add fdt_get_symbol() and fdt_get_symbol_namelen() functions

The fdt_get_symbol_namelen() function will be used in a subsequent
patch.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt_ro.c

@@ -545,6 +545,17 @@ const char *fdt_get_alias(const void *fdt, const char *name)
 	return fdt_get_alias_namelen(fdt, name, strlen(name));
 }
 
+const char *fdt_get_symbol_namelen(const void *fdt,
+				   const char *name, int namelen)
+{
+	return fdt_path_getprop_namelen(fdt, "/__symbols__", name, namelen, NULL);
+}
+
+const char *fdt_get_symbol(const void *fdt, const char *name)
+{
+	return fdt_get_symbol_namelen(fdt, name, strlen(name));
+}
+
 int fdt_get_path(const void *fdt, int nodeoffset, char *buf, int buflen)
 {
 	int pdepth = 0, p = 0;

libfdt/libfdt.h

@@ -869,6 +869,42 @@ const char *fdt_get_alias_namelen(const void *fdt,
  */
 const char *fdt_get_alias(const void *fdt, const char *name);
 
+/**
+ * fdt_get_symbol_namelen - get symbol based on substring
+ * @fdt: pointer to the device tree blob
+ * @name: name of the symbol to look up
+ * @namelen: number of characters of name to consider
+ *
+ * Identical to fdt_get_symbol(), but only examine the first @namelen
+ * characters of @name for matching the symbol name.
+ *
+ * Return: a pointer to the expansion of the symbol named @name, if it exists,
+ *	   NULL otherwise
+ */
+#ifndef SWIG /* Not available in Python */
+const char *fdt_get_symbol_namelen(const void *fdt,
+				   const char *name, int namelen);
+#endif
+
+/**
+ * fdt_get_symbol - retrieve the path referenced by a given symbol
+ * @fdt: pointer to the device tree blob
+ * @name: name of the symbol to look up
+ *
+ * fdt_get_symbol() retrieves the value of a given symbol.  That is,
+ * the value of the property named @name in the node
+ * /__symbols__. Such a node exists only for a device tree blob that
+ * has been compiled with the -@ dtc option. Each property corresponds
+ * to a label appearing in the device tree source, with the name of
+ * the property being the label and the value being the full path of
+ * the node it is attached to.
+ *
+ * returns:
+ *	a pointer to the expansion of the symbol named 'name', if it exists
+ *	NULL, if the given symbol or the /__symbols__ node does not exist
+ */
+const char *fdt_get_symbol(const void *fdt, const char *name);
+
 /**
  * fdt_get_path - determine the full path of a node
  * @fdt: pointer to the device tree blob