of: Add helpers to get one string in multiple strings property

Add of_property_read_string_index and of_property_count_strings
to retrieve one string inside a property that will contains
severals strings.
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kevin Hilman <khilman@ti.com>

drivers/of/base.c

@@ -661,6 +661,90 @@ int of_property_read_string(struct device_node *np, const char *propname,
 }
 EXPORT_SYMBOL_GPL(of_property_read_string);
 
+/**
+ * of_property_read_string_index - Find and read a string from a multiple
+ * strings property.
+ * @np:		device node from which the property value is to be read.
+ * @propname:	name of the property to be searched.
+ * @index:	index of the string in the list of strings
+ * @out_string:	pointer to null terminated return string, modified only if
+ *		return value is 0.
+ *
+ * Search for a property in a device tree node and retrieve a null
+ * terminated string value (pointer to data, not a copy) in the list of strings
+ * contained in that property.
+ * Returns 0 on success, -EINVAL if the property does not exist, -ENODATA if
+ * property does not have a value, and -EILSEQ if the string is not
+ * null-terminated within the length of the property data.
+ *
+ * The out_string pointer is modified only if a valid string can be decoded.
+ */
+int of_property_read_string_index(struct device_node *np, const char *propname,
+				  int index, const char **output)
+{
+	struct property *prop = of_find_property(np, propname, NULL);
+	int i = 0;
+	size_t l = 0, total = 0;
+	const char *p;
+
+	if (!prop)
+		return -EINVAL;
+	if (!prop->value)
+		return -ENODATA;
+	if (strnlen(prop->value, prop->length) >= prop->length)
+		return -EILSEQ;
+
+	p = prop->value;
+
+	for (i = 0; total < prop->length; total += l, p += l) {
+		l = strlen(p) + 1;
+		if ((*p != 0) && (i++ == index)) {
+			*output = p;
+			return 0;
+		}
+	}
+	return -ENODATA;
+}
+EXPORT_SYMBOL_GPL(of_property_read_string_index);
+
+
+/**
+ * of_property_count_strings - Find and return the number of strings from a
+ * multiple strings property.
+ * @np:		device node from which the property value is to be read.
+ * @propname:	name of the property to be searched.
+ *
+ * Search for a property in a device tree node and retrieve the number of null
+ * terminated string contain in it. Returns the number of strings on
+ * success, -EINVAL if the property does not exist, -ENODATA if property
+ * does not have a value, and -EILSEQ if the string is not null-terminated
+ * within the length of the property data.
+ */
+int of_property_count_strings(struct device_node *np, const char *propname)
+{
+	struct property *prop = of_find_property(np, propname, NULL);
+	int i = 0;
+	size_t l = 0, total = 0;
+	const char *p;
+
+	if (!prop)
+		return -EINVAL;
+	if (!prop->value)
+		return -ENODATA;
+	if (strnlen(prop->value, prop->length) >= prop->length)
+		return -EILSEQ;
+
+	p = prop->value;
+
+	for (i = 0; total < prop->length; total += l, p += l) {
+		l = strlen(p) + 1;
+		if (*p != 0)
+			i++;
+	}
+	return i;
+}
+EXPORT_SYMBOL_GPL(of_property_count_strings);
+
 /**
  * of_parse_phandle - Resolve a phandle property to a device_node pointer
  * @np: Pointer to device node holding phandle property

include/linux/of.h

@@ -203,6 +203,11 @@ extern int of_property_read_u32_array(const struct device_node *np,
 extern int of_property_read_string(struct device_node *np,
 				   const char *propname,
 				   const char **out_string);
+extern int of_property_read_string_index(struct device_node *np,
+					 const char *propname,
+					 int index, const char **output);
+extern int of_property_count_strings(struct device_node *np,
+				     const char *propname);
 extern int of_device_is_compatible(const struct device_node *device,
 				   const char *);
 extern int of_device_is_available(const struct device_node *device);
@@ -256,6 +261,19 @@ static inline int of_property_read_string(struct device_node *np,
 	return -ENOSYS;
 }
 
+static inline int of_property_read_string_index(struct device_node *np,
+						const char *propname, int index,
+						const char **out_string)
+{
+	return -ENOSYS;
+}
+
+static inline int of_property_count_strings(struct device_node *np,
+					    const char *propname)
+{
+	return -ENOSYS;
+}
+
 static inline const void *of_get_property(const struct device_node *node,
 				const char *name,
 				int *lenp)