dtc: introduce label relative path references

Since introduction of OF_UPSTREAM flag, U-Boot's dtc must be able
to compile Kernel's device tree.

Since kernel commit 7de129f5389b ("ARM: dts: stm32: stm32mp151a-prtt1l:
Fix QSPI configuration"), label relative path references has been
introduced. These label relative path references is not supported
by current U-Boot dtc version 1.5.0: (see mailing list discussion [1]).

In order to support such label relative patch references
adds following commit from upstream DTC tree:

commit 651410e54cb9 ("util: introduce xstrndup helper")
commit ec7986e682cf ("dtc: introduce label relative path references")

[1] https://lore.kernel.org/all/20250115144428.GZ3476@bill-the-cat/T/

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

scripts/dtc/dtc-lexer.l

@@ -215,7 +215,7 @@ static void PRINTF(1, 2) lexical_error(const char *fmt, ...);
 			return DT_REF;
 		}
 
-<*>"&{/"{PATHCHAR}*\}	{	/* new-style path reference */
+<*>"&{"{PATHCHAR}*\}	{	/* new-style path reference */
 			yytext[yyleng-1] = '\0';
 			DPRINT("Ref: %s\n", yytext+2);
 			yylval.labelref = xstrdup(yytext+2);

scripts/dtc/dtc-parser.y

@@ -34,6 +34,12 @@ extern void yyerror(char const *s);
 
 extern struct dt_info *parser_output;
 extern bool treesource_error;
+
+static bool is_ref_relative(const char *ref)
+{
+	return ref[0] != '/' && strchr(&ref[1], '/');
+}
+
 %}
 
 %union {
@@ -176,12 +182,17 @@ devicetree:
 			 */
 			if (!($<flags>-1 & DTSF_PLUGIN))
 				ERROR(&@2, "Label or path %s not found", $1);
+			else if (is_ref_relative($1))
+				ERROR(&@2, "Label-relative reference %s not supported in plugin", $1);
 			$$ = add_orphan_node(name_node(build_node(NULL, NULL), ""), $2, $1);
 		}
 	| devicetree DT_LABEL DT_REF nodedef
 		{
 			struct node *target = get_node_by_ref($1, $3);
 
+			if (($<flags>-1 & DTSF_PLUGIN) && is_ref_relative($3))
+				ERROR(&@2, "Label-relative reference %s not supported in plugin", $3);
+
 			if (target) {
 				add_label(&target->labels, $2);
 				merge_nodes(target, $4);
@@ -197,6 +208,8 @@ devicetree:
 			 * so $-1 is what we want (plugindecl)
 			 */
 			if ($<flags>-1 & DTSF_PLUGIN) {
+				if (is_ref_relative($2))
+					ERROR(&@2, "Label-relative reference %s not supported in plugin", $2);
 				add_orphan_node($1, $3, $2);
 			} else {
 				struct node *target = get_node_by_ref($1, $2);

scripts/dtc/livetree.c

@@ -583,12 +583,39 @@ struct node *get_node_by_phandle(struct node *tree, cell_t phandle)
 
 struct node *get_node_by_ref(struct node *tree, const char *ref)
 {
+	struct node *target = tree;
+	const char *label = NULL, *path = NULL;
+
 	if (streq(ref, "/"))
 		return tree;
-	else if (ref[0] == '/')
-		return get_node_by_path(tree, ref);
+
+	if (ref[0] == '/')
+		path = ref;
 	else
-		return get_node_by_label(tree, ref);
+		label = ref;
+
+	if (label) {
+		const char *slash = strchr(label, '/');
+		char *buf = NULL;
+
+		if (slash) {
+			buf = xstrndup(label, slash - label);
+			label = buf;
+			path = slash + 1;
+		}
+
+		target = get_node_by_label(tree, label);
+
+		free(buf);
+
+		if (!target)
+			return NULL;
+	}
+
+	if (path)
+		target = get_node_by_path(target, path);
+
+	return target;
 }
 
 cell_t get_node_phandle(struct node *root, struct node *node)

scripts/dtc/util.c

@@ -46,6 +46,17 @@ char *xstrdup(const char *s)
 	return d;
 }
 
+char *xstrndup(const char *s, size_t n)
+{
+	size_t len = strnlen(s, n) + 1;
+	char *d = xmalloc(len);
+
+	memcpy(d, s, len - 1);
+	d[len - 1] = '\0';
+
+	return d;
+}
+
 /* based in part from (3) vsnprintf */
 int xasprintf(char **strp, const char *fmt, ...)
 {

scripts/dtc/util.h

@@ -70,6 +70,7 @@ static inline void *xrealloc(void *p, size_t len)
 }
 
 extern char *xstrdup(const char *s);
+extern char *xstrndup(const char *s, size_t len);
 
 extern int PRINTF(2, 3) xasprintf(char **strp, const char *fmt, ...);
 extern char *join_path(const char *path, const char *name);