libfdt: Add max phandle retrieval function

Add a function to retrieve the highest phandle in a given device tree.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Acked-by: Simon Glass <sjg@chromium.org>

lib/libfdt/fdt_ro.c

@@ -47,6 +47,32 @@ static int _fdt_string_eq(const void *fdt, int stroffset,
 	return (strnlen(p, len + 1) == len) && (memcmp(p, s, len) == 0);
 }
 
+uint32_t fdt_get_max_phandle(const void *fdt)
+{
+	uint32_t max_phandle = 0;
+	int offset;
+
+	for (offset = fdt_next_node(fdt, -1, NULL);;
+	     offset = fdt_next_node(fdt, offset, NULL)) {
+		uint32_t phandle;
+
+		if (offset == -FDT_ERR_NOTFOUND)
+			return max_phandle;
+
+		if (offset < 0)
+			return 0;
+
+		phandle = fdt_get_phandle(fdt, offset);
+		if (phandle == (uint32_t)-1)
+			return 0;
+
+		if (phandle > max_phandle)
+			max_phandle = phandle;
+	}
+
+	return 0;
+}
+
 int fdt_get_mem_rsv(const void *fdt, int n, uint64_t *address, uint64_t *size)
 {
 	FDT_CHECK_HEADER(fdt);