From: Lukasz Raczylo <redacted>

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/ (local)
Fixes: dc110d1b23564 ("net: cadence: macb: Add support for Raspberry Pi 
RP1 ethernet controller")
Signed-off-by: Lukasz Raczylo <redacted>
Co-developed-by: Steffen Jaeckel <redacted>
Signed-off-by: Steffen Jaeckel <redacted>
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())

+		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,