net: xilinx: axienet: Fix Tx skb circular buffer occupancy check in dmaengine xmit

In Dmaengine flow, driver maintains struct skbuf_dma_descriptor rings each
element of which corresponds to a skb. In Tx datapath, compare available
space in skb ring with number of skbs instead of skb fragments.
Replace x * (MAX_SKB_FRAGS) in netif_txq_completed_wake() and
netif_txq_maybe_stop() with x * (1 skb) to fix the comparison.

Fixes: 6a91b84 ("net: axienet: Introduce dmaengine support")
Signed-off-by: Suraj Gupta <suraj.gupta2@amd.com>
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Link: https://patch.msgid.link/20250521181608.669554-1-suraj.gupta2@amd.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Suraj Gupta

drivers/net/ethernet/xilinx/xilinx_axienet_main.c

@@ -880,7 +880,7 @@ static void axienet_dma_tx_cb(void *data, const struct dmaengine_result *result)
 	dev_consume_skb_any(skbuf_dma->skb);
 	netif_txq_completed_wake(txq, 1, len,
 				 CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX),
-				 2 * MAX_SKB_FRAGS);
+				 2);
 }
 
 /**
@@ -914,7 +914,7 @@ axienet_start_xmit_dmaengine(struct sk_buff *skb, struct net_device *ndev)
 
 	dma_dev = lp->tx_chan->device;
 	sg_len = skb_shinfo(skb)->nr_frags + 1;
-	if (CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX) <= sg_len) {
+	if (CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX) <= 1) {
 		netif_stop_queue(ndev);
 		if (net_ratelimit())
 			netdev_warn(ndev, "TX ring unexpectedly full\n");
@@ -964,7 +964,7 @@ axienet_start_xmit_dmaengine(struct sk_buff *skb, struct net_device *ndev)
 	txq = skb_get_tx_queue(lp->ndev, skb);
 	netdev_tx_sent_queue(txq, skb->len);
 	netif_txq_maybe_stop(txq, CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX),
-			     MAX_SKB_FRAGS + 1, 2 * MAX_SKB_FRAGS);
+			     1, 2);
 
 	dmaengine_submit(dma_tx_desc);
 	dma_async_issue_pending(lp->tx_chan);