ixgbevf: introduce delay for checking VFLINKS on 82599

VFLINKS.LINKUP bit tends to flap when a DA or SFP+ cable is disconnected.
It can take up to 500 usecs for the LINKUP bit to be correct.

This patch resolves the issue by introducing a delay for 82599 VFs of at
least 500 usecs to make sure the VFLINKS value is correct.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbevf/vf.c

@@ -434,6 +434,21 @@ static s32 ixgbevf_check_mac_link_vf(struct ixgbe_hw *hw,
 	if (!(links_reg & IXGBE_LINKS_UP))
 		goto out;
 
+	/* for SFP+ modules and DA cables on 82599 it can take up to 500usecs
+	 * before the link status is correct
+	 */
+	if (mac->type == ixgbe_mac_82599_vf) {
+		int i;
+
+		for (i = 0; i < 5; i++) {
+			udelay(100);
+			links_reg = IXGBE_READ_REG(hw, IXGBE_VFLINKS);
+
+			if (!(links_reg & IXGBE_LINKS_UP))
+				goto out;
+		}
+	}
+
 	switch (links_reg & IXGBE_LINKS_SPEED_82599) {
 	case IXGBE_LINKS_SPEED_10G_82599:
 		*speed = IXGBE_LINK_SPEED_10GB_FULL;