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 <nerijus.bendziunas@gmail.com>
---
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