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path: root/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
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Diffstat (limited to 'drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c')
-rw-r--r--drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c12
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);