e1000e: workaround for packet drop on 82579 at 100Mbps

The MAC can drop short packets when the PHY detects noise on the line at
100Mbps due to a timing issue.  Workaround the issue by increasing the PLL
counter so the PHY properly recognizes the synchronization pattern from the
MAC.
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/e1000e/ich8lan.c

@@ -139,6 +139,7 @@
 /* PHY Low Power Idle Control */
 #define I82579_LPI_CTRL				PHY_REG(772, 20)
 #define I82579_LPI_CTRL_ENABLE_MASK		0x6000
+#define I82579_LPI_CTRL_FORCE_PLL_LOCK_COUNT	0x80
 
 /* EMI Registers */
 #define I82579_EMI_ADDR         0x10
@@ -1670,6 +1671,7 @@ static s32 e1000_k1_workaround_lv(struct e1000_hw *hw)
 	s32 ret_val = 0;
 	u16 status_reg = 0;
 	u32 mac_reg;
+	u16 phy_reg;
 
 	if (hw->mac.type != e1000_pch2lan)
 		goto out;
@@ -1684,12 +1686,19 @@ static s32 e1000_k1_workaround_lv(struct e1000_hw *hw)
 		mac_reg = er32(FEXTNVM4);
 		mac_reg &= ~E1000_FEXTNVM4_BEACON_DURATION_MASK;
 
-		if (status_reg & HV_M_STATUS_SPEED_1000)
+		ret_val = e1e_rphy(hw, I82579_LPI_CTRL, &phy_reg);
+		if (ret_val)
+			goto out;
+
+		if (status_reg & HV_M_STATUS_SPEED_1000) {
 			mac_reg |= E1000_FEXTNVM4_BEACON_DURATION_8USEC;
-		else
+			phy_reg &= ~I82579_LPI_CTRL_FORCE_PLL_LOCK_COUNT;
+		} else {
 			mac_reg |= E1000_FEXTNVM4_BEACON_DURATION_16USEC;
-
+			phy_reg |= I82579_LPI_CTRL_FORCE_PLL_LOCK_COUNT;
+		}
 		ew32(FEXTNVM4, mac_reg);
+		ret_val = e1e_wphy(hw, I82579_LPI_CTRL, phy_reg);
 	}
 
 out: