e1000e: 82579: workaround for link drop issue

When connected to certain switches, the 82579 PHY might drop link
unexpectedly.  Work around the issue by setting the Mean Square Error
higher than the hardware default.

Signed-off-by: Bruce Allan <bruce.w.allan@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/e1000e/ich8lan.c

@@ -145,6 +145,8 @@
 #define I82579_EMI_ADDR         0x10
 #define I82579_EMI_DATA         0x11
 #define I82579_LPI_UPDATE_TIMER 0x4805	/* in 40ns units + 40 ns base value */
+#define I82579_MSE_THRESHOLD    0x084F	/* Mean Square Error Threshold */
+#define I82579_MSE_LINK_DOWN    0x2411	/* MSE count before dropping link */
 
 /* Strapping Option Register - RO */
 #define E1000_STRAP                     0x0000C
@@ -1669,6 +1671,26 @@ static s32 e1000_lv_phy_workarounds_ich8lan(struct e1000_hw *hw)
 	/* Set MDIO slow mode before any other MDIO access */
 	ret_val = e1000_set_mdio_slow_mode_hv(hw);
 
+	ret_val = hw->phy.ops.acquire(hw);
+	if (ret_val)
+		goto out;
+	ret_val = hw->phy.ops.write_reg_locked(hw, I82579_EMI_ADDR,
+					       I82579_MSE_THRESHOLD);
+	if (ret_val)
+		goto release;
+	/* set MSE higher to enable link to stay up when noise is high */
+	ret_val = hw->phy.ops.write_reg_locked(hw, I82579_EMI_DATA, 0x0034);
+	if (ret_val)
+		goto release;
+	ret_val = hw->phy.ops.write_reg_locked(hw, I82579_EMI_ADDR,
+					       I82579_MSE_LINK_DOWN);
+	if (ret_val)
+		goto release;
+	/* drop link after 5 times MSE threshold was reached */
+	ret_val = hw->phy.ops.write_reg_locked(hw, I82579_EMI_DATA, 0x0005);
+release:
+	hw->phy.ops.release(hw);
+
 out:
 	return ret_val;
 }