EEE support for rp1 mac

[nbuchwitz]

This adds EEE support to the macb driver for the Pi 5 / CM5. Right now EEE is broken on the Pi because the PHY advertises EEE but the MAC has no LPI support, so it was marked as broken in #6900. This series fixes that by implementing proper software-managed TX LPI in the driver and reverting the DT workaround.

See #6855

This should go through mainline as the EEE registers are the same across all Cadence GEM variants (SAMA5D2, SAME70, PIC32CZ, RP1, ...) and the code is generic, just gated on a capability flag. I'm looking for early feedback from Pi users before sending it upstream though. If you've got a Pi 5 or CM5, give it a spin and let me know how it goes — link stability, ethtool --show-eee, ethtool -S | grep lpi, that kind of thing.

[nbuchwitz]

f0d41dc is not directly EEE related, but I noticed it was missing while debugging

[pelwell]

Thanks, Nicolai - this looks great.

For anyone wishing to try the new EEE capability, you can install a trial build using sudo rpi-update pulls/7251, after reading the caveats.

[pelwell]

For comparison, these are the values I get after being up for a few minutes:

pi@philpi5:~$ ethtool --show-eee eth0
EEE settings for eth0:
        EEE status: enabled - active
        Tx LPI: 0 (us)
        Supported EEE link modes:  100baseT/Full
                                   1000baseT/Full
        Advertised EEE link modes:  100baseT/Full
                                    1000baseT/Full
        Link partner advertised EEE link modes:  100baseT/Full
                                                 1000baseT/Full
pi@philpi5:~$ ethtool -S eth0 | grep lpi
     rx_lpi_transitions: 0
     rx_lpi_time: 0
     tx_lpi_transitions: 88
     tx_lpi_time: 85760892

[nbuchwitz]

For better comparison: is the ethernet link actively used or not? If yes, how do the tx lpi rate change when the ethernet is mostly idle (eg wifi used)?

[nbuchwitz]

After some more testing, I've improved the patch set further and fixed a bug.

Changes since v1:

• Use mod_delayed_work() instead of schedule_delayed_work() for LPI idle timer re-entry. schedule_delayed_work() is a no-op when work is already pending, so the timer was never reset by TX completions - causing LPI to be asserted periodically even under full load.
• Set MACB_TX_LPI_TIMER_DEFAULT_MS to 500ms (was 250ms). Chosen as a good compromise between energy savings and throughput stability - lower values cause more frequent LPI wake transitions with associated retransmission overhead on bursty workloads.
• Remove unused RX LPI status bit change interrupt definitions (RXLPISBC). The interrupt is not wired up in this series and can be added later if needed for diagnostics.
• Include fix for a probable upstream bug in phy_ethtool_set_eee() where EEE advertised modes were not correctly restored after an off/on toggle, because eee_cfg.eee_enabled was updated after genphy_c45_ethtool_set_eee() instead of before. -> already fixed in a615309 (not part of rpi-6.12.y yet)