net: fec: add dma_wmb to ensure correct descriptor values

Two dma_wmb() are added in the XDP TX path to ensure proper ordering of
descriptor and buffer updates:
1. A dma_wmb() is added after updating the last BD to make sure
   the updates to rest of the descriptor are visible before
   transferring ownership to FEC.
2. A dma_wmb() is also added after updating the bdp to ensure these
   updates are visible before updating txq->bd.cur.
3. Start the xmit of the frame immediately right after configuring the
   tx descriptor.

Fixes: 6d6b39f180b8 ("net: fec: add initial XDP support")
Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
Reviewed-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 577d94821b3e70e20c1714907bd761baa69fb294..38e5b5abe067cf6ce8a2bf8144c9dd7245ae2e8c 100644 (file)
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -3834,6 +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.
+        */
+       dma_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.
         */
@@ -3843,8 +3848,14 @@ 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 are performed before txq->bd.cur. */
+       dma_wmb();
+
        txq->bd.cur = bdp;
 
+       /* Trigger transmission start */
+       writel(0, txq->bd.reg_desc_active);
+
        return 0;
 }
 
@@ -3873,12 +3884,6 @@ static int fec_enet_xdp_xmit(struct net_device *dev,
                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;