igbvf: fix divide by zero

Using ethtool -C ethX rx-usecs 0 crashes with a divide by zero.
Refactor this function to fix this issue and make it more clear
what the intent of each conditional is. Add comment regarding
using a setting of zero.

CC: stable <stable@vger.kernel.org> [3.3+]
CC: David Ahern <daahern@cisco.com>
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/intel/igbvf/ethtool.c b/drivers/net/ethernet/intel/igbvf/ethtool.c
index 8ce6706..90eef07 100644 (file)
--- a/drivers/net/ethernet/intel/igbvf/ethtool.c
+++ b/drivers/net/ethernet/intel/igbvf/ethtool.c
@@ -357,21 +357,28 @@ static int igbvf_set_coalesce(struct net_device *netdev,
        struct igbvf_adapter *adapter = netdev_priv(netdev);
        struct e1000_hw *hw = &adapter->hw;
 
-       if ((ec->rx_coalesce_usecs > IGBVF_MAX_ITR_USECS) ||
-           ((ec->rx_coalesce_usecs > 3) &&
-            (ec->rx_coalesce_usecs < IGBVF_MIN_ITR_USECS)) ||
-           (ec->rx_coalesce_usecs == 2))
-               return -EINVAL;
-
-       /* convert to rate of irq's per second */
-       if (ec->rx_coalesce_usecs && ec->rx_coalesce_usecs <= 3) {
+       if ((ec->rx_coalesce_usecs >= IGBVF_MIN_ITR_USECS) &&
+            (ec->rx_coalesce_usecs <= IGBVF_MAX_ITR_USECS)) {
+               adapter->current_itr = ec->rx_coalesce_usecs << 2;
+               adapter->requested_itr = 1000000000 /
+                                       (adapter->current_itr * 256);
+       } else if ((ec->rx_coalesce_usecs == 3) ||
+                  (ec->rx_coalesce_usecs == 2)) {
                adapter->current_itr = IGBVF_START_ITR;
                adapter->requested_itr = ec->rx_coalesce_usecs;
-       } else {
-               adapter->current_itr = ec->rx_coalesce_usecs << 2;
+       } else if (ec->rx_coalesce_usecs == 0) {
+               /*
+                * The user's desire is to turn off interrupt throttling
+                * altogether, but due to HW limitations, we can't do that.
+                * Instead we set a very small value in EITR, which would
+                * allow ~967k interrupts per second, but allow the adapter's
+                * internal clocking to still function properly.
+                */
+               adapter->current_itr = 4;
                adapter->requested_itr = 1000000000 /
                                        (adapter->current_itr * 256);
-       }
+       } else
+               return -EINVAL;
 
        writel(adapter->current_itr,
               hw->hw_addr + adapter->rx_ring->itr_register);