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 only consumed by the link partner during auto-negotiation, so writing them while autoneg is disabled is semantically a no-op. On at least the Broadcom BCM54213PE PHY, however, the indirect MMD write triggered from this path while the link is currently forced (autoneg off) disturbs the receive datapath: the kernel still reports the link as UP at the configured speed/duplex, but no frames are received until the link is renegotiated. 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 --- drivers/net/phy/phy-c45.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/phy/phy-c45.c b/drivers/net/phy/phy-c45.c index d48aa7231b37..65de6a5fa204 100644 --- a/drivers/net/phy/phy-c45.c +++ b/drivers/net/phy/phy-c45.c @@ -940,6 +940,10 @@ EXPORT_SYMBOL_GPL(genphy_c45_read_eee_abilities); */ int genphy_c45_an_config_eee_aneg(struct phy_device *phydev) { + /* MMD AN advertisements are only consumed during autoneg. */ + if (phydev->autoneg == AUTONEG_DISABLE) + return 0; + if (!phydev->eee_cfg.eee_enabled) { __ETHTOOL_DECLARE_LINK_MODE_MASK(adv) = {}; -- 2.54.0