/*
   * devfreq: Generic Dynamic Voltage and Frequency Scaling (DVFS) Framework
   *	    for Non-CPU Devices.
   *
   * Copyright (C) 2011 Samsung Electronics
   *	MyungJoo Ham <myungjoo.ham@samsung.com>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   */
  
  #include <linux/kernel.h>
  #include <linux/sched.h>
  #include <linux/errno.h>
  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/stat.h>
  #include <linux/pm_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"
  
  static struct class *devfreq_class;
  
  /*
   * devfreq core provides delayed work based load monitoring helper
   * functions. Governors can use these or can implement their own
   * monitoring mechanism.
   */
  static struct workqueue_struct *devfreq_wq;
  
  /* 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);
  
  /**
   * find_device_devfreq() - find devfreq struct using device pointer
   * @dev:	device pointer used to lookup device devfreq.
   *
   * Search the list of device devfreqs and return the matched device's
   * devfreq info. devfreq_list_lock should be held by the caller.
   */
  static struct devfreq *find_device_devfreq(struct device *dev)
  {
  	struct devfreq *tmp_devfreq;
  
  	if (unlikely(IS_ERR_OR_NULL(dev))) {
  		pr_err("DEVFREQ: %s: Invalid parameters
  ", __func__);
  		return ERR_PTR(-EINVAL);
  	}
  	WARN(!mutex_is_locked(&devfreq_list_lock),
  	     "devfreq_list_lock must be locked.");
  
  	list_for_each_entry(tmp_devfreq, &devfreq_list, node) {
  		if (tmp_devfreq->dev.parent == dev)
  			return tmp_devfreq;
  	}
  
  	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
  ", __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.
   *
   * Note: Lock devfreq->lock before calling update_devfreq
   *	 This function is exported for governors.
   */
  int update_devfreq(struct devfreq *devfreq)
  {
  	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.
  ");
  		return -EINVAL;
  	}
  
  	if (!devfreq->governor)
  		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;
  
  	if (devfreq->profile->freq_table)
  		if (devfreq_update_status(devfreq, freq))
  			dev_err(&devfreq->dev,
  				"Couldn't update frequency transition information.
  ");
  
  	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
  ", 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_update_status(devfreq, devfreq->previous_freq);
  	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)
  {
  	unsigned long freq;
  
  	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->last_stat_updated = jiffies;
  	devfreq->stop_polling = false;
  
  	if (devfreq->profile->get_cur_freq &&
  		!devfreq->profile->get_cur_freq(devfreq->dev.parent, &freq))
  		devfreq->previous_freq = freq;
  
  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
   *
   * Called by a notifier that uses devfreq->nb.
   */
  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;
  }
  
  /**
   * _remove_devfreq() - Remove devfreq from the list and release its resources.
   * @devfreq:	the devfreq struct
   * @skip:	skip calling device_unregister().
   */
  static void _remove_devfreq(struct devfreq *devfreq, bool skip)
  {
  	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
  ");
  		return;
  	}
  	list_del(&devfreq->node);
  	mutex_unlock(&devfreq_list_lock);
  
  	if (devfreq->governor)
  		devfreq->governor->event_handler(devfreq,
  						 DEVFREQ_GOV_STOP, NULL);
  
  	if (devfreq->profile->exit)
  		devfreq->profile->exit(devfreq->dev.parent);
  
  	if (!skip && get_device(&devfreq->dev)) {
  		device_unregister(&devfreq->dev);
  		put_device(&devfreq->dev);
  	}
  
  	mutex_destroy(&devfreq->lock);
  	kfree(devfreq);
  }
  
  /**
   * 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.
   * 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);
  
  	_remove_devfreq(devfreq, true);
  }
  
  /**
   * devfreq_add_device() - Add devfreq feature to the device
   * @dev:	the device to add devfreq feature.
   * @profile:	device-specific profile to run devfreq.
   * @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 char *governor_name,
  				   void *data)
  {
  	struct devfreq *devfreq;
  	struct devfreq_governor *governor;
  	int err = 0;
  
  	if (!dev || !profile || !governor_name) {
  		dev_err(dev, "%s: Invalid parameters.
  ", __func__);
  		return ERR_PTR(-EINVAL);
  	}
  
  	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.
  ", __func__);
  		err = -EINVAL;
  		goto err_out;
  	}
  
  	devfreq = kzalloc(sizeof(struct devfreq), GFP_KERNEL);
  	if (!devfreq) {
  		dev_err(dev, "%s: Unable to create devfreq for the device
  ",
  			__func__);
  		err = -ENOMEM;
  		goto err_out;
  	}
  
  	mutex_init(&devfreq->lock);
  	mutex_lock(&devfreq->lock);
  	devfreq->dev.parent = dev;
  	devfreq->dev.class = devfreq_class;
  	devfreq->dev.release = devfreq_dev_release;
  	devfreq->profile = profile;
  	strncpy(devfreq->governor_name, governor_name, DEVFREQ_NAME_LEN);
  	devfreq->previous_freq = profile->initial_freq;
  	devfreq->data = data;
  	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, "%s", dev_name(dev));
  	err = device_register(&devfreq->dev);
  	if (err) {
  		put_device(&devfreq->dev);
  		mutex_unlock(&devfreq->lock);
  		goto err_dev;
  	}
  
  	mutex_unlock(&devfreq->lock);
  
  	mutex_lock(&devfreq_list_lock);
  	list_add(&devfreq->node, &devfreq_list);
  
  	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);
  	if (err) {
  		dev_err(dev, "%s: Unable to start governor for the device
  ",
  			__func__);
  		goto err_init;
  	}
  
  	return devfreq;
  
  err_init:
  	list_del(&devfreq->node);
  	device_unregister(&devfreq->dev);
  err_dev:
  	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
   *
   * The opposite of devfreq_add_device().
   */
  int devfreq_remove_device(struct devfreq *devfreq)
  {
  	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
   *
   * This function is intended to be called by the pm callbacks
   * (e.g., runtime_suspend, suspend) of the device driver that
   * holds the devfreq.
   */
  int devfreq_suspend_device(struct devfreq *devfreq)
  {
  	if (!devfreq)
  		return -EINVAL;
  
  	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
   *
   * This function is intended to be called by the pm callbacks
   * (e.g., runtime_resume, resume) of the device driver that
   * holds the devfreq.
   */
  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.
  ", __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
  ", __func__,
  		       g->name);
  		err = -EINVAL;
  		goto err_out;
  	}
  
  	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
  ",
  					 __func__, devfreq->governor->name);
  				ret = devfreq->governor->event_handler(devfreq,
  							DEVFREQ_GOV_STOP, NULL);
  				if (ret) {
  					dev_warn(dev,
  						 "%s: Governor %s stop = %d
  ",
  						 __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
  ",
  					 __func__, devfreq->governor->name,
  					 ret);
  			}
  		}
  	}
  
  err_out:
  	mutex_unlock(&devfreq_list_lock);
  
  	return err;
  }
  EXPORT_SYMBOL(devfreq_add_governor);
  
  /**
   * 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.
  ", __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
  ", __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
  ",
  					 __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
  ",
  					 __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 governor_show(struct device *dev,
  			     struct device_attribute *attr, char *buf)
  {
  	if (!to_devfreq(dev)->governor)
  		return -EINVAL;
  
  	return sprintf(buf, "%s
  ", to_devfreq(dev)->governor->name);
  }
  
  static ssize_t governor_store(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)
  ",
  				 __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)
  ",
  			 __func__, df->governor->name, ret);
  out:
  	mutex_unlock(&devfreq_list_lock);
  
  	if (!ret)
  		ret = count;
  	return ret;
  }
  static DEVICE_ATTR_RW(governor);
  
  static ssize_t available_governors_show(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], "
  ");
  
  	return count;
  }
  static DEVICE_ATTR_RO(available_governors);
  
  static ssize_t cur_freq_show(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
  ", freq);
  
  	return sprintf(buf, "%lu
  ", devfreq->previous_freq);
  }
  static DEVICE_ATTR_RO(cur_freq);
  
  static ssize_t target_freq_show(struct device *dev,
  				struct device_attribute *attr, char *buf)
  {
  	return sprintf(buf, "%lu
  ", to_devfreq(dev)->previous_freq);
  }
  static DEVICE_ATTR_RO(target_freq);
  
  static ssize_t polling_interval_show(struct device *dev,
  				     struct device_attribute *attr, char *buf)
  {
  	return sprintf(buf, "%d
  ", to_devfreq(dev)->profile->polling_ms);
  }
  
  static ssize_t polling_interval_store(struct device *dev,
  				      struct device_attribute *attr,
  				      const char *buf, size_t count)
  {
  	struct devfreq *df = to_devfreq(dev);
  	unsigned int value;
  	int ret;
  
  	if (!df->governor)
  		return -EINVAL;
  
  	ret = sscanf(buf, "%u", &value);
  	if (ret != 1)
  		return -EINVAL;
  
  	df->governor->event_handler(df, DEVFREQ_GOV_INTERVAL, &value);
  	ret = count;
  
  	return ret;
  }
  static DEVICE_ATTR_RW(polling_interval);
  
  static ssize_t min_freq_store(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)
  		return -EINVAL;
  
  	mutex_lock(&df->lock);
  	max = df->max_freq;
  	if (value && max && value > max) {
  		ret = -EINVAL;
  		goto unlock;
  	}
  
  	df->min_freq = value;
  	update_devfreq(df);
  	ret = count;
  unlock:
  	mutex_unlock(&df->lock);
  	return ret;
  }
  
  static ssize_t min_freq_show(struct device *dev, struct device_attribute *attr,
  			     char *buf)
  {
  	return sprintf(buf, "%lu
  ", to_devfreq(dev)->min_freq);
  }
  
  static ssize_t max_freq_store(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 min;
  
  	ret = sscanf(buf, "%lu", &value);
  	if (ret != 1)
  		return -EINVAL;
  
  	mutex_lock(&df->lock);
  	min = df->min_freq;
  	if (value && min && value < min) {
  		ret = -EINVAL;
  		goto unlock;
  	}
  
  	df->max_freq = value;
  	update_devfreq(df);
  	ret = count;
  unlock:
  	mutex_unlock(&df->lock);
  	return ret;
  }
  static DEVICE_ATTR_RW(min_freq);
  
  static ssize_t max_freq_show(struct device *dev, struct device_attribute *attr,
  			     char *buf)
  {
  	return sprintf(buf, "%lu
  ", to_devfreq(dev)->max_freq);
  }
  static DEVICE_ATTR_RW(max_freq);
  
  static ssize_t available_frequencies_show(struct device *d,
  					  struct device_attribute *attr,
  					  char *buf)
  {
  	struct devfreq *df = to_devfreq(d);
  	struct device *dev = df->dev.parent;
  	struct dev_pm_opp *opp;
  	ssize_t count = 0;
  	unsigned long freq = 0;
  
  	rcu_read_lock();
  	do {
  		opp = dev_pm_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], "
  ");
  
  	return count;
  }
  static DEVICE_ATTR_RO(available_frequencies);
  
  static ssize_t trans_stat_show(struct device *dev,
  			       struct device_attribute *attr, char *buf)
  {
  	struct devfreq *devfreq = to_devfreq(dev);
  	ssize_t len;
  	int i, j;
  	unsigned int max_state = devfreq->profile->max_state;
  
  	if (!devfreq->stop_polling &&
  			devfreq_update_status(devfreq, devfreq->previous_freq))
  		return 0;
  
  	len = sprintf(buf, "   From  :   To
  ");
  	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)
  ");
  
  	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
  ",
  			jiffies_to_msecs(devfreq->time_in_state[i]));
  	}
  
  	len += sprintf(buf + len, "Total transition : %u
  ",
  					devfreq->total_trans);
  	return len;
  }
  static DEVICE_ATTR_RO(trans_stat);
  
  static struct attribute *devfreq_attrs[] = {
  	&dev_attr_governor.attr,
  	&dev_attr_available_governors.attr,
  	&dev_attr_cur_freq.attr,
  	&dev_attr_available_frequencies.attr,
  	&dev_attr_target_freq.attr,
  	&dev_attr_polling_interval.attr,
  	&dev_attr_min_freq.attr,
  	&dev_attr_max_freq.attr,
  	&dev_attr_trans_stat.attr,
  	NULL,
  };
  ATTRIBUTE_GROUPS(devfreq);
  
  static int __init devfreq_init(void)
  {
  	devfreq_class = class_create(THIS_MODULE, "devfreq");
  	if (IS_ERR(devfreq_class)) {
  		pr_err("%s: couldn't create class
  ", __FILE__);
  		return PTR_ERR(devfreq_class);
  	}
  
  	devfreq_wq = create_freezable_workqueue("devfreq_wq");
  	if (!devfreq_wq) {
  		class_destroy(devfreq_class);
  		pr_err("%s: couldn't create workqueue
  ", __FILE__);
  		return -ENOMEM;
  	}
  	devfreq_class->dev_groups = devfreq_groups;
  
  	return 0;
  }
  subsys_initcall(devfreq_init);
  
  static void __exit devfreq_exit(void)
  {
  	class_destroy(devfreq_class);
  	destroy_workqueue(devfreq_wq);
  }
  module_exit(devfreq_exit);
  
  /*
   * The followings are helper functions for devfreq user device drivers with
   * OPP framework.
   */
  
  /**
   * 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.
   *
   * Locking: This function must be called under rcu_read_lock(). opp is a rcu
   * protected pointer. The reason for the same is that the opp pointer which is
   * returned will remain valid for use with opp_get_{voltage, freq} only while
   * under the locked area. The pointer returned must be used prior to unlocking
   * with rcu_read_unlock() to maintain the integrity of the pointer.
   */
  struct dev_pm_opp *devfreq_recommended_opp(struct device *dev,
  					   unsigned long *freq,
  					   u32 flags)
  {
  	struct dev_pm_opp *opp;
  
  	if (flags & DEVFREQ_FLAG_LEAST_UPPER_BOUND) {
  		/* The freq is an upper bound. opp should be lower */
  		opp = dev_pm_opp_find_freq_floor(dev, freq);
  
  		/* If not available, use the closest opp */
  		if (opp == ERR_PTR(-ERANGE))
  			opp = dev_pm_opp_find_freq_ceil(dev, freq);
  	} else {
  		/* The freq is an lower bound. opp should be higher */
  		opp = dev_pm_opp_find_freq_ceil(dev, freq);
  
  		/* If not available, use the closest opp */
  		if (opp == ERR_PTR(-ERANGE))
  			opp = dev_pm_opp_find_freq_floor(dev, freq);
  	}
  
  	return opp;
  }
  
  /**
   * 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.
   */
  int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
  {
  	struct srcu_notifier_head *nh;
  	int ret = 0;
  
  	rcu_read_lock();
  	nh = dev_pm_opp_get_notifier(dev);
  	if (IS_ERR(nh))
  		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.
   *
   * 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;
  	int ret = 0;
  
  	rcu_read_lock();
  	nh = dev_pm_opp_get_notifier(dev);
  	if (IS_ERR(nh))
  		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>");
  MODULE_DESCRIPTION("devfreq class support");
  MODULE_LICENSE("GPL");