drm/connector: Add support for out-of-band hotplug notification (v3)

Add a new drm_connector_oob_hotplug_event() function and
oob_hotplug_event drm_connector_funcs member.

On some hardware a hotplug event notification may come from outside the
display driver / device. An example of this is some USB Type-C setups
where the hardware muxes the DisplayPort data and aux-lines but does
not pass the altmode HPD status bit to the GPU's DP HPD pin.

In cases like this the new drm_connector_oob_hotplug_event() function can
be used to report these out-of-band events.

Changes in v2:
- Make drm_connector_oob_hotplug_event() take a fwnode as argument and
  have it call drm_connector_find_by_fwnode() internally. This allows
  making drm_connector_find_by_fwnode() a drm-internal function and
  avoids code outside the drm subsystem potentially holding on the
  a drm_connector reference for a longer period.

Changes in v3:
- Drop the data argument to the drm_connector_oob_hotplug_event
  function since it is not used atm. This can be re-added later when
  a use for it actually arises.

Tested-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20210817215201.795062-5-hdegoede@redhat.com

drivers/gpu/drm/drm_connector.c

@@ -2595,6 +2595,33 @@ struct drm_connector *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode)
 	return found;
 }
 
+/**
+ * drm_connector_oob_hotplug_event - Report out-of-band hotplug event to connector
+ * @connector: connector to report the event on
+ *
+ * On some hardware a hotplug event notification may come from outside the display
+ * driver / device. An example of this is some USB Type-C setups where the hardware
+ * muxes the DisplayPort data and aux-lines but does not pass the altmode HPD
+ * status bit to the GPU's DP HPD pin.
+ *
+ * This function can be used to report these out-of-band events after obtaining
+ * a drm_connector reference through calling drm_connector_find_by_fwnode().
+ */
+void drm_connector_oob_hotplug_event(struct fwnode_handle *connector_fwnode)
+{
+	struct drm_connector *connector;
+
+	connector = drm_connector_find_by_fwnode(connector_fwnode);
+	if (IS_ERR(connector))
+		return;
+
+	if (connector->funcs->oob_hotplug_event)
+		connector->funcs->oob_hotplug_event(connector);
+
+	drm_connector_put(connector);
+}
+EXPORT_SYMBOL(drm_connector_oob_hotplug_event);
+
 
 /**
  * DOC: Tile group

include/drm/drm_connector.h

@@ -1084,6 +1084,14 @@ struct drm_connector_funcs {
 	 */
 	void (*atomic_print_state)(struct drm_printer *p,
 				   const struct drm_connector_state *state);
+
+	/**
+	 * @oob_hotplug_event:
+	 *
+	 * This will get called when a hotplug-event for a drm-connector
+	 * has been received from a source outside the display driver / device.
+	 */
+	void (*oob_hotplug_event)(struct drm_connector *connector);
 };
 
 /**
@@ -1666,6 +1674,7 @@ drm_connector_is_unregistered(struct drm_connector *connector)
 		DRM_CONNECTOR_UNREGISTERED;
 }
 
+void drm_connector_oob_hotplug_event(struct fwnode_handle *connector_fwnode);
 const char *drm_get_connector_type_name(unsigned int connector_type);
 const char *drm_get_connector_status_name(enum drm_connector_status status);
 const char *drm_get_subpixel_order_name(enum subpixel_order order);