div_u64
return (div_u64(x1 + x2 - 1, x2) * x2);
diff = div_u64(adjust, 1000000000UL);
pdata->tstamp_addend = div_u64(dividend, pdata->ptpclk_rate);
div_u64((low_record_time - curr_time), NSEC_PER_SEC);