net: phy: smsc: Force predictable MDI-X state on LAN87xx

Override the hardware strap configuration for MDI-X mode to ensure a
predictable initial state for the driver. The initial mode of the LAN87xx
PHY is determined by the AUTOMDIX_EN strap pin, but the driver has no
documented way to read its latched status.

This unpredictability means the driver cannot know if the PHY has
initialized with Auto-MDIX enabled or disabled, preventing it from
providing a reliable interface to the user.

This patch introduces a `config_init` hook that forces the PHY into a
known state by explicitly enabling Auto-MDIX.

Fixes: 05b35e7 ("smsc95xx: add phylib support")
Signed-off-by: Oleksij Rempel <[email protected]>
Cc: Andre Edich <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: olerem

drivers/net/phy/smsc.c

@@ -262,6 +262,33 @@ int lan87xx_read_status(struct phy_device *phydev)
 }
 EXPORT_SYMBOL_GPL(lan87xx_read_status);
 
+static int lan87xx_phy_config_init(struct phy_device *phydev)
+{
+	int rc;
+
+	/* The LAN87xx PHY's initial MDI-X mode is determined by the AUTOMDIX_EN
+	 * hardware strap, but the driver cannot read the strap's status. This
+	 * creates an unpredictable initial state.
+	 *
+	 * To ensure consistent and reliable behavior across all boards,
+	 * override the strap configuration on initialization and force the PHY
+	 * into a known state with Auto-MDIX enabled, which is the expected
+	 * default for modern hardware.
+	 */
+	rc = phy_modify(phydev, SPECIAL_CTRL_STS,
+			SPECIAL_CTRL_STS_OVRRD_AMDIX_ |
+			SPECIAL_CTRL_STS_AMDIX_ENABLE_ |
+			SPECIAL_CTRL_STS_AMDIX_STATE_,
+			SPECIAL_CTRL_STS_OVRRD_AMDIX_ |
+			SPECIAL_CTRL_STS_AMDIX_ENABLE_);
+	if (rc < 0)
+		return rc;
+
+	phydev->mdix_ctrl = ETH_TP_MDI_AUTO;
+
+	return smsc_phy_config_init(phydev);
+}
+
 static int lan874x_phy_config_init(struct phy_device *phydev)
 {
 	u16 val;
@@ -696,7 +723,7 @@ static struct phy_driver smsc_phy_driver[] = {
 
 	/* basic functions */
 	.read_status	= lan87xx_read_status,
-	.config_init	= smsc_phy_config_init,
+	.config_init	= lan87xx_phy_config_init,
 	.soft_reset	= smsc_phy_reset,
 	.config_aneg	= lan87xx_config_aneg,