net: fec: fix the warning found by dma debug

Enable kernel config "CONFIG_HAVE_DMA_API_DEBUG", FEC have kernel warning:
[    6.650444] fec 2188000.ethernet: DMA-API: device driver tries to free DMA memory it has not allocated
[    6.664289] Modules linked in:
[    6.667378] CPU: 0 PID: 3 Comm: ksoftirqd/0 Not tainted 3.19.0-rc4-00688-g88340160-dirty #150
[    6.675841] Hardware name: Freescale i.MX6 SoloX (Device Tree)
[    6.681698] Backtrace:
[    6.684189] [<80011e3c>] (dump_backtrace) from [<80011fdc>] (show_stack+0x18/0x1c)
[    6.691789]  r6:80890154 r5:00000000 r4:00000000 r3:00000000
[    6.697533] [<80011fc4>] (show_stack) from [<806d2d88>] (dump_stack+0x80/0x9c)
[    6.704799] [<806d2d08>] (dump_stack) from [<8002a4e4>] (warn_slowpath_common+0x7c/0xb4)
[    6.712917]  r5:00000445 r4:00000000
[    6.716544] [<8002a468>] (warn_slowpath_common) from [<8002a5c0>] (warn_slowpath_fmt+0x38/0x40)
[    6.725265]  r8:809a2ee8 r7:00000000 r6:00000000 r5:00000000 r4:00000042
[    6.732087] [<8002a58c>] (warn_slowpath_fmt) from [<802d6268>] (check_unmap+0x86c/0x98c)
[    6.740202]  r3:808c79bc r2:8089060c
[    6.743826] [<802d59fc>] (check_unmap) from [<802d65e4>] (debug_dma_unmap_page+0x80/0x88)
[    6.752029]  r10:00000000 r9:00000000 r8:00000000 r7:00000001 r6:be12a410 r5:00000000
[    6.759967]  r4:00000042
[    6.762538] [<802d6564>] (debug_dma_unmap_page) from [<80440248>] (fec_enet_rx_napi+0x7ec/0xb9c)
[    6.771345]  r7:00000400 r6:be3e4000 r5:bf08fa20 r4:be036000
[    6.777094] [<8043fa5c>] (fec_enet_rx_napi) from [<8056ae24>] (net_rx_action+0x134/0x324)
[    6.785297]  r10:be089e60 r9:80998180 r8:ffff8d68 r7:0000012c r6:00000040 r5:00000001
[    6.793239]  r4:be036718
[    6.795801] [<8056acf0>] (net_rx_action) from [<8002db24>] (__do_softirq+0x138/0x2d0)
[    6.803655]  r10:00000003 r9:00000003 r8:80996378 r7:8099c080 r6:00000100 r5:8099c08c
[    6.811593]  r4:00000000
[    6.814157] [<8002d9ec>] (__do_softirq) from [<8002dd00>] (run_ksoftirqd+0x44/0x5c)
[    6.821836]  r10:00000000 r9:00000000 r8:809b133c r7:00000000 r6:00000001 r5:00000000
[    6.829775]  r4:be027e80
[    6.832346] [<8002dcbc>] (run_ksoftirqd) from [<80048290>] (smpboot_thread_fn+0x154/0x1c4)
[    6.840649] [<8004813c>] (smpboot_thread_fn) from [<80044780>] (kthread+0xdc/0xf8)
[    6.848224]  r10:00000000 r8:00000000 r7:8004813c r6:be027e80 r5:be027ec0 r4:00000000
[    6.856179] [<800446a4>] (kthread) from [<8000ebc8>] (ret_from_fork+0x14/0x2c)
[    6.863425]  r7:00000000 r6:00000000 r5:800446a4 r4:be027ec0
[    6.869156] ---[ end trace 861cf914d2461a8b ]---

There have one bug in .fec_enet_tx_queue() function to unmap the DMA memory:
For SG or TSO, get one buffer descriptor and then unmap the related DMA memory, and then
get the next buffer descriptor, loop to while() to check "TX_READY". If "TX_READY" bit
still __IS__ existed in the BD (The next fraglist or next TSO packet is not transmited
complitely), exit the current clean work. When the next work is triggered, it still repeat
above step with the same BD. The potential issue is that unmap the same DMA memory for
multiple times.

The patch fix the clean work for SG and TSO packet.
Reported-by: Anand Moon <moon.linux@yahoo.com>
Reported-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -1189,12 +1189,13 @@ static void
 fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 {
 	struct	fec_enet_private *fep;
-	struct bufdesc *bdp;
+	struct bufdesc *bdp, *bdp_t;
 	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);
@@ -1215,18 +1216,29 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 		if (bdp == txq->cur_tx)
 			break;
 
-		index = fec_enet_get_bd_index(txq->tx_bd_base, bdp, fep);
-
+		bdp_t = bdp;
+		bdnum = 1;
+		index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t, fep);
 		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;
+		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;
+
+		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);
+		}
+		txq->tx_skbuff[index] = NULL;
 
 		/* Check for errors. */
 		if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC |