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: 05b35e7eb9a1 ("smsc95xx: add phylib support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Andre Edich <andre.edich@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250703114941.3243890-3-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/phy/smsc.c b/drivers/net/phy/smsc.c
index adf12d7108b5c4c3d40cb18ec8bc0ef1edb44e54..ad9a3d91bb8ae46422690a1207c5e4ffc5b302f1 100644 (file)
--- a/drivers/net/phy/smsc.c
+++ b/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,