Re: [PATCH] net: macb: add TX stall timeout callback to recover from lost TSTART write

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

Hi Andrea

On 12.6.2026 11:01, Andrea della Porta wrote:
> From: Lukasz Raczylo <lukasz@raczylo.com>
> 
> The MACB found in the Raspberry Pi RP1 suffers from sporadic stalls on
> the TX queue.
> While the exact root cause is not yet fully understood, it is likely
> related to a hardware issue where a TSTART write to the NCR register
> is missed, preventing the transmission from being kicked off.
> 
> Implement a timeout callback to handle TX queue stalls, triggering the
> existing restart mechanism to recover.
> 
> Link: 
> https://lore.kernel.org/all/20260514215459.36109-1-lukasz@raczylo.com/
> Fixes: dc110d1b23564 ("net: cadence: macb: Add support for Raspberry Pi 
> RP1 ethernet controller")
> Signed-off-by: Lukasz Raczylo <lukasz@raczylo.com>
> Co-developed-by: Steffen Jaeckel <sjaeckel@suse.de>
> Signed-off-by: Steffen Jaeckel <sjaeckel@suse.de>
> Co-developed-by: Andrea della Porta <andrea.porta@suse.com>
> Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c 
> b/drivers/net/ethernet/cadence/macb_main.c
> index a12aa21244e83..615da65d5d68d 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -4522,6 +4522,16 @@ static int macb_setup_tc(struct net_device *dev, 
> enum tc_setup_type type,
>  	}
>  }
> 
> +static void macb_tx_timeout(struct net_device *dev, unsigned int q)
> +{
> +	struct macb *bp = netdev_priv(dev);
> +
> +	if (net_ratelimit())

Do we need the net_ratelimit() check (and message) here? AFAIU the 
watchdog core already prints a message for every timeout.

> +		netdev_err(dev, "TX stall detected, re-kicking TSTART\n");
> +	dev->stats.tx_errors++;
> +	macb_tx_restart(&bp->queues[q]);
> +}
> +
>  static const struct net_device_ops macb_netdev_ops = {
>  	.ndo_open		= macb_open,
>  	.ndo_stop		= macb_close,
> @@ -4540,6 +4550,7 @@ static const struct net_device_ops 
> macb_netdev_ops = {
>  	.ndo_hwtstamp_set	= macb_hwtstamp_set,
>  	.ndo_hwtstamp_get	= macb_hwtstamp_get,
>  	.ndo_setup_tc		= macb_setup_tc,
> +	.ndo_tx_timeout		= macb_tx_timeout,

The commit message describes it as RP1 specific, but it gets applied to 
all other variants?

>  };
> 
>  /* Configure peripheral capabilities according to device tree

Thanks
Nicolai