of: Add support for reading a u32 from a multi-value property.

This patch adds an of_property_read_u32_index() function to allow
reading a single indexed u32 value from a property containing multiple
u32 values.
Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robherring2@gmail.com>

drivers/of/base.c

@@ -745,6 +745,39 @@ struct device_node *of_find_node_by_phandle(phandle handle)
 }
 EXPORT_SYMBOL(of_find_node_by_phandle);
 
+/**
+ * of_property_read_u32_index - Find and read a u32 from a multi-value 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 u32 in the list of values
+ * @out_value:	pointer to return value, modified only if no error.
+ *
+ * Search for a property in a device node and read nth 32-bit value from
+ * it. Returns 0 on success, -EINVAL if the property does not exist,
+ * -ENODATA if property does not have a value, and -EOVERFLOW if the
+ * property data isn't large enough.
+ *
+ * The out_value is modified only if a valid u32 value can be decoded.
+ */
+int of_property_read_u32_index(const struct device_node *np,
+				       const char *propname,
+				       u32 index, u32 *out_value)
+{
+	struct property *prop = of_find_property(np, propname, NULL);
+
+	if (!prop)
+		return -EINVAL;
+	if (!prop->value)
+		return -ENODATA;
+	if (((index + 1) * sizeof(*out_value)) > prop->length)
+		return -EOVERFLOW;
+
+	*out_value = be32_to_cpup(((__be32 *)prop->value) + index);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_property_read_u32_index);
+
 /**
  * of_property_read_u8_array - Find and read an array of u8 from a property.
  *

include/linux/of.h

@@ -235,6 +235,9 @@ extern struct device_node *of_find_node_with_property(
 extern struct property *of_find_property(const struct device_node *np,
 					 const char *name,
 					 int *lenp);
+extern int of_property_read_u32_index(const struct device_node *np,
+				       const char *propname,
+				       u32 index, u32 *out_value);
 extern int of_property_read_u8_array(const struct device_node *np,
 			const char *propname, u8 *out_values, size_t sz);
 extern int of_property_read_u16_array(const struct device_node *np,
@@ -394,6 +397,12 @@ static inline struct device_node *of_find_compatible_node(
 	return NULL;
 }
 
+static inline int of_property_read_u32_index(const struct device_node *np,
+			const char *propname, u32 index, u32 *out_value)
+{
+	return -ENOSYS;
+}
+
 static inline int of_property_read_u8_array(const struct device_node *np,
 			const char *propname, u8 *out_values, size_t sz)
 {