of: Add of_property_match_string() to find index into a string list

commit 7aff0fe3 upstream.

Add a helper function for finding the index of a string in a string
list property.  This helper is useful for bindings that use a separate
*-name property for attaching names to tuples in another property such
as 'reg' or 'gpios'.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
[jt: dropped changes to files not existing in the 3.2 tree]
Signed-off-by: Jonathan Toppins <jtoppins@cumulusnetworks.com>
Reviewed-by: Andy Gospodarek <gospo@cumulusnetworks.com>
Acked-by: Curt Brune <curt@cumulusnetworks.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/of/base.c

@@ -761,6 +761,42 @@ int of_property_read_string_index(struct device_node *np, const char *propname,
 }
 EXPORT_SYMBOL_GPL(of_property_read_string_index);
 
+/**
+ * of_property_match_string() - Find string in a list and return index
+ * @np: pointer to node containing string list property
+ * @propname: string list property name
+ * @string: pointer to string to search for in string list
+ *
+ * This function searches a string list property and returns the index
+ * of a specific string value.
+ */
+int of_property_match_string(struct device_node *np, const char *propname,
+			     const char *string)
+{
+	struct property *prop = of_find_property(np, propname, NULL);
+	size_t l;
+	int i;
+	const char *p, *end;
+
+	if (!prop)
+		return -EINVAL;
+	if (!prop->value)
+		return -ENODATA;
+
+	p = prop->value;
+	end = p + prop->length;
+
+	for (i = 0; p < end; i++, p += l) {
+		l = strlen(p) + 1;
+		if (p + l > end)
+			return -EILSEQ;
+		pr_debug("comparing %s with %s\n", string, p);
+		if (strcmp(string, p) == 0)
+			return i; /* Found it; return index */
+	}
+	return -ENODATA;
+}
+EXPORT_SYMBOL_GPL(of_property_match_string);
 
 /**
  * of_property_count_strings - Find and return the number of strings from a

include/linux/of.h

@@ -211,6 +211,9 @@ extern int of_property_read_string(struct device_node *np,
 extern int of_property_read_string_index(struct device_node *np,
 					 const char *propname,
 					 int index, const char **output);
+extern int of_property_match_string(struct device_node *np,
+				    const char *propname,
+				    const char *string);
 extern int of_property_count_strings(struct device_node *np,
 				     const char *propname);
 extern int of_device_is_compatible(const struct device_node *device,