e1000e: Correct link check logic for 82571 serdes

SYNCH bit and IV bit of RXCW register are sticky. Before examining these bits,
RXCW should be read twice to filter out one-time false events and have correct
values for these bits. Incorrect values of these bits in link check logic can
cause weird link stability issues if auto-negotiation fails.

CC: stable <stable@vger.kernel.org> [2.6.38+]
Reported-by: NDean Nelson <dnelson@redhat.com>
Signed-off-by: NTushar Dave <tushar.n.dave@intel.com>
Reviewed-by: NBruce Allan <bruce.w.allan@intel.com>
Tested-by: NJeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/82571.c

@@ -1572,6 +1572,9 @@ static s32 e1000_check_for_serdes_link_82571(struct e1000_hw *hw)
 	ctrl = er32(CTRL);
 	status = er32(STATUS);
 	rxcw = er32(RXCW);
+	/* SYNCH bit and IV bit are sticky */
+	udelay(10);
+	rxcw = er32(RXCW);
 
 	if ((rxcw & E1000_RXCW_SYNCH) && !(rxcw & E1000_RXCW_IV)) {