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

[Mark Rutland]

On Thu, Jan 16, 2014 at 06:04:42PM +0000, Heiko Stübner wrote:
> 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 at arm.com>
> Signed-off-by: Heiko Stuebner <heiko at 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 :-)

Yes! This looks pretty nice! :)

> 
>  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);

As Rob said in his reply, it would be nice to split this into a static
helper that took elem size as a parameter, so we can have the full suite
of of_property_count_{u8,u16,u32,u64}_elems.

Also, I think you can get rid of len and always use prop->length, as
other helpers seem to do.

Cheers for putting this together!

Mark.