Re: [PATCH net-next 3/5] net: cadence: macb: implement EEE TX LPI support

On Mon, Feb 23, 2026 at 10:04:10AM +0100, Nicolai Buchwitz wrote:

Implement software-managed TX Low Power Idle (LPI) for the Cadence GEM
MAC as part of IEEE 802.3az Energy Efficient Ethernet support.

The GEM MAC has no built-in idle timer - the TXLPIEN bit (NCR bit 19)
immediately asserts LPI and blocks all TX while set. The MAC does not
auto-wake for transmit. Per Microchip GMAC documentation (section
40.6.19): "It is best to use firmware to control LPI."

This patch implements a software idle timer using delayed_work:
- On TX completion with an empty ring, schedule LPI entry after a
  configurable idle timeout (default 250ms). The work function
  verifies all TX queues are truly idle before entering LPI to
  prevent entering LPI while traffic is still active.
- On TX start, wake from LPI by clearing TXLPIEN, cancelling any
  pending re-entry, and waiting 50us for the PHY to exit LPI
  (conservative vs IEEE 802.3az Tw_sys of ~17us/~30us)
- On link up, check EEE negotiation via phy_init_eee() and defer
  first LPI entry by 1 second per IEEE 802.3az requirements
- On link down, immediately cancel pending work and clear TXLPIEN

The timer value is configurable at runtime via ethtool --set-eee
tx-timer.

The implementation is gated on MACB_CAPS_EEE so platforms must
explicitly opt in via their macb_config.

In addition to my comments, please check the nipabot status for this
patch which can be found at:

https://patchwork.kernel.org/project/netdevbpf/patch/20260223090412.44070-4-nb@tipi-net.de/

Thanks.

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