linux-kernel - Re: [PATCH] dt: add helper function to read u8 & u16 variables & arrays

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Date:	Tue, 20 Nov 2012 08:21:07 +0000
From:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"spear-devel@...t.st.com" <spear-devel@...t.st.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>
Subject: Re: [PATCH] dt: add helper function to read u8 & u16 variables &
 arrays

On Tue, 2012-11-20 at 10:15 +0530, Viresh Kumar wrote: 
> This adds following helper routines:
> - of_property_read_u8_array()
> - of_property_read_u16_array()
> - of_property_read_u8()
> - of_property_read_u16()
> 
> This expects arrays from DT to be passed as:
> - u8 array:
> 	property = /bits/ 8 <0x50 0x60 0x70>;
> - u16 array:
> 	property = /bits/ 16 <0x5000 0x6000 0x7000>;
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V2->V3:
> - Expect u8 & u16 arrays to be passed using: /bits/ 8 or 16
> - remove common macro, as not much common now :(

You could at least create macro to do a precheck if you want to.

Like 
#define CHECK_PROP(prop, sz, out)

{
if (!prop) 
		return -EINVAL;
	if (!prop->value)
		return -ENODATA;
	if ((sz * sizeof(*out)) > prop->length)
		return -EOVERFLOW;
}

Of course you can do even robust macro to cover types, but I don't like
ugly macros (as I can't see how it could be shaped nicely).

> - Tested on ARM platform.
> 

> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -671,12 +671,89 @@ struct device_node *of_find_node_by_phandle(phandle handle)
>  EXPORT_SYMBOL(of_find_node_by_phandle);
>  
>  /**
> + * 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.
> + * @propname:	name of the property to be searched.
> + * @out_value:	pointer to return value, modified only if return value is 0.
> + * @sz:		number of array elements to read
> + *
> + * Search for a property in a device node and read 8-bit value(s) from
> + * it. Returns 0 on success, -EINVAL if the property does not exist,
> + * -ENODATA if property does not have a value, and -EOVERFLOW if the
> + * property data isn't large enough.
> + *
> + * dts entry of array should be like:
> + *	property = /bits/ 8 <0x50 0x60 0x70>;
> + *
> + * The out_value is modified only if a valid u8 value can be decoded.
> + */
> +int of_property_read_u8_array(const struct device_node *np,
> +			const char *propname, u8 *out_values, size_t sz)
> +{
> +	struct property *prop = of_find_property(np, propname, NULL);
> +	const u8 *val;
> +
> +	if (!prop)
> +		return -EINVAL;
> +	if (!prop->value)
> +		return -ENODATA;
> +	if ((sz * sizeof(*out_values)) > prop->length)
> +		return -EOVERFLOW;
> +
> +	val = prop->value;
> +	while (sz--)
> +		*out_values++ = *val++;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_property_read_u8_array);
> +
> +/**
> + * of_property_read_u16_array - Find and read an array of u16 from a property.
> + *
> + * @np:		device node from which the property value is to be read.
> + * @propname:	name of the property to be searched.
> + * @out_value:	pointer to return value, modified only if return value is 0.
> + * @sz:		number of array elements to read
> + *
> + * Search for a property in a device node and read 16-bit value(s) from
> + * it. Returns 0 on success, -EINVAL if the property does not exist,
> + * -ENODATA if property does not have a value, and -EOVERFLOW if the
> + * property data isn't large enough.
> + *
> + * dts entry of array should be like:
> + *	property = /bits/ 16 <0x5000 0x6000 0x7000>;
> + *
> + * The out_value is modified only if a valid u16 value can be decoded.
> + */
> +int of_property_read_u16_array(const struct device_node *np,
> +			const char *propname, u16 *out_values, size_t sz)
> +{
> +	struct property *prop = of_find_property(np, propname, NULL);
> +	const __be16 *val;
> +
> +	if (!prop)
> +		return -EINVAL;
> +	if (!prop->value)
> +		return -ENODATA;
> +	if ((sz * sizeof(*out_values)) > prop->length)
> +		return -EOVERFLOW;
> +
> +	val = prop->value;
> +	while (sz--)
> +		*out_values++ = be16_to_cpup(val++);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_property_read_u16_array);
> +
> +/**
>   * of_property_read_u32_array - Find and read an array of 32 bit integers
>   * from a property.
>   *
>   * @np:		device node from which the property value is to be read.
>   * @propname:	name of the property to be searched.
>   * @out_value:	pointer to return value, modified only if return value is 0.
> + * @sz:		number of array elements to read
>   *
>   * Search for a property in a device node and read 32-bit value(s) from
>   * it. Returns 0 on success, -EINVAL if the property does not exist,

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy
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