[PATCH AUTOSEL 4.9 5/8] net: stmmac: fixed new system time seconds value calculation

[Sasha Levin]

From: Roland Hii <roland.king.guan.hii@xxxxxxxxx>

[ Upstream commit a1e5388b4d5fc78688e5e9ee6641f779721d6291 ]

When ADDSUB bit is set, the system time seconds field is calculated as
the complement of the seconds part of the update value.

For example, if 3.000000001 seconds need to be subtracted from the
system time, this field is calculated as
2^32 - 3 = 4294967296 - 3 = 0x100000000 - 3 = 0xFFFFFFFD

Previously, the 0x100000000 is mistakenly written as 100000000.

This is further simplified from
  sec = (0x100000000ULL - sec);
to
  sec = -sec;

Fixes: ba1ffd74df74 ("stmmac: fix PTP support for GMAC4")
Signed-off-by: Roland Hii <roland.king.guan.hii@xxxxxxxxx>
Signed-off-by: Ong Boon Leong <boon.leong.ong@xxxxxxxxx>
Signed-off-by: Voon Weifeng <weifeng.voon@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
index f4074e25fb71..25136941a964 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -125,7 +125,7 @@ static int stmmac_adjust_systime(void __iomem *ioaddr, u32 sec, u32 nsec,
 		 * programmed with (2^32 â <new_sec_value>)
 		 */
 		if (gmac4)
-			sec = (100000000ULL - sec);
+			sec = -sec;
 
 		value = readl(ioaddr + PTP_TCR);
 		if (value & PTP_TCR_TSCTRLSSR)
-- 
2.20.1