net: airoha: Fix possible TX queue stall in airoha_qdma_tx_napi_poll()

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>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260416-airoha-txq-potential-stall-v2-1-42c732074540@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index e1ab15f1ee7dd28f76b9eb77db03779c2f92d755..19f67c7dd8e10544cedafe7d63fd8d1a3076c50d 100644 (file)
--- 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 95e557638617fbdee6c8d28876915ddbc4bffce2..87b328cfefb08660eb83ef216a7dd02ba74d37a5 100644 (file)
--- 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;