e1000e: PHY loopback broken on 82578

PHY loopback on 82578 fails to work as a result of flushing the packets
in the FIFO buffer in the link stall workaround.  Don't perform the
workaround if in PHY loopback mode.
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>

drivers/net/e1000e/defines.h

@@ -575,6 +575,8 @@
 #define PHY_1000T_STATUS 0x0A /* 1000Base-T Status Reg */
 #define PHY_EXT_STATUS   0x0F /* Extended Status Reg */
 
+#define PHY_CONTROL_LB   0x4000 /* PHY Loopback bit */
+
 /* NVM Control */
 #define E1000_EECD_SK        0x00000001 /* NVM Clock */
 #define E1000_EECD_CS        0x00000002 /* NVM Chip Select */

drivers/net/e1000e/phy.c

@@ -2737,6 +2737,11 @@ s32 e1000_link_stall_workaround_hv(struct e1000_hw *hw)
 	if (hw->phy.type != e1000_phy_82578)
 		goto out;
 
+	/* Do not apply workaround if in PHY loopback bit 14 set */
+	hw->phy.ops.read_phy_reg(hw, PHY_CONTROL, &data);
+	if (data & PHY_CONTROL_LB)
+		goto out;
+
 	/* check if link is up and at 1Gbps */
 	ret_val = hw->phy.ops.read_phy_reg(hw, BM_CS_STATUS, &data);
 	if (ret_val)