e1000e: Correct link check logic for 82571 serdes

commit d0efa8f23a644f7cb7d1f8e78dd9a223efa412a3 upstream.

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.

Reported-by: Dean Nelson <dnelson@redhat.com>
Signed-off-by: Tushar Dave <tushar.n.dave@intel.com>
Reviewed-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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/e1000e/82571.c b/drivers/net/e1000e/82571.c
index 8295f21924393e805268d629881b446b8eeed69c..5278e8456b688a32842c0da8a85cf7f1dc127b09 100644 (file)
--- a/drivers/net/e1000e/82571.c
+++ b/drivers/net/e1000e/82571.c
@@ -1573,6 +1573,9 @@ 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)) {