]> git.openfabrics.org - ~shefty/rdma-dev.git/blobdiff - drivers/devfreq/devfreq.c
Merge branch 'pm-devfreq'
[~shefty/rdma-dev.git] / drivers / devfreq / devfreq.c
index 4fa1a22c55eabe578cb8e285d0630290c957a891..53766f39aaddfd5db9147842b40825fb1399453b 100644 (file)
 #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);
@@ -72,6 +68,79 @@ static struct devfreq *find_device_devfreq(struct device *dev)
        return ERR_PTR(-ENODEV);
 }
 
+/**
+ * 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);
@@ -383,91 +463,315 @@ 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>");