drm/hdcp: update content protection property with uevent

drm function is defined and exported to update a connector's
content protection property state and to generate a uevent along
with it.

Pekka have completed the Weston DRM-backend review in
https://gitlab.freedesktop.org/wayland/weston/merge_requests/48
and the UAPI for HDCP 2.2 looks good.

The userspace is accepted in Weston.

v2:
  Update only when state is different from old one.
v3:
  KDoc is added [Daniel]
v4:
  KDoc is extended bit more [pekka]
v5:
  Uevent usage is documented at kdoc of "Content Protection" also
  [pekka]
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/320963/?series=57232&rev=14

drivers/gpu/drm/drm_connector.c

@@ -983,10 +983,19 @@ static const struct drm_prop_enum_list hdmi_colorspaces[] = {
  *	- If the state is DESIRED, kernel should attempt to re-authenticate the
  *	  link whenever possible. This includes across disable/enable, dpms,
  *	  hotplug, downstream device changes, link status failures, etc..
- *	- Userspace is responsible for polling the property to determine when
- *	  the value transitions from ENABLED to DESIRED. This signifies the link
- *	  is no longer protected and userspace should take appropriate action
- *	  (whatever that might be).
+ *	- Kernel sends uevent with the connector id and property id through
+ *	  @drm_hdcp_update_content_protection, upon below kernel triggered
+ *	  scenarios:
+ *		DESIRED -> ENABLED	(authentication success)
+ *		ENABLED -> DESIRED	(termination of authentication)
+ *	- Please note no uevents for userspace triggered property state changes,
+ *	  which can't fail such as
+ *		DESIRED/ENABLED -> UNDESIRED
+ *		UNDESIRED -> DESIRED
+ *	- Userspace is responsible for polling the property or listen to uevents
+ *	  to determine when the value transitions from ENABLED to DESIRED.
+ *	  This signifies the link is no longer protected and userspace should
+ *	  take appropriate action (whatever that might be).
  *
  * HDCP Content Type:
  *	This Enum property is used by the userspace to declare the content type

drivers/gpu/drm/drm_hdcp.c

@@ -374,6 +374,10 @@ DRM_ENUM_NAME_FN(drm_get_hdcp_content_type_name,
  *
  * The content protection will be set to &drm_connector_state.content_protection
  *
+ * When kernel triggered content protection state change like DESIRED->ENABLED
+ * and ENABLED->DESIRED, will use drm_hdcp_update_content_protection() to update
+ * the content protection state of a connector.
+ *
  * Returns:
  * Zero on success, negative errno on failure.
  */
@@ -414,3 +418,33 @@ int drm_connector_attach_content_protection_property(
 	return 0;
 }
 EXPORT_SYMBOL(drm_connector_attach_content_protection_property);
+
+/**
+ * drm_hdcp_update_content_protection - Updates the content protection state
+ * of a connector
+ *
+ * @connector: drm_connector on which content protection state needs an update
+ * @val: New state of the content protection property
+ *
+ * This function can be used by display drivers, to update the kernel triggered
+ * content protection state changes of a drm_connector such as DESIRED->ENABLED
+ * and ENABLED->DESIRED. No uevent for DESIRED->UNDESIRED or ENABLED->UNDESIRED,
+ * as userspace is triggering such state change and kernel performs it without
+ * fail.This function update the new state of the property into the connector's
+ * state and generate an uevent to notify the userspace.
+ */
+void drm_hdcp_update_content_protection(struct drm_connector *connector,
+					u64 val)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_connector_state *state = connector->state;
+
+	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
+	if (state->content_protection == val)
+		return;
+
+	state->content_protection = val;
+	drm_sysfs_connector_status_event(connector,
+				 dev->mode_config.content_protection_property);
+}
+EXPORT_SYMBOL(drm_hdcp_update_content_protection);

include/drm/drm_hdcp.h

@@ -292,6 +292,8 @@ bool drm_hdcp_check_ksvs_revoked(struct drm_device *dev,
 				 u8 *ksvs, u32 ksv_count);
 int drm_connector_attach_content_protection_property(
 		struct drm_connector *connector, bool hdcp_content_type);
+void drm_hdcp_update_content_protection(struct drm_connector *connector,
+					u64 val);
 
 /* Content Type classification for HDCP2.2 vs others */
 #define DRM_MODE_HDCP_CONTENT_TYPE0		0