UBUNTU: SAUCE: (no-up) Allow filtering of cpufreq drivers

Harmless patch that allows k8 powernow machines to boot. Carry until
conflict.

BugLink: http://bugs.launchpad.net/bugs/984288Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Herton Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

Documentation/kernel-parameters.txt

@@ -750,6 +750,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			/proc/<pid>/coredump_filter.
 			See also Documentation/filesystems/proc.txt.
 
+	cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
+			to register. Example: cpufreq_driver=powernow-k8
+			Format: { none | STRING }
+
 	cpuidle.off=1	[CPU_IDLE]
 			disable the cpuidle sub-system
 

drivers/cpufreq/cpufreq.c

@@ -2392,6 +2392,20 @@ EXPORT_SYMBOL_GPL(cpufreq_boost_enabled);
  *               REGISTER / UNREGISTER CPUFREQ DRIVER                *
  *********************************************************************/
 
+static char cpufreq_driver_name[CPUFREQ_NAME_LEN];
+
+static int __init cpufreq_driver_setup(char *str)
+{
+	strlcpy(cpufreq_driver_name, str, CPUFREQ_NAME_LEN);
+	return 1;
+}
+
+/*
+ * Set this name to only allow one specific cpu freq driver, e.g.,
+ * cpufreq_driver=powernow-k8
+ */
+__setup("cpufreq_driver=", cpufreq_driver_setup);
+
 /**
  * cpufreq_register_driver - register a CPU Frequency driver
  * @driver_data: A struct cpufreq_driver containing the values#
@@ -2418,7 +2432,13 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	     (!!driver_data->get_intermediate != !!driver_data->target_intermediate))
 		return -EINVAL;
 
-	pr_debug("trying to register driver %s\n", driver_data->name);
+	pr_debug("trying to register driver %s, cpufreq_driver=%s\n",
+		driver_data->name, cpufreq_driver_name);
+
+	if (cpufreq_driver_name[0])
+		if (!driver_data->name ||
+			strcmp(cpufreq_driver_name, driver_data->name))
+				return -EINVAL;
 
 	/* Protect against concurrent CPU online/offline. */
 	get_online_cpus();