netdev - [PATCH net] net: phy: mscc: Stop clearing the the UDPv4 checksum for L2 frames

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Message-ID: <20250523082716.2935895-1-horatiu.vultur@microchip.com>
Date: Fri, 23 May 2025 10:27:16 +0200
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: <andrew@...n.ch>, <hkallweit1@...il.com>, <linux@...linux.org.uk>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <richardcochran@...il.com>, <kory.maincent@...tlin.com>,
	<wintera@...ux.ibm.com>, <viro@...iv.linux.org.uk>,
	<quentin.schulz@...tlin.com>, <atenart@...nel.org>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Horatiu Vultur
	<horatiu.vultur@...rochip.com>
Subject: [PATCH net] net: phy: mscc: Stop clearing the the UDPv4 checksum for L2 frames

We have noticed that when PHY timestamping is enabled, L2 frames seems
to be modified by changing two 2 bytes with a value of 0. The place were
these 2 bytes seems to be random(or I couldn't find a pattern).  In most
of the cases the userspace can ignore these frames but if for example
those 2 bytes are in the correction field there is nothing to do.  This
seems to happen when configuring the HW for IPv4 even that the flow is
not enabled.
These 2 bytes correspond to the UDPv4 checksum and once we don't enable
clearing the checksum when using L2 frames then the frame doesn't seem
to be changed anymore.

Fixes: 7d272e63e0979d ("net: phy: mscc: timestamping and PHC support")
Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
---
 drivers/net/phy/mscc/mscc_ptp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/mscc/mscc_ptp.c b/drivers/net/phy/mscc/mscc_ptp.c
index 6f96f2679f0bf..6b800081eed52 100644
--- a/drivers/net/phy/mscc/mscc_ptp.c
+++ b/drivers/net/phy/mscc/mscc_ptp.c
@@ -946,7 +946,9 @@ static int vsc85xx_ip1_conf(struct phy_device *phydev, enum ts_blk blk,
 	/* UDP checksum offset in IPv4 packet
 	 * according to: https://tools.ietf.org/html/rfc768
 	 */
-	val |= IP1_NXT_PROT_UDP_CHKSUM_OFF(26) | IP1_NXT_PROT_UDP_CHKSUM_CLEAR;
+	val |= IP1_NXT_PROT_UDP_CHKSUM_OFF(26);
+	if (enable)
+		val |= IP1_NXT_PROT_UDP_CHKSUM_CLEAR;
 	vsc85xx_ts_write_csr(phydev, blk, MSCC_ANA_IP1_NXT_PROT_UDP_CHKSUM,
 			     val);
 
-- 
2.34.1