viortc_read
ret = viortc_read(viortc_class->viortc, viortc_class->vio_clk_id, &ns);
int viortc_read(struct viortc_dev *viortc, u16 vio_clk_id, u64 *reading);
ret = viortc_read(vio_ptp->viortc, vio_ptp->vio_clk_id, &ns);