diff options
Diffstat (limited to 'drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c')
| -rw-r--r-- | drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c index fcf080243a0f..d291612eeafb 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c @@ -27,12 +27,16 @@ static void config_sub_second_increment(void __iomem *ioaddr, unsigned long data; u32 reg_value; - /* For GMAC3.x, 4.x versions, convert the ptp_clock to nano second - * formula = (1/ptp_clock) * 1000000000 - * where ptp_clock is 50MHz if fine method is used to update system + /* For GMAC3.x, 4.x versions, in "fine adjustement mode" set sub-second + * increment to twice the number of nanoseconds of a clock cycle. + * The calculation of the default_addend value by the caller will set it + * to mid-range = 2^31 when the remainder of this division is zero, + * which will make the accumulator overflow once every 2 ptp_clock + * cycles, adding twice the number of nanoseconds of a clock cycle : + * 2000000000ULL / ptp_clock. */ if (value & PTP_TCR_TSCFUPDT) - data = (1000000000ULL / 50000000); + data = (2000000000ULL / ptp_clock); else data = (1000000000ULL / ptp_clock); |