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>

1 files changed, 18 insertions, 11 deletions

diff --git a/drivers/net/ethernet/intel/igbvf/ethtool.c b/drivers/net/ethernet/intel/igbvf/ethtool.c
index 8ce67064b9c5..90eef07943f4 100644
--- 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);