linux-kernel - [PATCH net-next] net: dsa: mxl-gsw1xx: fix SerDes RX polarity

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Message-ID: <ca10e9f780c0152ecf9ae8cbac5bf975802e8f99.1764668951.git.daniel@makrotopia.org>
Date: Tue, 2 Dec 2025 09:57:21 +0000
From: Daniel Golle <daniel@...rotopia.org>
To: Hauke Mehrtens <hauke@...ke-m.de>, Andrew Lunn <andrew@...n.ch>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Daniel Golle <daniel@...rotopia.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Rasmus Villemoes <ravi@...vas.dk>,
	"Benny (Ying-Tsan) Weng" <yweng@...linear.com>
Subject: [PATCH net-next] net: dsa: mxl-gsw1xx: fix SerDes RX polarity

According to MaxLinear engineer Benny Weng the RX lane of the SerDes
port of the GSW1xx switches is inverted in hardware, and the
SGMII_PHY_RX0_CFG2_INVERT bit is set by default in order to compensate
for that. Hence also set the SGMII_PHY_RX0_CFG2_INVERT bit by default in
gsw1xx_pcs_reset().

Fixes: 22335939ec90 ("net: dsa: add driver for MaxLinear GSW1xx switch family")
Reported-by: Rasmus Villemoes <ravi@...vas.dk>
Signed-off-by: Daniel Golle <daniel@...rotopia.org>
---
Sent to net-next as the commit to be fixed is only in net-next.

 drivers/net/dsa/lantiq/mxl-gsw1xx.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/lantiq/mxl-gsw1xx.c b/drivers/net/dsa/lantiq/mxl-gsw1xx.c
index 0816c61a47f12..cf33a16fd183b 100644
--- a/drivers/net/dsa/lantiq/mxl-gsw1xx.c
+++ b/drivers/net/dsa/lantiq/mxl-gsw1xx.c
@@ -255,10 +255,16 @@ static int gsw1xx_pcs_reset(struct gsw1xx_priv *priv)
 	      FIELD_PREP(GSW1XX_SGMII_PHY_RX0_CFG2_FILT_CNT,
 			 GSW1XX_SGMII_PHY_RX0_CFG2_FILT_CNT_DEF);
 
-	/* TODO: Take care of inverted RX pair once generic property is
+	/* RX lane seems to be inverted internally, so bit
+	 * GSW1XX_SGMII_PHY_RX0_CFG2_INVERT needs to be set for normal
+	 * (ie. non-inverted) operation.
+	 *
+	 * TODO: Take care of inverted RX pair once generic property is
 	 *       available
 	 */
 
+	val |= GSW1XX_SGMII_PHY_RX0_CFG2_INVERT;
+
 	ret = regmap_write(priv->sgmii, GSW1XX_SGMII_PHY_RX0_CFG2, val);
 	if (ret < 0)
 		return ret;
-- 
2.52.0