[PATCH RFC 17/25] drm/connector: Add "qms_enabled" drm property

[Nicolas Frattaroli]

HDMI includes a feature called "Quick Media Switching", or QMS for
short, which builds upon the existing VRR to allow for quick switching
between a select few common frame rates.

Add a DRM property to the connector to allow userspace to request the
kernel to use QMS. Only connectors of sources which do support QMS
should register this property, though whether a specific sink supports
QMS is orthogonal to this.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_atomic_helper.c |  3 +++
 drivers/gpu/drm/drm_atomic_uapi.c   |  4 ++++
 drivers/gpu/drm/drm_connector.c     | 48 +++++++++++++++++++++++++++++++++++++
 include/drm/drm_connector.h         | 23 ++++++++++++++++++
 4 files changed, 78 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 0664d5779282..a2919e3975a8 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -749,6 +749,9 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 			    new_connector_state->color_format)
 				new_crtc_state->connectors_changed = true;
 
+			if (old_connector_state->hdmi.qms_enabled !=
+			    new_connector_state->hdmi.qms_enabled)
+				new_crtc_state->connectors_changed = true;
 		}
 
 		if (funcs->atomic_check)
diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index c9eb01d740b3..fe9516475451 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -993,6 +993,8 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
 		state->hdmi.broadcast_rgb = val;
 	} else if (property == connector->color_format_property) {
 		state->color_format = val;
+	} else if (property == connector->qms_enabled_property) {
+		state->hdmi.qms_enabled = val;
 	} else if (connector->funcs->atomic_set_property) {
 		return connector->funcs->atomic_set_property(connector,
 				state, property, val);
@@ -1080,6 +1082,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
 		*val = state->hdmi.broadcast_rgb;
 	} else if (property == connector->color_format_property) {
 		*val = state->color_format;
+	} else if (property == connector->qms_enabled_property) {
+		*val = state->hdmi.qms_enabled;
 	} else if (connector->funcs->atomic_get_property) {
 		return connector->funcs->atomic_get_property(connector,
 				state, property, val);
diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 5c07bd221977..7ea235a58781 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -2605,6 +2605,8 @@ EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
  *	numerator/denominator pair of a frame rate to set as the minimum VRR
  *	target rate. Set to 0 to disable.
  *
+ * .. _VRR-MIN-DENOMINATOR:
+ *
  * "VRR_MIN_DENOMINATOR":
  *	Default &drm_crtc integer property forming the denominator of a
  *	numerator/denominator pair of a frame rate to set as the minimum VRR
@@ -2619,11 +2621,30 @@ EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
  *	numerator/denominator pair of a frame rate to set as the maximum VRR
  *	target rate. Set to 0 to disable.
  *
+ * .. _VRR-MAX-DENOMINATOR:
+ *
  * "VRR_MAX_DENOMINATOR":
  *	Default &drm_crtc integer property forming the denominator of a
  *	numerator/denominator pair of a frame rate to set as the maximum VRR
  *	target rate. If :ref:`VRR_MAX_NUMERATOR <VRR-MAX-NUMERATOR>` is not
  *	zero, it must be non-zero. Otherwise, must also be zero.
+ *
+ * "qms_enabled":
+ *	Optional &drm_connector boolean property that drivers should attach with
+ *	drm_connector_attach_qms_enabled_property() on connectors that support
+ *	HDMI Quick Media Switching (QMS). Present only depending on source
+ *	capability, with no regards to sink capability. Userspace may set it to
+ *	true if the variable refresh target rate that's expressed through
+ *	:ref:`VRR_MIN_NUMERATOR <VRR-MIN-NUMERATOR>` divided by
+ *	:ref:`VRR_MIN_DENOMINATOR <VRR-MIN-DENOMINATOR>` (which, in this case,
+ *	should be equal to :ref:`VRR_MAX_NUMERATOR <VRR-MAX-NUMERATOR>` divided
+ *	by :ref:`VRR_MAX_DENOMINATOR <VRR-MAX-DENOMINATOR>` to signal a fixed
+ *	rate) should be achieved with signaling for HDMI Quick Media Switching.
+ *
+ *	Attempting to enable QMS when the attached display is not QMS capable,
+ *	or when the set fixed target rate is not possible with QMS, will result
+ *	in an error during the atomic check phase that will be passed up to
+ *	userspace to handle.
  */
 
 /**
@@ -3318,6 +3339,33 @@ int drm_connector_attach_color_format_property(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_connector_attach_color_format_property);
 
+/**
+ * drm_connector_attach_qms_enabled_property - attach "qms_enabled" property
+ * @connector: pointer to &struct drm_connector to attach this property on.
+ *
+ * Create and attach the "qms_enabled" property to the given @connector, which
+ * can be used by userspace to signal that it would like to achieve the CRTC's
+ * desired VRR target frame rate with HDMI "Quick Media Switching".
+ *
+ * Should only be called if the source actually supports generating the packets
+ * needed for QMS, but is present regardless of sink support for QMS.
+ *
+ * Returns:
+ * Zero on success, negative errno on failure.
+ */
+int drm_connector_attach_qms_enabled_property(struct drm_connector *connector)
+{
+	connector->qms_enabled_property =
+		drm_property_create_bool(connector->dev, 0, "qms_enabled");
+	if (!connector->qms_enabled_property)
+		return -ENOMEM;
+
+	drm_object_attach_property(&connector->base, connector->qms_enabled_property, 0);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_connector_attach_qms_enabled_property);
+
 /**
  * drm_connector_atomic_hdr_metadata_equal - checks if the hdr metadata changed
  * @old_state: old connector state to compare
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 8439c82db905..a5631bebb4df 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -1238,6 +1238,18 @@ struct drm_connector_hdmi_state {
 	 * deliberately not requested by the helper.
 	 */
 	bool scrambler_needed;
+
+	/**
+	 * @qms_tfr_byte: Target frame rate byte for HDMI QMS, or 0 if QMS is
+	 * not in use.
+	 */
+	u8 qms_tfr_byte;
+
+	/**
+	 * @qms_enabled: Whether or not userspace requests to use HDMI Quick
+	 * Media Switching to achieve the target frame rate.
+	 */
+	bool qms_enabled;
 };
 
 /**
@@ -2490,6 +2502,16 @@ struct drm_connector {
 	 */
 	struct drm_property *vrr_capable_property;
 
+	/**
+	 * @qms_enabled_property: Optional atomic boolean property through which
+	 * userspace can indicate that HDMI "Quick Media Switching" should be
+	 * used to achieve the CRTC's target frame rate.
+	 *
+	 * Only HDMI connectors of sources capable of generating the right HDMI
+	 * signalling packets should register this property.
+	 */
+	struct drm_property *qms_enabled_property;
+
 	/**
 	 * @colorspace_property: Connector property to set the suitable
 	 * colorspace supported by the sink.
@@ -3016,6 +3038,7 @@ const char *drm_get_colorspace_name(enum drm_colorspace colorspace);
 
 int drm_connector_attach_color_format_property(struct drm_connector *connector,
 					       unsigned long supported_color_formats);
+int drm_connector_attach_qms_enabled_property(struct drm_connector *connector);
 
 /**
  * drm_for_each_connector_iter - connector_list iterator macro

-- 
2.55.0