drm: Add CRTC background color property

Some display controllers can be hardware programmed to show non-black
colors for pixels that are either not covered by any plane or are
exposed through transparent regions of higher planes.  This feature can
help reduce memory bandwidth usage, e.g. in compositors managing a UI
with a solid background color while using smaller planes to render the
remaining content.

To support this capability, introduce the BACKGROUND_COLOR standard DRM
mode property, which can be attached to a CRTC through the
drm_crtc_attach_background_color_property() helper function.

Additionally, define a 64-bit ARGB format value to be built with the
help of a dedicated drm_argb64() utility macro.  Individual color
components can be extracted with desired precision using the
corresponding DRM_ARGB64_*() macros.

Co-developed-by: Matt Roper <[email protected]>
Signed-off-by: Matt Roper <[email protected]>
Signed-off-by: Cristian Ciocaltea <[email protected]>

Author: cristicc

drivers/gpu/drm/drm_atomic_state_helper.c

@@ -74,6 +74,7 @@ __drm_atomic_helper_crtc_state_reset(struct drm_crtc_state *crtc_state,
 				     struct drm_crtc *crtc)
 {
 	crtc_state->crtc = crtc;
+	crtc_state->background_color = drm_argb64(0xffff, 0, 0, 0);
 }
 EXPORT_SYMBOL(__drm_atomic_helper_crtc_state_reset);
 

drivers/gpu/drm/drm_atomic_uapi.c

@@ -405,6 +405,8 @@ static int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
 					&replaced);
 		state->color_mgmt_changed |= replaced;
 		return ret;
+	} else if (property == config->background_color_property) {
+		state->background_color = val;
 	} else if (property == config->prop_out_fence_ptr) {
 		s32 __user *fence_ptr = u64_to_user_ptr(val);
 
@@ -450,6 +452,8 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc,
 		*val = (state->ctm) ? state->ctm->base.id : 0;
 	else if (property == config->gamma_lut_property)
 		*val = (state->gamma_lut) ? state->gamma_lut->base.id : 0;
+	else if (property == config->background_color_property)
+		*val = state->background_color;
 	else if (property == config->prop_out_fence_ptr)
 		*val = 0;
 	else if (property == crtc->scaling_filter_property)

drivers/gpu/drm/drm_blend.c

@@ -185,10 +185,6 @@
  *		 plane does not expose the "alpha" property, then this is
  *		 assumed to be 1.0
  *
- * Note that all the property extensions described here apply either to the
- * plane or the CRTC (e.g. for the background color, which currently is not
- * exposed and assumed to be black).
- *
  * SCALING_FILTER:
  *     Indicates scaling filter to be used for plane scaler
  *
@@ -201,6 +197,23 @@
  *
  * Drivers can set up this property for a plane by calling
  * drm_plane_create_scaling_filter_property
+ *
+ * The property extensions described above all apply to the plane.  Drivers
+ * may also expose the following crtc property extension:
+ *
+ * BACKGROUND_COLOR:
+ *	Background color is set via drm_crtc_attach_background_color_property().
+ *	It controls the ARGB color of a full-screen layer that exists below all
+ *	planes.  This color will be used for pixels not covered by any plane and
+ *	may also be blended with plane contents as allowed by a plane's alpha
+ *	values.  The background color defaults to black, and is assumed to be
+ *	black for drivers that do not expose this property.  Although background
+ *	color isn't a plane, it is assumed that the color provided here
+ *	undergoes the same pipe-level degamma/CSC/gamma transformations that
+ *	planes undergo.  Note that the color value provided here includes an
+ *	alpha channel, hence non-opaque background color values are allowed, but
+ *	are generally only honored in special cases (e.g. when a memory
+ *	writeback connector is in use).
  */
 
 /**
@@ -648,3 +661,19 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane,
 	return 0;
 }
 EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
+
+/**
+ * drm_crtc_attach_background_color_property - attach background color property
+ * @crtc: drm crtc
+ *
+ * Attaches the background color property to @crtc.  The property defaults to
+ * solid black and will accept 64-bit ARGB values in the format generated by
+ * drm_argb64().
+ */
+void drm_crtc_attach_background_color_property(struct drm_crtc *crtc)
+{
+	drm_object_attach_property(&crtc->base,
+				   crtc->dev->mode_config.background_color_property,
+				   drm_argb64(0xffff, 0, 0, 0));
+}
+EXPORT_SYMBOL(drm_crtc_attach_background_color_property);

drivers/gpu/drm/drm_mode_config.c

@@ -365,6 +365,12 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
 		return -ENOMEM;
 	dev->mode_config.gamma_lut_size_property = prop;
 
+	prop = drm_property_create_range(dev, 0,
+					 "BACKGROUND_COLOR", 0, U64_MAX);
+	if (!prop)
+		return -ENOMEM;
+	dev->mode_config.background_color_property = prop;
+
 	prop = drm_property_create(dev,
 				   DRM_MODE_PROP_IMMUTABLE | DRM_MODE_PROP_BLOB,
 				   "IN_FORMATS", 0);

include/drm/drm_blend.h

@@ -31,8 +31,9 @@
 #define DRM_MODE_BLEND_COVERAGE		1
 #define DRM_MODE_BLEND_PIXEL_NONE	2
 
-struct drm_device;
 struct drm_atomic_state;
+struct drm_crtc;
+struct drm_device;
 struct drm_plane;
 struct drm_connector;
 
@@ -59,7 +60,7 @@ 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);
-
+void drm_crtc_attach_background_color_property(struct drm_crtc *crtc);
 int drm_connector_create_rotation_property(struct drm_connector *conn,
 					   unsigned int rotation,
 					   unsigned int supported_rotations);

include/drm/drm_crtc.h

@@ -274,6 +274,18 @@ struct drm_crtc_state {
 	 */
 	struct drm_property_blob *gamma_lut;
 
+	/**
+	 * @background_color:
+	 *
+	 * RGB value representing the pipe's background color.  The background
+	 * color (aka "canvas color") of a pipe is the color that will be used
+	 * for pixels not covered by a plane, or covered by transparent pixels
+	 * of a plane.  The value here should be built using drm_argb64(), while
+	 * the individual color components can be extracted with desired
+	 * precision via the DRM_ARGB64_*() macros.
+	 */
+	u64 background_color;
+
 	/**
 	 * @target_vblank:
 	 *

include/drm/drm_mode_config.h

@@ -813,6 +813,11 @@ struct drm_mode_config {
 	 * gamma LUT as supported by the driver (read-only).
 	 */
 	struct drm_property *gamma_lut_size_property;
+	/**
+	 * @background_color_property: Optional CRTC property to set the
+	 * background color.
+	 */
+	struct drm_property *background_color_property;
 
 	/**
 	 * @suggested_x_property: Optional connector property with a hint for

include/uapi/drm/drm_mode.h

@@ -1356,6 +1356,36 @@ struct drm_mode_closefb {
 	__u32 pad;
 };
 
+/*
+ * Put 16-bit ARGB values into a standard 64-bit representation that
+ * can be used for ioctl parameters, inter-driver communication, etc.
+ */
+static inline __u64
+drm_argb64(__u16 alpha, __u16 red, __u16 green, __u16 blue)
+{
+	return (__u64)alpha << 48 | (__u64)red << 32 | (__u64)green << 16 | blue;
+}
+
+/*
+ * Extract the specified number of least-significant bits of a specific
+ * color component from a standard 64-bit ARGB value.
+ */
+#define DRM_ARGB64_COMP(c, shift, numlsb) \
+	((__u16)(((c) >> (shift)) & ((1UL << (numlsb) % 17) - 1)))
+#define DRM_ARGB64_ALPHA_LSB(c, numlsb) DRM_ARGB64_COMP(c, 48, numlsb)
+#define DRM_ARGB64_RED_LSB(c, numlsb)   DRM_ARGB64_COMP(c, 32, numlsb)
+#define DRM_ARGB64_GREEN_LSB(c, numlsb) DRM_ARGB64_COMP(c, 16, numlsb)
+#define DRM_ARGB64_BLUE_LSB(c, numlsb)  DRM_ARGB64_COMP(c, 0, numlsb)
+
+/*
+ * Convenience wrappers to extract all 16 bits of a specific color
+ * component from a standard 64-bit ARGB value.
+ */
+#define DRM_ARGB64_ALPHA(c)		DRM_ARGB64_ALPHA_LSB(c, 16)
+#define DRM_ARGB64_RED(c)		DRM_ARGB64_RED_LSB(c, 16)
+#define DRM_ARGB64_GREEN(c)		DRM_ARGB64_GREEN_LSB(c, 16)
+#define DRM_ARGB64_BLUE(c)		DRM_ARGB64_BLUE_LSB(c, 16)
+
 #if defined(__cplusplus)
 }
 #endif