linux-kernel - [PATCH 1/2] net: stmmac: Fix TX timestamp calculation

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Message-Id: <20171218223400.29644-1-megahallon@gmail.com>
Date:   Mon, 18 Dec 2017 23:33:59 +0100
From:   Fredrik Hallenberg <megahallon@...il.com>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Jose Abreu <Jose.Abreu@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Fredrik Hallenberg <megahallon@...il.com>
Subject: [PATCH 1/2] 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@...il.com>
---
 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 721b61655..08c19ebd5 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;
 }
-- 
2.15.1