sky2: turn off Rx checksum on bad hardware

On Yukon FE, occasional hardware receive checksum errors are seen.
An early indication of the problem is single bit differences in the two
checksum engines.  Use this as a detection mechanism to turn off Rx
checksumming.
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/sky2.c

@@ -2165,9 +2165,27 @@ force_update:
 			/* fall through */
 #endif
 		case OP_RXCHKS:
-			skb = sky2->rx_ring[sky2->rx_next].skb;
-			skb->ip_summed = CHECKSUM_COMPLETE;
-			skb->csum = status & 0xffff;
+			if (!sky2->rx_csum)
+				break;
+
+			/* Both checksum counters are programmed to start at
+			 * the same offset, so unless there is a problem they
+			 * should match. This failure is an early indication that
+			 * hardware receive checksumming won't work.
+			 */
+			if (likely(status >> 16 == (status & 0xffff))) {
+				skb = sky2->rx_ring[sky2->rx_next].skb;
+				skb->ip_summed = CHECKSUM_COMPLETE;
+				skb->csum = status & 0xffff;
+			} else {
+				printk(KERN_NOTICE PFX "%s: hardware receive "
+				       "checksum problem (status = %#x)\n",
+				       dev->name, status);
+				sky2->rx_csum = 0;
+				sky2_write32(sky2->hw,
+					     Q_ADDR(rxqaddr[le->link], Q_CSR),
+					     BMU_DIS_RX_CHKSUM);
+			}
 			break;
 
 		case OP_TXINDEXLE: