[PATCH net-next v3 0/5] net: cadence: macb: add IEEE 802.3az EEE support

[Nicolai Buchwitz <nb@tipi-net.de>]

Add Energy Efficient Ethernet (IEEE 802.3az) support to the Cadence GEM
(macb) driver using phylink's managed EEE framework. The GEM MAC has
hardware LPI registers but no built-in idle timer, so the driver
implements software-managed TX LPI using a delayed_work timer while
delegating EEE negotiation and ethtool state to phylink.

Changes from v2:
  - macb_tx_lpi_set() now returns bool indicating whether the register
    value actually changed, avoiding redundant writes.
  - Removed tx_lpi_enabled field from struct macb; LPI state is tracked
    entirely within the spinlock-protected register read/modify/write.
  - macb_tx_lpi_wake() uses the return value of macb_tx_lpi_set() to
    skip the cancel/udelay when TXLPIEN was already clear.
  All changes based on feedback from Russell King.

Changes from v1:
  - Rewrote to use phylink managed EEE (mac_enable_tx_lpi /
    mac_disable_tx_lpi callbacks) instead of the obsolete
    phy_init_eee() approach, as recommended by Russell King.
  - ethtool get_eee/set_eee are now pure phylink passthroughs.
  - Removed all manual EEE state tracking from mac_link_up/down;
    phylink handles the lifecycle.

The series is structured as follows:

  1. Register definitions: LPI counter offsets (0x270-0x27c), TXLPIEN
     bitfield (NCR bit 19), and MACB_CAPS_EEE capability flag.

  2. LPI statistics: Expose the four hardware EEE counters (RX/TX LPI
     transitions and time) through ethtool -S, accumulated in software
     since they are clear-on-read.

  3. TX LPI engine: phylink mac_enable_tx_lpi / mac_disable_tx_lpi
     callbacks with a delayed_work-based idle timer. LPI entry is
     deferred 1 second after link-up per IEEE 802.3az. Wake before
     transmit with a conservative 50us PHY wake delay.

  4. ethtool EEE ops: get_eee/set_eee delegating to phylink for PHY
     negotiation and timer management.

  5. RP1 enablement: Set MACB_CAPS_EEE for the Raspberry Pi 5's RP1
     southbridge (Cadence GEM_GXL rev 0x00070109 + BCM54213PE PHY).

Tested on Raspberry Pi 5 (1000BASE-T, BCM54213PE PHY, 250ms LPI timer):

  iperf3 throughput (no regression):
    TCP TX: 937.8 Mbit/s (EEE on) vs 937.0 Mbit/s (EEE off)
    TCP RX: 936.5 Mbit/s both

  Latency (ping RTT, small expected increase from LPI wake):
    1s interval:  0.273 ms (EEE on) vs 0.181 ms (EEE off)
    10ms interval: 0.206 ms (EEE on) vs 0.168 ms (EEE off)
    flood ping:   0.200 ms (EEE on) vs 0.156 ms (EEE off)

  LPI counters (ethtool -S, 1s-interval ping, EEE on):
    tx_lpi_transitions: 112
    tx_lpi_time: 15574651

  Zero packet loss across all tests. Also verified with
  ethtool --show-eee / --set-eee and cable unplug/replug cycling.

Nicolai Buchwitz (5):
  net: cadence: macb: add EEE register definitions and capability flag
  net: cadence: macb: add EEE LPI statistics counters
  net: cadence: macb: implement EEE TX LPI support
  net: cadence: macb: add ethtool EEE support
  net: cadence: macb: enable EEE for Raspberry Pi RP1

 drivers/net/ethernet/cadence/macb.h      |  20 ++++
 drivers/net/ethernet/cadence/macb_main.c | 136 ++++++++++++++++++++++-
 2 files changed, 155 insertions(+), 1 deletion(-)

-- 
2.51.0