[PATCH] dt: add helper functions to read u32 and string property values

[Shawn Guo]

On Thu, Jun 30, 2011 at 12:13:53PM -0600, Grant Likely wrote:
> On Thu, Jun 30, 2011 at 09:26:10PM +0530, Thomas Abraham wrote:
> > Add helper functions to retrive unsigned integer and string property values from
> > properties of a device node. These helper functions can be used to lookup a
> > property in a device node, perform error checking and read the property value.
> > 
> > [grant.likely at secretlab.ca: Proposal and initial implementation]
> > Signed-off-by: Thomas Abraham <thomas.abraham at linaro.org>
> 
> Merged, thanks.  Bonus points to anyone who submits patches converting
> existing code to this new api.
> 
> g.
> 
> > ---
> >  drivers/of/base.c  |   59 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/of.h |    4 +++
> >  2 files changed, 63 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > index 632ebae..4823b53 100644
> > --- a/drivers/of/base.c
> > +++ b/drivers/of/base.c
> > @@ -596,6 +596,65 @@ struct device_node *of_find_node_by_phandle(phandle handle)
> >  EXPORT_SYMBOL(of_find_node_by_phandle);
> >  
> >  /**
> > + * of_property_read_u32 - Find a property in a device node and read the
> > + *				32-bit property value
> > + * @np:		device node from which the property value is to be read.
> > + * @propname:	name of the property to be searched.
> > + * @out_value:	returned value, valid if return value is 0.
> > + *
> > + * Search for a property in a device node and read a 32-bit value from a
> > + * property. Returns -EINVAL, if the property does not exist, -ENODATA, if
> > + * property does not have a value, -EOVERFLOW, if the property data isn't
> > + * large enough, and 0 on success.
> > + *
> > + * The out_value is modified only if a valid u32 value can be decoded.
> > + */
> > +int of_property_read_u32(struct device_node *np, char *propname, u32 *out_value)
> > +{
> > +	struct property *prop = of_find_property(np, propname, NULL);
> > +
> > +	if (!prop)
> > +		return -EINVAL;
> > +	if (!prop->value)
> > +		return -ENODATA;
> > +	if (sizeof(*out_value) > prop->length)
> > +		return -EOVERFLOW;
> > +	*out_value = be32_to_cpup(prop->value);
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(of_property_read_u32);
> > +
> > +/**
> > + * of_property_read_string - Find a property in a device node and return a
> > + *				pointer to the property string value.
> > + * @np:		device node from which the property value is to be read.
> > + * @propname:	name of the property to be searched.
> > + * @out_string:	pointer to a null terminated string, valid only if the return
> > + *		value is 0.
> > + *
> > + * Returns a pointer to a null terminated property value string. Returns
> > + * -EINVAL, if the property does not exist, -ENODATA, if property does not have
> > + * a value, -EILSEQ, if the string is not null-terminated within the length of
> > + * the property value, and 0 on success.
> > + *
> > + * The out_string value is modified only if a valid string can be decoded.
> > + */
> > +int of_property_read_string(struct device_node *np, char *propname,
> > +				char **out_string)

When converting my dt code to use this api, the following type
mismatch warning is being seen in a lot of places.

'char **' but argument is of type 'const char **'

This is because the existing codes usually get string from
of_get_property and assign it to a 'const char *'.

I'm wondering if we should drop the const during converting or
change the api with const added to out_string to get converting
a little bit easier.

Regards,
Shawn

> > +{
> > +	struct property *prop = of_find_property(np, propname, NULL);
> > +	if (!prop)
> > +		return -EINVAL;
> > +	if (!prop->value)
> > +		return -ENODATA;
> > +	if (strnlen(prop->value, prop->length) == prop->length)
> > +		return -EILSEQ;
> > +	*out_string = prop->value;
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(of_property_read_string);
> > +
> > +/**
> >   * of_parse_phandle - Resolve a phandle property to a device_node pointer
> >   * @np: Pointer to device node holding phandle property
> >   * @phandle_name: Name of property holding a phandle value
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index bfc0ed1..4fc4c1b 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -195,6 +195,10 @@ extern struct device_node *of_find_node_with_property(
> >  extern struct property *of_find_property(const struct device_node *np,
> >  					 const char *name,
> >  					 int *lenp);
> > +extern int of_property_read_u32(struct device_node *np, char *propname,
> > +					u32 *out_value);
> > +extern int of_property_read_string(struct device_node *np, char *propname,
> > +					char **out_string);
> >  extern int of_device_is_compatible(const struct device_node *device,
> >  				   const char *);
> >  extern int of_device_is_available(const struct device_node *device);
> > -- 
> > 1.6.6.rc2
> > 
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