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

["Théo Lebrun" <theo.lebrun@bootlin.com>]

On Wed Feb 25, 2026 at 10:15 AM CET, Nicolai Buchwitz wrote:
> Implement Energy Efficient Ethernet TX Low Power Idle using phylink's
> managed EEE framework. The Cadence GEM MAC has no built-in idle timer
> — TXLPIEN (NCR bit 19) immediately blocks all TX when set and the MAC
> does NOT auto-wake — so the driver uses a software delayed_work timer
> for idle detection.
>
> The TX LPI lifecycle:
>   - phylink calls mac_enable_tx_lpi() after link-up with the negotiated
>     timer value. The driver defers the first LPI entry by 1 second per
>     IEEE 802.3az section 22.7a.
>   - macb_tx_complete() reschedules the idle timer after each TX drain.
>   - macb_start_xmit() wakes from LPI by clearing TXLPIEN, cancelling
>     the pending work, and waiting 50us (conservative Tw_sys) before
>     initiating the transmit.
>   - phylink calls mac_disable_tx_lpi() before link-down, which cancels
>     the work and clears TXLPIEN.
>
> The phylink_config is populated with LPI capabilities (MII, GMII, RGMII
> modes; 100FD and 1000FD speeds) and a 250ms default idle timer, gated
> on MACB_CAPS_EEE.
>
> Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
> ---
>  drivers/net/ethernet/cadence/macb.h      |   5 +
>  drivers/net/ethernet/cadence/macb_main.c | 111 +++++++++++++++++++++++
>  2 files changed, 116 insertions(+)
>
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 43cd013bb70e..a9ae7ecf9fe9 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c

[...]

> +/* Wake from LPI before transmitting. The MAC must deassert TXLPIEN
> + * and wait for the PHY to exit LPI before any frame can be sent.
> + * IEEE 802.3az Tw_sys is ~17us for 1000BASE-T, ~30us for 100BASE-TX;
> + * we use a conservative 50us.
> + */
> +static void macb_tx_lpi_wake(struct macb *bp)
> +{
> +	if (!macb_tx_lpi_set(bp, false))
> +		return;
> +
> +	cancel_delayed_work(&bp->tx_lpi_work);
> +	udelay(50);
> +}

[...]

> @@ -2349,6 +2454,8 @@ static netdev_tx_t macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  	netdev_tx_sent_queue(netdev_get_tx_queue(bp->dev, queue_index),
>  			     skb->len);
>  
> +	macb_tx_lpi_wake(bp);

Should this be protected by a bp->eee_active condition? It could go
in macb_tx_lpi_wake(). We avoid a spinlock acquire per xmit for most
platforms. Probably negligeable though.

For the full series:

Reviewed-by: Théo Lebrun <theo.lebrun@bootlin.com>

Thanks!

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com