linux-kernel - Re: [PATCH] of: add function to count number of u32 elements in a property

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Message-ID: <20140117144456.GG19578@e106331-lin.cambridge.arm.com>
Date:	Fri, 17 Jan 2014 14:44:57 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"arm@...nel.org" <arm@...nel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <robherring2@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>
Subject: Re: [PATCH] of: add function to count number of u32 elements in a
 property

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@....com>
> Signed-off-by: Heiko Stuebner <heiko@...ech.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.
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