genphy_c45_an_config_eee_aneg() writes the EEE advertisement to the auto-negotiation device's MMD register space (MDIO_MMD_AN, register MDIO_AN_EEE_ADV). These registers are read by the link partner only during auto-negotiation, so writing them while autoneg is disabled cannot influence the link. On some PHYs (e.g. Broadcom BCM54213PE) the write nevertheless reaches the chip and disturbs the receive datapath. Concretely, running ethtool -s eth0 speed 100 duplex full autoneg off ethtool --set-eee eth0 eee off leaves eth0 with TX working and RX completely silent on a Raspberry Pi 4 / CM4 board (bcmgenet + BCM54213PE in rgmii-rxid). Switching back to autoneg recovers the link. Prior to commit f26a29a038ee ("net: phy: ensure that genphy_c45_an_config_eee_aneg() sees new value of phydev->eee_cfg.eee_enabled"), the disable path was effectively a no-op because the helper read the stale eee_cfg.eee_enabled, so the underlying PHY behavior never surfaced. Bisected on rpi-6.12.y between commits 83943264 (good) and effcbc88 (bad) to f26a29a038ee. Fixes: f26a29a038ee ("net: phy: ensure that genphy_c45_an_config_eee_aneg() sees new value of phydev->eee_cfg.eee_enabled") Cc: stable@vger.kernel.org Signed-off-by: Nerijus Bendžiūnas --- Changes since v1: - Reworded the inline comment and commit message: the MMD AN write is read by the chip with side-effects, not silently ignored. Suggested by Andrew Lunn. - Tightened the reproducer paragraph (was repeating paragraph 1). v1: https://lore.kernel.org/netdev/20260516114334.812828-1-nerijus.bendziunas@gmail.com/ drivers/net/phy/phy-c45.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/net/phy/phy-c45.c b/drivers/net/phy/phy-c45.c index d48aa7231b37..126951741428 100644 --- a/drivers/net/phy/phy-c45.c +++ b/drivers/net/phy/phy-c45.c @@ -940,6 +940,14 @@ EXPORT_SYMBOL_GPL(genphy_c45_read_eee_abilities); */ int genphy_c45_an_config_eee_aneg(struct phy_device *phydev) { + /* Writing MMD AN advertisements while autoneg is disabled has no + * effect on link-partner negotiation, but on some PHYs (e.g. the + * Broadcom BCM54213PE) the write itself disturbs the receive + * datapath. Skip it. + */ + if (phydev->autoneg == AUTONEG_DISABLE) + return 0; + if (!phydev->eee_cfg.eee_enabled) { __ETHTOOL_DECLARE_LINK_MODE_MASK(adv) = {}; -- 2.54.0