devicetree: add macros to deal with endpoints

Add macros to access the port/endpoint constructs from drivers and
application.

Devicetrees currently use "port { endpoint { ... }; };" to describe
interconnection between devices. With introduction of the
"remote-endpoint-label = string" syntax, it is now possible to
describe circular dependencies until #57708 is addressed.

Signed-off-by: Josuah Demangeon <me@josuah.net>

Author: josuah

dts/bindings/test/vnd,video.yaml

@@ -0,0 +1,10 @@
+# Copyright (c) 2024 tinyVision.ai Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+description: Test Video device
+
+compatible: "vnd,video"
+
+child-binding:
+  child-binding:
+    include: video-interfaces.yaml

include/zephyr/devicetree.h

@@ -3787,6 +3787,70 @@
  */
 #define DT_ON_BUS(node_id, bus) IS_ENABLED(DT_CAT3(node_id, _BUS_, bus))
 
+/**
+ * @}
+ */
+
+/**
+ * @defgroup devicetree-generic-endpoint Endpoint helpers
+ * @ingroup devicetree
+ * @{
+ */
+
+/**
+ * @brief Get the remote endpoint node connected to a local endpoint.
+ *
+ * Devices can be interconnected through ports and endpoints.
+ *
+ * Example devicetree overlay:
+ *
+ * @code{.dts}
+ *	&source {
+ *		port {
+ *			source_out: endpoint {
+ *				remote-endpoint-label = "sink_in";
+ *				source-property = <1>;
+ *			};
+ *		};
+ *	};
+ *
+ *	&sink {
+ *		port {
+ *			sink_in: endpoint {
+ *				remote-endpoint-label = "source_out";
+ *				sink-property = <2>;
+ *			};
+ *		};
+ *	};
+ * @endcode
+ *
+ * @c DT_REMOTE_ENDPOINT(endpoint_node) permits to access the other endpoint
+ * connected to @c endpoint_node.
+ *
+ * Example usage: starting from the sink, access the source endpoint connected
+ * to the @c sink_in endpoint:
+ *
+ * @code{.c}
+ *	DT_PROP(DT_REMOTE_ENDPOINT(DT_NODELABEL(sink_in)), source_property)
+ * @endcode
+ *
+ * Example usage, starting from the source, to access the sink endpoint
+ * connected to the @c source_out endpoint:
+ *
+ * @code{.c}
+ *	DT_PROP(DT_REMOTE_ENDPOINT(DT_NODELABEL(source_out)), sink_property)
+ * @endcode
+ *
+ * @note Once circular phandle references are supported in Zephyr devicetree,
+ *       @c remote-endpoint-label (string) may be changed into
+ *       @c remote-endpoint (phandle).
+ *
+ * @param node The local endpoint node to use.
+ *
+ * @return The remote endpoint node connected to @p node.
+ */
+#define DT_REMOTE_ENDPOINT(node) DT_NODELABEL(DT_STRING_TOKEN(node, remote_endpoint_label))
+
 /**
  * @}
  */

tests/lib/devicetree/api/app.overlay

@@ -506,6 +506,26 @@
 			status = "okay";
 		};
 
+		test_video_source: video_source {
+			compatible = "vnd,video";
+
+			port {
+				test_video_source_out: endpoint {
+					remote-endpoint-label = "test_video_sink_in";
+				};
+			};
+		};
+
+		test_video_sink: video_sink {
+			compatible = "vnd,video";
+
+			port {
+				test_video_sink_in: endpoint {
+					remote-endpoint-label = "test_video_source_out";
+				};
+			};
+		};
+
 		test_pwm1: pwm@55551111 {
 			compatible = "vnd,pwm";
 			#pwm-cells = <3>;

tests/lib/devicetree/api/src/main.c

@@ -76,6 +76,9 @@
 #define TEST_DMA_CTLR_1 DT_NODELABEL(test_dma1)
 #define TEST_DMA_CTLR_2 DT_NODELABEL(test_dma2)
 
+#define TEST_VIDEO_SOURCE_OUT DT_NODELABEL(test_video_source_out)
+#define TEST_VIDEO_SINK_IN    DT_NODELABEL(test_video_sink_in)
+
 #define TEST_IO_CHANNEL_CTLR_1 DT_NODELABEL(test_adc_1)
 #define TEST_IO_CHANNEL_CTLR_2 DT_NODELABEL(test_adc_2)
 
@@ -1278,6 +1281,19 @@ ZTEST(devicetree_api, test_dma)
 	zassert_false(DT_INST_DMAS_HAS_IDX(0, 2), "");
 }
 
+#undef DT_DRV_COMPAT
+#define DT_DRV_COMPAT vnd_video_device
+ZTEST(devicetree_api, test_video)
+{
+	/* DT_REMOTE_ENDPOINT(source) */
+	zassert_true(DT_SAME_NODE(DT_REMOTE_ENDPOINT(TEST_VIDEO_SOURCE_OUT),
+				  TEST_VIDEO_SINK_IN), "");
+
+	/* DT_REMOTE_ENDPOINT(sink) */
+	zassert_true(DT_SAME_NODE(DT_REMOTE_ENDPOINT(TEST_VIDEO_SINK_IN),
+				  TEST_VIDEO_SOURCE_OUT), "");
+}
+
 #undef DT_DRV_COMPAT
 #define DT_DRV_COMPAT vnd_phandle_holder
 ZTEST(devicetree_api, test_pwms)