Merge branch 'pm-devfreq'

* pm-devfreq: (23 commits)
  PM / devfreq: remove compiler error with module governors (2)
  PM / devfreq: Fix return value in devfreq_remove_governor()
  PM / devfreq: Fix incorrect argument in error message
  PM / devfreq: missing rcu_read_lock() added for find_device_opp()
  PM / devfreq: remove compiler error when a governor is module
  PM / devfreq: exynos4_bus.c: Fixed an alignment of the func call args.
  PM / devfreq: Add sysfs node to expose available governors
  PM / devfreq: allow sysfs governor node to switch governor
  PM / devfreq: governors: add GPL module license and allow module build
  PM / devfreq: map devfreq drivers to governor using name
  PM / devfreq: register governors with devfreq framework
  PM / devfreq: provide hooks for governors to be registered
  PM / devfreq: export update_devfreq
  PM / devfreq: Add sysfs node for representing frequency transition information.
  PM / devfreq: Add sysfs node to expose available frequencies
  PM / devfreq: documentation cleanups for devfreq header
  PM / devfreq: Use devm_* functions in exynos4_bus.c
  PM / devfreq: make devfreq_class static
  PM / devfreq: fix sscanf handling for writable sysfs entries
  PM / devfreq: kernel-doc typo corrections
  ...

8 files changed, 835 insertions, 328 deletions

diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
index f6b0a6e2ea5..0f079be1330 100644
--- a/drivers/devfreq/Kconfig
+++ b/drivers/devfreq/Kconfig
@@ -30,7 +30,7 @@ if PM_DEVFREQ
 comment "DEVFREQ Governors"
 
 config DEVFREQ_GOV_SIMPLE_ONDEMAND
-	bool "Simple Ondemand"
+	tristate "Simple Ondemand"
 	help
 	  Chooses frequency based on the recent load on the device. Works
 	  similar as ONDEMAND governor of CPUFREQ does. A device with
@@ -39,7 +39,7 @@ config DEVFREQ_GOV_SIMPLE_ONDEMAND
 	  values to the governor with data field at devfreq_add_device().
 
 config DEVFREQ_GOV_PERFORMANCE
-	bool "Performance"
+	tristate "Performance"
 	help
 	  Sets the frequency at the maximum available frequency.
 	  This governor always returns UINT_MAX as frequency so that
@@ -47,7 +47,7 @@ config DEVFREQ_GOV_PERFORMANCE
 	  at any time.
 
 config DEVFREQ_GOV_POWERSAVE
-	bool "Powersave"
+	tristate "Powersave"
 	help
 	  Sets the frequency at the minimum available frequency.
 	  This governor always returns 0 as frequency so that
@@ -55,7 +55,7 @@ config DEVFREQ_GOV_POWERSAVE
 	  at any time.
 
 config DEVFREQ_GOV_USERSPACE
-	bool "Userspace"
+	tristate "Userspace"
 	help
 	  Sets the frequency at the user specified one.
 	  This governor returns the user configured frequency if there
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 4fa1a22c55e..53766f39aad 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -27,21 +27,17 @@
 #include <linux/hrtimer.h>
 #include "governor.h"
 
-struct class *devfreq_class;
+static struct class *devfreq_class;
 
 /*
- * devfreq_work periodically monitors every registered device.
- * The minimum polling interval is one jiffy. The polling interval is
- * determined by the minimum polling period among all polling devfreq
- * devices. The resolution of polling interval is one jiffy.
+ * devfreq core provides delayed work based load monitoring helper
+ * functions. Governors can use these or can implement their own
+ * monitoring mechanism.
  */
-static bool polling;
 static struct workqueue_struct *devfreq_wq;
-static struct delayed_work devfreq_work;
-
-/* wait removing if this is to be removed */
-static struct devfreq *wait_remove_device;
 
+/* The list of all device-devfreq governors */
+static LIST_HEAD(devfreq_governor_list);
 /* The list of all device-devfreq */
 static LIST_HEAD(devfreq_list);
 static DEFINE_MUTEX(devfreq_list_lock);
@@ -73,6 +69,79 @@ static struct devfreq *find_device_devfreq(struct device *dev)
 }
 
 /**
+ * devfreq_get_freq_level() - Lookup freq_table for the frequency
+ * @devfreq:	the devfreq instance
+ * @freq:	the target frequency
+ */
+static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
+{
+	int lev;
+
+	for (lev = 0; lev < devfreq->profile->max_state; lev++)
+		if (freq == devfreq->profile->freq_table[lev])
+			return lev;
+
+	return -EINVAL;
+}
+
+/**
+ * devfreq_update_status() - Update statistics of devfreq behavior
+ * @devfreq:	the devfreq instance
+ * @freq:	the update target frequency
+ */
+static int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
+{
+	int lev, prev_lev;
+	unsigned long cur_time;
+
+	lev = devfreq_get_freq_level(devfreq, freq);
+	if (lev < 0)
+		return lev;
+
+	cur_time = jiffies;
+	devfreq->time_in_state[lev] +=
+			 cur_time - devfreq->last_stat_updated;
+	if (freq != devfreq->previous_freq) {
+		prev_lev = devfreq_get_freq_level(devfreq,
+						devfreq->previous_freq);
+		devfreq->trans_table[(prev_lev *
+				devfreq->profile->max_state) + lev]++;
+		devfreq->total_trans++;
+	}
+	devfreq->last_stat_updated = cur_time;
+
+	return 0;
+}
+
+/**
+ * find_devfreq_governor() - find devfreq governor from name
+ * @name:	name of the governor
+ *
+ * Search the list of devfreq governors and return the matched
+ * governor's pointer. devfreq_list_lock should be held by the caller.
+ */
+static struct devfreq_governor *find_devfreq_governor(const char *name)
+{
+	struct devfreq_governor *tmp_governor;
+
+	if (unlikely(IS_ERR_OR_NULL(name))) {
+		pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
+		return ERR_PTR(-EINVAL);
+	}
+	WARN(!mutex_is_locked(&devfreq_list_lock),
+	     "devfreq_list_lock must be locked.");
+
+	list_for_each_entry(tmp_governor, &devfreq_governor_list, node) {
+		if (!strncmp(tmp_governor->name, name, DEVFREQ_NAME_LEN))
+			return tmp_governor;
+	}
+
+	return ERR_PTR(-ENODEV);
+}
+
+/* Load monitoring helper functions for governors use */
+
+/**
  * update_devfreq() - Reevaluate the device and configure frequency.
  * @devfreq:	the devfreq instance.
  *
@@ -90,6 +159,9 @@ int update_devfreq(struct devfreq *devfreq)
 		return -EINVAL;
 	}
 
+	if (!devfreq->governor)
+		return -EINVAL;
+
 	/* Reevaluate the proper frequency */
 	err = devfreq->governor->get_target_freq(devfreq, &freq);
 	if (err)
@@ -116,16 +188,173 @@ int update_devfreq(struct devfreq *devfreq)
 	if (err)
 		return err;
 
+	if (devfreq->profile->freq_table)
+		if (devfreq_update_status(devfreq, freq))
+			dev_err(&devfreq->dev,
+				"Couldn't update frequency transition information.\n");
+
 	devfreq->previous_freq = freq;
 	return err;
 }
+EXPORT_SYMBOL(update_devfreq);
+
+/**
+ * devfreq_monitor() - Periodically poll devfreq objects.
+ * @work:	the work struct used to run devfreq_monitor periodically.
+ *
+ */
+static void devfreq_monitor(struct work_struct *work)
+{
+	int err;
+	struct devfreq *devfreq = container_of(work,
+					struct devfreq, work.work);
+
+	mutex_lock(&devfreq->lock);
+	err = update_devfreq(devfreq);
+	if (err)
+		dev_err(&devfreq->dev, "dvfs failed with (%d) error\n", err);
+
+	queue_delayed_work(devfreq_wq, &devfreq->work,
+				msecs_to_jiffies(devfreq->profile->polling_ms));
+	mutex_unlock(&devfreq->lock);
+}
+
+/**
+ * devfreq_monitor_start() - Start load monitoring of devfreq instance
+ * @devfreq:	the devfreq instance.
+ *
+ * Helper function for starting devfreq device load monitoing. By
+ * default delayed work based monitoring is supported. Function
+ * to be called from governor in response to DEVFREQ_GOV_START
+ * event when device is added to devfreq framework.
+ */
+void devfreq_monitor_start(struct devfreq *devfreq)
+{
+	INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
+	if (devfreq->profile->polling_ms)
+		queue_delayed_work(devfreq_wq, &devfreq->work,
+			msecs_to_jiffies(devfreq->profile->polling_ms));
+}
+EXPORT_SYMBOL(devfreq_monitor_start);
+
+/**
+ * devfreq_monitor_stop() - Stop load monitoring of a devfreq instance
+ * @devfreq:	the devfreq instance.
+ *
+ * Helper function to stop devfreq device load monitoing. Function
+ * to be called from governor in response to DEVFREQ_GOV_STOP
+ * event when device is removed from devfreq framework.
+ */
+void devfreq_monitor_stop(struct devfreq *devfreq)
+{
+	cancel_delayed_work_sync(&devfreq->work);
+}
+EXPORT_SYMBOL(devfreq_monitor_stop);
+
+/**
+ * devfreq_monitor_suspend() - Suspend load monitoring of a devfreq instance
+ * @devfreq:	the devfreq instance.
+ *
+ * Helper function to suspend devfreq device load monitoing. Function
+ * to be called from governor in response to DEVFREQ_GOV_SUSPEND
+ * event or when polling interval is set to zero.
+ *
+ * Note: Though this function is same as devfreq_monitor_stop(),
+ * intentionally kept separate to provide hooks for collecting
+ * transition statistics.
+ */
+void devfreq_monitor_suspend(struct devfreq *devfreq)
+{
+	mutex_lock(&devfreq->lock);
+	if (devfreq->stop_polling) {
+		mutex_unlock(&devfreq->lock);
+		return;
+	}
+
+	devfreq->stop_polling = true;
+	mutex_unlock(&devfreq->lock);
+	cancel_delayed_work_sync(&devfreq->work);
+}
+EXPORT_SYMBOL(devfreq_monitor_suspend);
+
+/**
+ * devfreq_monitor_resume() - Resume load monitoring of a devfreq instance
+ * @devfreq:    the devfreq instance.
+ *
+ * Helper function to resume devfreq device load monitoing. Function
+ * to be called from governor in response to DEVFREQ_GOV_RESUME
+ * event or when polling interval is set to non-zero.
+ */
+void devfreq_monitor_resume(struct devfreq *devfreq)
+{
+	mutex_lock(&devfreq->lock);
+	if (!devfreq->stop_polling)
+		goto out;
+
+	if (!delayed_work_pending(&devfreq->work) &&
+			devfreq->profile->polling_ms)
+		queue_delayed_work(devfreq_wq, &devfreq->work,
+			msecs_to_jiffies(devfreq->profile->polling_ms));
+	devfreq->stop_polling = false;
+
+out:
+	mutex_unlock(&devfreq->lock);
+}
+EXPORT_SYMBOL(devfreq_monitor_resume);
+
+/**
+ * devfreq_interval_update() - Update device devfreq monitoring interval
+ * @devfreq:    the devfreq instance.
+ * @delay:      new polling interval to be set.
+ *
+ * Helper function to set new load monitoring polling interval. Function
+ * to be called from governor in response to DEVFREQ_GOV_INTERVAL event.
+ */
+void devfreq_interval_update(struct devfreq *devfreq, unsigned int *delay)
+{
+	unsigned int cur_delay = devfreq->profile->polling_ms;
+	unsigned int new_delay = *delay;
+
+	mutex_lock(&devfreq->lock);
+	devfreq->profile->polling_ms = new_delay;
+
+	if (devfreq->stop_polling)
+		goto out;
+
+	/* if new delay is zero, stop polling */
+	if (!new_delay) {
+		mutex_unlock(&devfreq->lock);
+		cancel_delayed_work_sync(&devfreq->work);
+		return;
+	}
+
+	/* if current delay is zero, start polling with new delay */
+	if (!cur_delay) {
+		queue_delayed_work(devfreq_wq, &devfreq->work,
+			msecs_to_jiffies(devfreq->profile->polling_ms));
+		goto out;
+	}
+
+	/* if current delay is greater than new delay, restart polling */
+	if (cur_delay > new_delay) {
+		mutex_unlock(&devfreq->lock);
+		cancel_delayed_work_sync(&devfreq->work);
+		mutex_lock(&devfreq->lock);
+		if (!devfreq->stop_polling)
+			queue_delayed_work(devfreq_wq, &devfreq->work,
+			      msecs_to_jiffies(devfreq->profile->polling_ms));
+	}
+out:
+	mutex_unlock(&devfreq->lock);
+}
+EXPORT_SYMBOL(devfreq_interval_update);
 
 /**
  * devfreq_notifier_call() - Notify that the device frequency requirements
  *			   has been changed out of devfreq framework.
- * @nb		the notifier_block (supposed to be devfreq->nb)
- * @type	not used
- * @devp	not used
+ * @nb:		the notifier_block (supposed to be devfreq->nb)
+ * @type:	not used
+ * @devp:	not used
  *
  * Called by a notifier that uses devfreq->nb.
  */
@@ -143,59 +372,34 @@ static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
 }
 
 /**
- * _remove_devfreq() - Remove devfreq from the device.
+ * _remove_devfreq() - Remove devfreq from the list and release its resources.
  * @devfreq:	the devfreq struct
  * @skip:	skip calling device_unregister().
- *
- * Note that the caller should lock devfreq->lock before calling
- * this. _remove_devfreq() will unlock it and free devfreq
- * internally. devfreq_list_lock should be locked by the caller
- * as well (not relased at return)
- *
- * Lock usage:
- * devfreq->lock: locked before call.
- *		  unlocked at return (and freed)
- * devfreq_list_lock: locked before call.
- *		      kept locked at return.
- *		      if devfreq is centrally polled.
- *
- * Freed memory:
- * devfreq
  */
 static void _remove_devfreq(struct devfreq *devfreq, bool skip)
 {
-	if (!mutex_is_locked(&devfreq->lock)) {
-		WARN(true, "devfreq->lock must be locked by the caller.\n");
-		return;
-	}
-	if (!devfreq->governor->no_central_polling &&
-	    !mutex_is_locked(&devfreq_list_lock)) {
-		WARN(true, "devfreq_list_lock must be locked by the caller.\n");
+	mutex_lock(&devfreq_list_lock);
+	if (IS_ERR(find_device_devfreq(devfreq->dev.parent))) {
+		mutex_unlock(&devfreq_list_lock);
+		dev_warn(&devfreq->dev, "releasing devfreq which doesn't exist\n");
 		return;
 	}
+	list_del(&devfreq->node);
+	mutex_unlock(&devfreq_list_lock);
 
-	if (devfreq->being_removed)
-		return;
-
-	devfreq->being_removed = true;
+	if (devfreq->governor)
+		devfreq->governor->event_handler(devfreq,
+						 DEVFREQ_GOV_STOP, NULL);
 
 	if (devfreq->profile->exit)
 		devfreq->profile->exit(devfreq->dev.parent);
 
-	if (devfreq->governor->exit)
-		devfreq->governor->exit(devfreq);
-
 	if (!skip && get_device(&devfreq->dev)) {
 		device_unregister(&devfreq->dev);
 		put_device(&devfreq->dev);
 	}
 
-	if (!devfreq->governor->no_central_polling)
-		list_del(&devfreq->node);
-
-	mutex_unlock(&devfreq->lock);
 	mutex_destroy(&devfreq->lock);
-
 	kfree(devfreq);
 }
 
@@ -210,163 +414,39 @@ static void _remove_devfreq(struct devfreq *devfreq, bool skip)
 static void devfreq_dev_release(struct device *dev)
 {
 	struct devfreq *devfreq = to_devfreq(dev);
-	bool central_polling = !devfreq->governor->no_central_polling;
-
-	/*
-	 * If devfreq_dev_release() was called by device_unregister() of
-	 * _remove_devfreq(), we cannot mutex_lock(&devfreq->lock) and
-	 * being_removed is already set. This also partially checks the case
-	 * where devfreq_dev_release() is called from a thread other than
-	 * the one called _remove_devfreq(); however, this case is
-	 * dealt completely with another following being_removed check.
-	 *
-	 * Because being_removed is never being
-	 * unset, we do not need to worry about race conditions on
-	 * being_removed.
-	 */
-	if (devfreq->being_removed)
-		return;
-
-	if (central_polling)
-		mutex_lock(&devfreq_list_lock);
-
-	mutex_lock(&devfreq->lock);
 
-	/*
-	 * Check being_removed flag again for the case where
-	 * devfreq_dev_release() was called in a thread other than the one
-	 * possibly called _remove_devfreq().
-	 */
-	if (devfreq->being_removed) {
-		mutex_unlock(&devfreq->lock);
-		goto out;
-	}
-
-	/* devfreq->lock is unlocked and removed in _removed_devfreq() */
 	_remove_devfreq(devfreq, true);
-
-out:
-	if (central_polling)
-		mutex_unlock(&devfreq_list_lock);
-}
-
-/**
- * devfreq_monitor() - Periodically poll devfreq objects.
- * @work: the work struct used to run devfreq_monitor periodically.
- *
- */
-static void devfreq_monitor(struct work_struct *work)
-{
-	static unsigned long last_polled_at;
-	struct devfreq *devfreq, *tmp;
-	int error;
-	unsigned long jiffies_passed;
-	unsigned long next_jiffies = ULONG_MAX, now = jiffies;
-	struct device *dev;
-
-	/* Initially last_polled_at = 0, polling every device at bootup */
-	jiffies_passed = now - last_polled_at;
-	last_polled_at = now;
-	if (jiffies_passed == 0)
-		jiffies_passed = 1;
-
-	mutex_lock(&devfreq_list_lock);
-	list_for_each_entry_safe(devfreq, tmp, &devfreq_list, node) {
-		mutex_lock(&devfreq->lock);
-		dev = devfreq->dev.parent;
-
-		/* Do not remove tmp for a while */
-		wait_remove_device = tmp;
-
-		if (devfreq->governor->no_central_polling ||
-		    devfreq->next_polling == 0) {
-			mutex_unlock(&devfreq->lock);
-			continue;
-		}
-		mutex_unlock(&devfreq_list_lock);
-
-		/*
-		 * Reduce more next_polling if devfreq_wq took an extra
-		 * delay. (i.e., CPU has been idled.)
-		 */
-		if (devfreq->next_polling <= jiffies_passed) {
-			error = update_devfreq(devfreq);
-
-			/* Remove a devfreq with an error. */
-			if (error && error != -EAGAIN) {
-
-				dev_err(dev, "Due to update_devfreq error(%d), devfreq(%s) is removed from the device\n",
-					error, devfreq->governor->name);
-
-				/*
-				 * Unlock devfreq before locking the list
-				 * in order to avoid deadlock with
-				 * find_device_devfreq or others
-				 */
-				mutex_unlock(&devfreq->lock);
-				mutex_lock(&devfreq_list_lock);
-				/* Check if devfreq is already removed */
-				if (IS_ERR(find_device_devfreq(dev)))
-					continue;
-				mutex_lock(&devfreq->lock);
-				/* This unlocks devfreq->lock and free it */
-				_remove_devfreq(devfreq, false);
-				continue;
-			}
-			devfreq->next_polling = devfreq->polling_jiffies;
-		} else {
-			devfreq->next_polling -= jiffies_passed;
-		}
-
-		if (devfreq->next_polling)
-			next_jiffies = (next_jiffies > devfreq->next_polling) ?
-					devfreq->next_polling : next_jiffies;
-
-		mutex_unlock(&devfreq->lock);
-		mutex_lock(&devfreq_list_lock);
-	}
-	wait_remove_device = NULL;
-	mutex_unlock(&devfreq_list_lock);
-
-	if (next_jiffies > 0 && next_jiffies < ULONG_MAX) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work, next_jiffies);
-	} else {
-		polling = false;
-	}
 }
 
 /**
  * devfreq_add_device() - Add devfreq feature to the device
  * @dev:	the device to add devfreq feature.
  * @profile:	device-specific profile to run devfreq.
- * @governor:	the policy to choose frequency.
+ * @governor_name:	name of the policy to choose frequency.
  * @data:	private data for the governor. The devfreq framework does not
  *		touch this value.
  */
 struct devfreq *devfreq_add_device(struct device *dev,
 				   struct devfreq_dev_profile *profile,
-				   const struct devfreq_governor *governor,
+				   const char *governor_name,
 				   void *data)
 {
 	struct devfreq *devfreq;
+	struct devfreq_governor *governor;
 	int err = 0;
 
-	if (!dev || !profile || !governor) {
+	if (!dev || !profile || !governor_name) {
 		dev_err(dev, "%s: Invalid parameters.\n", __func__);
 		return ERR_PTR(-EINVAL);
 	}
 
-
-	if (!governor->no_central_polling) {
-		mutex_lock(&devfreq_list_lock);
-		devfreq = find_device_devfreq(dev);
-		mutex_unlock(&devfreq_list_lock);
-		if (!IS_ERR(devfreq)) {
-			dev_err(dev, "%s: Unable to create devfreq for the device. It already has one.\n", __func__);
-			err = -EINVAL;
-			goto err_out;
-		}
+	mutex_lock(&devfreq_list_lock);
+	devfreq = find_device_devfreq(dev);
+	mutex_unlock(&devfreq_list_lock);
+	if (!IS_ERR(devfreq)) {
+		dev_err(dev, "%s: Unable to create devfreq for the device. It already has one.\n", __func__);
+		err = -EINVAL;
+		goto err_out;
 	}
 
 	devfreq = kzalloc(sizeof(struct devfreq), GFP_KERNEL);
@@ -383,92 +463,316 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	devfreq->dev.class = devfreq_class;
 	devfreq->dev.release = devfreq_dev_release;
 	devfreq->profile = profile;
-	devfreq->governor = governor;
+	strncpy(devfreq->governor_name, governor_name, DEVFREQ_NAME_LEN);
 	devfreq->previous_freq = profile->initial_freq;
 	devfreq->data = data;
-	devfreq->next_polling = devfreq->polling_jiffies
-			      = msecs_to_jiffies(devfreq->profile->polling_ms);
 	devfreq->nb.notifier_call = devfreq_notifier_call;
 
+	devfreq->trans_table =	devm_kzalloc(dev, sizeof(unsigned int) *
+						devfreq->profile->max_state *
+						devfreq->profile->max_state,
+						GFP_KERNEL);
+	devfreq->time_in_state = devm_kzalloc(dev, sizeof(unsigned int) *
+						devfreq->profile->max_state,
+						GFP_KERNEL);
+	devfreq->last_stat_updated = jiffies;
+
 	dev_set_name(&devfreq->dev, dev_name(dev));
 	err = device_register(&devfreq->dev);
 	if (err) {
 		put_device(&devfreq->dev);
+		mutex_unlock(&devfreq->lock);
 		goto err_dev;
 	}
 
-	if (governor->init)
-		err = governor->init(devfreq);
-	if (err)
-		goto err_init;
-
 	mutex_unlock(&devfreq->lock);
 
-	if (governor->no_central_polling)
-		goto out;
-
 	mutex_lock(&devfreq_list_lock);
-
 	list_add(&devfreq->node, &devfreq_list);
 
-	if (devfreq_wq && devfreq->next_polling && !polling) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work,
-				   devfreq->next_polling);
-	}
+	governor = find_devfreq_governor(devfreq->governor_name);
+	if (!IS_ERR(governor))
+		devfreq->governor = governor;
+	if (devfreq->governor)
+		err = devfreq->governor->event_handler(devfreq,
+					DEVFREQ_GOV_START, NULL);
 	mutex_unlock(&devfreq_list_lock);
-out:
+	if (err) {
+		dev_err(dev, "%s: Unable to start governor for the device\n",
+			__func__);
+		goto err_init;
+	}
+
 	return devfreq;
 
 err_init:
+	list_del(&devfreq->node);
 	device_unregister(&devfreq->dev);
 err_dev:
-	mutex_unlock(&devfreq->lock);
 	kfree(devfreq);
 err_out:
 	return ERR_PTR(err);
 }
+EXPORT_SYMBOL(devfreq_add_device);
 
 /**
  * devfreq_remove_device() - Remove devfreq feature from a device.
- * @devfreq	the devfreq instance to be removed
+ * @devfreq:	the devfreq instance to be removed
  */
 int devfreq_remove_device(struct devfreq *devfreq)
 {
-	bool central_polling;
+	if (!devfreq)
+		return -EINVAL;
+
+	_remove_devfreq(devfreq, false);
 
+	return 0;
+}
+EXPORT_SYMBOL(devfreq_remove_device);
+
+/**
+ * devfreq_suspend_device() - Suspend devfreq of a device.
+ * @devfreq: the devfreq instance to be suspended
+ */
+int devfreq_suspend_device(struct devfreq *devfreq)
+{
 	if (!devfreq)
 		return -EINVAL;
 
-	central_polling = !devfreq->governor->no_central_polling;
+	if (!devfreq->governor)
+		return 0;
+
+	return devfreq->governor->event_handler(devfreq,
+				DEVFREQ_GOV_SUSPEND, NULL);
+}
+EXPORT_SYMBOL(devfreq_suspend_device);
+
+/**
+ * devfreq_resume_device() - Resume devfreq of a device.
+ * @devfreq: the devfreq instance to be resumed
+ */
+int devfreq_resume_device(struct devfreq *devfreq)
+{
+	if (!devfreq)
+		return -EINVAL;
+
+	if (!devfreq->governor)
+		return 0;
+
+	return devfreq->governor->event_handler(devfreq,
+				DEVFREQ_GOV_RESUME, NULL);
+}
+EXPORT_SYMBOL(devfreq_resume_device);
+
+/**
+ * devfreq_add_governor() - Add devfreq governor
+ * @governor:	the devfreq governor to be added
+ */
+int devfreq_add_governor(struct devfreq_governor *governor)
+{
+	struct devfreq_governor *g;
+	struct devfreq *devfreq;
+	int err = 0;
+
+	if (!governor) {
+		pr_err("%s: Invalid parameters.\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&devfreq_list_lock);
+	g = find_devfreq_governor(governor->name);
+	if (!IS_ERR(g)) {
+		pr_err("%s: governor %s already registered\n", __func__,
+		       g->name);
+		err = -EINVAL;
+		goto err_out;
+	}
 
-	if (central_polling) {
-		mutex_lock(&devfreq_list_lock);
-		while (wait_remove_device == devfreq) {
-			mutex_unlock(&devfreq_list_lock);
-			schedule();
-			mutex_lock(&devfreq_list_lock);
+	list_add(&governor->node, &devfreq_governor_list);
+
+	list_for_each_entry(devfreq, &devfreq_list, node) {
+		int ret = 0;
+		struct device *dev = devfreq->dev.parent;
+
+		if (!strncmp(devfreq->governor_name, governor->name,
+			     DEVFREQ_NAME_LEN)) {
+			/* The following should never occur */
+			if (devfreq->governor) {
+				dev_warn(dev,
+					 "%s: Governor %s already present\n",
+					 __func__, devfreq->governor->name);
+				ret = devfreq->governor->event_handler(devfreq,
+							DEVFREQ_GOV_STOP, NULL);
+				if (ret) {
+					dev_warn(dev,
+						 "%s: Governor %s stop = %d\n",
+						 __func__,
+						 devfreq->governor->name, ret);
+				}
+				/* Fall through */
+			}
+			devfreq->governor = governor;
+			ret = devfreq->governor->event_handler(devfreq,
+						DEVFREQ_GOV_START, NULL);
+			if (ret) {
+				dev_warn(dev, "%s: Governor %s start=%d\n",
+					 __func__, devfreq->governor->name,
+					 ret);
+			}
 		}
 	}
 
-	mutex_lock(&devfreq->lock);
-	_remove_devfreq(devfreq, false); /* it unlocks devfreq->lock */
+err_out:
+	mutex_unlock(&devfreq_list_lock);
 
-	if (central_polling)
-		mutex_unlock(&devfreq_list_lock);
+	return err;
+}
+EXPORT_SYMBOL(devfreq_add_governor);
 
-	return 0;
+/**
+ * devfreq_remove_device() - Remove devfreq feature from a device.
+ * @governor:	the devfreq governor to be removed
+ */
+int devfreq_remove_governor(struct devfreq_governor *governor)
+{
+	struct devfreq_governor *g;
+	struct devfreq *devfreq;
+	int err = 0;
+
+	if (!governor) {
+		pr_err("%s: Invalid parameters.\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&devfreq_list_lock);
+	g = find_devfreq_governor(governor->name);
+	if (IS_ERR(g)) {
+		pr_err("%s: governor %s not registered\n", __func__,
+		       governor->name);
+		err = PTR_ERR(g);
+		goto err_out;
+	}
+	list_for_each_entry(devfreq, &devfreq_list, node) {
+		int ret;
+		struct device *dev = devfreq->dev.parent;
+
+		if (!strncmp(devfreq->governor_name, governor->name,
+			     DEVFREQ_NAME_LEN)) {
+			/* we should have a devfreq governor! */
+			if (!devfreq->governor) {
+				dev_warn(dev, "%s: Governor %s NOT present\n",
+					 __func__, governor->name);
+				continue;
+				/* Fall through */
+			}
+			ret = devfreq->governor->event_handler(devfreq,
+						DEVFREQ_GOV_STOP, NULL);
+			if (ret) {
+				dev_warn(dev, "%s: Governor %s stop=%d\n",
+					 __func__, devfreq->governor->name,
+					 ret);
+			}
+			devfreq->governor = NULL;
+		}
+	}
+
+	list_del(&governor->node);
+err_out:
+	mutex_unlock(&devfreq_list_lock);
+
+	return err;
 }
+EXPORT_SYMBOL(devfreq_remove_governor);
 
 static ssize_t show_governor(struct device *dev,
 			     struct device_attribute *attr, char *buf)
 {
+	if (!to_devfreq(dev)->governor)
+		return -EINVAL;
+
 	return sprintf(buf, "%s\n", to_devfreq(dev)->governor->name);
 }
 
+static ssize_t store_governor(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct devfreq *df = to_devfreq(dev);
+	int ret;
+	char str_governor[DEVFREQ_NAME_LEN + 1];
+	struct devfreq_governor *governor;
+
+	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
+	if (ret != 1)
+		return -EINVAL;
+
+	mutex_lock(&devfreq_list_lock);
+	governor = find_devfreq_governor(str_governor);
+	if (IS_ERR(governor)) {
+		ret = PTR_ERR(governor);
+		goto out;
+	}
+	if (df->governor == governor)
+		goto out;
+
+	if (df->governor) {
+		ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
+		if (ret) {
+			dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
+				 __func__, df->governor->name, ret);
+			goto out;
+		}
+	}
+	df->governor = governor;
+	strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
+	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
+	if (ret)
+		dev_warn(dev, "%s: Governor %s not started(%d)\n",
+			 __func__, df->governor->name, ret);
+out:
+	mutex_unlock(&devfreq_list_lock);
+
+	if (!ret)
+		ret = count;
+	return ret;
+}
+static ssize_t show_available_governors(struct device *d,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct devfreq_governor *tmp_governor;
+	ssize_t count = 0;
+
+	mutex_lock(&devfreq_list_lock);
+	list_for_each_entry(tmp_governor, &devfreq_governor_list, node)
+		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
+				   "%s ", tmp_governor->name);
+	mutex_unlock(&devfreq_list_lock);
+
+	/* Truncate the trailing space */
+	if (count)
+		count--;
+
+	count += sprintf(&buf[count], "\n");
+
+	return count;
+}
+
 static ssize_t show_freq(struct device *dev,
 			 struct device_attribute *attr, char *buf)
 {
+	unsigned long freq;
+	struct devfreq *devfreq = to_devfreq(dev);
+
+	if (devfreq->profile->get_cur_freq &&
+		!devfreq->profile->get_cur_freq(devfreq->dev.parent, &freq))
+			return sprintf(buf, "%lu\n", freq);
+
+	return sprintf(buf, "%lu\n", devfreq->previous_freq);
+}
+
+static ssize_t show_target_freq(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
 	return sprintf(buf, "%lu\n", to_devfreq(dev)->previous_freq);
 }
 
@@ -486,39 +790,19 @@ static ssize_t store_polling_interval(struct device *dev,
 	unsigned int value;
 	int ret;
 
+	if (!df->governor)
+		return -EINVAL;
+
 	ret = sscanf(buf, "%u", &value);
 	if (ret != 1)
-		goto out;
-
-	mutex_lock(&df->lock);
-	df->profile->polling_ms = value;
-	df->next_polling = df->polling_jiffies
-			 = msecs_to_jiffies(value);
-	mutex_unlock(&df->lock);
+		return -EINVAL;
 
+	df->governor->event_handler(df, DEVFREQ_GOV_INTERVAL, &value);
 	ret = count;
 
-	if (df->governor->no_central_polling)
-		goto out;
-
-	mutex_lock(&devfreq_list_lock);
-	if (df->next_polling > 0 && !polling) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work,
-				   df->next_polling);
-	}
-	mutex_unlock(&devfreq_list_lock);
-out:
 	return ret;
 }
 
-static ssize_t show_central_polling(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	return sprintf(buf, "%d\n",
-		       !to_devfreq(dev)->governor->no_central_polling);
-}
-
 static ssize_t store_min_freq(struct device *dev, struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
@@ -529,7 +813,7 @@ static ssize_t store_min_freq(struct device *dev, struct device_attribute *attr,
 
 	ret = sscanf(buf, "%lu", &value);
 	if (ret != 1)
-		goto out;
+		return -EINVAL;
 
 	mutex_lock(&df->lock);
 	max = df->max_freq;
@@ -543,7 +827,6 @@ static ssize_t store_min_freq(struct device *dev, struct device_attribute *attr,
 	ret = count;
 unlock:
 	mutex_unlock(&df->lock);
-out:
 	return ret;
 }
 
@@ -563,7 +846,7 @@ static ssize_t store_max_freq(struct device *dev, struct device_attribute *attr,
 
 	ret = sscanf(buf, "%lu", &value);
 	if (ret != 1)
-		goto out;
+		return -EINVAL;
 
 	mutex_lock(&df->lock);
 	min = df->min_freq;
@@ -577,7 +860,6 @@ static ssize_t store_max_freq(struct device *dev, struct device_attribute *attr,
 	ret = count;
 unlock:
 	mutex_unlock(&df->lock);
-out:
 	return ret;
 }
 
@@ -587,34 +869,92 @@ static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
 	return sprintf(buf, "%lu\n", to_devfreq(dev)->max_freq);
 }
 
+static ssize_t show_available_freqs(struct device *d,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct devfreq *df = to_devfreq(d);
+	struct device *dev = df->dev.parent;
+	struct opp *opp;
+	ssize_t count = 0;
+	unsigned long freq = 0;
+
+	rcu_read_lock();
+	do {
+		opp = opp_find_freq_ceil(dev, &freq);
+		if (IS_ERR(opp))
+			break;
+
+		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
+				   "%lu ", freq);
+		freq++;
+	} while (1);
+	rcu_read_unlock();
+
+	/* Truncate the trailing space */
+	if (count)
+		count--;
+
+	count += sprintf(&buf[count], "\n");
+
+	return count;
+}
+
+static ssize_t show_trans_table(struct device *dev, struct device_attribute *attr,
+				char *buf)
+{
+	struct devfreq *devfreq = to_devfreq(dev);
+	ssize_t len;
+	int i, j, err;
+	unsigned int max_state = devfreq->profile->max_state;
+
+	err = devfreq_update_status(devfreq, devfreq->previous_freq);
+	if (err)
+		return 0;
+
+	len = sprintf(buf, "   From  :   To\n");
+	len += sprintf(buf + len, "         :");
+	for (i = 0; i < max_state; i++)
+		len += sprintf(buf + len, "%8u",
+				devfreq->profile->freq_table[i]);
+
+	len += sprintf(buf + len, "   time(ms)\n");
+
+	for (i = 0; i < max_state; i++) {
+		if (devfreq->profile->freq_table[i]
+					== devfreq->previous_freq) {
+			len += sprintf(buf + len, "*");
+		} else {
+			len += sprintf(buf + len, " ");
+		}
+		len += sprintf(buf + len, "%8u:",
+				devfreq->profile->freq_table[i]);
+		for (j = 0; j < max_state; j++)
+			len += sprintf(buf + len, "%8u",
+				devfreq->trans_table[(i * max_state) + j]);
+		len += sprintf(buf + len, "%10u\n",
+			jiffies_to_msecs(devfreq->time_in_state[i]));
+	}
+
+	len += sprintf(buf + len, "Total transition : %u\n",
+					devfreq->total_trans);
+	return len;
+}
+
 static struct device_attribute devfreq_attrs[] = {
-	__ATTR(governor, S_IRUGO, show_governor, NULL),
+	__ATTR(governor, S_IRUGO | S_IWUSR, show_governor, store_governor),
+	__ATTR(available_governors, S_IRUGO, show_available_governors, NULL),
 	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
-	__ATTR(central_polling, S_IRUGO, show_central_polling, NULL),
+	__ATTR(available_frequencies, S_IRUGO, show_available_freqs, NULL),
+	__ATTR(target_freq, S_IRUGO, show_target_freq, NULL),
 	__ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
 	       store_polling_interval),
 	__ATTR(min_freq, S_IRUGO | S_IWUSR, show_min_freq, store_min_freq),
 	__ATTR(max_freq, S_IRUGO | S_IWUSR, show_max_freq, store_max_freq),
+	__ATTR(trans_stat, S_IRUGO, show_trans_table, NULL),
 	{ },
 };
 
-/**
- * devfreq_start_polling() - Initialize data structure for devfreq framework and
- *			   start polling registered devfreq devices.
- */
-static int __init devfreq_start_polling(void)
-{
-	mutex_lock(&devfreq_list_lock);
-	polling = false;
-	devfreq_wq = create_freezable_workqueue("devfreq_wq");
-	INIT_DEFERRABLE_WORK(&devfreq_work, devfreq_monitor);
-	mutex_unlock(&devfreq_list_lock);
-
-	devfreq_monitor(&devfreq_work.work);
-	return 0;
-}
-late_initcall(devfreq_start_polling);
-
 static int __init devfreq_init(void)
 {
 	devfreq_class = class_create(THIS_MODULE, "devfreq");
@@ -622,7 +962,15 @@ static int __init devfreq_init(void)
 		pr_err("%s: couldn't create class\n", __FILE__);
 		return PTR_ERR(devfreq_class);
 	}
+
+	devfreq_wq = create_freezable_workqueue("devfreq_wq");
+	if (IS_ERR(devfreq_wq)) {
+		class_destroy(devfreq_class);
+		pr_err("%s: couldn't create workqueue\n", __FILE__);
+		return PTR_ERR(devfreq_wq);
+	}
 	devfreq_class->dev_attrs = devfreq_attrs;
+
 	return 0;
 }
 subsys_initcall(devfreq_init);
@@ -630,6 +978,7 @@ subsys_initcall(devfreq_init);
 static void __exit devfreq_exit(void)
 {
 	class_destroy(devfreq_class);
+	destroy_workqueue(devfreq_wq);
 }
 module_exit(devfreq_exit);
 
@@ -641,9 +990,9 @@ module_exit(devfreq_exit);
 /**
  * devfreq_recommended_opp() - Helper function to get proper OPP for the
  *			     freq value given to target callback.
- * @dev		The devfreq user device. (parent of devfreq)
- * @freq	The frequency given to target function
- * @flags	Flags handed from devfreq framework.
+ * @dev:	The devfreq user device. (parent of devfreq)
+ * @freq:	The frequency given to target function
+ * @flags:	Flags handed from devfreq framework.
  *
  */
 struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq,
@@ -674,35 +1023,49 @@ struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq,
  * devfreq_register_opp_notifier() - Helper function to get devfreq notified
  *				   for any changes in the OPP availability
  *				   changes
- * @dev		The devfreq user device. (parent of devfreq)
- * @devfreq	The devfreq object.
+ * @dev:	The devfreq user device. (parent of devfreq)
+ * @devfreq:	The devfreq object.
  */
 int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
 {
-	struct srcu_notifier_head *nh = opp_get_notifier(dev);
+	struct srcu_notifier_head *nh;
+	int ret = 0;
 
+	rcu_read_lock();
+	nh = opp_get_notifier(dev);
 	if (IS_ERR(nh))
-		return PTR_ERR(nh);
-	return srcu_notifier_chain_register(nh, &devfreq->nb);
+		ret = PTR_ERR(nh);
+	rcu_read_unlock();
+	if (!ret)
+		ret = srcu_notifier_chain_register(nh, &devfreq->nb);
+
+	return ret;
 }
 
 /**
  * devfreq_unregister_opp_notifier() - Helper function to stop getting devfreq
  *				     notified for any changes in the OPP
  *				     availability changes anymore.
- * @dev		The devfreq user device. (parent of devfreq)
- * @devfreq	The devfreq object.
+ * @dev:	The devfreq user device. (parent of devfreq)
+ * @devfreq:	The devfreq object.
  *
  * At exit() callback of devfreq_dev_profile, this must be included if
  * devfreq_recommended_opp is used.
  */
 int devfreq_unregister_opp_notifier(struct device *dev, struct devfreq *devfreq)
 {
-	struct srcu_notifier_head *nh = opp_get_notifier(dev);
+	struct srcu_notifier_head *nh;
+	int ret = 0;
 
+	rcu_read_lock();
+	nh = opp_get_notifier(dev);
 	if (IS_ERR(nh))
-		return PTR_ERR(nh);
-	return srcu_notifier_chain_unregister(nh, &devfreq->nb);
+		ret = PTR_ERR(nh);
+	rcu_read_unlock();
+	if (!ret)
+		ret = srcu_notifier_chain_unregister(nh, &devfreq->nb);
+
+	return ret;
 }
 
 MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@samsung.com>");
diff --git a/drivers/devfreq/exynos4_bus.c b/drivers/devfreq/exynos4_bus.c
index 88ddc77a9bb..74183720871 100644
--- a/drivers/devfreq/exynos4_bus.c
+++ b/drivers/devfreq/exynos4_bus.c
@@ -987,7 +987,7 @@ static __devinit int exynos4_busfreq_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	int err = 0;
 
-	data = kzalloc(sizeof(struct busfreq_data), GFP_KERNEL);
+	data = devm_kzalloc(&pdev->dev, sizeof(struct busfreq_data), GFP_KERNEL);
 	if (data == NULL) {
 		dev_err(dev, "Cannot allocate memory.\n");
 		return -ENOMEM;
@@ -1012,31 +1012,26 @@ static __devinit int exynos4_busfreq_probe(struct platform_device *pdev)
 		err = -EINVAL;
 	}
 	if (err)
-		goto err_regulator;
+		return err;
 
-	data->vdd_int = regulator_get(dev, "vdd_int");
+	data->vdd_int = devm_regulator_get(dev, "vdd_int");
 	if (IS_ERR(data->vdd_int)) {
 		dev_err(dev, "Cannot get the regulator \"vdd_int\"\n");
-		err = PTR_ERR(data->vdd_int);
-		goto err_regulator;
+		return PTR_ERR(data->vdd_int);
 	}
 	if (data->type == TYPE_BUSF_EXYNOS4x12) {
-		data->vdd_mif = regulator_get(dev, "vdd_mif");
+		data->vdd_mif = devm_regulator_get(dev, "vdd_mif");
 		if (IS_ERR(data->vdd_mif)) {
 			dev_err(dev, "Cannot get the regulator \"vdd_mif\"\n");
-			err = PTR_ERR(data->vdd_mif);
-			regulator_put(data->vdd_int);
-			goto err_regulator;
-
+			return PTR_ERR(data->vdd_mif);
 		}
 	}
 
 	opp = opp_find_freq_floor(dev, &exynos4_devfreq_profile.initial_freq);
 	if (IS_ERR(opp)) {
 		dev_err(dev, "Invalid initial frequency %lu kHz.\n",
-		       exynos4_devfreq_profile.initial_freq);
-		err = PTR_ERR(opp);
-		goto err_opp_add;
+			exynos4_devfreq_profile.initial_freq);
+		return PTR_ERR(opp);
 	}
 	data->curr_opp = opp;
 
@@ -1045,30 +1040,20 @@ static __devinit int exynos4_busfreq_probe(struct platform_device *pdev)
 	busfreq_mon_reset(data);
 
 	data->devfreq = devfreq_add_device(dev, &exynos4_devfreq_profile,
-					   &devfreq_simple_ondemand, NULL);
-	if (IS_ERR(data->devfreq)) {
-		err = PTR_ERR(data->devfreq);
-		goto err_opp_add;
-	}
+					   "simple_ondemand", NULL);
+	if (IS_ERR(data->devfreq))
+		return PTR_ERR(data->devfreq);
 
 	devfreq_register_opp_notifier(dev, data->devfreq);
 
 	err = register_pm_notifier(&data->pm_notifier);
 	if (err) {
 		dev_err(dev, "Failed to setup pm notifier\n");
-		goto err_devfreq_add;
+		devfreq_remove_device(data->devfreq);
+		return err;
 	}
 
 	return 0;
-err_devfreq_add:
-	devfreq_remove_device(data->devfreq);
-err_opp_add:
-	if (data->vdd_mif)
-		regulator_put(data->vdd_mif);
-	regulator_put(data->vdd_int);
-err_regulator:
-	kfree(data);
-	return err;
 }
 
 static __devexit int exynos4_busfreq_remove(struct platform_device *pdev)
@@ -1077,10 +1062,6 @@ static __devexit int exynos4_busfreq_remove(struct platform_device *pdev)
 
 	unregister_pm_notifier(&data->pm_notifier);
 	devfreq_remove_device(data->devfreq);
-	regulator_put(data->vdd_int);
-	if (data->vdd_mif)
-		regulator_put(data->vdd_mif);
-	kfree(data);
 
 	return 0;
 }
diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
index ea7f13c58de..fad7d632197 100644
--- a/drivers/devfreq/governor.h
+++ b/drivers/devfreq/governor.h
@@ -18,7 +18,24 @@
 
 #define to_devfreq(DEV)	container_of((DEV), struct devfreq, dev)
 
+/* Devfreq events */
+#define DEVFREQ_GOV_START			0x1
+#define DEVFREQ_GOV_STOP			0x2
+#define DEVFREQ_GOV_INTERVAL			0x3
+#define DEVFREQ_GOV_SUSPEND			0x4
+#define DEVFREQ_GOV_RESUME			0x5
+
 /* Caution: devfreq->lock must be locked before calling update_devfreq */
 extern int update_devfreq(struct devfreq *devfreq);
 
+extern void devfreq_monitor_start(struct devfreq *devfreq);
+extern void devfreq_monitor_stop(struct devfreq *devfreq);
+extern void devfreq_monitor_suspend(struct devfreq *devfreq);
+extern void devfreq_monitor_resume(struct devfreq *devfreq);
+extern void devfreq_interval_update(struct devfreq *devfreq,
+					unsigned int *delay);
+
+extern int devfreq_add_governor(struct devfreq_governor *governor);
+extern int devfreq_remove_governor(struct devfreq_governor *governor);
+
 #endif /* _GOVERNOR_H */
diff --git a/drivers/devfreq/governor_performance.c b/drivers/devfreq/governor_performance.c
index af75ddd4f15..c72f942f30a 100644
--- a/drivers/devfreq/governor_performance.c
+++ b/drivers/devfreq/governor_performance.c
@@ -10,6 +10,7 @@
  */
 
 #include <linux/devfreq.h>
+#include <linux/module.h>
 #include "governor.h"
 
 static int devfreq_performance_func(struct devfreq *df,
@@ -26,14 +27,41 @@ static int devfreq_performance_func(struct devfreq *df,
 	return 0;
 }
 
-static int performance_init(struct devfreq *devfreq)
+static int devfreq_performance_handler(struct devfreq *devfreq,
+				unsigned int event, void *data)
 {
-	return update_devfreq(devfreq);
+	int ret = 0;
+
+	if (event == DEVFREQ_GOV_START) {
+		mutex_lock(&devfreq->lock);
+		ret = update_devfreq(devfreq);
+		mutex_unlock(&devfreq->lock);
+	}
+
+	return ret;
 }
 
-const struct devfreq_governor devfreq_performance = {
+static struct devfreq_governor devfreq_performance = {
 	.name = "performance",
-	.init = performance_init,
 	.get_target_freq = devfreq_performance_func,
-	.no_central_polling = true,
+	.event_handler = devfreq_performance_handler,
 };
+
+static int __init devfreq_performance_init(void)
+{
+	return devfreq_add_governor(&devfreq_performance);
+}
+subsys_initcall(devfreq_performance_init);
+
+static void __exit devfreq_performance_exit(void)
+{
+	int ret;
+
+	ret = devfreq_remove_governor(&devfreq_performance);
+	if (ret)
+		pr_err("%s: failed remove governor %d\n", __func__, ret);
+
+	return;
+}
+module_exit(devfreq_performance_exit);
+MODULE_LICENSE("GPL");
diff --git a/drivers/devfreq/governor_powersave.c b/drivers/devfreq/governor_powersave.c
index fec0cdbd247..0c6bed567e6 100644
--- a/drivers/devfreq/governor_powersave.c
+++ b/drivers/devfreq/governor_powersave.c
@@ -10,6 +10,7 @@
  */
 
 #include <linux/devfreq.h>
+#include <linux/module.h>
 #include "governor.h"
 
 static int devfreq_powersave_func(struct devfreq *df,
@@ -23,14 +24,41 @@ static int devfreq_powersave_func(struct devfreq *df,
 	return 0;
 }
 
-static int powersave_init(struct devfreq *devfreq)
+static int devfreq_powersave_handler(struct devfreq *devfreq,
+				unsigned int event, void *data)
 {
-	return update_devfreq(devfreq);
+	int ret = 0;
+
+	if (event == DEVFREQ_GOV_START) {
+		mutex_lock(&devfreq->lock);
+		ret = update_devfreq(devfreq);
+		mutex_unlock(&devfreq->lock);
+	}
+
+	return ret;
 }
 
-const struct devfreq_governor devfreq_powersave = {
+static struct devfreq_governor devfreq_powersave = {
 	.name = "powersave",
-	.init = powersave_init,
 	.get_target_freq = devfreq_powersave_func,
-	.no_central_polling = true,
+	.event_handler = devfreq_powersave_handler,
 };
+
+static int __init devfreq_powersave_init(void)
+{
+	return devfreq_add_governor(&devfreq_powersave);
+}
+subsys_initcall(devfreq_powersave_init);
+
+static void __exit devfreq_powersave_exit(void)
+{
+	int ret;
+
+	ret = devfreq_remove_governor(&devfreq_powersave);
+	if (ret)
+		pr_err("%s: failed remove governor %d\n", __func__, ret);
+
+	return;
+}
+module_exit(devfreq_powersave_exit);
+MODULE_LICENSE("GPL");
diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
index a2e3eae7901..0720ba84ca9 100644
--- a/drivers/devfreq/governor_simpleondemand.c
+++ b/drivers/devfreq/governor_simpleondemand.c
@@ -10,8 +10,10 @@
  */
 
 #include <linux/errno.h>
+#include <linux/module.h>
 #include <linux/devfreq.h>
 #include <linux/math64.h>
+#include "governor.h"
 
 /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
 #define DFSO_UPTHRESHOLD	(90)
@@ -88,7 +90,58 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
 	return 0;
 }
 
-const struct devfreq_governor devfreq_simple_ondemand = {
+static int devfreq_simple_ondemand_handler(struct devfreq *devfreq,
+				unsigned int event, void *data)
+{
+	switch (event) {
+	case DEVFREQ_GOV_START:
+		devfreq_monitor_start(devfreq);
+		break;
+
+	case DEVFREQ_GOV_STOP:
+		devfreq_monitor_stop(devfreq);
+		break;
+
+	case DEVFREQ_GOV_INTERVAL:
+		devfreq_interval_update(devfreq, (unsigned int *)data);
+		break;
+
+	case DEVFREQ_GOV_SUSPEND:
+		devfreq_monitor_suspend(devfreq);
+		break;
+
+	case DEVFREQ_GOV_RESUME:
+		devfreq_monitor_resume(devfreq);
+		break;
+
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+static struct devfreq_governor devfreq_simple_ondemand = {
 	.name = "simple_ondemand",
 	.get_target_freq = devfreq_simple_ondemand_func,
+	.event_handler = devfreq_simple_ondemand_handler,
 };
+
+static int __init devfreq_simple_ondemand_init(void)
+{
+	return devfreq_add_governor(&devfreq_simple_ondemand);
+}
+subsys_initcall(devfreq_simple_ondemand_init);
+
+static void __exit devfreq_simple_ondemand_exit(void)
+{
+	int ret;
+
+	ret = devfreq_remove_governor(&devfreq_simple_ondemand);
+	if (ret)
+		pr_err("%s: failed remove governor %d\n", __func__, ret);
+
+	return;
+}
+module_exit(devfreq_simple_ondemand_exit);
+MODULE_LICENSE("GPL");
diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
index 0681246fc89..35de6e83c1f 100644
--- a/drivers/devfreq/governor_userspace.c
+++ b/drivers/devfreq/governor_userspace.c
@@ -14,6 +14,7 @@
 #include <linux/devfreq.h>
 #include <linux/pm.h>
 #include <linux/mutex.h>
+#include <linux/module.h>
 #include "governor.h"
 
 struct userspace_data {
@@ -116,10 +117,46 @@ static void userspace_exit(struct devfreq *devfreq)
 	devfreq->data = NULL;
 }
 
-const struct devfreq_governor devfreq_userspace = {
+static int devfreq_userspace_handler(struct devfreq *devfreq,
+			unsigned int event, void *data)
+{
+	int ret = 0;
+
+	switch (event) {
+	case DEVFREQ_GOV_START:
+		ret = userspace_init(devfreq);
+		break;
+	case DEVFREQ_GOV_STOP:
+		userspace_exit(devfreq);
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+static struct devfreq_governor devfreq_userspace = {
 	.name = "userspace",
 	.get_target_freq = devfreq_userspace_func,
-	.init = userspace_init,
-	.exit = userspace_exit,
-	.no_central_polling = true,
+	.event_handler = devfreq_userspace_handler,
 };
+
+static int __init devfreq_userspace_init(void)
+{
+	return devfreq_add_governor(&devfreq_userspace);
+}
+subsys_initcall(devfreq_userspace_init);
+
+static void __exit devfreq_userspace_exit(void)
+{
+	int ret;
+
+	ret = devfreq_remove_governor(&devfreq_userspace);
+	if (ret)
+		pr_err("%s: failed remove governor %d\n", __func__, ret);
+
+	return;
+}
+module_exit(devfreq_userspace_exit);
+MODULE_LICENSE("GPL");