devicetree: Add DT_FOREACH_ANCESTOR macro

doc/build/dts/api/api.rst

@@ -104,6 +104,9 @@ does not apply to macros which take cell names as arguments.
 For-each macros
 ===============
 
+The :c:macro:`DT_FOREACH_CHILD` macro allows iterating over the ancestor node
+of a devicetree node.
+
 There is currently only one "generic" for-each macro,
 :c:func:`DT_FOREACH_CHILD`, which allows iterating over the children of a
 devicetree node.

include/zephyr/devicetree.h

@@ -2961,6 +2961,55 @@
  */
 #define DT_FOREACH_STATUS_OKAY_NODE_VARGS(fn, ...) DT_FOREACH_OKAY_VARGS_HELPER(fn, __VA_ARGS__)
 
+/**
+ * @brief Invokes @p fn for each ancestor of @p node_id
+ *
+ * The macro @p fn must take one parameter, which will be the identifier
+ * of a child node of @p node_id to enable traversal of all ancestor nodes.
+ *
+ * The ancestor will be iterated over in the same order as they
+ * appear in the final devicetree.
+ *
+ * Example devicetree fragment:
+ *
+ * @code{.dts}
+ *     n: node1 {
+ *             foobar = "foo1";
+ *
+ *             n_2: node2 {
+ *                        foobar = "foo2";
+ *
+ *                        n_3: node3 {
+ *                                   foobar = "foo3";
+ *                        };
+ *             };
+ *     };
+ * @endcode
+ *
+ * Example usage:
+ *
+ * @code{.c}
+ *     #define GET_PROP(n) DT_PROP(n, foobar),
+ *
+ *     const char *ancestor_names[] = {
+ *         DT_FOREACH_ANCESTOR(DT_NODELABEL(n_3), GET_PROP)
+ *     };
+ * @endcode
+ *
+ * This expands to:
+ *
+ * @code{.c}
+ *     const char *ancestor_names[] = {
+ *         "foo2", "foo1",
+ *     };
+ * @endcode
+ *
+ * @param node_id node identifier
+ * @param fn macro to invoke
+ */
+#define DT_FOREACH_ANCESTOR(node_id, fn) \
+	DT_CAT(node_id, _FOREACH_ANCESTOR)(fn)
+
 /**
  * @brief Invokes @p fn for each child of @p node_id
  *

scripts/dts/gen_defines.py

@@ -97,6 +97,7 @@ def main():
             out_dt_define(f"{node.z_path_id}_FOREACH_NODELABEL_VARGS(fn, ...)",
                           " ".join(f"fn({nodelabel}, __VA_ARGS__)" for nodelabel in node.labels))
 
+            write_parent(node)
             write_children(node)
             write_dep_info(node)
             write_idents_and_existence(node)
@@ -457,6 +458,17 @@ def write_compatibles(node: edtlib.Node) -> None:
             out_dt_define(f"{node.z_path_id}_COMPAT_MODEL_IDX_{i}",
                           quote_str(node.edt.compat2model[compat]))
 
+def write_parent(node: edtlib.Node) -> None:
+    # Visit all parent nodes.
+    def _visit_parent_node(node: edtlib.Node):
+        while node is not None:
+            yield node.parent
+            node = node.parent
+
+    # Writes helper macros for dealing with node's parent.
+    out_dt_define(f"{node.z_path_id}_FOREACH_ANCESTOR(fn)",
+            " ".join(f"fn(DT_{parent.z_path_id})" for parent in
+            _visit_parent_node(node) if parent is not None))
 
 def write_children(node: edtlib.Node) -> None:
     # Writes helper macros for dealing with node's children.

tests/lib/devicetree/api/app.overlay

@@ -570,6 +570,18 @@
 			phys = <&test_transceiver1>;
 		};
 
+		test_parent: test-parent {
+			compatible = "vnd,parent-bindings";
+
+			test_parent_a: parent-a {
+				val = <0>;
+
+				test_parent_b: parent-b {
+					val = <0>;
+				};
+			};
+		};
+
 		/* there should only be one of these */
 		test_children: test-children {
 			compatible = "vnd,child-bindings";

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

@@ -2225,6 +2225,31 @@
 				  TEST_SPI_BUS_0), "");
 }
 
+#undef DT_DRV_COMPAT
+#define DT_DRV_COMPAT vnd_parent_bindings
+ZTEST(devicetree_api, test_parent_nodes_list)
+{
+	/* When traversing upwards, there are no fixed attributes and labels */
+	#define TEST_FUNC(parent) { /* No operation */ }
+	#define TEST_FUNC_AND_COMMA(parent) TEST_FUNC(parent),
+
+	struct vnd_parent_binding {
+		int val;
+	};
+
+	struct vnd_parent_binding vals_a[] = {
+		DT_FOREACH_ANCESTOR(DT_NODELABEL(test_parent_a), TEST_FUNC_AND_COMMA)};
+
+	struct vnd_parent_binding vals_b[] = {
+		DT_FOREACH_ANCESTOR(DT_NODELABEL(test_parent_b), TEST_FUNC_AND_COMMA)};
+
+	zassert_equal(ARRAY_SIZE(vals_a), 3, "");
+	zassert_equal(ARRAY_SIZE(vals_b), 4, "");
+
+	#undef TEST_FUNC_AND_COMMA
+	#undef TEST_FUNC
+}
+
 #undef DT_DRV_COMPAT
 #define DT_DRV_COMPAT vnd_i2c_mux_controller
 ZTEST(devicetree_api, test_gparent)