[PATCH net v2] net: airoha: Fix possible TX queue stall in airoha_qdma_tx_napi_poll()

[Lorenzo Bianconi <lorenzo@kernel.org>]

Since multiple net_device TX queues can share the same hw QDMA TX queue,
there is no guarantee we have inflight packets queued in hw belonging to a
net_device TX queue stopped in the xmit path because hw QDMA TX queue
can be full. In this corner case the net_device TX queue will never be
re-activated. In order to avoid any potential net_device TX queue stall,
we need to wake all the net_device TX queues feeding the same hw QDMA TX
queue in airoha_qdma_tx_napi_poll routine.

Fixes: 23020f0493270 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
Changes in v2:
- Add txq_stopped parameter to avoid any possible corner cases where the
  netdev queue stalls.
- Link to v1: https://lore.kernel.org/r/20260413-airoha-txq-potential-stall-v1-1-7830363b1543@kernel.org
---
 drivers/net/ethernet/airoha/airoha_eth.c | 37 +++++++++++++++++++++++++++-----
 drivers/net/ethernet/airoha/airoha_eth.h |  1 +
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index e1ab15f1ee7d..19f67c7dd8e1 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -843,6 +843,21 @@ static int airoha_qdma_init_rx(struct airoha_qdma *qdma)
 	return 0;
 }
 
+static void airoha_qdma_wake_netdev_txqs(struct airoha_queue *q)
+{
+	struct airoha_qdma *qdma = q->qdma;
+	struct airoha_eth *eth = qdma->eth;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(eth->ports); i++) {
+		struct airoha_gdm_port *port = eth->ports[i];
+
+		if (port && port->qdma == qdma)
+			netif_tx_wake_all_queues(port->dev);
+	}
+	q->txq_stopped = false;
+}
+
 static int airoha_qdma_tx_napi_poll(struct napi_struct *napi, int budget)
 {
 	struct airoha_tx_irq_queue *irq_q;
@@ -919,12 +934,21 @@ static int airoha_qdma_tx_napi_poll(struct napi_struct *napi, int budget)
 
 			txq = netdev_get_tx_queue(skb->dev, queue);
 			netdev_tx_completed_queue(txq, 1, skb->len);
-			if (netif_tx_queue_stopped(txq) &&
-			    q->ndesc - q->queued >= q->free_thr)
-				netif_tx_wake_queue(txq);
-
 			dev_kfree_skb_any(skb);
 		}
+
+		if (q->txq_stopped && q->ndesc - q->queued >= q->free_thr) {
+			/* Since multiple net_device TX queues can share the
+			 * same hw QDMA TX queue, there is no guarantee we have
+			 * inflight packets queued in hw belonging to a
+			 * net_device TX queue stopped in the xmit path.
+			 * In order to avoid any potential net_device TX queue
+			 * stall, we need to wake all the net_device TX queues
+			 * feeding the same hw QDMA TX queue.
+			 */
+			airoha_qdma_wake_netdev_txqs(q);
+		}
+
 unlock:
 		spin_unlock_bh(&q->lock);
 	}
@@ -1984,6 +2008,7 @@ static netdev_tx_t airoha_dev_xmit(struct sk_buff *skb,
 	if (q->queued + nr_frags >= q->ndesc) {
 		/* not enough space in the queue */
 		netif_tx_stop_queue(txq);
+		q->txq_stopped = true;
 		spin_unlock_bh(&q->lock);
 		return NETDEV_TX_BUSY;
 	}
@@ -2039,8 +2064,10 @@ static netdev_tx_t airoha_dev_xmit(struct sk_buff *skb,
 				TX_RING_CPU_IDX_MASK,
 				FIELD_PREP(TX_RING_CPU_IDX_MASK, index));
 
-	if (q->ndesc - q->queued < q->free_thr)
+	if (q->ndesc - q->queued < q->free_thr) {
 		netif_tx_stop_queue(txq);
+		q->txq_stopped = true;
+	}
 
 	spin_unlock_bh(&q->lock);
 
diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index 95e557638617..87b328cfefb0 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h
@@ -193,6 +193,7 @@ struct airoha_queue {
 	int ndesc;
 	int free_thr;
 	int buf_size;
+	bool txq_stopped;
 
 	struct napi_struct napi;
 	struct page_pool *page_pool;

---
base-commit: 1f5ffc672165ff851063a5fd044b727ab2517ae3
change-id: 20260407-airoha-txq-potential-stall-ad52c53094e8

Best regards,
-- 
Lorenzo Bianconi <lorenzo@kernel.org>