e1000e: 82571 SerDes link handle null code word from partner

SerDes Link detection on certain 82571 mezzanine cards can fail when the
link is forced, the link partner does not recognize forced link and the
link partner sends null code words.  Detect the null code words and return
to auto-negotiation state which causes the link partner to begin responding
with valid code words.  Within a reasonable interval the link will finally
settle as forced by both partners.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/net/e1000e/82571.c b/drivers/net/e1000e/82571.c
index 7236f1a53ba0..235856375ff3 100644
--- a/drivers/net/e1000e/82571.c
+++ b/drivers/net/e1000e/82571.c
@@ -1431,8 +1431,10 @@ static s32 e1000_check_for_serdes_link_82571(struct e1000_hw *hw)
                          * auto-negotiation in the TXCW register and disable
                          * forced link in the Device Control register in an
                          * attempt to auto-negotiate with our link partner.
+                         * If the partner code word is null, stop forcing
+                         * and restart auto negotiation.
                          */
-                        if (rxcw & E1000_RXCW_C) {
+                        if ((rxcw & E1000_RXCW_C) || !(rxcw & E1000_RXCW_CW))  {
                                 /* Enable autoneg, and unforce link up */
                                 ew32(TXCW, mac->txcw);
                                 ew32(CTRL, (ctrl & ~E1000_CTRL_SLU));