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From:   Shenwei Wang <shenwei.wang@nxp.com>
To:     Wei Fang <wei.fang@nxp.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     Shenwei Wang <shenwei.wang@nxp.com>,
        Clark Wang <xiaoning.wang@nxp.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Alexander Lobakin <alexandr.lobakin@intel.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        imx@lists.linux.dev
Subject: [PATCH net 1/1] net: fec: using the standard return codes when xdp xmit errors
Date:   Tue,  9 May 2023 14:38:45 -0500
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The existing logic did not properly handle unsuccessful xdp xmit frames,
this patch revises the logic to return standard error codes (-EBUSY or
-ENOMEM) on unsuccessful transmit.

Start the xmit of the frame immediately right after configuring the
tx descriptors.

Fixes: e8a17397180f ("net: fec: correct the counting of XDP sent frames")
Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 25 ++++++++++++++---------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 42ec6ca3bf03..438fc1c3aea2 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -3798,8 +3798,7 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
 	entries_free = fec_enet_get_free_txdesc_num(txq);
 	if (entries_free < MAX_SKB_FRAGS + 1) {
 		netdev_err(fep->netdev, "NOT enough BD for SG!\n");
-		xdp_return_frame(frame);
-		return NETDEV_TX_BUSY;
+		return -EBUSY;
 	}
 
 	/* Fill in a Tx ring entry */
@@ -3813,7 +3812,7 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
 	dma_addr = dma_map_single(&fep->pdev->dev, frame->data,
 				  frame->len, DMA_TO_DEVICE);
 	if (dma_mapping_error(&fep->pdev->dev, dma_addr))
-		return FEC_ENET_XDP_CONSUMED;
+		return -ENOMEM;
 
 	status |= (BD_ENET_TX_INTR | BD_ENET_TX_LAST);
 	if (fep->bufdesc_ex)
@@ -3835,6 +3834,11 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
 	index = fec_enet_get_bd_index(last_bdp, &txq->bd);
 	txq->tx_skbuff[index] = NULL;
 
+	/* Make sure the updates to rest of the descriptor are performed before
+	 * transferring ownership.
+	 */
+	wmb();
+
 	/* Send it on its way.  Tell FEC it's ready, interrupt when done,
 	 * it's the last BD of the frame, and to put the CRC on the end.
 	 */
@@ -3844,8 +3848,15 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
 	/* If this was the last BD in the ring, start at the beginning again. */
 	bdp = fec_enet_get_nextdesc(last_bdp, &txq->bd);
 
+	/* Make sure the update to bdp and tx_skbuff are performed before
+	 * txq->bd.cur.
+	 */
+	wmb();
 	txq->bd.cur = bdp;
 
+	/* Trigger transmission start */
+	writel(0, txq->bd.reg_desc_active);
+
 	return 0;
 }
 
@@ -3869,17 +3880,11 @@ static int fec_enet_xdp_xmit(struct net_device *dev,
 	__netif_tx_lock(nq, cpu);
 
 	for (i = 0; i < num_frames; i++) {
-		if (fec_enet_txq_xmit_frame(fep, txq, frames[i]) != 0)
+		if (fec_enet_txq_xmit_frame(fep, txq, frames[i]) < 0)
 			break;
 		sent_frames++;
 	}
 
-	/* Make sure the update to bdp and tx_skbuff are performed. */
-	wmb();
-
-	/* Trigger transmission start */
-	writel(0, txq->bd.reg_desc_active);
-
 	__netif_tx_unlock(nq);
 
 	return sent_frames;
-- 
2.34.1