_spi_transport_min_period(struct device *cdev,          struct device_attribute *attr, char *buf) {  struct scsi_target *starget = transport_class_to_starget(cdev);  struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);  struct spi_internal *i = to_spi_internal(shost->transportt);  struct spi_transport_attrs *tp =   (struct spi_transport_attrs *)&starget->starget_data;   if (!i->f->set_period)   return -EINVAL;   return show_spi_transport_period_helper(buf, tp->