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drm/drm_blend: allow blend mode property without PREMULTI

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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 <leandro.ribeiro@collabora.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Link: https://patch.msgid.link/20260526181700.25310-2-leandro.ribeiro@collabora.com
Signed-off-by: Daniel Stone <daniels@collabora.com>
This commit is contained in:
Leandro Ribeiro 2026-05-26 15:16:59 -03:00 committed by Daniel Stone
parent a3bbe1f487
commit 9813e158d1
1 changed files with 14 additions and 6 deletions
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20
drivers/gpu/drm/drm_blend.c
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@ -563,10 +563,10 @@ EXPORT_SYMBOL(drm_atomic_normalize_zpos);
/** /**
* drm_plane_create_blend_mode_property - create a new blend mode property * drm_plane_create_blend_mode_property - create a new blend mode property
* @plane: drm plane * @plane: drm plane
* @supported_modes: bitmask of supported modes, must include * @supported_modes: bitmask of supported modes. When
* BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is * BIT(DRM_MODE_BLEND_PREMULTI) is included, it will be used
* that alpha is premultiplied, and old userspace can break if * as the default. Otherwise, the default will fallback to one
* the property defaults to anything else. * of the supported modes.
* *
* This creates a new property describing the blend mode. * 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_PREMULTI, "Pre-multiplied" },
{ DRM_MODE_BLEND_COVERAGE, "Coverage" }, { DRM_MODE_BLEND_COVERAGE, "Coverage" },
}; };
unsigned int default_mode;
unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) | unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
BIT(DRM_MODE_BLEND_PREMULTI) | BIT(DRM_MODE_BLEND_PREMULTI) |
BIT(DRM_MODE_BLEND_COVERAGE); BIT(DRM_MODE_BLEND_COVERAGE);
int i; int i;
if (WARN_ON((supported_modes & ~valid_mode_mask) || if (WARN_ON((supported_modes & ~valid_mode_mask) ||
((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0))) (supported_modes == 0)))
return -EINVAL; return -EINVAL;
prop = drm_property_create(dev, DRM_MODE_PROP_ENUM, 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; plane->blend_mode_property = prop;
return 0; return 0;