[PATCH v2] net: macb: add TX stall timeout callback to recover from lost TSTART write

[Andrea della Porta]

From: Lukasz Raczylo <lukasz at 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 at raczylo.com>
Co-developed-by: Steffen Jaeckel <sjaeckel at suse.de>
Signed-off-by: Steffen Jaeckel <sjaeckel at suse.de>
Co-developed-by: Andrea della Porta <andrea.porta at suse.com>
Signed-off-by: Andrea della Porta <andrea.porta at suse.com>
---

CHANGES IN v2:

- dropped the rate-limited log message
- avoid incrementing tx_error as this is per packet

---
 drivers/net/ethernet/cadence/macb_main.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index a12aa21244e83..fd282a1700fb9 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -4522,6 +4522,13 @@ 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);
+
+	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 +4547,7 @@ 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,
 };
 
 /* Configure peripheral capabilities according to device tree
-- 
2.35.3