iio_read_const_attr
EXPORT_SYMBOL(iio_read_const_attr);
ssize_t iio_read_const_attr(struct device *dev,
.dev_attr = __ATTR(_name, S_IRUGO, iio_read_const_attr, NULL)}
.dev_attr = __ATTR(_name, S_IRUGO, iio_read_const_attr, NULL)}