edtlib: add "hash" attribute to nodes

Add a new "hash" attribute to all Devicetree EDT nodes. The hash is
calculated on the full path of the node; this means that its value
remains stable across rebuilds.
The hash is checked for uniqueness among nodes in the same EDT.

This computed token is then added to `devicetree_generated.h` and made
accessible to Zephyr code via a new DT_NODE_HASH(node_id) macro.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

include/zephyr/devicetree.h

@@ -242,6 +242,16 @@
  */
 #define DT_HAS_ALIAS(alias_name) DT_NODE_EXISTS(DT_ALIAS(alias_name))
 
+/**
+ * @brief Get the hash associated with a DT node
+ *
+ * Get the hash for the specified node_id. The hash is calculated on the
+ * full devicetree path of the node.
+ * @param node_id node identifier
+ * @return hash value as a preprocessor token
+ */
+#define DT_NODE_HASH(node_id) DT_CAT(node_id, _HASH)
+
 /**
  * @brief Get a node identifier for an instance of a compatible
  *

scripts/dts/gen_defines.py

@@ -720,6 +720,9 @@ def write_dep_info(node: edtlib.Node) -> None:
         else:
             return "/* nothing */"
 
+    out_comment("Node's hash:")
+    out_dt_define(f"{node.z_path_id}_HASH", node.hash)
+
     out_comment("Node's dependency ordinal:")
     out_dt_define(f"{node.z_path_id}_ORD", node.dep_ordinal)
     out_dt_define(f"{node.z_path_id}_ORD_STR_SORTABLE", f"{node.dep_ordinal:0>5}")

scripts/dts/python-devicetree/src/devicetree/edtlib.py

@@ -72,6 +72,8 @@ from copy import deepcopy
 from dataclasses import dataclass
 from typing import (Any, Callable, Iterable, NoReturn,
                     Optional, TYPE_CHECKING, Union)
+import base64
+import hashlib
 import logging
 import os
 import re
@@ -90,6 +92,12 @@ from devicetree.dtlib import Property as dtlib_Property
 from devicetree.grutils import Graph
 from devicetree._private import _slice_helper
 
+def _compute_hash(path: str) -> str:
+    # Calculates the hash associated with the node's full path.
+    hasher = hashlib.sha256()
+    hasher.update(path.encode())
+    return base64.b64encode(hasher.digest(), altchars=b'__').decode().rstrip('=')
+
 #
 # Public classes
 #
@@ -912,6 +920,11 @@ class Node:
       The ordinal is defined for all Nodes, and is unique among nodes in its
       EDT 'nodes' list.
 
+    hash:
+      A hashed value of the devicetree path of the node. This is defined for
+      all Nodes, and is checked for uniqueness among nodes in its EDT 'nodes'
+      list.
+
     required_by:
       A list with the nodes that directly depend on the node
 
@@ -1027,6 +1040,7 @@ class Node:
         self.interrupts: list[ControllerAndData] = []
         self.pinctrls: list[PinCtrl] = []
         self.bus_node = self._bus_node(support_fixed_partitions_on_any_bus)
+        self.hash: str = _compute_hash(dt_node.path)
 
         self._init_binding()
         self._init_regs()
@@ -2268,10 +2282,18 @@ class EDT:
         # Creates a list of edtlib.Node objects from the dtlib.Node objects, in
         # self.nodes
 
+        hash2node: dict[str, Node] = {}
+
         for dt_node in self._dt.node_iter():
             # Warning: We depend on parent Nodes being created before their
             # children. This is guaranteed by node_iter().
             node = Node(dt_node, self, self._fixed_partitions_no_bus)
+
+            if node.hash in hash2node:
+                _err(f"hash collision between '{node.path}' and "
+                     f"'{hash2node[node.hash].path}'")
+            hash2node[node.hash] = node
+
             self.nodes.append(node)
             self._node2enode[dt_node] = node
 

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

@@ -338,6 +338,16 @@ ZTEST(devicetree_api, test_has_alias)
 	zassert_equal(DT_NODE_HAS_STATUS(DT_ALIAS(test_undef), okay), 0, "");
 }
 
+ZTEST(devicetree_api, test_node_hashes)
+{
+	zassert_str_equal(TO_STRING(DT_NODE_HASH(DT_ROOT)),
+			  "il7asoJjJEMhngUeSt4tHVu8Zxx4EFG_FDeJfL3_oPE");
+	zassert_str_equal(TO_STRING(DT_NODE_HASH(TEST_DEADBEEF)),
+			  "kPPqtBX5DX_QDQMO0_cOls2ebJMevAWHhAPY1JCKTyU");
+	zassert_str_equal(TO_STRING(DT_NODE_HASH(TEST_ABCD1234)),
+			  "Bk4fvF6o3Mgslz_xiIZaJcuwo6_IeelozwOaxtUsSos");
+}
+
 ZTEST(devicetree_api, test_inst_checks)
 {
 	zassert_equal(DT_NODE_EXISTS(DT_INST(0, vnd_gpio_device)), 1, "");