igb: Unset sigdetect for SERDES loopback on 82580 and i350

This patch unsets the sigdetect bit for SERDES loopback tests on 82580 and
i350 parts.  The loopback test can fail on these parts without this
setting.
Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb.h

@@ -42,6 +42,8 @@
 
 struct igb_adapter;
 
+#define E1000_PCS_CFG_IGN_SD               1
+
 /* Interrupt defines */
 #define IGB_START_ITR                    648 /* ~6000 ints/sec */
 #define IGB_4K_ITR                       980

drivers/net/ethernet/intel/igb/igb_ethtool.c

@@ -1624,6 +1624,20 @@ static int igb_setup_loopback_test(struct igb_adapter *adapter)
 		reg &= ~E1000_CONNSW_ENRGSRC;
 		wr32(E1000_CONNSW, reg);
 
+		/* Unset sigdetect for SERDES loopback on
+		 * 82580 and i350 devices.
+		 */
+		switch (hw->mac.type) {
+		case e1000_82580:
+		case e1000_i350:
+			reg = rd32(E1000_PCS_CFG0);
+			reg |= E1000_PCS_CFG_IGN_SD;
+			wr32(E1000_PCS_CFG0, reg);
+			break;
+		default:
+			break;
+		}
+
 		/* Set PCS register for forced speed */
 		reg = rd32(E1000_PCS_LCTL);
 		reg &= ~E1000_PCS_LCTL_AN_ENABLE;     /* Disable Autoneg*/