[PATCH v2 2/3] drm: Add CRTC background color property (v2)

[Matt Roper <matthew.d.roper@intel.com>]

Some display controllers can be programmed to present non-black colors
for pixels not covered by any plane (or pixels covered by the
transparent regions of higher planes).  Compositors that want a UI with
a solid color background can potentially save memory bandwidth by
setting the CRTC background property and using smaller planes to display
the rest of the content.

To avoid confusion between different ways of encoding RGB data, we
define a standard 64-bit format that should be used for this property's
value.  Helper functions and macros are provided to generate and dissect
values in this standard format with varying component precision values.

v2:
 - Swap internal representation's blue and red bits to make it easier
   to read if printed out.  (Ville)
 - Document bgcolor property in drm_blend.c.  (Sean Paul)
 - s/background_color/bgcolor/ for consistency between property name and
   value storage field.  (Sean Paul)
 - Add a convenience function to attach property to a given crtc.

Cc: dri-devel@lists.freedesktop.org
Cc: wei.c.li@intel.com
Cc: harish.krupo.kps@intel.com
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Sean Paul <sean@poorly.run>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
---
 drivers/gpu/drm/drm_atomic_state_helper.c |  1 +
 drivers/gpu/drm/drm_atomic_uapi.c         |  5 +++++
 drivers/gpu/drm/drm_blend.c               | 21 ++++++++++++++++++---
 drivers/gpu/drm/drm_mode_config.c         |  6 ++++++
 include/drm/drm_blend.h                   |  1 +
 include/drm/drm_crtc.h                    | 17 +++++++++++++++++
 include/drm/drm_mode_config.h             |  5 +++++
 include/uapi/drm/drm_mode.h               | 26 ++++++++++++++++++++++++++
 8 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
index 3ba996069d69..2f8c55668089 100644
--- a/drivers/gpu/drm/drm_atomic_state_helper.c
+++ b/drivers/gpu/drm/drm_atomic_state_helper.c
@@ -101,6 +101,7 @@ void __drm_atomic_helper_crtc_duplicate_state(struct drm_crtc *crtc,
 	state->planes_changed = false;
 	state->connectors_changed = false;
 	state->color_mgmt_changed = false;
+	state->bgcolor_changed = false;
 	state->zpos_changed = false;
 	state->commit = NULL;
 	state->event = NULL;
diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index 86ac33922b09..b95a55a778e2 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -467,6 +467,9 @@ static int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
 			return -EFAULT;
 
 		set_out_fence_for_crtc(state->state, crtc, fence_ptr);
+	} else if (property == config->bgcolor_property) {
+		state->bgcolor = val;
+		state->bgcolor_changed = true;
 	} else if (crtc->funcs->atomic_set_property) {
 		return crtc->funcs->atomic_set_property(crtc, state, property, val);
 	} else {
@@ -499,6 +502,8 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc,
 		*val = (state->gamma_lut) ? state->gamma_lut->base.id : 0;
 	else if (property == config->prop_out_fence_ptr)
 		*val = 0;
+	else if (property == config->bgcolor_property)
+		*val = state->bgcolor;
 	else if (crtc->funcs->atomic_get_property)
 		return crtc->funcs->atomic_get_property(crtc, state, property, val);
 	else
diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
index 0c78ca386cbe..7c73cb83874a 100644
--- a/drivers/gpu/drm/drm_blend.c
+++ b/drivers/gpu/drm/drm_blend.c
@@ -175,9 +175,16 @@
  *		 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).
+ * The property extensions described above all apply to the plane.  Drivers
+ * may also expose the following crtc property extension:
+ *
+ * bgcolor:
+ *	Background color is setup with drm_crtc_add_bgcolor_property().  It
+ *	controls the RGB color of a full-screen, fully-opaque 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.
  */
 
 /**
@@ -593,3 +600,11 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane,
 	return 0;
 }
 EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
+
+void drm_crtc_add_bgcolor_property(struct drm_crtc *crtc)
+{
+	drm_object_attach_property(&crtc->base,
+				   crtc->dev->mode_config.bgcolor_property,
+				   drm_rgba(16, 0, 0, 0, 0xffff));
+}
+EXPORT_SYMBOL(drm_crtc_add_bgcolor_property);
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index ee80788f2c40..75e376755176 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -352,6 +352,12 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
 		return -ENOMEM;
 	dev->mode_config.modifiers_property = prop;
 
+	prop = drm_property_create_range(dev, 0, "BACKGROUND_COLOR",
+					 0, GENMASK_ULL(63, 0));
+	if (!prop)
+		return -ENOMEM;
+	dev->mode_config.bgcolor_property = prop;
+
 	return 0;
 }
 
diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
index 88bdfec3bd88..9e2538dd7b9a 100644
--- a/include/drm/drm_blend.h
+++ b/include/drm/drm_blend.h
@@ -58,4 +58,5 @@ 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_add_bgcolor_property(struct drm_crtc *crtc);
 #endif
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index b21437bc95bf..d78f82f954e4 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -168,6 +168,11 @@ struct drm_crtc_state {
 	 * drivers to steer the atomic commit control flow.
 	 */
 	bool color_mgmt_changed : 1;
+	/**
+	 * @bgcolor_changed: Background color value has changed.  Used by
+	 * drivers to steer the atomic commit control flow.
+	 */
+	bool bgcolor_changed : 1;
 
 	/**
 	 * @no_vblank:
@@ -274,6 +279,18 @@ struct drm_crtc_state {
 	 */
 	struct drm_property_blob *gamma_lut;
 
+	/**
+	 * @bgcolor:
+	 *
+	 * 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 via drm_rgba();
+	 * individual color components can be extracted with desired precision
+	 * via the DRM_RGBA_*() macros.
+	 */
+	u64 bgcolor;
+
 	/**
 	 * @target_vblank:
 	 *
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 5dbeabdbaf91..8b686d228feb 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -813,6 +813,11 @@ struct drm_mode_config {
 	 */
 	struct drm_property *writeback_out_fence_ptr_property;
 
+	/**
+	 * @bgcolor_property: RGBA background color for CRTC.
+	 */
+	struct drm_property *bgcolor_property;
+
 	/* dumb ioctl parameters */
 	uint32_t preferred_depth, prefer_shadow;
 
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index d3e0fe31efc5..7c4f902aa290 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -888,6 +888,32 @@ struct drm_mode_revoke_lease {
 	__u32 lessee_id;
 };
 
+/*
+ * Put RGBA values into a standard 64-bit representation that can be used
+ * for ioctl parameters, inter-driver commmunication, etc.  If the component
+ * values being provided contain less than 16 bits of precision, they'll
+ * be shifted into the most significant bits.
+ */
+static inline __u64
+drm_rgba(__u8 bpc, __u16 red, __u16 green, __u16 blue, __u16 alpha)
+{
+	int msb_shift = 16 - bpc;
+
+	return (__u64)alpha << msb_shift << 48 |
+	       (__u64)red   << msb_shift << 32 |
+	       (__u64)green << msb_shift << 16 |
+	       (__u64)blue  << msb_shift;
+}
+
+/*
+ * Extract the specified number of bits of a specific color component from a
+ * standard 64-bit RGBA value.
+ */
+#define DRM_RGBA_BLUE(c, numbits)  (__u16)((c & 0xFFFFull)     >> (16-numbits))
+#define DRM_RGBA_GREEN(c, numbits) (__u16)((c & 0xFFFFull<<16) >> (32-numbits))
+#define DRM_RGBA_RED(c, numbits)   (__u16)((c & 0xFFFFull<<32) >> (48-numbits))
+#define DRM_RGBA_ALPHA(c, numbits) (__u16)((c & 0xFFFFull<<48) >> (64-numbits))
+
 #if defined(__cplusplus)
 }
 #endif
-- 
2.14.4

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