netdev - [PATCH net] net: phy: dp83869: Set auto mdix bit for forced 100Base-Tx mode

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Message-ID: <20260211131033.2525617-1-m-malladi@ti.com>
Date: Wed, 11 Feb 2026 18:40:32 +0530
From: Meghana Malladi <m-malladi@...com>
To: <pabeni@...hat.com>, <kuba@...nel.org>, <edumazet@...gle.com>,
	<davem@...emloft.net>, <linux@...linux.org.uk>, <hkallweit1@...il.com>,
	<andrew@...n.ch>
CC: <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>, <srk@...com>,
	Vignesh Raghavendra <vigneshr@...com>, Roger Quadros <rogerq@...nel.org>,
	<danishanwar@...com>, <m-malladi@...com>
Subject: [PATCH net] net: phy: dp83869: Set auto mdix bit for forced 100Base-Tx mode

When using DP83869 in force 100Base-Tx mode, the PHY is required
to have robust Auto-MDIX feature enabled from register 1Eh.
Refer to 7.4.1.2 100BASE-TX section in the TRM [1] for more details.

[1]: https://www.ti.com/lit/ds/symlink/dp83869hm.pdf
Signed-off-by: Meghana Malladi <m-malladi@...com>
---
 drivers/net/phy/dp83869.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/net/phy/dp83869.c b/drivers/net/phy/dp83869.c
index 1f381d7b13ff..70d759c45c6a 100644
--- a/drivers/net/phy/dp83869.c
+++ b/drivers/net/phy/dp83869.c
@@ -110,6 +110,7 @@
 
 /* CFG4 bits */
 #define DP83869_INT_OE	BIT(7)
+#define DP83869_CFG4_ENABLE_AUTO_MDIX_100FD	BIT(9)
 
 /* OP MODE */
 #define DP83869_OP_MODE_MII			BIT(5)
@@ -900,6 +901,23 @@ static int dp83869_phy_reset(struct phy_device *phydev)
 	return dp83869_config_init(phydev);
 }
 
+static void dp83869_link_change_notify(struct phy_device *phydev)
+{
+	int cfg4;
+
+	/* When using DP83869 in force 100Base-Tx mode, the PHY is required
+	 * to have robust Auto-MDIX feature enabled
+	 */
+	if (phydev->autoneg == AUTONEG_DISABLE &&
+	    phydev->speed == SPEED_100 &&
+	    phydev->duplex == DUPLEX_FULL) {
+		cfg4 = phy_read(phydev, DP83869_CFG4);
+		if (cfg4 >= 0) {
+			cfg4 |= DP83869_CFG4_ENABLE_AUTO_MDIX_100FD;
+			phy_write(phydev, DP83869_CFG4, cfg4);
+		}
+	}
+}
 
 #define DP83869_PHY_DRIVER(_id, _name)				\
 {								\
@@ -918,6 +936,7 @@ static int dp83869_phy_reset(struct phy_device *phydev)
 	.set_wol	= dp83869_set_wol,			\
 	.suspend	= genphy_suspend,			\
 	.resume		= genphy_resume,			\
+	.link_change_notify = dp83869_link_change_notify,	\
 }
 
 static struct phy_driver dp83869_driver[] = {

base-commit: e9a5073a98d940837cbb95e71eed1f28f48e7b30
-- 
2.43.0