net: fec: recycle pages for transmitted XDP frames

Once the XDP frames have been successfully transmitted through the
ndo_xdp_xmit() interface, it's the driver responsibility to free
the frames so that the page_pool can recycle the pages and reuse
them. However, this action is not implemented in the fec driver.
This leads to a user-visible problem that the console will print
the following warning log.

[  157.568851] page_pool_release_retry() stalled pool shutdown 1389 inflight 60 sec
[  217.983446] page_pool_release_retry() stalled pool shutdown 1389 inflight 120 sec
[  278.399006] page_pool_release_retry() stalled pool shutdown 1389 inflight 181 sec
[  338.812885] page_pool_release_retry() stalled pool shutdown 1389 inflight 241 sec
[  399.226946] page_pool_release_retry() stalled pool shutdown 1389 inflight 302 sec

Therefore, to solve this issue, we free XDP frames via xdp_return_frame()
while cleaning the tx BD ring.

Fixes: 6d6b39f1 ("net: fec: add initial XDP support")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/freescale/fec.h

@@ -544,10 +544,23 @@ enum {
 	XDP_STATS_TOTAL,
 };
 
+enum fec_txbuf_type {
+	FEC_TXBUF_T_SKB,
+	FEC_TXBUF_T_XDP_NDO,
+};
+
+struct fec_tx_buffer {
+	union {
+		struct sk_buff *skb;
+		struct xdp_frame *xdp;
+	};
+	enum fec_txbuf_type type;
+};
+
 struct fec_enet_priv_tx_q {
 	struct bufdesc_prop bd;
 	unsigned char *tx_bounce[TX_RING_SIZE];
-	struct  sk_buff *tx_skbuff[TX_RING_SIZE];
+	struct fec_tx_buffer tx_buf[TX_RING_SIZE];
 
 	unsigned short tx_stop_threshold;
 	unsigned short tx_wake_threshold;

drivers/net/ethernet/freescale/fec_main.c

@@ -397,7 +397,7 @@ static void fec_dump(struct net_device *ndev)
 			fec16_to_cpu(bdp->cbd_sc),
 			fec32_to_cpu(bdp->cbd_bufaddr),
 			fec16_to_cpu(bdp->cbd_datlen),
-			txq->tx_skbuff[index]);
+			txq->tx_buf[index].skb);
 		bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
 		index++;
 	} while (bdp != txq->bd.base);
@@ -654,7 +654,7 @@ static int fec_enet_txq_submit_skb(struct fec_enet_priv_tx_q *txq,
 
 	index = fec_enet_get_bd_index(last_bdp, &txq->bd);
 	/* Save skb pointer */
-	txq->tx_skbuff[index] = skb;
+	txq->tx_buf[index].skb = skb;
 
 	/* Make sure the updates to rest of the descriptor are performed before
 	 * transferring ownership.
@@ -672,9 +672,7 @@ static int fec_enet_txq_submit_skb(struct fec_enet_priv_tx_q *txq,
 
 	skb_tx_timestamp(skb);
 
-	/* Make sure the update to bdp and tx_skbuff are performed before
-	 * txq->bd.cur.
-	 */
+	/* Make sure the update to bdp is performed before txq->bd.cur. */
 	wmb();
 	txq->bd.cur = bdp;
 
@@ -862,7 +860,7 @@ static int fec_enet_txq_submit_tso(struct fec_enet_priv_tx_q *txq,
 	}
 
 	/* Save skb pointer */
-	txq->tx_skbuff[index] = skb;
+	txq->tx_buf[index].skb = skb;
 
 	skb_tx_timestamp(skb);
 	txq->bd.cur = bdp;
@@ -952,16 +950,33 @@ static void fec_enet_bd_init(struct net_device *dev)
 		for (i = 0; i < txq->bd.ring_size; i++) {
 			/* Initialize the BD for every fragment in the page. */
 			bdp->cbd_sc = cpu_to_fec16(0);
+			if (txq->tx_buf[i].type == FEC_TXBUF_T_SKB) {
 				if (bdp->cbd_bufaddr &&
 				    !IS_TSO_HEADER(txq, fec32_to_cpu(bdp->cbd_bufaddr)))
 					dma_unmap_single(&fep->pdev->dev,
 							 fec32_to_cpu(bdp->cbd_bufaddr),
 							 fec16_to_cpu(bdp->cbd_datlen),
 							 DMA_TO_DEVICE);
-			if (txq->tx_skbuff[i]) {
-				dev_kfree_skb_any(txq->tx_skbuff[i]);
-				txq->tx_skbuff[i] = NULL;
+				if (txq->tx_buf[i].skb) {
+					dev_kfree_skb_any(txq->tx_buf[i].skb);
+					txq->tx_buf[i].skb = NULL;
+				}
+			} else {
+				if (bdp->cbd_bufaddr)
+					dma_unmap_single(&fep->pdev->dev,
+							 fec32_to_cpu(bdp->cbd_bufaddr),
+							 fec16_to_cpu(bdp->cbd_datlen),
+							 DMA_TO_DEVICE);
+
+				if (txq->tx_buf[i].xdp) {
+					xdp_return_frame(txq->tx_buf[i].xdp);
+					txq->tx_buf[i].xdp = NULL;
 				}
+
+				/* restore default tx buffer type: FEC_TXBUF_T_SKB */
+				txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
+			}
+
 			bdp->cbd_bufaddr = cpu_to_fec32(0);
 			bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
 		}
@@ -1360,6 +1375,7 @@ static void
 fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 {
 	struct	fec_enet_private *fep;
+	struct xdp_frame *xdpf;
 	struct bufdesc *bdp;
 	unsigned short status;
 	struct	sk_buff	*skb;
@@ -1387,16 +1403,31 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 
 		index = fec_enet_get_bd_index(bdp, &txq->bd);
 
-		skb = txq->tx_skbuff[index];
-		txq->tx_skbuff[index] = NULL;
-		if (!IS_TSO_HEADER(txq, fec32_to_cpu(bdp->cbd_bufaddr)))
+		if (txq->tx_buf[index].type == FEC_TXBUF_T_SKB) {
+			skb = txq->tx_buf[index].skb;
+			txq->tx_buf[index].skb = NULL;
+			if (bdp->cbd_bufaddr &&
+			    !IS_TSO_HEADER(txq, fec32_to_cpu(bdp->cbd_bufaddr)))
 				dma_unmap_single(&fep->pdev->dev,
 						 fec32_to_cpu(bdp->cbd_bufaddr),
 						 fec16_to_cpu(bdp->cbd_datlen),
 						 DMA_TO_DEVICE);
 			bdp->cbd_bufaddr = cpu_to_fec32(0);
 			if (!skb)
-			goto skb_done;
+				goto tx_buf_done;
+		} else {
+			xdpf = txq->tx_buf[index].xdp;
+			if (bdp->cbd_bufaddr)
+				dma_unmap_single(&fep->pdev->dev,
+						 fec32_to_cpu(bdp->cbd_bufaddr),
+						 fec16_to_cpu(bdp->cbd_datlen),
+						 DMA_TO_DEVICE);
+			bdp->cbd_bufaddr = cpu_to_fec32(0);
+			if (!xdpf) {
+				txq->tx_buf[index].type = FEC_TXBUF_T_SKB;
+				goto tx_buf_done;
+			}
+		}
 
 		/* Check for errors. */
 		if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC |
@@ -1415,16 +1446,26 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 				ndev->stats.tx_carrier_errors++;
 		} else {
 			ndev->stats.tx_packets++;
+
+			if (txq->tx_buf[index].type == FEC_TXBUF_T_SKB)
 				ndev->stats.tx_bytes += skb->len;
+			else
+				ndev->stats.tx_bytes += xdpf->len;
 		}
 
+		/* Deferred means some collisions occurred during transmit,
+		 * but we eventually sent the packet OK.
+		 */
+		if (status & BD_ENET_TX_DEF)
+			ndev->stats.collisions++;
+
+		if (txq->tx_buf[index].type == FEC_TXBUF_T_SKB) {
 			/* NOTE: SKBTX_IN_PROGRESS being set does not imply it's we who
 			 * are to time stamp the packet, so we still need to check time
 			 * stamping enabled flag.
 			 */
 			if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS &&
-			     fep->hwts_tx_en) &&
-		    fep->bufdesc_ex) {
+				     fep->hwts_tx_en) && fep->bufdesc_ex) {
 				struct skb_shared_hwtstamps shhwtstamps;
 				struct bufdesc_ex *ebdp = (struct bufdesc_ex *)bdp;
 
@@ -1432,16 +1473,18 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 				skb_tstamp_tx(skb, &shhwtstamps);
 			}
 
-		/* Deferred means some collisions occurred during transmit,
-		 * but we eventually sent the packet OK.
-		 */
-		if (status & BD_ENET_TX_DEF)
-			ndev->stats.collisions++;
-
 			/* Free the sk buffer associated with this last transmit */
 			dev_kfree_skb_any(skb);
-skb_done:
-		/* Make sure the update to bdp and tx_skbuff are performed
+		} else {
+			xdp_return_frame(xdpf);
+
+			txq->tx_buf[index].xdp = NULL;
+			/* restore default tx buffer type: FEC_TXBUF_T_SKB */
+			txq->tx_buf[index].type = FEC_TXBUF_T_SKB;
+		}
+
+tx_buf_done:
+		/* Make sure the update to bdp and tx_buf are performed
 		 * before dirty_tx
 		 */
 		wmb();
@@ -3249,9 +3292,19 @@ static void fec_enet_free_buffers(struct net_device *ndev)
 		for (i = 0; i < txq->bd.ring_size; i++) {
 			kfree(txq->tx_bounce[i]);
 			txq->tx_bounce[i] = NULL;
-			skb = txq->tx_skbuff[i];
-			txq->tx_skbuff[i] = NULL;
+
+			if (txq->tx_buf[i].type == FEC_TXBUF_T_SKB) {
+				skb = txq->tx_buf[i].skb;
+				txq->tx_buf[i].skb = NULL;
 				dev_kfree_skb(skb);
+			} else {
+				if (txq->tx_buf[i].xdp) {
+					xdp_return_frame(txq->tx_buf[i].xdp);
+					txq->tx_buf[i].xdp = NULL;
+				}
+
+				txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
+			}
 		}
 	}
 }
@@ -3817,7 +3870,8 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
 		ebdp->cbd_esc = cpu_to_fec32(estatus);
 	}
 
-	txq->tx_skbuff[index] = NULL;
+	txq->tx_buf[index].type = FEC_TXBUF_T_XDP_NDO;
+	txq->tx_buf[index].xdp = frame;
 
 	/* Make sure the updates to rest of the descriptor are performed before
 	 * transferring ownership.