[PATCH v7 1/3] drm: Add CRTC background color property

[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.

v3:
 - Restructure ARGB component extraction macros to be easier to
   understand and enclose the parameters in () to avoid calculations
   if expressions are passed.  (Sean Paul)
 - s/rgba/argb/ in helper function/macro names.  Even though the idea is
   to not worry about the internal representation of the u64, it can
   still be confusing to look at code that uses 'rgba' terminology, but
   stores values with argb ordering.  (Ville)

v4:
 - Drop the bgcolor_changed flag.  (Ville, Brian Starkey)
 - Clarify in kerneldoc that background color is expected to undergo the
   same pipe-level degamma/csc/gamma transformations that planes do.
   (Brian Starkey)
 - Update kerneldoc to indicate non-opaque colors are allowed, but are
   generally only useful in special cases such as when writeback
   connectors are used (Brian Starkey / Eric Anholt)

v5:
 - Set crtc->state->bgcolor to solid black inside
   drm_crtc_add_bgcolor_property() in case drivers don't do this
   themselves.  (Ville)
 - Add kerneldoc to drm_crtc_add_bgcolor_property() function.

v7:
 - Don't update CRTC state at attach time; instead set the default value
   in __drm_atomic_helper_crtc_reset.  (Maarten)

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>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: Stéphane Marchesin <marcheu@chromium.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Jean-Jacques Hiblot <jjhiblot@ti.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Sean Paul <sean@poorly.run>            # v2
Reviewed-by: Brian Starkey <brian.starkey@arm.com>  # v4
---
 drivers/gpu/drm/drm_atomic_state_helper.c |  4 ++-
 drivers/gpu/drm/drm_atomic_uapi.c         |  4 +++
 drivers/gpu/drm/drm_blend.c               | 35 +++++++++++++++++++++--
 drivers/gpu/drm/drm_mode_config.c         |  6 ++++
 include/drm/drm_blend.h                   |  1 +
 include/drm/drm_crtc.h                    | 12 ++++++++
 include/drm/drm_mode_config.h             |  5 ++++
 include/uapi/drm/drm_mode.h               | 28 ++++++++++++++++++
 8 files changed, 91 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
index d0a937fb0c56..b8cc12579024 100644
--- a/drivers/gpu/drm/drm_atomic_state_helper.c
+++ b/drivers/gpu/drm/drm_atomic_state_helper.c
@@ -73,8 +73,10 @@ void
 __drm_atomic_helper_crtc_reset(struct drm_crtc *crtc,
 			       struct drm_crtc_state *crtc_state)
 {
-	if (crtc_state)
+	if (crtc_state) {
 		crtc_state->crtc = crtc;
+		crtc_state->bgcolor = drm_argb(16, 0xffff, 0, 0, 0);
+	}
 
 	crtc->state = crtc_state;
 }
diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index 7a26bfb5329c..038e6a38ae5f 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -469,6 +469,8 @@ 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;
 	} else if (crtc->funcs->atomic_set_property) {
 		return crtc->funcs->atomic_set_property(crtc, state, property, val);
 	} else {
@@ -503,6 +505,8 @@ 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 d02709dd2d4a..f71af04101e5 100644
--- a/drivers/gpu/drm/drm_blend.c
+++ b/drivers/gpu/drm/drm_blend.c
@@ -183,9 +183,22 @@
  *		 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:
+ *
+ * BACKGROUND_COLOR:
+ *	Background color is setup with drm_crtc_add_bgcolor_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...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).
  */
 
 /**
@@ -601,3 +614,19 @@ int drm_plane_create_blend_mode_property(struct drm_plane *plane,
 	return 0;
 }
 EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
+
+/**
+ * drm_crtc_add_bgcolor_property - add background color property
+ * @crtc: drm crtc
+ *
+ * Adds 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_argb().
+ */
+void drm_crtc_add_bgcolor_property(struct drm_crtc *crtc)
+{
+	drm_object_attach_property(&crtc->base,
+				   crtc->dev->mode_config.bgcolor_property,
+				   drm_argb(16, 0xffff, 0, 0, 0));
+}
+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 7bc03c3c154f..dc714050ed2b 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -369,6 +369,12 @@ 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 5e9b15a0e8c5..5b46dabec546 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -275,6 +275,18 @@ 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_argb();
+	 * individual color components can be extracted with desired precision
+	 * via the DRM_ARGB_*() macros.
+	 */
+	u64 bgcolor;
+
 	/**
 	 * @target_vblank:
 	 *
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 3bcbe30339f0..8ee29f992d25 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -855,6 +855,11 @@ struct drm_mode_config {
 	 */
 	struct drm_property *hdcp_content_type_property;
 
+	/**
+	 * @bgcolor_property: RGB 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 735c8cfdaaa1..1fc7f2bcd150 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -1025,6 +1025,34 @@ struct drm_mode_rect {
 	__s32 y2;
 };
 
+/*
+ * Put ARGB 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_argb(__u8 bpc, __u16 alpha, __u16 red, __u16 green, __u16 blue)
+{
+	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 ARGB value.
+ */
+#define DRM_ARGB_COMP(c, shift, numbits) \
+	(__u16)(((c) & 0xFFFFull << (shift)) >> ((shift) + 16 - (numbits)))
+#define DRM_ARGB_BLUE(c, numbits)  DRM_ARGB_COMP(c, 0, numbits)
+#define DRM_ARGB_GREEN(c, numbits) DRM_ARGB_COMP(c, 16, numbits)
+#define DRM_ARGB_RED(c, numbits)   DRM_ARGB_COMP(c, 32, numbits)
+#define DRM_ARGB_ALPHA(c, numbits) DRM_ARGB_COMP(c, 48, numbits)
+
 #if defined(__cplusplus)
 }
 #endif
-- 
2.21.0

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