netdev - [PATCH net-next v3 1/1] net: phy: clear link parameters on admin link down

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Message-ID: <20250917094751.2101285-1-o.rempel@pengutronix.de>
Date: Wed, 17 Sep 2025 11:47:51 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Russell King <linux@...linux.org.uk>
Subject: [PATCH net-next v3 1/1] net: phy: clear link parameters on admin link down

When a PHY is halted (e.g. `ip link set dev lan2 down`), several
fields in struct phy_device may still reflect the last active
connection. This leads to ethtool showing stale values even though
the link is down.

Reset selected fields in _phy_state_machine() when transitioning
to PHY_HALTED and the link was previously up:

- speed/duplex -> UNKNOWN, but only in autoneg mode (in forced mode
  these fields carry configuration, not status)
- master_slave_state -> UNKNOWN if previously supported
- mdix -> INVALID (state only, same meaning as "unknown")
- lp_advertising -> always cleared

The cleanup is skipped if the PHY is in PHY_ERROR state, so the
last values remain available for diagnostics.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
changes v3:
- rework commit message
- move cleaning sequence to PHY_HALTED case in _phy_state_machine()
changes v2:
- rebase and resned against net-next

 drivers/net/phy/phy.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index e046dd858f15..02da4a203ddd 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -1548,6 +1548,19 @@ static enum phy_state_work _phy_state_machine(struct phy_device *phydev)
 		}
 		break;
 	case PHY_HALTED:
+		if (phydev->link) {
+			if (phydev->autoneg == AUTONEG_ENABLE) {
+				phydev->speed = SPEED_UNKNOWN;
+				phydev->duplex = DUPLEX_UNKNOWN;
+			}
+			if (phydev->master_slave_state !=
+						MASTER_SLAVE_STATE_UNSUPPORTED)
+				phydev->master_slave_state =
+						MASTER_SLAVE_STATE_UNKNOWN;
+			phydev->mdix = ETH_TP_MDI_INVALID;
+			linkmode_zero(phydev->lp_advertising);
+		}
+		fallthrough;
 	case PHY_ERROR:
 		if (phydev->link) {
 			phydev->link = 0;
--
2.47.3