devicetree: Add DT_CHILD_BY_UNIT_ADDR

Allow fetching child node identifiers by unit address.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

Author: pdgendt

doc/build/dts/macros.bnf

@@ -77,6 +77,8 @@ node-macro =/ %s"DT_N" path-id %s"_P_" prop-id %s"_FOREACH_PROP_ELEM_SEP_VARGS"
 ; These are used by DT_CHILD_NUM and DT_CHILD_NUM_STATUS_OKAY macros
 node-macro =/ %s"DT_N" path-id %s"_CHILD_NUM"
 node-macro =/ %s"DT_N" path-id %s"_CHILD_NUM_STATUS_OKAY"
+; This is used by DT_CHILD_BY_UNIT_ADDR
+node-macro =/ %s"DT_N" path-id %s"_CHILD_UNIT_ADDR_" unit-addr
 ; These are used internally by DT_FOREACH_CHILD, which iterates over
 ; each child node.
 node-macro =/ %s"DT_N" path-id %s"_FOREACH_CHILD"
@@ -394,6 +396,17 @@ other-macro =/ %s"DT_COMPAT_" dt-name %s"_LABEL_" dt-name
 alternate-id =  ( %s"ALIAS" / %s"NODELABEL" ) dt-name
 alternate-id =/ %s"INST_" 1*DIGIT "_" dt-name
 
+; --------------------------------------------------------------------
+; unit-addr: a unit address token for child lookup helpers
+;
+; Children that have a unique unit address get helper macros using either
+; decimal or lowercase hexadecimal forms of that address.
+unit-addr = 1*DIGIT
+unit-addr =/ %s"0x" 1*hexdig-lower
+
+; Lowercase hexadecimal digit.
+hexdig-lower = DIGIT / %s"a" / %s"b" / %s"c" / %s"d" / %s"e" / %s"f"
+
 ; --------------------------------------------------------------------
 ; miscellaneous helper definitions
 

include/zephyr/devicetree.h

@@ -435,6 +435,42 @@
  */
 #define DT_CHILD(node_id, child) UTIL_CAT(node_id, DT_S_PREFIX(child))
 
+/**
+ * @brief Get a node identifier for a child node with a matching unit address
+ *
+ * @note Only works for children with unique unit addresses.
+ *
+ * Example devicetree fragment:
+ *
+ * @code{.dts}
+ *     / {
+ *             soc-label: soc {
+ *                     serial1: serial@40001000 {
+ *                             status = "okay";
+ *                             current-speed = <115200>;
+ *                             ...
+ *                     };
+ *             };
+ *     };
+ * @endcode
+ *
+ * Example usage with DT_PROP() to get the status of the
+ * `serial@40001000` node:
+ *
+ * @code{.c}
+ *     #define SOC_NODE DT_NODELABEL(soc_label)
+ *     DT_PROP(DT_CHILD_BY_UNIT_ADDR(SOC_NODE, 0x40001000), status) // "okay"
+ * @endcode
+ *
+ * @param node_id node identifier
+ * @param addr Unit address for the child node. Can be decimal or
+ *             hexadecimal (lowercase and prefixed with 0x)
+ *
+ * @return node identifier for the child node with the specified unit address
+ */
+#define DT_CHILD_BY_UNIT_ADDR(node_id, addr) \
+	DT_CAT3(node_id, _CHILD_UNIT_ADDR_, addr)
+
 /**
  * @brief Get a node identifier for a status `okay` node with a compatible
  *
@@ -4066,6 +4102,22 @@
 #define DT_INST_CHILD(inst, child) \
 	DT_CHILD(DT_DRV_INST(inst), child)
 
+/**
+ * @brief Get a node identifier for a child node with a matching unit address of DT_DRV_INST(inst)
+ *
+ * @note Only works for children with unique unit addresses.
+ *
+ * @param inst instance number
+ * @param addr Unit address for the child node. Can be decimal or
+ *             hexadecimal (lowercase and prefixed with 0x)
+ *
+ * @return node identifier for the child node with the specified unit address
+ *
+ * @see DT_CHILD_BY_UNIT_ADDR
+ */
+#define DT_INST_CHILD_BY_UNIT_ADDR(inst, addr) \
+	DT_CHILD_BY_UNIT_ADDR(DT_DRV_INST(inst), addr)
+
 /**
  * @brief Get the number of child nodes of a given node
  *

scripts/dts/gen_defines.py

@@ -484,6 +484,23 @@ def write_children(node: edtlib.Node) -> None:
 
     out_dt_define(f"{node.z_path_id}_CHILD_NUM_STATUS_OKAY", ok_nodes_num)
 
+    child_unit_addrs = {}
+    for child in node.children.values():
+        # Provide a way to query child nodes
+        if (addr := child.unit_addr) is not None:
+            child_unit_addrs.setdefault(addr, []).append(child)
+
+    for addr, children in child_unit_addrs.items():
+        if len(children) != 1:
+            # Duplicate unit addresses for different children, skip
+            continue
+
+        # Decimal and hexadecimal variants
+        out_dt_define(f"{node.z_path_id}_CHILD_UNIT_ADDR_{addr}", f"DT_{children[0].z_path_id}")
+        out_dt_define(
+            f"{node.z_path_id}_CHILD_UNIT_ADDR_{hex(addr)}", f"DT_{children[0].z_path_id}"
+        )
+
     out_dt_define(f"{node.z_path_id}_FOREACH_CHILD(fn)",
             " ".join(f"fn(DT_{child.z_path_id})" for child in
                 node.children.values()))