e1000e: disable K1 on PCH LOM when in PHY loopback mode

When performing the ethtool PHY loopback test on PCH-based LOMs (82577 and
82578), disable K1 (a MAC-PHY interconnect low power mode) otherwise
packets might get corrupted.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/e1000e/ethtool.c b/drivers/net/e1000e/ethtool.c
index 67e06fd..fd79214 100644
--- a/drivers/net/e1000e/ethtool.c
+++ b/drivers/net/e1000e/ethtool.c
@@ -1260,6 +1260,10 @@
 
 	hw->mac.autoneg = 0;
 
+	/* Workaround: K1 must be disabled for stable 1Gbps operation */
+	if (hw->mac.type == e1000_pchlan)
+		e1000_configure_k1_ich8lan(hw, false);
+
 	if (hw->phy.type == e1000_phy_m88) {
 		/* Auto-MDI/MDIX Off */
 		e1e_wphy(hw, M88E1000_PHY_SPEC_CTRL, 0x0808);