drm: Introduce 'power saving policy' drm property

The `power saving policy` DRM property is an optional property that
can be added to a connector by a driver.

This property is for compositors to indicate intent of policy of
whether a driver can use power saving features that may compromise
the experience intended by the compositor.

Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240703051722.328-2-mario.limonciello@amd.com

drivers/gpu/drm/drm_connector.c

@@ -1043,6 +1043,11 @@ static const struct drm_prop_enum_list drm_scaling_mode_enum_list[] = {
 	{ DRM_MODE_SCALE_ASPECT, "Full aspect" },
 };
 
+static const struct drm_prop_enum_list drm_power_saving_policy_enum_list[] = {
+	{ __builtin_ffs(DRM_MODE_REQUIRE_COLOR_ACCURACY) - 1, "Require color accuracy" },
+	{ __builtin_ffs(DRM_MODE_REQUIRE_LOW_LATENCY) - 1, "Require low latency" },
+};
+
 static const struct drm_prop_enum_list drm_aspect_ratio_enum_list[] = {
 	{ DRM_MODE_PICTURE_ASPECT_NONE, "Automatic" },
 	{ DRM_MODE_PICTURE_ASPECT_4_3, "4:3" },
@@ -1629,6 +1634,16 @@ EXPORT_SYMBOL(drm_hdmi_connector_get_output_format_name);
  *
  *	Drivers can set up these properties by calling
  *	drm_mode_create_tv_margin_properties().
+ * power saving policy:
+ *	This property is used to set the power saving policy for the connector.
+ *	This property is populated with a bitmask of optional requirements set
+ *	by the drm master for the drm driver to respect:
+ *	- "Require color accuracy": Disable power saving features that will
+ *	  affect color fidelity.
+ *	  For example: Hardware assisted backlight modulation.
+ *	- "Require low latency": Disable power saving features that will
+ *	  affect latency.
+ *	  For example: Panel self refresh (PSR)
  */
 
 int drm_connector_create_standard_properties(struct drm_device *dev)
@@ -2131,6 +2146,39 @@ int drm_mode_create_scaling_mode_property(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
 
+/**
+ * drm_mode_create_power_saving_policy_property - create power saving policy property
+ * @dev: DRM device
+ * @supported_policies: bitmask of supported power saving policies
+ *
+ * Called by a driver the first time it's needed, must be attached to desired
+ * connectors.
+ *
+ * Returns: %0
+ */
+int drm_mode_create_power_saving_policy_property(struct drm_device *dev,
+						 uint64_t supported_policies)
+{
+	struct drm_property *power_saving;
+
+	if (dev->mode_config.power_saving_policy)
+		return 0;
+	WARN_ON((supported_policies & DRM_MODE_POWER_SAVING_POLICY_ALL) == 0);
+
+	power_saving =
+		drm_property_create_bitmask(dev, 0, "power saving policy",
+					    drm_power_saving_policy_enum_list,
+					    ARRAY_SIZE(drm_power_saving_policy_enum_list),
+					    supported_policies);
+	if (!power_saving)
+		return -ENOMEM;
+
+	dev->mode_config.power_saving_policy = power_saving;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_mode_create_power_saving_policy_property);
+
 /**
  * DOC: Variable refresh properties
  *

include/drm/drm_connector.h

@@ -2267,6 +2267,8 @@ int drm_mode_create_dp_colorspace_property(struct drm_connector *connector,
 					   u32 supported_colorspaces);
 int drm_mode_create_content_type_property(struct drm_device *dev);
 int drm_mode_create_suggested_offset_properties(struct drm_device *dev);
+int drm_mode_create_power_saving_policy_property(struct drm_device *dev,
+						 uint64_t supported_policies);
 
 int drm_connector_set_path_property(struct drm_connector *connector,
 				    const char *path);

include/drm/drm_mode_config.h

@@ -969,6 +969,11 @@ struct drm_mode_config {
 	 */
 	struct drm_atomic_state *suspend_state;
 
+	/**
+	 * @power_saving_policy: bitmask for power saving policy requests.
+	 */
+	struct drm_property *power_saving_policy;
+
 	const struct drm_mode_config_helper_funcs *helper_private;
 };
 

include/uapi/drm/drm_mode.h

@@ -152,6 +152,13 @@ extern "C" {
 #define DRM_MODE_SCALE_CENTER		2 /* Centered, no scaling */
 #define DRM_MODE_SCALE_ASPECT		3 /* Full screen, preserve aspect */
 
+/* power saving policy options */
+#define DRM_MODE_REQUIRE_COLOR_ACCURACY	BIT(0)	/* Compositor requires color accuracy */
+#define DRM_MODE_REQUIRE_LOW_LATENCY	BIT(1)	/* Compositor requires low latency */
+
+#define DRM_MODE_POWER_SAVING_POLICY_ALL	(DRM_MODE_REQUIRE_COLOR_ACCURACY |\
+						 DRM_MODE_REQUIRE_LOW_LATENCY)
+
 /* Dithering mode options */
 #define DRM_MODE_DITHERING_OFF	0
 #define DRM_MODE_DITHERING_ON	1