cpuidle: Add cpuidle.governor= command line parameter

commit 61cb5758d3c46bc1ba87694fefc0d9653613ce6b upstream

Add cpuidle.governor= command line parameter to allow the default
cpuidle governor to be replaced.

That is useful, for example, if someone running a tickful kernel
wants to use the menu governor on it.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: NYihao Wu <wuyihao@linux.alibaba.com>
Acked-by: NMichael Wang <yun.wang@linux.alibaba.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -677,6 +677,9 @@
 	cpuidle.off=1	[CPU_IDLE]
 			disable the cpuidle sub-system
 
+	cpuidle.governor=
+			[CPU_IDLE] Name of the cpuidle governor to use.
+
 	cpufreq.off=1	[CPU_FREQ]
 			disable the cpufreq sub-system
 

drivers/cpuidle/cpuidle.c

@@ -702,4 +702,5 @@ static int __init cpuidle_init(void)
 }
 
 module_param(off, int, 0444);
+module_param_string(governor, param_governor, CPUIDLE_NAME_LEN, 0444);
 core_initcall(cpuidle_init);

drivers/cpuidle/cpuidle.h

@@ -7,6 +7,7 @@
 #define __DRIVER_CPUIDLE_H
 
 /* For internal use only */
+extern char param_governor[];
 extern struct cpuidle_governor *cpuidle_curr_governor;
 extern struct list_head cpuidle_governors;
 extern struct list_head cpuidle_detected_devices;

drivers/cpuidle/governor.c

@@ -11,10 +11,13 @@
 #include <linux/cpu.h>
 #include <linux/cpuidle.h>
 #include <linux/mutex.h>
+#include <linux/module.h>
 #include <linux/pm_qos.h>
 
 #include "cpuidle.h"
 
+char param_governor[CPUIDLE_NAME_LEN];
+
 LIST_HEAD(cpuidle_governors);
 struct cpuidle_governor *cpuidle_curr_governor;
 
@@ -86,9 +89,11 @@ int cpuidle_register_governor(struct cpuidle_governor *gov)
 	mutex_lock(&cpuidle_lock);
 	if (__cpuidle_find_governor(gov->name) == NULL) {
 		ret = 0;
-		list_add_tail(&gov->governor_list, &cpuidle_governors);
 		if (!cpuidle_curr_governor ||
-		    cpuidle_curr_governor->rating < gov->rating)
+		    !strncasecmp(param_governor, gov->name, CPUIDLE_NAME_LEN) ||
+		    (cpuidle_curr_governor->rating < gov->rating &&
+		     strncasecmp(param_governor, cpuidle_curr_governor->name,
+				 CPUIDLE_NAME_LEN)))
 			cpuidle_switch_governor(gov);
 	}
 	mutex_unlock(&cpuidle_lock);