net: phy: microchip: Reset LAN88xx PHY to ensure clean link state on LAN7800/7850

Fix outdated MII_LPA data in the LAN88xx PHY, which is used in LAN7800
and LAN7850 USB Ethernet controllers. Due to a hardware limitation, the
PHY cannot reliably update link status after parallel detection when the
link partner does not support auto-negotiation. To mitigate this, add a
PHY reset in `lan88xx_link_change_notify()` when `phydev->state` is
`PHY_NOLINK`, ensuring the PHY starts in a clean state and reports
accurate fixed link parallel detection results.

Fixes: 792aec47d59d9 ("add microchip LAN88xx phy driver")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20241125084050.414352-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/phy/microchip.c b/drivers/net/phy/microchip.c
index d3273bc0da4a1feac5ec22349783c0891b3665c1..691969a4910f2b4821d4ed53bd1458e7c4834339 100644 (file)
--- a/drivers/net/phy/microchip.c
+++ b/drivers/net/phy/microchip.c
@@ -351,6 +351,22 @@ static int lan88xx_config_aneg(struct phy_device *phydev)
 static void lan88xx_link_change_notify(struct phy_device *phydev)
 {
        int temp;
+       int ret;
+
+       /* Reset PHY to ensure MII_LPA provides up-to-date information. This
+        * issue is reproducible only after parallel detection, as described
+        * in IEEE 802.3-2022, Section 28.2.3.1 ("Parallel detection function"),
+        * where the link partner does not support auto-negotiation.
+        */
+       if (phydev->state == PHY_NOLINK) {
+               ret = phy_init_hw(phydev);
+               if (ret < 0)
+                       goto link_change_notify_failed;
+
+               ret = _phy_start_aneg(phydev);
+               if (ret < 0)
+                       goto link_change_notify_failed;
+       }
 
        /* At forced 100 F/H mode, chip may fail to set mode correctly
         * when cable is switched between long(~50+m) and short one.
@@ -377,6 +393,11 @@ static void lan88xx_link_change_notify(struct phy_device *phydev)
                temp |= LAN88XX_INT_MASK_MDINTPIN_EN_;
                phy_write(phydev, LAN88XX_INT_MASK, temp);
        }
+
+       return;
+
+link_change_notify_failed:
+       phydev_err(phydev, "Link change process failed %pe\n", ERR_PTR(ret));
 }
 
 /**