[PATCH net-next v1 3/5] net: lan743x: quiesce TX before freeing the rings

lan743x_pcidev_shutdown(), which suspend also uses, calls
netif_device_detach() and then lan743x_netdev_close() with the qdisc
still attached. Detaching only sets the queue stop bits. It does not wait
for an ndo_start_xmit() that is already running, and the TX NAPI poll
still wakes a stopped queue as soon as it has reclaimed descriptors. The
TX NAPI of a channel that has not been closed yet can therefore restart
its queue, and the stack then transmits on a ring that
lan743x_tx_close() is freeing.

Only wake a queue from TX NAPI while the device is present. In
lan743x_netdev_close(), wait for any NAPI poll that may have missed the
detach with synchronize_net(), then stop all queues with
netif_tx_disable(), which also waits for transmits in progress, before
closing the channels. For ndo_stop the qdisc is already deactivated, so
this only adds a grace period there.

Fixes: 23f0703c125b ("lan743x: Add main source files for new lan743x driver")
Assisted-by: LLM
Signed-off-by: Chris Babroski <redacted>
---
 drivers/net/ethernet/microchip/lan743x_main.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
index 583f631df701..8d256a80dac6 100644
--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c

@@ -2125,7 +2125,8 @@ static int lan743x_tx_napi_poll(struct napi_struct *napi, int weight)
 	/* clean up tx ring */
 	lan743x_tx_release_completed_descriptors(tx);
 	txq = netdev_get_tx_queue(adapter->netdev, tx->channel_number);
-	if (netif_tx_queue_stopped(txq)) {
+	if (netif_tx_queue_stopped(txq) &&
+	    netif_device_present(adapter->netdev)) {
 		if (tx->rqd_descriptors) {
 			if (tx->rqd_descriptors <=
 			    lan743x_tx_get_avail_desc(tx)) {

@@ -3336,6 +3337,9 @@ static int lan743x_netdev_close(struct net_device *netdev)
 
 	lan743x_phylink_disconnect(adapter);
 
+	synchronize_net();
+	netif_tx_disable(netdev);
+
 	for (index = 0; index < adapter->used_tx_channels; index++)
 		lan743x_tx_close(&adapter->tx[index]);
 

-- 
2.34.1