drm/connector: Add drm_connector_find_by_fwnode() function (v3)

Add a function to find a connector based on a fwnode.

This will be used by the new drm_connector_oob_hotplug_event()
function which is added by the next patch in this patch-set.

Changes in v2:
- Complete rewrite to use a global connector list in drm_connector.c
  rather then using a class-dev-iter in drm_sysfs.c

Changes in v3:
- Add forward declaration for struct fwnode_handle to drm_crtc_internal.h
  (fixes warning reported by kernel test robot <lkp@intel.com>)

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/20210817215201.795062-4-hdegoede@redhat.com

drivers/gpu/drm/drm_connector.c

@@ -65,6 +65,14 @@
  * support can instead use e.g. drm_helper_hpd_irq_event().
  */
 
+/*
+ * Global connector list for drm_connector_find_by_fwnode().
+ * Note drm_connector_[un]register() first take connector->lock and then
+ * take the connector_list_lock.
+ */
+static DEFINE_MUTEX(connector_list_lock);
+static LIST_HEAD(connector_list);
+
 struct drm_conn_prop_enum_list {
 	int type;
 	const char *name;
@@ -267,6 +275,7 @@ int drm_connector_init(struct drm_device *dev,
 		goto out_put_type_id;
 	}
 
+	INIT_LIST_HEAD(&connector->global_connector_list_entry);
 	INIT_LIST_HEAD(&connector->probed_modes);
 	INIT_LIST_HEAD(&connector->modes);
 	mutex_init(&connector->mutex);
@@ -534,6 +543,9 @@ int drm_connector_register(struct drm_connector *connector)
 	/* Let userspace know we have a new connector */
 	drm_sysfs_hotplug_event(connector->dev);
 
+	mutex_lock(&connector_list_lock);
+	list_add_tail(&connector->global_connector_list_entry, &connector_list);
+	mutex_unlock(&connector_list_lock);
 	goto unlock;
 
 err_debugfs:
@@ -562,6 +574,10 @@ void drm_connector_unregister(struct drm_connector *connector)
 		return;
 	}
 
+	mutex_lock(&connector_list_lock);
+	list_del_init(&connector->global_connector_list_entry);
+	mutex_unlock(&connector_list_lock);
+
 	if (connector->funcs->early_unregister)
 		connector->funcs->early_unregister(connector);
 
@@ -2545,6 +2561,40 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 	return ret;
 }
 
+/**
+ * drm_connector_find_by_fwnode - Find a connector based on the associated fwnode
+ * @fwnode: fwnode for which to find the matching drm_connector
+ *
+ * This functions looks up a drm_connector based on its associated fwnode. When
+ * a connector is found a reference to the connector is returned. The caller must
+ * call drm_connector_put() to release this reference when it is done with the
+ * connector.
+ *
+ * Returns: A reference to the found connector or an ERR_PTR().
+ */
+struct drm_connector *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode)
+{
+	struct drm_connector *connector, *found = ERR_PTR(-ENODEV);
+
+	if (!fwnode)
+		return ERR_PTR(-ENODEV);
+
+	mutex_lock(&connector_list_lock);
+
+	list_for_each_entry(connector, &connector_list, global_connector_list_entry) {
+		if (connector->fwnode == fwnode ||
+		    (connector->fwnode && connector->fwnode->secondary == fwnode)) {
+			drm_connector_get(connector);
+			found = connector;
+			break;
+		}
+	}
+
+	mutex_unlock(&connector_list_lock);
+
+	return found;
+}
+
 
 /**
  * DOC: Tile group

drivers/gpu/drm/drm_crtc_internal.h

@@ -58,6 +58,7 @@ struct drm_property;
 struct edid;
 struct kref;
 struct work_struct;
+struct fwnode_handle;
 
 /* drm_crtc.c */
 int drm_mode_crtc_set_obj_prop(struct drm_mode_object *obj,
@@ -186,6 +187,7 @@ int drm_connector_set_obj_prop(struct drm_mode_object *obj,
 int drm_connector_create_standard_properties(struct drm_device *dev);
 const char *drm_get_connector_force_name(enum drm_connector_force force);
 void drm_connector_free_work_fn(struct work_struct *work);
+struct drm_connector *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode);
 
 /* IOCTL */
 int drm_connector_property_set_ioctl(struct drm_device *dev,

include/drm/drm_connector.h

@@ -1247,6 +1247,14 @@ struct drm_connector {
 	 */
 	struct list_head head;
 
+	/**
+	 * @global_connector_list_entry:
+	 *
+	 * Connector entry in the global connector-list, used by
+	 * drm_connector_find_by_fwnode().
+	 */
+	struct list_head global_connector_list_entry;
+
 	/** @base: base KMS object */
 	struct drm_mode_object base;