[net v1] net: stmmac: fixed new system time seconds value calculation

[net v1] net: stmmac: fixed new system time seconds value calculation

[Voon Weifeng]

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

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@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
index 2dcdf761d525..020159622559 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -112,7 +112,7 @@ static int adjust_systime(void __iomem *ioaddr, u32 sec, u32 nsec,
 		 * programmed with (2^32 – <new_sec_value>)
 		 */
 		if (gmac4)
-			sec = (100000000ULL - sec);
+			sec = -sec;
 
 		value = readl(ioaddr + PTP_TCR);
 		if (value & PTP_TCR_TSCTRLSSR)
-- 
1.9.1

Re: [net v1] net: stmmac: fixed new system time seconds value calculation

[David Miller]

From: Voon Weifeng <weifeng.voon@intel.com>
Date: Wed, 19 Jun 2019 22:13:48 +0800

> From: Roland Hii <roland.king.guan.hii@intel.com>
> 
> 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@intel.com>
> Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
> Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>

Applied and queued up for -stable.