Mediatek: EEE problems with the MT7530 PHYs on OpenWRT 24.10

[Mateusz Jończyk]

Hello,

Multiple users have reported a regression [1] in OpenWRT 24.10
(Linux 6.6) with the ramips/mt7621 target and the MT7530 PHYs:
the Ethernet link is periodically going down for a brief period
of time. It was determined that:

1. The symptoms stop after disabling EEE.

2. EEE is enabled by default for these devices in OpenWRT 24.10
    whereas in the previous version (OpenWRT 23.05, Linux 5.15) it
    was not.

3. In Linux 6.6, the PHY driver tries to disable EEE in
    mtk_gephy_config_init() in drivers/net/phy/mediatek-ge.c:

         /* Disable EEE */
         phy_write_mmd(phydev, MDIO_MMD_AN, MDIO_AN_EEE_ADV, 0);

    but this is later overridden by a subsequent execution of the
    genphy_c45_write_eee_adv() function, which enables every EEE mode
    supported.

In 2021, Landen Chao wrote [2]:

> EEE of the 10-year-old MT7530 internal gephy has many IOT problems, so
> it is recommended to disable its EEE.

I'd like to ask Mediatek to clarify whether it is possible to fine-tune
the EEE of this PHY in some way, or rather that it should be hard-disabled
by setting:

     phydev->eee_broken_modes = -1;

in the PHY driver, like it is in ksz9477_config_init() in
drivers/net/phy/micrel.c.

Greetings,

Mateusz

[1] https://github.com/openwrt/openwrt/issues/17351

[2] https://lore.kernel.org/all/0adde34f936a2dafca40b06b408d82afe0852327.camel@mediatek.com/