kernel-4.4includelinuxof.h

extern int of_property_read_string(struct device_node *np,const char *propname,const char **out_string);

static inline int of_property_read_string(struct device_node *np,const char *propname,const char **out_string)
{return -ENOSYS;
}

Open Firmware. This was invented long time ago when Apple was producing laptops based on PowerPC CPUs. Openfirmware provides a good description of the devices connected to the platform. In Linux kernel the part that works with device data is called Device Tree (DT). More details in theUsage model.

"./drivers/of/base.c"

/*** of_property_read_string - Find and read a string from a property* @np:         device node from which the property value is to be read.* @propname:   name of the property to be searched.* @out_string: pointer to null terminated return string, modified only if*              return value is 0.** Search for a property in a device tree node and retrieve a null* terminated string value (pointer to data, not a copy). Returns 0 on* success, -EINVAL if the property does not exist, -ENODATA if property* does not have a value, and -EILSEQ if the string is not null-terminated* within the length of the property data.** The out_string pointer is modified only if a valid string can be decoded.*/
int of_property_read_string(struct device_node *np, const char *propname,const char **out_string)
{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);

int of_property_read_string(struct device_node *np, const char *propname,const char **out_string)
{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);

struct property {char   *name;int   length;void *value;struct property *next;unsigned long _flags;unsigned int unique_id;struct bin_attribute attr;
};