalize_zpos); /** * drm_plane_create_blend_mode_property - create a new blend mode property * @plane: drm plane - * @supported_modes: bitmask of supported modes, must include - * BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is - * that alpha is premultiplied, and old userspace can break if - * the property defaults to anything else. + * @supported_modes: bitmask of supported modes. When + * BIT(DRM_MODE_BLEND_PREMULTI) is included, it will be used + * as the default. Otherwise, the default will fallback to one + * of the supported modes. * * This creates a new property describing the blend mode. * @@ -599,13 +599,14 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane, { DRM_MODE_BLEND_PREMULTI, "Pre-multiplied" }, { DRM_MODE_BLEND_COVERAGE, "Coverage" }, }; + unsigned int default_mode; unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) | BIT(DRM_MODE_BLEND_PREMULTI) | BIT(DRM_MODE_BLEND_COVERAGE); int i; if (WARN_ON((supported_modes & ~valid_mode_mask) || - ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0))) + (supported_modes == 0))) return -EINVAL; prop = drm_property_create(dev, DRM_MODE_PROP_ENUM, @@ -630,7 +631,14 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane, } } - drm_object_attach_property(&plane->base, prop, DRM_MODE_BLEND_PREMULTI); + if (supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) + default_mode = DRM_MODE_BLEND_PREMULTI; + else if (supported_modes & BIT(DRM_MODE_BLEND_COVERAGE)) + default_mode = DRM_MODE_BLEND_COVERAGE; + else + default_mode = DRM_MODE_BLEND_PIXEL_NONE; + + drm_object_attach_property(&plane->base, prop, default_mode); plane->blend_mode_property = prop; return 0;