e1000e: Set InterruptThrottleRate to default when invalid value used

During module load, seting the InterruptThrottleRate parameter to an
invalid value would result in the itr/itr_setting pair being set to
unexpected values which would result in poor performance.
Signed-off-by: NBruce Allan <bruce.w.allan@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/net/e1000e/param.c

@@ -327,11 +327,26 @@ void __devinit e1000e_check_options(struct e1000_adapter *adapter)
 				e1000_validate_option(&adapter->itr, &opt,
 					adapter);
 				/*
-				 * save the setting, because the dynamic bits
-				 * change itr. clear the lower two bits
-				 * because they are used as control
+				 * Save the setting, because the dynamic bits
+				 * change itr.
 				 */
-				adapter->itr_setting = adapter->itr & ~3;
+				if (e1000_validate_option(&adapter->itr, &opt,
+							  adapter) &&
+				    (adapter->itr == 3)) {
+					/*
+					 * In case of invalid user value,
+					 * default to conservative mode.
+					 */
+					adapter->itr_setting = adapter->itr;
+					adapter->itr = 20000;
+				} else {
+					/*
+					 * Clear the lower two bits because
+					 * they are used as control.
+					 */
+					adapter->itr_setting =
+						adapter->itr & ~3;
+				}
 				break;
 			}
 		} else {