linux-kernel - [PATCH v2 1/4] drm/drm_blend: Allow specifying blend mode default

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Message-Id: <20260106164247.472544-2-sean.anderson@linux.dev>
Date: Tue,  6 Jan 2026 11:42:44 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
	dri-devel@...ts.freedesktop.org
Cc: Simona Vetter <simona@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	linux-kernel@...r.kernel.org,
	Maxime Ripard <mripard@...nel.org>,
	David Airlie <airlied@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Michal Simek <michal.simek@....com>,
	Anatoliy Klymenko <anatoliy.klymenko@....com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Mike Looijmans <mike.looijmans@...ic.nl>,
	Sean Anderson <sean.anderson@...ux.dev>
Subject: [PATCH v2 1/4] drm/drm_blend: Allow specifying blend mode default

Not all devices support pre-multiplied blend mode. In these cases,
userspace cannot expect this mode to be the default, since the hardware
cannot produce it (and could not default to it before a blend mode
property existed). Therefore, add a variant of
drm_plane_create_blend_mode_property that allows specifying the default.

Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
---

Changes in v2:
- New

 drivers/gpu/drm/drm_blend.c | 22 ++++++++++------------
 include/drm/drm_blend.h     | 26 ++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
index 6852d73c931c..fac0f1478385 100644
--- a/drivers/gpu/drm/drm_blend.c
+++ b/drivers/gpu/drm/drm_blend.c
@@ -546,12 +546,10 @@ int drm_atomic_normalize_zpos(struct drm_device *dev,
 EXPORT_SYMBOL(drm_atomic_normalize_zpos);
 
 /**
- * drm_plane_create_blend_mode_property - create a new blend mode property
+ * drm_plane_create_blend_mode_default - 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, must include BIT(@def)
+ * @def: Default blend mode
  *
  * This creates a new property describing the blend mode.
  *
@@ -571,11 +569,11 @@ EXPORT_SYMBOL(drm_atomic_normalize_zpos);
  *	pre-multiplied and will do so when blending them to the background color
  *	values.
  *
- * RETURNS:
- * Zero for success or -errno
+ * Return: Zero for success or -errno
  */
-int drm_plane_create_blend_mode_property(struct drm_plane *plane,
-					 unsigned int supported_modes)
+int drm_plane_create_blend_mode_default(struct drm_plane *plane,
+					unsigned int supported_modes,
+					unsigned int def)
 {
 	struct drm_device *dev = plane->dev;
 	struct drm_property *prop;
@@ -590,7 +588,7 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane,
 	int i;
 
 	if (WARN_ON((supported_modes & ~valid_mode_mask) ||
-		    ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0)))
+		    !(supported_modes & BIT(def))))
 		return -EINVAL;
 
 	prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
@@ -615,9 +613,9 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane,
 		}
 	}
 
-	drm_object_attach_property(&plane->base, prop, DRM_MODE_BLEND_PREMULTI);
+	drm_object_attach_property(&plane->base, prop, def);
 	plane->blend_mode_property = prop;
 
 	return 0;
 }
-EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
+EXPORT_SYMBOL(drm_plane_create_blend_mode_default);
diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
index 88bdfec3bd88..244f0694d0a5 100644
--- a/include/drm/drm_blend.h
+++ b/include/drm/drm_blend.h
@@ -56,6 +56,28 @@ int drm_plane_create_zpos_immutable_property(struct drm_plane *plane,
 					     unsigned int zpos);
 int drm_atomic_normalize_zpos(struct drm_device *dev,
 			      struct drm_atomic_state *state);
-int drm_plane_create_blend_mode_property(struct drm_plane *plane,
-					 unsigned int supported_modes);
+int drm_plane_create_blend_mode_default(struct drm_plane *plane,
+					unsigned int supported_modes,
+					unsigned int def);
+
+/**
+ * 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.
+ *
+ * This creates a new property describing the blend mode. See
+ * drm_plane_create_blend_mode_default() for details.
+ *
+ * Return: Zero for success or -errno
+ */
+static inline int
+drm_plane_create_blend_mode_property(struct drm_plane *plane,
+				     unsigned int supported_modes)
+{
+	return drm_plane_create_blend_mode_default(plane, supported_modes,
+						   DRM_MODE_BLEND_PREMULTI);
+}
 #endif
-- 
2.35.1.1320.gc452695387.dirty