e1000e: Resolve intermittent negotiation issue on 82574/82583.

For 82574 and 82583 devices, resolve an intermittent link issue where
the link negotiates to 100Mbps rather than 1Gbps when powering off the
PHY and powering on the PHY after several seconds.
Signed-off-by: NMatthew Vick <matthew.vick@intel.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/phy.c

@@ -722,8 +722,24 @@ s32 e1000e_copper_link_setup_m88(struct e1000_hw *hw)
 		phy_data |= M88E1000_PSCR_POLARITY_REVERSAL;
 
 	/* Enable downshift on BM (disabled by default) */
-	if (phy->type == e1000_phy_bm)
+	if (phy->type == e1000_phy_bm) {
+		/* For 82574/82583, first disable then enable downshift */
+		if (phy->id == BME1000_E_PHY_ID_R2) {
+			phy_data &= ~BME1000_PSCR_ENABLE_DOWNSHIFT;
+			ret_val = e1e_wphy(hw, M88E1000_PHY_SPEC_CTRL,
+					   phy_data);
+			if (ret_val)
+				return ret_val;
+			/* Commit the changes. */
+			ret_val = e1000e_commit_phy(hw);
+			if (ret_val) {
+				e_dbg("Error committing the PHY changes\n");
+				return ret_val;
+			}
+		}
+
 		phy_data |= BME1000_PSCR_ENABLE_DOWNSHIFT;
+	}
 
 	ret_val = e1e_wphy(hw, M88E1000_PHY_SPEC_CTRL, phy_data);
 	if (ret_val)