fdt: Add a function to get the index of a string

Given a device tree node and a property name, the new fdt_find_string()
function will look up a given string in the string list contained in the
property's value and return its index.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

lib/libfdt/fdt_ro.c

@@ -511,6 +511,32 @@ int fdt_count_strings(const void *fdt, int node, const char *property)
 	return count;
 }
 
+int fdt_find_string(const void *fdt, int node, const char *property,
+		    const char *string)
+{
+	const char *list, *end;
+	int len, index = 0;
+
+	list = fdt_getprop(fdt, node, property, &len);
+	if (!list)
+		return len;
+
+	end = list + len;
+	len = strlen(string);
+
+	while (list < end) {
+		int l = strlen(list);
+
+		if (l == len && memcmp(list, string, len) == 0)
+			return index;
+
+		list += l + 1;
+		index++;
+	}
+
+	return -FDT_ERR_NOTFOUND;
+}
+
 int fdt_node_check_compatible(const void *fdt, int nodeoffset,
 			      const char *compatible)
 {