[PATCH] mv643xx_eth: Fix tx_timeout to only conditionally wake tx queue

After resetting the hardware on a tx_timeout, call netif_wake_queue()
only if we have free tx descriptors.

Also, attempt to recover if mv643xx_eth_start_xmit() is called when
there are fewer free tx descriptors than expected.

The BUG_ON() call we are replacing was hit on a tx_timeout that
called netif_wake_queue(), indirectly via netif_device_attach(),
even though we did not have enough free tx descriptors.
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/mv643xx_eth.c

@@ -281,10 +281,16 @@ static void mv643xx_eth_tx_timeout_task(struct net_device *dev)
 {
 	struct mv643xx_private *mp = netdev_priv(dev);
 
-	netif_device_detach(dev);
+	if (!netif_running(dev))
+		return;
+
+	netif_stop_queue(dev);
+
 	eth_port_reset(mp->port_num);
 	eth_port_start(dev);
-	netif_device_attach(dev);
+
+	if (mp->tx_ring_size - mp->tx_desc_count >= MAX_DESCS_PER_SKB)
+		netif_wake_queue(dev);
 }
 
 /**
@@ -1186,7 +1192,12 @@ static int mv643xx_eth_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	BUG_ON(netif_queue_stopped(dev));
 	BUG_ON(skb == NULL);
-	BUG_ON(mp->tx_ring_size - mp->tx_desc_count < MAX_DESCS_PER_SKB);
+
+	if (mp->tx_ring_size - mp->tx_desc_count < MAX_DESCS_PER_SKB) {
+		printk(KERN_ERR "%s: transmit with queue full\n", dev->name);
+		netif_stop_queue(dev);
+		return 1;
+	}
 
 	if (has_tiny_unaligned_frags(skb)) {
 		if ((skb_linearize(skb, GFP_ATOMIC) != 0)) {