gen_defines: add _CHILD_IDX macros for nodes with parents

These expose every node's index in its parent's list of children to C.
The root node has no parent, so no _CHILD_IDX macro is generated for
it.

Keep macros.bnf up to date with the new generated macros.

Signed-off-by: Martí Bolívar <[email protected]>

Author: mbolivar-nordic

doc/guides/dts/macros.bnf

@@ -67,6 +67,8 @@ node-macro =/ %s"DT_N" path-id %s"_FOREACH_CHILD_VARGS"
 ; over each child node with status "okay".
 node-macro =/ %s"DT_N" path-id %s"_FOREACH_CHILD_STATUS_OKAY"
 node-macro =/ %s"DT_N" path-id %s"_FOREACH_CHILD_STATUS_OKAY_VARGS"
+; The node's zero-based index in the list of it's parent's child nodes.
+node-macro =/ %s"DT_N" path-id %s"_CHILD_IDX"
 ; The node's status macro; dt-name in this case is something like "okay"
 ; or "disabled".
 node-macro =/ %s"DT_N" path-id %s"_STATUS_" dt-name

scripts/dts/gen_defines.py

@@ -132,6 +132,10 @@ def main():
                 out_dt_define(f"{node.z_path_id}_PARENT",
                               f"DT_{node.parent.z_path_id}")
 
+                out_comment(f"Node's index in its parent's list of children:")
+                out_dt_define(f"{node.z_path_id}_CHILD_IDX",
+                              node.parent.child_index(node))
+
             write_children(node)
             write_dep_info(node)
             write_idents_and_existence(node)