[PATCH 1/2] e1000: Fix DMA mapping error handling on TX

[Anton Blanchard <anton@samba.org>]

There were a few issues in the DMA mapping error handling in e1000_tx_map
which I found via fault injection.

If we fail to map the first descriptor count will end up as -1 but the
check of (count >= 0) will still be true since count is unsigned. Instead
of changing count to be signed, just simplify the logic.

Secondly, when we wrap the tx ring we rely on i to go negative, but it
was unsigned.

Signed-off-by: Anton Blanchard <anton@samba.org>
---

Index: linux.trees.git/drivers/net/e1000/e1000_main.c
===================================================================
--- linux.trees.git.orig/drivers/net/e1000/e1000_main.c	2010-01-21 11:10:00.000000000 +1100
+++ linux.trees.git/drivers/net/e1000/e1000_main.c	2010-01-21 11:12:52.000000000 +1100
@@ -2693,8 +2693,9 @@ static int e1000_tx_map(struct e1000_ada
 	struct pci_dev *pdev = adapter->pdev;
 	struct e1000_buffer *buffer_info;
 	unsigned int len = skb_headlen(skb);
-	unsigned int offset = 0, size, count = 0, i;
+	unsigned int offset = 0, size, count = 0;
 	unsigned int f;
+	int i;
 
 	i = tx_ring->next_to_use;
 
@@ -2802,10 +2803,8 @@ static int e1000_tx_map(struct e1000_ada
 dma_error:
 	dev_err(&pdev->dev, "TX DMA map failed\n");
 	buffer_info->dma = 0;
-	count--;
 
-	while (count >= 0) {
-		count--;
+	while (count--) {
 		i--;
 		if (i < 0)
 			i += tx_ring->count;