Revert "net: fec: fix the warning found by dma debug"

This reverts commit 2b995f63987013bacde99168218f9c7b252bdcf1.

Панов Андрей reported the following regression:

"Commit 2b995f63987013bacde99168218f9c7b252bdcf1 in 4.0.0-rc3 introduces a
nasty bug in transmit, corrupting packets.

To reproduce:

$ dd if=/dev/zero of=zeros bs=1M count=20
$ md5sum -b zeros
8f4e33f3dc3e414ff94e5fb6905cba8c *zeros

This checksum is correct.

Copy file "zeros" to another host with NFS, and it gets corrupted, checksum is
changed.
File should be big, small amounts of transmit isn't affected.

I use an i.MX6 Quad board.

If this commit is reverted, all works fine."

Reported-by: Панов Андрей <rockford@yandex.ru>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -1189,13 +1189,12 @@ static void
 fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 {
 	struct	fec_enet_private *fep;
-	struct bufdesc *bdp, *bdp_t;
+	struct bufdesc *bdp;
 	unsigned short status;
 	struct	sk_buff	*skb;
 	struct fec_enet_priv_tx_q *txq;
 	struct netdev_queue *nq;
 	int	index = 0;
-	int	i, bdnum;
 	int	entries_free;
 
 	fep = netdev_priv(ndev);
@@ -1216,29 +1215,18 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 		if (bdp == txq->cur_tx)
 			break;
 
-		bdp_t = bdp;
-		bdnum = 1;
-		index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t, fep);
-		skb = txq->tx_skbuff[index];
-		while (!skb) {
-			bdp_t = fec_enet_get_nextdesc(bdp_t, fep, queue_id);
-			index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t, fep);
-			skb = txq->tx_skbuff[index];
-			bdnum++;
-		}
-		if (skb_shinfo(skb)->nr_frags &&
-		    (status = bdp_t->cbd_sc) & BD_ENET_TX_READY)
-			break;
+		index = fec_enet_get_bd_index(txq->tx_bd_base, bdp, fep);
 
-		for (i = 0; i < bdnum; i++) {
-			if (!IS_TSO_HEADER(txq, bdp->cbd_bufaddr))
-				dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr,
-						 bdp->cbd_datlen, DMA_TO_DEVICE);
-			bdp->cbd_bufaddr = 0;
-			if (i < bdnum - 1)
-				bdp = fec_enet_get_nextdesc(bdp, fep, queue_id);
-		}
+		skb = txq->tx_skbuff[index];
 		txq->tx_skbuff[index] = NULL;
+		if (!IS_TSO_HEADER(txq, bdp->cbd_bufaddr))
+			dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr,
+					bdp->cbd_datlen, DMA_TO_DEVICE);
+		bdp->cbd_bufaddr = 0;
+		if (!skb) {
+			bdp = fec_enet_get_nextdesc(bdp, fep, queue_id);
+			continue;
+		}
 
 		/* Check for errors. */
 		if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC |