dm: core: Add a helper to retrieve devices through graph endpoints

There are already several helpers to find a udevice based on its
position in a device tree, like getting a child or a node pointed by a
phandle, but there was no support for graph endpoints, which are very
common in display pipelines.

Add a new helper, named uclass_get_device_by_endpoint() which enters the
child graph reprensentation, looks for a specific port, then follows the
remote endpoint, and finally retrieves the first parent of the given
uclass_id.

This is a very handy and straightforward way to get a bridge or a panel
handle.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

2 files changed, 43 insertions, 0 deletions

diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index f846a35d6b2..ce5e61bbaa6 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -16,6 +16,7 @@
 #include <dm/device.h>
 #include <dm/device-internal.h>
 #include <dm/lists.h>
+#include <dm/ofnode_graph.h>
 #include <dm/uclass.h>
 #include <dm/uclass-internal.h>
 #include <dm/util.h>
@@ -582,6 +583,24 @@ int uclass_get_device_by_phandle(enum uclass_id id, struct udevice *parent,
 	ret = uclass_find_device_by_phandle(id, parent, name, &dev);
 	return uclass_get_device_tail(dev, ret, devp);
 }
+
+int uclass_get_device_by_endpoint(enum uclass_id class_id, struct udevice *dev,
+				  int port_idx, int ep_idx, struct udevice **devp)
+{
+	ofnode node_source = dev_ofnode(dev);
+	ofnode node_dest = ofnode_graph_get_remote_node(node_source, port_idx, ep_idx);
+	struct udevice *target = NULL;
+	int ret;
+
+	if (!ofnode_valid(node_dest))
+		return -EINVAL;
+
+	ret = uclass_find_device_by_ofnode(class_id, node_dest, &target);
+	if (ret)
+		return -ENODEV;
+
+	return uclass_get_device_tail(target, 0, devp);
+}
 #endif
 
 /*
diff --git a/include/dm/uclass.h b/include/dm/uclass.h
index c2793040923..8fdd7272511 100644
--- a/include/dm/uclass.h
+++ b/include/dm/uclass.h
@@ -334,6 +334,30 @@ int uclass_get_device_by_driver(enum uclass_id id, const struct driver *drv,
 				struct udevice **devp);
 
 /**
+ * uclass_get_device_by_endpoint() - Get a uclass device for a remote endpoint
+ *
+ * This searches through the parents of the specified remote endpoint
+ * for the first device matching the uclass. Said otherwise, this helper
+ * goes through the graph (endpoint) representation and searches for
+ * matching devices. Endpoints can be subnodes of the "port" node or
+ * subnodes of ports identified with a reg property, themselves in a
+ * "ports" container.
+ *
+ * The device is probed to activate it ready for use.
+ *
+ * @class_id: uclass ID to look up
+ * @dev: Device to start from
+ * @port_idx: Index of the port to follow, -1 if there is a single 'port'
+ *            node without reg.
+ * @ep_idx: Index of the endpoint to follow, -1 if there is a single 'endpoint'
+ *          node without reg.
+ * @target: Returns pointer to the first device matching the expected uclass.
+ * Return: 0 if OK, -ve on error
+ */
+int uclass_get_device_by_endpoint(enum uclass_id class_id, struct udevice *dev,
+				  int port_idx, int ep_idx, struct udevice **target);
+
+/**
  * uclass_first_device() - Get the first device in a uclass
  *
  * The device returned is probed if necessary, and ready for use