[PATCH net-next v6 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 v5:
  - macb_tx_lpi_set() no longer manages its own spinlock; it now
    requires bp->lock to be held by the caller and asserts this with
    lockdep_assert_held(). All callers (macb_tx_lpi_work_fn,
    macb_mac_enable_tx_lpi, macb_mac_disable_tx_lpi) take bp->lock
    explicitly. Based on feedback from Jakub Kicinski.
  - macb_tx_lpi_wake() is now called under the existing bp->lock in
    macb_start_xmit(), eliminating the redundant lock acquire/release.
    An eee_active check at the top of macb_tx_lpi_wake() short-circuits
    the register read on the common (EEE-disabled) path. Based on
    feedback from Jakub Kicinski.
  - macb_tx_all_queues_idle() uses READ_ONCE for tx_head/tx_tail
    (called under bp->lock; taking tx_ptr_lock here would invert the
    established lock order). Loop rewritten to match the driver
    convention: for (q = 0, queue = bp->queues; ...; ++q, ++queue).
    Based on feedback from Jakub Kicinski and Claudiu Beznea.
  - Added Reviewed-by: Claudiu Beznea <claudiu.beznea@tuxon.dev> to
    patches 1-4.

Changes from v4:
  - Removed redundant MACB_CAPS_EEE guards from macb_get_eee/set_eee;
    phylink already returns -EOPNOTSUPP when lpi_capabilities and
    lpi_interfaces are not populated. Based on feedback from Russell King.
  - Added patch 5 enabling EEE for Mobileye EyeQ5, tested by Théo Lebrun
    using a hardware loopback.

Changes from v3:
  - Dropped the register-definitions-only patch; LPI counter offsets
    (GEM_RXLPI/RXLPITIME/TXLPI/TXLPITIME) now land in the statistics
    patch, and TXLPIEN + MACB_CAPS_EEE are introduced alongside the TX
    LPI implementation where they are first used. Series is now 4 patches.
  - Add Reviewed-by: Théo Lebrun <theo.lebrun@bootlin.com> to all patches.
  - Split chained assignment in macb_tx_lpi_set() (suggested by
    checkpatch).

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. 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. Adds register offset definitions
     GEM_RXLPI/RXLPITIME/TXLPI/TXLPITIME (0x270-0x27c).

  2. TX LPI engine: Introduces GEM_TXLPIEN (NCR bit 19) and
     MACB_CAPS_EEE alongside the implementation that uses them.
     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 (IEEE 802.3az Tw_sys_tx).

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

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

  5. EyeQ5 enablement: Set MACB_CAPS_EEE for the Mobileye EyeQ5 GEM
     instance, verified with a hardware loopback by Théo Lebrun.

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 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
  net: cadence: macb: enable EEE for Mobileye EyeQ5

 drivers/net/ethernet/cadence/macb.h      |  20 +++++
 drivers/net/ethernet/cadence/macb_main.c | 145 ++++++++++++++++++++++++++++++-
 2 files changed, 163 insertions(+), 2 deletions(-)

--
2.51.0