sky2: status ring race fix

The D-Link PCI-X board (and maybe others) can lie about status
ring entries. It seems it will update the register for last status
index before completing the DMA for the ring entry. To avoid reading
stale data, zap the old entry and check.
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/sky2.c

@@ -2247,20 +2247,26 @@ static int sky2_status_intr(struct sky2_hw *hw, int to_do, u16 idx)
 	do {
 		struct sky2_port *sky2;
 		struct sky2_status_le *le  = hw->st_le + hw->st_idx;
-		unsigned port = le->css & CSS_LINK_BIT;
+		unsigned port;
 		struct net_device *dev;
 		struct sk_buff *skb;
 		u32 status;
 		u16 length;
+		u8 opcode = le->opcode;
+
+		if (!(opcode & HW_OWNER))
+			break;
 
 		hw->st_idx = RING_NEXT(hw->st_idx, STATUS_RING_SIZE);
 
+		port = le->css & CSS_LINK_BIT;
 		dev = hw->dev[port];
 		sky2 = netdev_priv(dev);
 		length = le16_to_cpu(le->length);
 		status = le32_to_cpu(le->status);
 
-		switch (le->opcode & ~HW_OWNER) {
+		le->opcode = 0;
+		switch (opcode & ~HW_OWNER) {
 		case OP_RXSTAT:
 			++rx[port];
 			skb = sky2_receive(dev, length, status);
@@ -2353,7 +2359,7 @@ static int sky2_status_intr(struct sky2_hw *hw, int to_do, u16 idx)
 		default:
 			if (net_ratelimit())
 				printk(KERN_WARNING PFX
-				       "unknown status opcode 0x%x\n", le->opcode);
+				       "unknown status opcode 0x%x\n", opcode);
 		}
 	} while (hw->st_idx != idx);