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>

2 files changed, 26 insertions, 14 deletions

diff --git a/drivers/net/ixgbe/ixgbe_ethtool.c b/drivers/net/ixgbe/ixgbe_ethtool.c
index 1ae0201f5aa6..5f8c6ab7a98a 100644
--- a/drivers/net/ixgbe/ixgbe_ethtool.c
+++ b/drivers/net/ixgbe/ixgbe_ethtool.c
@@ -2083,7 +2083,7 @@ static int ixgbe_get_coalesce(struct net_device *netdev,
  * this function must be called before setting the new value of
  * rx_itr_setting
  */
-static void ixgbe_reenable_rsc(struct ixgbe_adapter *adapter,
+static bool ixgbe_reenable_rsc(struct ixgbe_adapter *adapter,
                                struct ethtool_coalesce *ec)
 {
         /* check the old value and enable RSC if necessary */
@@ -2093,11 +2093,9 @@ static void ixgbe_reenable_rsc(struct ixgbe_adapter *adapter,
                 adapter->netdev->features |= NETIF_F_LRO;
                 DPRINTK(PROBE, INFO, "rx-usecs set to %d, re-enabling RSC\n",
                         ec->rx_coalesce_usecs);
-                if (netif_running(adapter->netdev))
-                        ixgbe_reinit_locked(adapter);
-                else
-                        ixgbe_reset(adapter);
+                return true;
         }
+        return false;
 }
 
 static int ixgbe_set_coalesce(struct net_device *netdev,
@@ -2106,6 +2104,7 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
         struct ixgbe_adapter *adapter = netdev_priv(netdev);
         struct ixgbe_q_vector *q_vector;
         int i;
+        bool need_reset = false;
 
         /* don't accept tx specific changes if we've got mixed RxTx vectors */
         if (adapter->q_vector[0]->txr_count && adapter->q_vector[0]->rxr_count
@@ -2128,7 +2127,7 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
                         return -EINVAL;
 
                 /* check the old value and enable RSC if necessary */
-                ixgbe_reenable_rsc(adapter, ec);
+                need_reset = ixgbe_reenable_rsc(adapter, ec);
 
                 /* store the value in ints/second */
                 adapter->rx_eitr_param = 1000000/ec->rx_coalesce_usecs;
@@ -2139,7 +2138,7 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
                 adapter->rx_itr_setting &= ~1;
         } else if (ec->rx_coalesce_usecs == 1) {
                 /* check the old value and enable RSC if necessary */
-                ixgbe_reenable_rsc(adapter, ec);
+                need_reset = ixgbe_reenable_rsc(adapter, ec);
 
                 /* 1 means dynamic mode */
                 adapter->rx_eitr_param = 20000;
@@ -2164,11 +2163,7 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
                         DPRINTK(PROBE, INFO,
                                 "rx-usecs set to 0, disabling RSC\n");
 
-                        if (netif_running(netdev))
-                                ixgbe_reinit_locked(adapter);
-                        else
-                                ixgbe_reset(adapter);
-                        return 0;
+                        need_reset = true;
                 }
         }
 
@@ -2220,6 +2215,18 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
                 ixgbe_write_eitr(q_vector);
         }
 
+        /*
+         * do reset here at the end to make sure EITR==0 case is handled
+         * correctly w.r.t stopping tx, and changing TXDCTL.WTHRESH settings
+         * also locks in RSC enable/disable which requires reset
+         */
+        if (need_reset) {
+                if (netif_running(netdev))
+                        ixgbe_reinit_locked(adapter);
+                else
+                        ixgbe_reset(adapter);
+        }
+
         return 0;
 }
 
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);
         }