[PATCH AUTOSEL for 4.9 19/52] net: stmmac: Fix TX timestamp calculation

[Sasha Levin]

From: Fredrik Hallenberg <megahallon@xxxxxxxxx>

[ Upstream commit 200922c93f008e03ddc804c6dacdf26ca1ba86d7 ]

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@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c | 6 ++++--
 1 file 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 10d6059b2f26..f4074e25fb71 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -38,6 +38,7 @@ 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
@@ -54,10 +55,11 @@ 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;
 }
-- 
2.11.0