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 f6b0a6e2ea50..0f079be13305 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 4fa1a22c55ea..53766f39aadd 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 88ddc77a9bb1..741837208716 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 ea7f13c58ded..fad7d6321978 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 af75ddd4f158..c72f942f30a8 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 fec0cdbd2477..0c6bed567e6d 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 a2e3eae79011..0720ba84ca92 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 0681246fc89d..35de6e83c1fe 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");