drm/bridge: add of_drm_get_bridge_by_endpoint()

drm_of_find_panel_or_bridge() is widely used, but many callers pass NULL
into the @panel or the @bridge arguments, thus making a very partial usage
of this rather complex function.

Besides, the bridge returned in @bridge is not refcounted, thus making this
API unsafe when DRM bridge hotplug will be introduced.

Solve both issues for the cases of calls to drm_of_find_panel_or_bridge()
with a NULL @panel pointer by adding a new function that only looks for
bridges (and is thus much simpler) and increments the refcount of the
returned bridge.

The new function is identical to drm_of_find_panel_or_bridge() except it:

 - handles bridge refcounting: uses of_drm_find_and_get_bridge() instead of
   of_drm_find_bridge() internally to return a refcounted bridge
 - is simpler to use: just takes no @panel parameter, returns the pointer
   in the return value instead of a double pointer argument
 - has a simpler implementation: it is equal to
   drm_of_find_panel_or_bridge() after removing the code that becomes dead
   when @panel == NULL

Also add this function to drm_bridge.c and not drm_of.c because it returns
bridges only.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://patch.msgid.link/20260511-drm-bridge-alloc-getput-panel_or_bridge-v6-2-f61c9e498b3f@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

drivers/gpu/drm/drm_bridge.c

@@ -1582,6 +1582,47 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np)
 	return bridge;
 }
 EXPORT_SYMBOL(of_drm_find_bridge);
+
+/**
+ * of_drm_get_bridge_by_endpoint - return DRM bridge connected to a port/endpoint
+ * @np: device tree node containing output ports
+ * @port: port in the device tree node, or -1 for the first port found
+ * @endpoint: endpoint in the device tree node, or -1 for the first endpoint found
+ *
+ * Given a DT node's port and endpoint number, find the connected node and
+ * return the associated drm_bridge device.
+ *
+ * The refcount of the returned bridge is incremented. Use drm_bridge_put()
+ * when done with it.
+ *
+ * Returns a pointer to the connected drm_bridge, or a negative error on failure
+ */
+struct drm_bridge *of_drm_get_bridge_by_endpoint(const struct device_node *np,
+						 int port, int endpoint)
+{
+	struct drm_bridge *bridge;
+
+	/*
+	 * of_graph_get_remote_node() produces a noisy error message if port
+	 * node isn't found and the absence of the port is a legit case here,
+	 * so at first we silently check whether graph is present in the
+	 * device-tree node.
+	 */
+	if (!of_graph_is_present(np))
+		return ERR_PTR(-ENODEV);
+
+	struct device_node *remote __free(device_node) =
+		of_graph_get_remote_node(np, port, endpoint);
+	if (!remote)
+		return ERR_PTR(-ENODEV);
+
+	bridge = of_drm_find_and_get_bridge(remote);
+	if (!bridge)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return bridge;
+}
+EXPORT_SYMBOL_GPL(of_drm_get_bridge_by_endpoint);
 #endif
 
 /**

include/drm/drm_bridge.h

@@ -1327,6 +1327,8 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
 #ifdef CONFIG_OF
 struct drm_bridge *of_drm_find_and_get_bridge(struct device_node *np);
 struct drm_bridge *of_drm_find_bridge(struct device_node *np);
+struct drm_bridge *of_drm_get_bridge_by_endpoint(const struct device_node *np,
+						 int port, int endpoint);
 #else
 static inline struct drm_bridge *of_drm_find_and_get_bridge(struct device_node *np)
 {
@@ -1336,6 +1338,11 @@ static inline struct drm_bridge *of_drm_find_bridge(struct device_node *np)
 {
 	return NULL;
 }
+static inline struct drm_bridge *of_drm_get_bridge_by_endpoint(const struct device_node *np,
+							       int port, int endpoint)
+{
+	return ERR_PTR(-ENODEV);
+}
 #endif
 
 static inline bool drm_bridge_is_last(struct drm_bridge *bridge)