[1/3,RFC] devfreq: Core updates to support devices which can idle

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index 23d78b5..c083433 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -21,27 +21,32 @@  Description:
 		The /sys/class/devfreq/.../cur_freq shows the current
 		frequency of the corresponding devfreq object.
 
-What:		/sys/class/devfreq/.../central_polling
+What:		/sys/class/devfreq/.../max_freq
 Date:		September 2011
 Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
 Description:
-		The /sys/class/devfreq/.../central_polling shows whether
-		the devfreq ojbect is using devfreq-provided central
-		polling mechanism or not.
+		The /sys/class/devfreq/.../max_freq shows the current
+		max frequency of the corresponding devfreq object. This
+		max frequency is guaranteed to be with in device
+		operating frequency limits.
 
-What:		/sys/class/devfreq/.../polling_interval
+What:		/sys/class/devfreq/.../min_freq
 Date:		September 2011
 Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
 Description:
-		The /sys/class/devfreq/.../polling_interval shows and sets
-		the requested polling interval of the corresponding devfreq
-		object. The values are represented in ms. If the value is
-		less than 1 jiffy, it is considered to be 0, which means
-		no polling. This value is meaningless if the governor is
-		not polling; thus. If the governor is not using
-		devfreq-provided central polling
-		(/sys/class/devfreq/.../central_polling is 0), this value
-		may be useless.
+		The /sys/class/devfreq/.../min_freq shows the current
+		min frequency of the corresponding devfreq object. This
+		min frequency is guaranteed to be with in device
+		operating frequency limits.
+
+What:		/sys/class/devfreq/.../ondemand/polling_interval
+Date:		September 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../ondemand/polling_interval shows
+		and sets the requested polling interval of the corresponding
+		devfreq	object if ondemand governor is in effect. The values
+		are represented in ms.
 
 What:		/sys/class/devfreq/.../userspace/set_freq
 Date:		September 2011
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 70c31d4..5aa23a8 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -11,7 +11,6 @@ 
  */
 
 #include <linux/kernel.h>
-#include <linux/sched.h>
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/init.h>
@@ -20,28 +19,12 @@ 
 #include <linux/stat.h>
 #include <linux/opp.h>
 #include <linux/devfreq.h>
-#include <linux/workqueue.h>
 #include <linux/platform_device.h>
 #include <linux/list.h>
-#include <linux/printk.h>
-#include <linux/hrtimer.h>
 #include "governor.h"
 
 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.
- */
-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 */
 static LIST_HEAD(devfreq_list);
 static DEFINE_MUTEX(devfreq_list_lock);
@@ -73,51 +56,15 @@  static struct devfreq *find_device_devfreq(struct device *dev)
 }
 
 /**
- * update_devfreq() - Reevaluate the device and configure frequency.
- * @devfreq:	the devfreq instance.
- *
- * Note: Lock devfreq->lock before calling update_devfreq
- *	 This function is exported for governors.
+ * devfreq_device_target - Set device target frequency.
+ * @devfreq	device devfreq instance
+ * @freq	target freq to be set
+ * @flags	influences how target freq is set
  */
-int update_devfreq(struct devfreq *devfreq)
+int devfreq_device_target(struct devfreq *devfreq,
+				unsigned long freq, u32 flags)
 {
-	unsigned long freq;
-	int err = 0;
-	u32 flags = 0;
-
-	if (!mutex_is_locked(&devfreq->lock)) {
-		WARN(true, "devfreq->lock must be locked by the caller.\n");
-		return -EINVAL;
-	}
-
-	/* Reevaluate the proper frequency */
-	err = devfreq->governor->get_target_freq(devfreq, &freq);
-	if (err)
-		return err;
-
-	/*
-	 * Adjust the freuqency with user freq and QoS.
-	 *
-	 * List from the highest proiority
-	 * max_freq (probably called by thermal when it's too hot)
-	 * min_freq
-	 */
-
-	if (devfreq->min_freq && freq < devfreq->min_freq) {
-		freq = devfreq->min_freq;
-		flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use GLB */
-	}
-	if (devfreq->max_freq && freq > devfreq->max_freq) {
-		freq = devfreq->max_freq;
-		flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use LUB */
-	}
-
-	err = devfreq->profile->target(devfreq->dev.parent, &freq, flags);
-	if (err)
-		return err;
-
-	devfreq->previous_freq = freq;
-	return err;
+	return devfreq->profile->target(devfreq->dev.parent, &freq, flags);
 }
 
 /**
@@ -133,69 +80,37 @@  static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
 				 void *devp)
 {
 	struct devfreq *devfreq = container_of(nb, struct devfreq, nb);
-	int ret;
-
-	mutex_lock(&devfreq->lock);
-	ret = update_devfreq(devfreq);
-	mutex_unlock(&devfreq->lock);
-
-	return ret;
+	return devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_LIMITS);
 }
 
 /**
- * _remove_devfreq() - Remove devfreq from the device.
+ * _remove_devfreq() - Remove device devfreq from the devfreq 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 (!find_device_devfreq(&devfreq->dev)) {
+		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;
+	devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_STOP);
 
 	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);
 }
 
@@ -203,137 +118,15 @@  static void _remove_devfreq(struct devfreq *devfreq, bool skip)
  * devfreq_dev_release() - Callback for struct device to release the device.
  * @dev:	the devfreq device
  *
- * This calls _remove_devfreq() if _remove_devfreq() is not called.
+ * This calls _remove_devfreq() to release device and its devfreq.
  * Note that devfreq_dev_release() could be called by _remove_devfreq() as
  * well as by others unregistering the device.
  */
 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;
-	}
 }
 
 /**
@@ -352,21 +145,20 @@  struct devfreq *devfreq_add_device(struct device *dev,
 	struct devfreq *devfreq;
 	int err = 0;
 
-	if (!dev || !profile || !governor) {
+	if (!dev || !profile || !governor ||
+		!profile->min_freq || !profile->max_freq) {
 		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);
@@ -385,49 +177,44 @@  struct devfreq *devfreq_add_device(struct device *dev,
 	devfreq->profile = profile;
 	devfreq->governor = governor;
 	devfreq->previous_freq = profile->initial_freq;
-	devfreq->data = data;
-	devfreq->next_polling = devfreq->polling_jiffies
-			      = msecs_to_jiffies(devfreq->profile->polling_ms);
+	devfreq->governor_data = data;
 	devfreq->nb.notifier_call = devfreq_notifier_call;
+	devfreq->min_freq = profile->min_freq;
+	devfreq->max_freq = profile->max_freq;
 
 	dev_set_name(&devfreq->dev, dev_name(dev));
 	err = device_register(&devfreq->dev);
 	if (err) {
 		put_device(&devfreq->dev);
+		dev_err(dev, "%s: Unable to register devfreq device\n",
+			__func__);
 		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);
+	mutex_unlock(&devfreq_list_lock);
 
-	if (devfreq_wq && devfreq->next_polling && !polling) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work,
-				   devfreq->next_polling);
+	err = devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_START);
+	if (err) {
+		dev_err(dev, "%s: Unable to start governor for the device\n",
+			__func__);
+		list_del(&devfreq->node);
+		device_unregister(&devfreq->dev);
+		goto err_init;
 	}
-	mutex_unlock(&devfreq_list_lock);
-out:
+
 	return devfreq;
 
-err_init:
-	device_unregister(&devfreq->dev);
 err_dev:
 	mutex_unlock(&devfreq->lock);
+err_init:
 	kfree(devfreq);
 err_out:
 	return ERR_PTR(err);
 }
+EXPORT_SYMBOL(devfreq_add_device);
 
 /**
  * devfreq_remove_device() - Remove devfreq feature from a device.
@@ -435,30 +222,16 @@  err_out:
  */
 int devfreq_remove_device(struct devfreq *devfreq)
 {
-	bool central_polling;
-
 	if (!devfreq)
 		return -EINVAL;
 
-	central_polling = !devfreq->governor->no_central_polling;
-
-	if (central_polling) {
-		mutex_lock(&devfreq_list_lock);
-		while (wait_remove_device == devfreq) {
-			mutex_unlock(&devfreq_list_lock);
-			schedule();
-			mutex_lock(&devfreq_list_lock);
-		}
-	}
-
 	mutex_lock(&devfreq->lock);
-	_remove_devfreq(devfreq, false); /* it unlocks devfreq->lock */
-
-	if (central_polling)
-		mutex_unlock(&devfreq_list_lock);
+	_remove_devfreq(devfreq, false);
+	mutex_unlock(&devfreq->lock);
 
 	return 0;
 }
+EXPORT_SYMBOL(devfreq_remove_device);
 
 static ssize_t show_governor(struct device *dev,
 			     struct device_attribute *attr, char *buf)
@@ -472,77 +245,28 @@  static ssize_t show_freq(struct device *dev,
 	return sprintf(buf, "%lu\n", to_devfreq(dev)->previous_freq);
 }
 
-static ssize_t show_polling_interval(struct device *dev,
-				     struct device_attribute *attr, char *buf)
-{
-	return sprintf(buf, "%d\n", to_devfreq(dev)->profile->polling_ms);
-}
-
-static ssize_t store_polling_interval(struct device *dev,
-				      struct device_attribute *attr,
-				      const char *buf, size_t count)
-{
-	struct devfreq *df = to_devfreq(dev);
-	unsigned int value;
-	int ret;
-
-	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);
-
-	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)
 {
 	struct devfreq *df = to_devfreq(dev);
 	unsigned long value;
 	int ret;
-	unsigned long max;
 
 	ret = sscanf(buf, "%lu", &value);
 	if (ret != 1)
 		goto out;
 
-	mutex_lock(&df->lock);
-	max = df->max_freq;
-	if (value && max && value > max) {
+	if (value < df->profile->min_freq || value > df->profile->max_freq) {
 		ret = -EINVAL;
-		goto unlock;
+		goto out;
 	}
 
+	mutex_lock(&df->lock);
 	df->min_freq = value;
-	update_devfreq(df);
-	ret = count;
-unlock:
 	mutex_unlock(&df->lock);
+
+	df->governor->event_handler(df, DEVFREQ_GOV_LIMITS);
+	ret = count;
 out:
 	return ret;
 }
@@ -559,24 +283,22 @@  static ssize_t store_max_freq(struct device *dev, struct device_attribute *attr,
 	struct devfreq *df = to_devfreq(dev);
 	unsigned long value;
 	int ret;
-	unsigned long min;
 
 	ret = sscanf(buf, "%lu", &value);
 	if (ret != 1)
 		goto out;
 
-	mutex_lock(&df->lock);
-	min = df->min_freq;
-	if (value && min && value < min) {
+	if (value < df->profile->min_freq || value > df->profile->max_freq) {
 		ret = -EINVAL;
-		goto unlock;
+		goto out;
 	}
 
+	mutex_lock(&df->lock);
 	df->max_freq = value;
-	update_devfreq(df);
-	ret = count;
-unlock:
 	mutex_unlock(&df->lock);
+
+	df->governor->event_handler(df, DEVFREQ_GOV_LIMITS);
+	ret = count;
 out:
 	return ret;
 }
@@ -590,31 +312,11 @@  static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
 static struct device_attribute devfreq_attrs[] = {
 	__ATTR(governor, S_IRUGO, show_governor, NULL),
 	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
-	__ATTR(central_polling, S_IRUGO, show_central_polling, 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),
 	{ },
 };
 
-/**
- * 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_DELAYED_WORK_DEFERRABLE(&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");
@@ -623,6 +325,8 @@  static int __init devfreq_init(void)
 		return PTR_ERR(devfreq_class);
 	}
 	devfreq_class->dev_attrs = devfreq_attrs;
+	mutex_init(&devfreq_list_lock);
+
 	return 0;
 }
 subsys_initcall(devfreq_init);
diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
index ea7f13c..15b4c52 100644
--- a/drivers/devfreq/governor.h
+++ b/drivers/devfreq/governor.h
@@ -16,9 +16,9 @@ 
 
 #include <linux/devfreq.h>
 
-#define to_devfreq(DEV)	container_of((DEV), struct devfreq, dev)
+int devfreq_device_target(struct devfreq *devfreq,
+				unsigned long freq, u32 flags);
 
-/* Caution: devfreq->lock must be locked before calling update_devfreq */
-extern int update_devfreq(struct devfreq *devfreq);
+#define to_devfreq(DEV)	container_of((DEV), struct devfreq, dev)
 
 #endif /* _GOVERNOR_H */
diff --git a/drivers/devfreq/governor_performance.c b/drivers/devfreq/governor_performance.c
index af75ddd..ffc694d 100644
--- a/drivers/devfreq/governor_performance.c
+++ b/drivers/devfreq/governor_performance.c
@@ -13,27 +13,27 @@ 
 #include "governor.h"
 
 static int devfreq_performance_func(struct devfreq *df,
-				    unsigned long *freq)
+				    unsigned int event)
 {
-	/*
-	 * target callback should be able to get floor value as
-	 * said in devfreq.h
-	 */
-	if (!df->max_freq)
-		*freq = UINT_MAX;
-	else
-		*freq = df->max_freq;
-	return 0;
-}
+	int ret = 0;
+	u32 flags = DEVFREQ_FLAG_LEAST_UPPER_BOUND;
 
-static int performance_init(struct devfreq *devfreq)
-{
-	return update_devfreq(devfreq);
+	switch (event) {
+	case DEVFREQ_GOV_START:
+	case DEVFREQ_GOV_LIMITS:
+		mutex_lock(&df->lock);
+		ret = devfreq_device_target(df, df->max_freq, flags);
+		mutex_unlock(&df->lock);
+		break;
+	default:
+		break;
+
+	}
+
+	return ret;
 }
 
 const struct devfreq_governor devfreq_performance = {
 	.name = "performance",
-	.init = performance_init,
-	.get_target_freq = devfreq_performance_func,
-	.no_central_polling = true,
+	.event_handler = devfreq_performance_func,
 };
diff --git a/drivers/devfreq/governor_powersave.c b/drivers/devfreq/governor_powersave.c
index fec0cdb..a19474c 100644
--- a/drivers/devfreq/governor_powersave.c
+++ b/drivers/devfreq/governor_powersave.c
@@ -13,24 +13,27 @@ 
 #include "governor.h"
 
 static int devfreq_powersave_func(struct devfreq *df,
-				  unsigned long *freq)
+				  unsigned int event)
 {
-	/*
-	 * target callback should be able to get ceiling value as
-	 * said in devfreq.h
-	 */
-	*freq = df->min_freq;
-	return 0;
-}
+	int ret = 0;
+	u32 flags = ~DEVFREQ_FLAG_LEAST_UPPER_BOUND;
 
-static int powersave_init(struct devfreq *devfreq)
-{
-	return update_devfreq(devfreq);
+	switch (event) {
+	case DEVFREQ_GOV_START:
+	case DEVFREQ_GOV_LIMITS:
+		mutex_lock(&df->lock);
+		ret = devfreq_device_target(df, df->min_freq, flags);
+		mutex_unlock(&df->lock);
+		break;
+	default:
+		break;
+
+	}
+
+	return ret;
 }
 
 const struct devfreq_governor devfreq_powersave = {
 	.name = "powersave",
-	.init = powersave_init,
-	.get_target_freq = devfreq_powersave_func,
-	.no_central_polling = true,
+	.event_handler = devfreq_powersave_func,
 };
diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
index a2e3eae..7c70c30 100644
--- a/drivers/devfreq/governor_simpleondemand.c
+++ b/drivers/devfreq/governor_simpleondemand.c
@@ -9,41 +9,87 @@ 
  * published by the Free Software Foundation.
  */
 
+#include <linux/slab.h>
 #include <linux/errno.h>
+#include <linux/stat.h>
 #include <linux/devfreq.h>
 #include <linux/math64.h>
+#include <linux/workqueue.h>
+#include "governor.h"
 
 /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
 #define DFSO_UPTHRESHOLD	(90)
 #define DFSO_DOWNDIFFERENCTIAL	(5)
-static int devfreq_simple_ondemand_func(struct devfreq *df,
-					unsigned long *freq)
+
+static struct workqueue_struct *devfreq_wq;
+
+struct ondemand_data {
+	struct devfreq *devfreq;
+	struct delayed_work work;
+	unsigned int upthreshold;
+	unsigned int downdifferential;
+	bool stop_queuing;
+};
+
+static ssize_t show_polling_interval(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", to_devfreq(dev)->profile->polling_ms);
+}
+
+static ssize_t store_polling_interval(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct devfreq *df = to_devfreq(dev);
+	unsigned int value;
+	int ret;
+
+	ret = sscanf(buf, "%u", &value);
+	if (ret != 1)
+		return ret;
+
+	mutex_lock(&df->lock);
+	df->profile->polling_ms = value;
+	mutex_unlock(&df->lock);
+
+	return count;
+}
+
+static DEVICE_ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
+	       store_polling_interval);
+static struct attribute *dev_entries[] = {
+	&dev_attr_polling_interval.attr,
+	NULL,
+};
+static struct attribute_group dev_attr_group = {
+	.name = "ondemand",
+	.attrs = dev_entries,
+};
+
+static int update_devfreq(struct devfreq *df)
 {
 	struct devfreq_dev_status stat;
+	struct ondemand_data *data = df->governor_data;
 	int err = df->profile->get_dev_status(df->dev.parent, &stat);
+	unsigned int dfso_upthreshold = data->upthreshold;
+	unsigned int dfso_downdifferential = data->downdifferential;
+
 	unsigned long long a, b;
-	unsigned int dfso_upthreshold = DFSO_UPTHRESHOLD;
-	unsigned int dfso_downdifferential = DFSO_DOWNDIFFERENCTIAL;
-	struct devfreq_simple_ondemand_data *data = df->data;
-	unsigned long max = (df->max_freq) ? df->max_freq : UINT_MAX;
+	unsigned long freq;
+	u32 flags = 0;
 
 	if (err)
 		return err;
 
-	if (data) {
-		if (data->upthreshold)
-			dfso_upthreshold = data->upthreshold;
-		if (data->downdifferential)
-			dfso_downdifferential = data->downdifferential;
-	}
 	if (dfso_upthreshold > 100 ||
 	    dfso_upthreshold < dfso_downdifferential)
 		return -EINVAL;
 
-	/* Assume MAX if it is going to be divided by zero */
+	/* Perhaps device is inactive, set device min frequency */
 	if (stat.total_time == 0) {
-		*freq = max;
-		return 0;
+		freq = df->min_freq;
+		goto target;
 	}
 
 	/* Prevent overflow */
@@ -55,21 +101,21 @@  static int devfreq_simple_ondemand_func(struct devfreq *df,
 	/* Set MAX if it's busy enough */
 	if (stat.busy_time * 100 >
 	    stat.total_time * dfso_upthreshold) {
-		*freq = max;
-		return 0;
+		freq = df->max_freq;
+		goto target;
 	}
 
 	/* Set MAX if we do not know the initial frequency */
 	if (stat.current_frequency == 0) {
-		*freq = max;
-		return 0;
+		freq = df->max_freq;
+		goto target;
 	}
 
 	/* Keep the current frequency */
 	if (stat.busy_time * 100 >
 	    stat.total_time * (dfso_upthreshold - dfso_downdifferential)) {
-		*freq = stat.current_frequency;
-		return 0;
+		freq = stat.current_frequency;
+		goto target;
 	}
 
 	/* Set the desired frequency based on the load */
@@ -78,17 +124,131 @@  static int devfreq_simple_ondemand_func(struct devfreq *df,
 	b = div_u64(a, stat.total_time);
 	b *= 100;
 	b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
-	*freq = (unsigned long) b;
+	freq = (unsigned long) b;
+
+	if (df->min_freq && freq < df->min_freq) {
+		freq = df->min_freq;
+		flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND;
+	}
+	if (df->max_freq && freq > df->max_freq) {
+		freq = df->max_freq;
+		flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND;
+	}
 
-	if (df->min_freq && *freq < df->min_freq)
-		*freq = df->min_freq;
-	if (df->max_freq && *freq > df->max_freq)
-		*freq = df->max_freq;
+target:
+	err = devfreq_device_target(df, freq, flags);
+	return err;
+}
 
-	return 0;
+static void devfreq_monitor(struct work_struct *work)
+{
+	int ret;
+	struct ondemand_data *data = container_of(work,
+					struct ondemand_data, work.work);
+	struct devfreq *df = data->devfreq;
+
+	mutex_lock(&df->lock);
+	ret = update_devfreq(df);
+	mutex_unlock(&df->lock);
+	if (ret)
+		dev_err(&df->dev, "dvfs failed with (%d) error\n", ret);
+
+	if (!data->stop_queuing)
+		queue_delayed_work(devfreq_wq, &data->work,
+				msecs_to_jiffies(df->profile->polling_ms));
+}
+
+static int ondemand_init(struct devfreq *df)
+{
+	int err;
+	struct ondemand_data *data = kzalloc(sizeof(struct ondemand_data),
+							GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	/**
+	 * check if devfreq user has passed governor configurable
+	 * parameters. if no, use default values.
+	 */
+	if (df->governor_data) {
+		struct devfreq_simple_ondemand_data *drv = df->governor_data;
+		data->upthreshold = drv->upthreshold;
+		data->downdifferential = drv->downdifferential;
+	} else {
+		data->upthreshold = DFSO_UPTHRESHOLD;
+		data->downdifferential = DFSO_DOWNDIFFERENCTIAL;
+	}
+
+	data->stop_queuing = false;
+	data->devfreq = df;
+	df->governor_data = data;
+	INIT_DELAYED_WORK_DEFERRABLE(&data->work, devfreq_monitor);
+
+	err = sysfs_create_group(&df->dev.kobj, &dev_attr_group);
+	if (err)
+		kfree(data);
+
+	return err;
+}
+
+static void ondemand_exit(struct devfreq *df)
+{
+	sysfs_remove_group(&df->dev.kobj, &dev_attr_group);
+	kfree(df->governor_data);
+	df->governor_data = NULL;
+}
+
+static int devfreq_simple_ondemand_func(struct devfreq *df,
+					unsigned int event)
+{
+	int ret = 0;
+	struct ondemand_data *data = df->governor_data;
+
+	switch (event) {
+	case DEVFREQ_GOV_START:
+		ret = ondemand_init(df);
+		if (ret)
+			goto out;
+
+		data = df->governor_data;
+		queue_delayed_work(devfreq_wq, &data->work,
+				msecs_to_jiffies(df->profile->polling_ms));
+		break;
+
+	case DEVFREQ_GOV_STOP:
+		data->stop_queuing = true;
+		cancel_delayed_work_sync(&data->work);
+		ondemand_exit(df);
+		break;
+
+	case DEVFREQ_GOV_LIMITS:
+		if (delayed_work_pending(&data->work)) {
+			mutex_lock(&df->lock);
+			ret = update_devfreq(df);
+			mutex_unlock(&df->lock);
+		}
+		break;
+	default:
+		break;
+	}
+
+out:
+	return ret;
 }
 
 const struct devfreq_governor devfreq_simple_ondemand = {
 	.name = "simple_ondemand",
-	.get_target_freq = devfreq_simple_ondemand_func,
+	.event_handler = devfreq_simple_ondemand_func,
 };
+
+static int __init devfreq_ondemand_init(void)
+{
+	devfreq_wq = create_freezable_workqueue("devfreq_wq");
+	if (IS_ERR(devfreq_wq)) {
+		pr_err("%s: couldn't create workqueue\n", __FILE__);
+		return PTR_ERR(devfreq_wq);
+	}
+
+	return 0;
+}
+fs_initcall(devfreq_ondemand_init);
diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
index 0681246..c20a937 100644
--- a/drivers/devfreq/governor_userspace.c
+++ b/drivers/devfreq/governor_userspace.c
@@ -18,67 +18,34 @@ 
 
 struct userspace_data {
 	unsigned long user_frequency;
-	bool valid;
 };
 
-static int devfreq_userspace_func(struct devfreq *df, unsigned long *freq)
-{
-	struct userspace_data *data = df->data;
-
-	if (data->valid) {
-		unsigned long adjusted_freq = data->user_frequency;
-
-		if (df->max_freq && adjusted_freq > df->max_freq)
-			adjusted_freq = df->max_freq;
-
-		if (df->min_freq && adjusted_freq < df->min_freq)
-			adjusted_freq = df->min_freq;
-
-		*freq = adjusted_freq;
-	} else {
-		*freq = df->previous_freq; /* No user freq specified yet */
-	}
-	return 0;
-}
+static int devfreq_userspace_func(struct devfreq *df, unsigned int event);
 
 static ssize_t store_freq(struct device *dev, struct device_attribute *attr,
 			  const char *buf, size_t count)
 {
-	struct devfreq *devfreq = to_devfreq(dev);
-	struct userspace_data *data;
-	unsigned long wanted;
-	int err = 0;
-
-
-	mutex_lock(&devfreq->lock);
-	data = devfreq->data;
-
-	sscanf(buf, "%lu", &wanted);
-	data->user_frequency = wanted;
-	data->valid = true;
-	err = update_devfreq(devfreq);
-	if (err == 0)
-		err = count;
-	mutex_unlock(&devfreq->lock);
-	return err;
+	unsigned long val;
+	int ret;
+	struct devfreq *df = to_devfreq(dev);
+	struct userspace_data *data = df->governor_data;
+
+	ret = sscanf(buf, "%lu", &val);
+	if (ret != 1)
+		return ret;
+
+	data->user_frequency = val;
+	devfreq_userspace_func(df, DEVFREQ_GOV_LIMITS);
+
+	return count;
 }
 
 static ssize_t show_freq(struct device *dev, struct device_attribute *attr,
 			 char *buf)
 {
-	struct devfreq *devfreq = to_devfreq(dev);
-	struct userspace_data *data;
-	int err = 0;
-
-	mutex_lock(&devfreq->lock);
-	data = devfreq->data;
-
-	if (data->valid)
-		err = sprintf(buf, "%lu\n", data->user_frequency);
-	else
-		err = sprintf(buf, "undefined\n");
-	mutex_unlock(&devfreq->lock);
-	return err;
+	struct devfreq *df = to_devfreq(dev);
+	struct userspace_data *data = df->governor_data;
+	return sprintf(buf, "%lu\n", data->user_frequency);
 }
 
 static DEVICE_ATTR(set_freq, 0644, show_freq, store_freq);
@@ -91,35 +58,74 @@  static struct attribute_group dev_attr_group = {
 	.attrs	= dev_entries,
 };
 
-static int userspace_init(struct devfreq *devfreq)
+static int userspace_init(struct devfreq *df)
 {
-	int err = 0;
+	int err;
 	struct userspace_data *data = kzalloc(sizeof(struct userspace_data),
 					      GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
 
-	if (!data) {
-		err = -ENOMEM;
-		goto out;
-	}
-	data->valid = false;
-	devfreq->data = data;
+	df->governor_data = data;
+
+	err = sysfs_create_group(&df->dev.kobj, &dev_attr_group);
+	if (err)
+		kfree(data);
 
-	err = sysfs_create_group(&devfreq->dev.kobj, &dev_attr_group);
-out:
 	return err;
 }
 
-static void userspace_exit(struct devfreq *devfreq)
+static void userspace_exit(struct devfreq *df)
 {
-	sysfs_remove_group(&devfreq->dev.kobj, &dev_attr_group);
-	kfree(devfreq->data);
-	devfreq->data = NULL;
+	sysfs_remove_group(&df->dev.kobj, &dev_attr_group);
+	kfree(df->governor_data);
+	df->governor_data = NULL;
+}
+
+static int update_devfreq(struct devfreq *df)
+{
+	u32 flags = 0;
+	struct userspace_data *data = df->governor_data;
+
+	if (!data->user_frequency)
+		return 0;
+
+	if (data->user_frequency > df->max_freq) {
+		data->user_frequency = df->max_freq;
+		flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND;
+	}
+
+	if (data->user_frequency < df->min_freq) {
+		data->user_frequency = df->min_freq;
+		flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND;
+	}
+
+	return devfreq_device_target(df, data->user_frequency, flags);
+}
+
+static int devfreq_userspace_func(struct devfreq *df, unsigned int event)
+{
+	int ret = 0;
+	switch (event) {
+	case DEVFREQ_GOV_START:
+		ret = userspace_init(df);
+		break;
+	case DEVFREQ_GOV_STOP:
+		userspace_exit(df);
+		break;
+	case DEVFREQ_GOV_LIMITS:
+		mutex_lock(&df->lock);
+		ret = update_devfreq(df);
+		mutex_unlock(&df->lock);
+		break;
+	default:
+		break;
+	}
+
+	return ret;
 }
 
 const 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_func,
 };
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 281c72a..600cc2e 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -52,11 +52,19 @@  struct devfreq_dev_status {
  */
 #define DEVFREQ_FLAG_LEAST_UPPER_BOUND		0x1
 
+/* Devfreq events */
+#define DEVFREQ_GOV_START			0x1
+#define DEVFREQ_GOV_STOP			0x2
+#define DEVFREQ_GOV_LIMITS			0x3
+
 /**
  * struct devfreq_dev_profile - Devfreq's user device profile
  * @initial_freq	The operating frequency when devfreq_add_device() is
  *			called.
- * @polling_ms		The polling interval in ms. 0 disables polling.
+ * @max_freq		Maximum frequency supported by device
+ * @min_freq		Minimum frequency supported by device
+ * @polling_ms		The polling interval in ms. optional, valid only
+ *			for ondemand users.
  * @target		The device should set its operating frequency at
  *			freq or lowest-upper-than-freq value. If freq is
  *			higher than any operable frequency, set maximum.
@@ -74,6 +82,8 @@  struct devfreq_dev_status {
  */
 struct devfreq_dev_profile {
 	unsigned long initial_freq;
+	unsigned long max_freq;
+	unsigned long min_freq;
 	unsigned int polling_ms;
 
 	int (*target)(struct device *dev, unsigned long *freq, u32 flags);
@@ -85,31 +95,14 @@  struct devfreq_dev_profile {
 /**
  * struct devfreq_governor - Devfreq policy governor
  * @name		Governor's name
- * @get_target_freq	Returns desired operating frequency for the device.
- *			Basically, get_target_freq will run
- *			devfreq_dev_profile.get_dev_status() to get the
- *			status of the device (load = busy_time / total_time).
- *			If no_central_polling is set, this callback is called
- *			only with update_devfreq() notified by OPP.
- * @init		Called when the devfreq is being attached to a device
- * @exit		Called when the devfreq is being removed from a
- *			device. Governor should stop any internal routines
- *			before return because related data may be
- *			freed after exit().
- * @no_central_polling	Do not use devfreq's central polling mechanism.
- *			When this is set, devfreq will not call
- *			get_target_freq with devfreq_monitor(). However,
- *			devfreq will call get_target_freq with
- *			devfreq_update() notified by OPP framework.
- *
- * Note that the callbacks are called with devfreq->lock locked by devfreq.
+ * @event_handler	Callback for devfreq core framework to notify events
+ *			to governors. Events include per device governor
+ *			init and exit, opp changes out of devfreq, suspend
+ *			and resume of per device devfreq during device idle.
  */
 struct devfreq_governor {
 	const char name[DEVFREQ_NAME_LEN];
-	int (*get_target_freq)(struct devfreq *this, unsigned long *freq);
-	int (*init)(struct devfreq *this);
-	void (*exit)(struct devfreq *this);
-	const bool no_central_polling;
+	int (*event_handler)(struct devfreq *devfreq, unsigned int event);
 };
 
 /**
@@ -124,16 +117,9 @@  struct devfreq_governor {
  * @nb		notifier block used to notify devfreq object that it should
  *		reevaluate operable frequencies. Devfreq users may use
  *		devfreq.nb to the corresponding register notifier call chain.
- * @polling_jiffies	interval in jiffies.
  * @previous_freq	previously configured frequency value.
- * @next_polling	the number of remaining jiffies to poll with
- *			"devfreq_monitor" executions to reevaluate
- *			frequency/voltage of the device. Set by
- *			profile's polling_ms interval.
- * @data	Private data of the governor. The devfreq framework does not
- *		touch this.
- * @being_removed	a flag to mark that this object is being removed in
- *			order to prevent trying to remove the object multiple times.
+ * @governor_data	Private data of the governor. The devfreq framework
+ *			does not touch this.
  * @min_freq	Limit minimum frequency requested by user (0: none)
  * @max_freq	Limit maximum frequency requested by user (0: none)
  *
@@ -154,13 +140,9 @@  struct devfreq {
 	const struct devfreq_governor *governor;
 	struct notifier_block nb;
 
-	unsigned long polling_jiffies;
 	unsigned long previous_freq;
-	unsigned int next_polling;
-
-	void *data; /* private data for governors */
 
-	bool being_removed;
+	void *governor_data; /* private data for governors */
 
 	unsigned long min_freq;
 	unsigned long max_freq;