drm/dsi: Get DSI host by DT device node

MIPI DSI devices are inherently aware of their host because they share a
parent-child hierarchy in the device tree.

Non-DSI drivers that create DSI device don't have this data. In order to
get this information, they require to a phandle to the DSI host in the
device tree.

Maintain a list of all the DSI hosts that are currently registered. This
list will be used to find the struct mipi_dsi_host corresponding to the
device tree node passed to of_find_mipi_dsi_host_by_node().

Reviewed-by: Andrzej Hajda <[e-mail]>
Signed-off-by: Archit Taneja <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/drm/drm_mipi_dsi.c

···
 }
 EXPORT_SYMBOL(mipi_dsi_device_unregister);
 
+static DEFINE_MUTEX(host_lock);
+static LIST_HEAD(host_list);
+
+/**
+ * of_find_mipi_dsi_host_by_node() - find the MIPI DSI host matching a
+ *				     device tree node
+ * @node: device tree node
+ *
+ * Returns:
+ * A pointer to the MIPI DSI host corresponding to @node or NULL if no
+ * such device exists (or has not been registered yet).
+ */
+struct mipi_dsi_host *of_find_mipi_dsi_host_by_node(struct device_node *node)
+{
+	struct mipi_dsi_host *host;
+
+	mutex_lock(&host_lock);
+
+	list_for_each_entry(host, &host_list, list) {
+		if (host->dev->of_node == node) {
+			mutex_unlock(&host_lock);
+			return host;
+		}
+	}
+
+	mutex_unlock(&host_lock);
+
+	return NULL;
+}
+EXPORT_SYMBOL(of_find_mipi_dsi_host_by_node);
+
 int mipi_dsi_host_register(struct mipi_dsi_host *host)
 {
 	struct device_node *node;
···
 			continue;
 		of_mipi_dsi_device_add(host, node);
 	}
+
+	mutex_lock(&host_lock);
+	list_add_tail(&host->list, &host_list);
+	mutex_unlock(&host_lock);
 
 	return 0;
 }
···
 void mipi_dsi_host_unregister(struct mipi_dsi_host *host)
 {
 	device_for_each_child(host->dev, NULL, mipi_dsi_remove_device_fn);
+
+	mutex_lock(&host_lock);
+	list_del_init(&host->list);
+	mutex_unlock(&host_lock);
 }
 EXPORT_SYMBOL(mipi_dsi_host_unregister);
 

include/drm/drm_mipi_dsi.h

···
  * struct mipi_dsi_host - DSI host device
  * @dev: driver model device node for this DSI host
  * @ops: DSI host operations
+ * @list: list management
  */
 struct mipi_dsi_host {
 	struct device *dev;
 	const struct mipi_dsi_host_ops *ops;
+	struct list_head list;
 };
 
 int mipi_dsi_host_register(struct mipi_dsi_host *host);
 void mipi_dsi_host_unregister(struct mipi_dsi_host *host);
+struct mipi_dsi_host *of_find_mipi_dsi_host_by_node(struct device_node *node);
 
 /* DSI mode flags */