linux-kernel - Re: [PATCH v2] of: add functions to count number of elements in a property

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Date:	Fri, 17 Jan 2014 11:42:14 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <Pawel.Moll@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>
Subject: Re: [PATCH v2] of: add functions to count number of elements in a property

On Fri, Jan 17, 2014 at 9:44 AM, Heiko Stübner <heiko@...ech.de> 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 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@....com>
> Signed-off-by: Heiko Stuebner <heiko@...ech.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;
> +}

Export this one.

> +
> +/**
> + * of_property_count_u8_elems - Count the number of u8 elements 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 u8 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 u8 and -ENODATA if the
> + * property does not have a value.
> + */
> +int of_property_count_u8_elems(const struct device_node *np,
> +                               const char *propname)
> +{
> +       return of_count_property_elems_of_size(np, propname, sizeof(u8));
> +}
> +EXPORT_SYMBOL_GPL(of_property_count_u8_elems);

And make all these static inline.

Then you only need a single empty function for !OF.

Rob
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