[RFC,3/3] drm/color: Add sdr boost property

Commit Message

Harry Wentland April 26, 2021, 5:38 p.m. UTC

From: Bhawanpreet Lakha <[e-mail]>

SDR is typically mastered at 200 nits and HDR is mastered at up to 10,000
nits. Due to this luminance range difference if we blend a SDR and
HDR plane together, we can run into problems where the HDR plane is too
bright or the SDR plane is too dim

A common solution to this problem is to boost the SDR plane so that its
not too dim.

This patch introduces a "sdr_white_level" property, this property can be
used by the userspace to boost the SDR content luminance. The boost
value is a explicit luiminance value in nits. This allows the userspace
to set the maximum white level for the SDR plane.

Signed-off-by: Bhawanpreet Lakha <[e-mail]>
Signed-off-by: Harry Wentland <[e-mail]>
---
 drivers/gpu/drm/drm_atomic_uapi.c |  4 ++++
 drivers/gpu/drm/drm_color_mgmt.c  | 17 +++++++++++++++++
 include/drm/drm_color_mgmt.h      |  6 ++++++
 include/drm/drm_plane.h           | 14 ++++++++++++++
 4 files changed, 41 insertions(+)

Patch

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index ea95c1224253..b3b6de7b74aa 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -597,6 +597,8 @@  static int drm_atomic_plane_set_property(struct drm_plane *plane,
 		state->color_range = val;
 	} else if (property == plane->color_tf_property) {
 		state->color_tf = val;
+	} else if (property == plane->sdr_white_level_property) {
+		state->sdr_white_level = val;
 	} else if (property == config->prop_fb_damage_clips) {
 		ret = drm_atomic_replace_property_blob_from_id(dev,
 					&state->fb_damage_clips,
@@ -665,6 +667,8 @@  drm_atomic_plane_get_property(struct drm_plane *plane,
 		*val = state->color_range;
 	} else if (property == plane->color_tf_property) {
 		*val = state->color_tf;
+	} else if (property == plane->sdr_white_level_property) {
+		*val = state->sdr_white_level;
 	} else if (property == config->prop_fb_damage_clips) {
 		*val = (state->fb_damage_clips) ?
 			state->fb_damage_clips->base.id : 0;
diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 2404b07046c5..a0b77d7d0565 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -519,6 +519,23 @@  const char *drm_get_color_range_name(enum drm_color_range range)
 	return color_range_name[range];
 }
 
+int drm_plane_create_sdr_white_level_property(struct drm_plane *plane){
+
+	struct drm_property *prop;
+
+	prop = drm_property_create_range(plane->dev, 0, "SDR_WHITE_LEVEL", 0, UINT_MAX);
+
+	if (!prop)
+		return -ENOMEM;
+
+	plane->sdr_white_level_property = prop;
+	drm_object_attach_property(&plane->base, prop, DRM_DEFAULT_SDR_WHITE_LEVEL);
+
+	if (plane->state)
+		plane->state->sdr_white_level = DRM_DEFAULT_SDR_WHITE_LEVEL;
+
+	return 0;
+}
 /**
  * drm_get_color_transfer_function - return a string for color transfer function
  * @tf: transfer function to compute name of
diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
index f59806366855..a020346b1747 100644
--- a/include/drm/drm_color_mgmt.h
+++ b/include/drm/drm_color_mgmt.h
@@ -26,6 +26,12 @@ 
 #include <linux/ctype.h>
 #include <drm/drm_property.h>
 
+/**
+ * Default SDR white level in nits. Although there is no standard SDR nit level, 200
+ * is chosen as the default since that is the generally accepted value.
+ */
+#define DRM_DEFAULT_SDR_WHITE_LEVEL 200
+
 struct drm_crtc;
 struct drm_plane;
 
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index c85c59501a7a..fad8b7dd430c 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -187,6 +187,11 @@  struct drm_plane_state {
 	 * format for a proper HDR color/luminance output.
 	 */
 	enum drm_color_transfer_function color_tf;
+	/**
+	 * @sdr_white_level:
+	 * SDR white level boost for HDR+SDR multi plane usecases. max white level in nits
+	 */
+	unsigned int sdr_white_level;
 	/**
 	 * @fb_damage_clips:
 	 *
@@ -757,6 +762,15 @@  struct drm_plane {
 	 * See drm_plane_create_color_properties().
 	 */
 	struct drm_property *color_tf_property;
+	/**
+	 * @sdr_white_level:
+	 *
+	 * Optional sdr_white_level. When HDR and SDR are combined in multi plane
+	 * overlay cases, the sdr plane will be very dim. This property allows
+	 * the driver to boost the sdr plane's white level. The value should be
+	 * max white level in nits.
+	 */
+	struct drm_property *sdr_white_level_property;
 
 	/**
 	 * @scaling_filter_property: property to apply a particular filter while