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 static function that also centralises strict sanity
checking and DTB format details, as well as a set of wrapper functions
for u8, u16, u32 and u64.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
changes since v1:
address comments from Rob Herring and Mark Rutland:
- provide a helper and a set of wrappers for u8-u64
- get rid of extra len variable, prop->length is enough
- include node name in error message

 drivers/of/base.c  |   98 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/of.h |   32 +++++++++++++++++
 2 files changed, 130 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index f807d0e..b6e6d4a 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -862,6 +862,104 @@ struct device_node *of_find_node_by_phandle(phandle handle)
 EXPORT_SYMBOL(of_find_node_by_phandle);

 /**
+ * of_count_property_elems_of_size - Count the number of elements in a property
+ *
+ * @np:                device node from which the property value is to be read.
+ * @propname:  name of the property to be searched.
+ * @elem_size: size of the individual element
+ */
+static int of_count_property_elems_of_size(const struct device_node *np,
+                               const char *propname, int elem_size)
+{
+       struct property *prop = of_find_property(np, propname, NULL);
+
+       if (!prop)
+               return -EINVAL;
+       if (!prop->value)
+               return -ENODATA;
+
+       if (prop->length % elem_size != 0) {
+               pr_err("size of %s in node %s is not a multiple of %d\n",
+                      propname, np->name, elem_size);
+               return -EINVAL;
+       }
+
+       return prop->length / elem_size;
+}