cpufreq / Longhaul: Disable driver by default

This is only solution I can think of. User decides if he wants this
driver on his machine. I don't have enough knowledge and time to find
the reason why same code works on some machines and doesn't on others
which use the same, or very similar, chipset and processor.
Signed-off-by: Rafał Bilski <rafalbilski@interia.pl>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/longhaul.c

@@ -77,7 +77,7 @@ static unsigned int longhaul_index;
 static int scale_voltage;
 static int disable_acpi_c3;
 static int revid_errata;
-
+static int enable;
 
 /* Clock ratios multiplied by 10 */
 static int mults[32];
@@ -965,6 +965,10 @@ static int __init longhaul_init(void)
 	if (!x86_match_cpu(longhaul_id))
 		return -ENODEV;
 
+	if (!enable) {
+		printk(KERN_ERR PFX "Option \"enable\" not set. Aborting.\n");
+		return -ENODEV;
+	}
 #ifdef CONFIG_SMP
 	if (num_online_cpus() > 1) {
 		printk(KERN_ERR PFX "More than 1 CPU detected, "
@@ -1021,6 +1025,10 @@ MODULE_PARM_DESC(scale_voltage, "Scale voltage of processor");
  * such. */
 module_param(revid_errata, int, 0644);
 MODULE_PARM_DESC(revid_errata, "Ignore CPU Revision ID");
+/* By default driver is disabled to prevent incompatible
+ * system freeze. */
+module_param(enable, int, 0644);
+MODULE_PARM_DESC(enable, "Enable driver");
 
 MODULE_AUTHOR("Dave Jones <davej@redhat.com>");
 MODULE_DESCRIPTION("Longhaul driver for VIA Cyrix processors.");