[PATCH AUTOSEL 6.17-6.6] net: phy: clear link parameters on admin link down

[Sasha Levin <sashal@kernel.org>]

From: Oleksij Rempel <o.rempel@pengutronix.de>

[ Upstream commit 60f887b1290b43a4f5a3497982a725687b193fa4 ]

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@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250917094751.2101285-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES
- `_phy_state_machine()` now clears the runtime status fields (speed,
  duplex, master/slave, MDI-X, partner advertising) when transitioning a
  previously up PHY into `PHY_HALTED`, so administrative link-down stops
  reporting stale values to ethtool (`drivers/net/phy/phy.c:1551-1561`).
- These members are exactly what `phy_ethtool_ksettings_get()` surfaces
  to user space, so leaving them stale makes `ethtool link`/`ip link`
  misreport the link after an admin down; the new resets ensure the
  user-visible API reflects that the link is unknown/down
  (`drivers/net/phy/phy.c:273-296`).
- The change is careful to leave forced-mode configurations intact
  (`phydev->autoneg == AUTONEG_ENABLE` guard at
  `drivers/net/phy/phy.c:1552-1555`) and avoids touching hardware
  registers, which keeps the risk of behavioural regressions low.
- Master/slave state is only reset when the feature is supported, while
  diagnostics in `PHY_ERROR` still retain the last negotiated
  information thanks to the guarded fall-through
  (`drivers/net/phy/phy.c:1556-1569`).
- The touched fields are long-standing members of `struct phy_device`
  (`include/linux/phy.h:665-713`), so the patch is self-contained,
  architecture-neutral, and aligns with an earlier mainline fix that
  already clears EEE runtime flags on the same state transition.

 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 e046dd858f151..02da4a203ddd4 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;
-- 
2.51.0