5.15-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 dd4360c0e8504f2f7639c7f5d07c93cfd6a98333 ]
Restrict the 100Mbit forced-mode workaround to link-down transitions only, to prevent repeated link reset cycles in certain configurations.
The workaround was originally introduced to improve signal reliability when switching cables between long and short distances. It temporarily forces the PHY into 10 Mbps before returning to 100 Mbps.
However, when used with autonegotiating link partners (e.g., Intel i350), executing this workaround on every link change can confuse the partner and cause constant renegotiation loops. This results in repeated link down/up transitions and the PHY never reaching a stable state.
Limit the workaround to only run during the PHY_NOLINK state. This ensures it is triggered only once per link drop, avoiding disruptive toggling while still preserving its intended effect.
Note: I am not able to reproduce the original issue that this workaround addresses. I can only confirm that 100 Mbit mode works correctly in my test setup. Based on code inspection, I assume the workaround aims to reset some internal state machine or signal block by toggling speeds. However, a PHY reset is already performed earlier in the function via phy_init_hw(), which may achieve a similar effect. Without a reproducer, I conservatively keep the workaround but restrict its conditions.
Fixes: e57cf3639c32 ("net: lan78xx: fix accessing the LAN7800's internal phy specific registers from the MAC driver") Signed-off-by: Oleksij Rempel o.rempel@pengutronix.de Reviewed-by: Andrew Lunn andrew@lunn.ch Link: https://patch.msgid.link/20250709130753.3994461-3-o.rempel@pengutronix.de Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/phy/microchip.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/phy/microchip.c b/drivers/net/phy/microchip.c index 230f2fcf9c46a..f2860ec7ac17e 100644 --- a/drivers/net/phy/microchip.c +++ b/drivers/net/phy/microchip.c @@ -351,7 +351,7 @@ static void lan88xx_link_change_notify(struct phy_device *phydev) * As workaround, set to 10 before setting to 100 * at forced 100 F/H mode. */ - if (!phydev->autoneg && phydev->speed == 100) { + if (phydev->state == PHY_NOLINK && !phydev->autoneg && phydev->speed == 100) { /* disable phy interrupt */ temp = phy_read(phydev, LAN88XX_INT_MASK); temp &= ~LAN88XX_INT_MASK_MDINTPIN_EN_;