igb: Add message when malformed packets detected by hw

This patch adds a check and prints the error cause register value when
the hardware detects a malformed packet.  This is a very unlikely
scenario but has been seen occasionally, so printing the message to
assist the user.

Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index 4d2dc17..bd8de67 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -4167,6 +4167,26 @@
 }
 
 /**
+ *  igb_check_lvmmc - check for malformed packets received
+ *  and indicated in LVMMC register
+ *  @adapter: pointer to adapter
+ **/
+static void igb_check_lvmmc(struct igb_adapter *adapter)
+{
+	struct e1000_hw *hw = &adapter->hw;
+	u32 lvmmc;
+
+	lvmmc = rd32(E1000_LVMMC);
+	if (lvmmc) {
+		if (unlikely(net_ratelimit())) {
+			netdev_warn(adapter->netdev,
+				    "malformed Tx packet detected and dropped, LVMMC:0x%08x\n",
+				    lvmmc);
+		}
+	}
+}
+
+/**
  *  igb_watchdog - Timer Call-back
  *  @data: pointer to adapter cast into an unsigned long
  **/
@@ -4361,6 +4381,11 @@
 	igb_spoof_check(adapter);
 	igb_ptp_rx_hang(adapter);
 
+	/* Check LVMMC register on i350/i354 only */
+	if ((adapter->hw.mac.type == e1000_i350) ||
+	    (adapter->hw.mac.type == e1000_i354))
+		igb_check_lvmmc(adapter);
+
 	/* Reset the timer */
 	if (!test_bit(__IGB_DOWN, &adapter->state)) {
 		if (adapter->flags & IGB_FLAG_NEED_LINK_UPDATE)