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>
Signed-off-by: Guangyu Sun <guangyu.sun@oracle.com>

diff --git a/drivers/net/e1000e/82571.c b/drivers/net/e1000e/82571.c
index 04cdf5038544b972cb50c70ae68923a4180002a3..8ec520d5b3d3847d6092d224222afde2ecc17a4b 100644 (file)
--- a/drivers/net/e1000e/82571.c
+++ b/drivers/net/e1000e/82571.c
@@ -1577,6 +1577,9 @@ 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)) {