[PATCH] of: add function to count number of u32 elements in a property

["Heiko Stübner" <heiko@sntech.de>]

The need to know the number of array elements in a property is
a common pattern. To prevent duplication of open-coded implementations
add a helper function that also centralises strict sanity checking
and DTB format details.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
Hi Mark,
did you mean it like this? I've tested it with the sram-reserve change and
it made the part of the determining the number elements a lot nicer :-)

 drivers/of/base.c  |   32 ++++++++++++++++++++++++++++++++
 include/linux/of.h |    8 ++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index f807d0e..0f40ea5 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -920,6 +920,38 @@ int of_property_read_u32_index(const struct device_node *np,
 EXPORT_SYMBOL_GPL(of_property_read_u32_index);
 
 /**
+ * of_property_count_u32_elems - Count the number of u32 values in a 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 node and count the number of u32 elements
+ * in it. Returns number of elements on sucess, -EINVAL if the property does
+ * not exist or its length does not match a multiple of u32 and -ENODATA if the
+ * property does not have a value.
+ */
+int of_property_count_u32_elems(const struct device_node *np,
+				const char *propname)
+{
+	int elem_size = sizeof(u32);
+	int len;
+	struct property *prop = of_find_property(np, propname, &len);
+
+	if (!prop)
+		return -EINVAL;
+	if (!prop->value)
+		return -ENODATA;
+
+	if (prop->length % elem_size != 0) {
+		pr_err("size of %s is not a multiple of u32\n", propname);
+		return -EINVAL;
+	}
+
+	return len / elem_size;
+}
+EXPORT_SYMBOL_GPL(of_property_count_u32_elems);
+
+/**
  * of_property_read_u8_array - Find and read an array of u8 from a property.
  *
  * @np:		device node from which the property value is to be read.
diff --git a/include/linux/of.h b/include/linux/of.h
index 276c546..5794942 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -253,6 +253,8 @@ extern struct property *of_find_property(const struct device_node *np,
 extern int of_property_read_u32_index(const struct device_node *np,
 				       const char *propname,
 				       u32 index, u32 *out_value);
+extern int of_property_count_u32_elems(const struct device_node *np,
+				       const char *propname);
 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,
@@ -432,6 +434,12 @@ static inline int of_property_read_u32_index(const struct device_node *np,
 	return -ENOSYS;
 }
 
+static inline int of_property_count_u32_elems(const struct device_node *np,
+			const char *propname)
+{
+	return -ENOSYS;
+}
+
 static inline int of_property_read_u8_array(const struct device_node *np,
 			const char *propname, u8 *out_values, size_t sz)
 {
-- 
1.7.10.4