net: stmmac: Fix TX timestamp calculation

When using GMAC4 the value written in PTP_SSIR should be shifted however
the shifted value is also used in subsequent calculations which results
in a bad timestamp value.

Signed-off-by: Fredrik Hallenberg <megahallon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
index 721b61655261..08c19ebd5306 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -34,6 +34,7 @@ static u32 stmmac_config_sub_second_increment(void __iomem *ioaddr,
 {
         u32 value = readl(ioaddr + PTP_TCR);
         unsigned long data;
+        u32 reg_value;
 
         /* For GMAC3.x, 4.x versions, convert the ptp_clock to nano second
          *      formula = (1/ptp_clock) * 1000000000
@@ -50,10 +51,11 @@ static u32 stmmac_config_sub_second_increment(void __iomem *ioaddr,
 
         data &= PTP_SSIR_SSINC_MASK;
 
+        reg_value = data;
         if (gmac4)
-                data = data << GMAC4_PTP_SSIR_SSINC_SHIFT;
+                reg_value <<= GMAC4_PTP_SSIR_SSINC_SHIFT;
 
-        writel(data, ioaddr + PTP_SSIR);
+        writel(reg_value, ioaddr + PTP_SSIR);
 
         return data;
 }