6.15-stable review patch. If anyone has any objections, please let me know.
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From: Oleksij Rempel o.rempel@pengutronix.de
[ Upstream commit 9dfe110cc0f6ef42af8e81ce52aef34a647d0b8a ]
Force a fixed MDI-X mode when auto-negotiation is disabled to prevent link instability.
When forcing the link speed and duplex on a LAN9500 PHY (e.g., with `ethtool -s eth0 autoneg off ...`) while leaving MDI-X control in auto mode, the PHY fails to establish a stable link. This occurs because the PHY's Auto-MDIX algorithm is not designed to operate when auto-negotiation is disabled. In this state, the PHY continuously toggles the TX/RX signal pairs, which prevents the link partner from synchronizing.
This patch resolves the issue by detecting when auto-negotiation is disabled. If the MDI-X control mode is set to 'auto', the driver now forces a specific, stable mode (ETH_TP_MDI) to prevent the pair toggling. This choice of a fixed MDI mode mirrors the behavior the hardware would exhibit if the AUTOMDIX_EN strap were configured for a fixed MDI connection.
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/20250703114941.3243890-4-o.rempel@pengutronix.de Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/phy/smsc.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/drivers/net/phy/smsc.c b/drivers/net/phy/smsc.c index ad9a3d91bb8ae..b6489da5cfcdf 100644 --- a/drivers/net/phy/smsc.c +++ b/drivers/net/phy/smsc.c @@ -155,10 +155,29 @@ static int smsc_phy_reset(struct phy_device *phydev)
static int lan87xx_config_aneg(struct phy_device *phydev) { - int rc; + u8 mdix_ctrl; int val; + int rc; + + /* When auto-negotiation is disabled (forced mode), the PHY's + * Auto-MDIX will continue toggling the TX/RX pairs. + * + * To establish a stable link, we must select a fixed MDI mode. + * If the user has not specified a fixed MDI mode (i.e., mdix_ctrl is + * 'auto'), we default to ETH_TP_MDI. This choice of a ETH_TP_MDI mode + * mirrors the behavior the hardware would exhibit if the AUTOMDIX_EN + * strap were configured for a fixed MDI connection. + */ + if (phydev->autoneg == AUTONEG_DISABLE) { + if (phydev->mdix_ctrl == ETH_TP_MDI_AUTO) + mdix_ctrl = ETH_TP_MDI; + else + mdix_ctrl = phydev->mdix_ctrl; + } else { + mdix_ctrl = phydev->mdix_ctrl; + }
- switch (phydev->mdix_ctrl) { + switch (mdix_ctrl) { case ETH_TP_MDI: val = SPECIAL_CTRL_STS_OVRRD_AMDIX_; break; @@ -184,7 +203,7 @@ static int lan87xx_config_aneg(struct phy_device *phydev) rc |= val; phy_write(phydev, SPECIAL_CTRL_STS, rc);
- phydev->mdix = phydev->mdix_ctrl; + phydev->mdix = mdix_ctrl; return genphy_config_aneg(phydev); }