ixgbe: fix bug when EITR=0 causing no writebacks

writebacks can be held indefinitely by hardware if EITR=0, when
combined with TXDCTL.WTHRESH=8.  When EITR=0, WTHRESH should be
set back to zero.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
index 0c4ca6822b70..fe7e260e0157 100644
--- a/drivers/net/ixgbe/ixgbe_main.c
+++ b/drivers/net/ixgbe/ixgbe_main.c
@@ -2945,8 +2945,13 @@ static int ixgbe_up_complete(struct ixgbe_adapter *adapter)
         for (i = 0; i < adapter->num_tx_queues; i++) {
                 j = adapter->tx_ring[i]->reg_idx;
                 txdctl = IXGBE_READ_REG(hw, IXGBE_TXDCTL(j));
-                /* enable WTHRESH=8 descriptors, to encourage burst writeback */
-                txdctl |= (8 << 16);
+                if (adapter->rx_itr_setting == 0) {
+                        /* cannot set wthresh when itr==0 */
+                        txdctl &= ~0x007F0000;
+                } else {
+                        /* enable WTHRESH=8 descriptors, to encourage burst writeback */
+                        txdctl |= (8 << 16);
+                }
                 IXGBE_WRITE_REG(hw, IXGBE_TXDCTL(j), txdctl);
         }