drm: convert drivers to use of_graph_get_remote_node

Convert drivers to use the new of_graph_get_remote_node() helper
instead of parsing the endpoint node and then getting the remote device
node. Now drivers can just specify the device node and which
port/endpoint and get back the connected remote device node. The details
of the graph binding are nicely abstracted into the core OF graph code.

This changes some error messages to debug messages (in the graph core).
Graph connections are often "no connects" depending on the particular
board, so we want to avoid spurious messages. Plus the kernel is not a
DT validator.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Liviu Dudau <liviu.dudau@arm.com>
Tested-by: Eric Anholt <eric@anholt.net>
Tested-by: Jyri Sarha <jsarha@ti.com>
Tested by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c

@@ -230,34 +230,6 @@ static const struct component_master_ops kirin_drm_ops = {
 	.unbind = kirin_drm_unbind,
 };
 
-static struct device_node *kirin_get_remote_node(struct device_node *np)
-{
-	struct device_node *endpoint, *remote;
-
-	/* get the first endpoint, in our case only one remote node
-	 * is connected to display controller.
-	 */
-	endpoint = of_graph_get_next_endpoint(np, NULL);
-	if (!endpoint) {
-		DRM_ERROR("no valid endpoint node\n");
-		return ERR_PTR(-ENODEV);
-	}
-
-	remote = of_graph_get_remote_port_parent(endpoint);
-	of_node_put(endpoint);
-	if (!remote) {
-		DRM_ERROR("no valid remote node\n");
-		return ERR_PTR(-ENODEV);
-	}
-
-	if (!of_device_is_available(remote)) {
-		DRM_ERROR("not available for remote node\n");
-		return ERR_PTR(-ENODEV);
-	}
-
-	return remote;
-}
-
 static int kirin_drm_platform_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -271,7 +243,7 @@ static int kirin_drm_platform_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	remote = kirin_get_remote_node(np);
+	remote = of_graph_get_remote_node(np, 0, 0);
 	if (IS_ERR(remote))
 		return PTR_ERR(remote);