8139cp: Fix DMA unmapping of transmitted buffers

The low 16 bits of the 'opts1' field in the TX descriptor are supposed
to still contain the buffer length when the descriptor is handed back to
us. In practice, at least on my hardware, they don't. So stash the
original value of the opts1 field and get the length to unmap from
there.

There are other ways we could have worked out the length, but I actually
want a stash of the opts1 field anyway so that I can dump it alongside
the contents of the descriptor ring when we suffer a TX timeout.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/8139cp.c

@@ -341,6 +341,7 @@ struct cp_private {
 	unsigned		tx_tail;
 	struct cp_desc		*tx_ring;
 	struct sk_buff		*tx_skb[CP_TX_RING_SIZE];
+	u32			tx_opts[CP_TX_RING_SIZE];
 
 	unsigned		rx_buf_sz;
 	unsigned		wol_enabled : 1; /* Is Wake-on-LAN enabled? */
@@ -665,7 +666,7 @@ static void cp_tx (struct cp_private *cp)
 		BUG_ON(!skb);
 
 		dma_unmap_single(&cp->pdev->dev, le64_to_cpu(txd->addr),
-				 le32_to_cpu(txd->opts1) & 0xffff,
+				 cp->tx_opts[tx_tail] & 0xffff,
 				 PCI_DMA_TODEVICE);
 
 		if (status & LastFrag) {
@@ -789,6 +790,7 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
 		wmb();
 
 		cp->tx_skb[entry] = skb;
+		cp->tx_opts[entry] = opts1;
 		netif_dbg(cp, tx_queued, cp->dev, "tx queued, slot %d, skblen %d\n",
 			  entry, skb->len);
 	} else {
@@ -839,6 +841,8 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
 
 			txd->opts1 = cpu_to_le32(ctrl);
 			wmb();
+
+			cp->tx_opts[entry] = ctrl;
 			cp->tx_skb[entry] = skb;
 		}
 
@@ -851,6 +855,7 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
 		txd->opts1 = cpu_to_le32(ctrl);
 		wmb();
 
+		cp->tx_opts[first_entry] = ctrl;
 		netif_dbg(cp, tx_queued, cp->dev, "tx queued, slots %d-%d, skblen %d\n",
 			  first_entry, entry, skb->len);
 	}
@@ -1093,6 +1098,7 @@ static int cp_init_rings (struct cp_private *cp)
 {
 	memset(cp->tx_ring, 0, sizeof(struct cp_desc) * CP_TX_RING_SIZE);
 	cp->tx_ring[CP_TX_RING_SIZE - 1].opts1 = cpu_to_le32(RingEnd);
+	memset(cp->tx_opts, 0, sizeof(cp->tx_opts));
 
 	cp_init_rings_index(cp);
 
@@ -1150,6 +1156,7 @@ static void cp_clean_rings (struct cp_private *cp)
 
 	memset(cp->rx_ring, 0, sizeof(struct cp_desc) * CP_RX_RING_SIZE);
 	memset(cp->tx_ring, 0, sizeof(struct cp_desc) * CP_TX_RING_SIZE);
+	memset(cp->tx_opts, 0, sizeof(cp->tx_opts));
 
 	memset(cp->rx_skb, 0, sizeof(struct sk_buff *) * CP_RX_RING_SIZE);
 	memset(cp->tx_skb, 0, sizeof(struct sk_buff *) * CP_TX_RING_SIZE);