text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * devfreq: Generic Dynamic Voltage and Frequency Scaling (DVFS) Framework
   *	    for Non-CPU Devices.
   *
   * Copyright (C) 2011 Samsung Electronics
   *	MyungJoo Ham <myungjoo.ham@samsung.com>
   */
  
  #include <linux/kernel.h>
  #include <linux/kmod.h>
  #include <linux/sched.h>
  #include <linux/errno.h>
  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/export.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 <linux/of.h>
  #include "governor.h"
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/devfreq.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 (IS_ERR_OR_NULL(dev)) {
  		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_devfreq, &devfreq_list, node) {
  		if (tmp_devfreq->dev.parent == dev)
  			return tmp_devfreq;
  	}
  
  	return ERR_PTR(-ENODEV);
  }
  
  static unsigned long find_available_min_freq(struct devfreq *devfreq)
  {
  	struct dev_pm_opp *opp;
  	unsigned long min_freq = 0;
  
  	opp = dev_pm_opp_find_freq_ceil(devfreq->dev.parent, &min_freq);
  	if (IS_ERR(opp))
  		min_freq = 0;
  	else
  		dev_pm_opp_put(opp);
  
  	return min_freq;
  }
  
  static unsigned long find_available_max_freq(struct devfreq *devfreq)
  {
  	struct dev_pm_opp *opp;
  	unsigned long max_freq = ULONG_MAX;
  
  	opp = dev_pm_opp_find_freq_floor(devfreq->dev.parent, &max_freq);
  	if (IS_ERR(opp))
  		max_freq = 0;
  	else
  		dev_pm_opp_put(opp);
  
  	return max_freq;
  }
  
  /**
   * 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;
  }
  
  static int set_freq_table(struct devfreq *devfreq)
  {
  	struct devfreq_dev_profile *profile = devfreq->profile;
  	struct dev_pm_opp *opp;
  	unsigned long freq;
  	int i, count;
  
  	/* Initialize the freq_table from OPP table */
  	count = dev_pm_opp_get_opp_count(devfreq->dev.parent);
  	if (count <= 0)
  		return -EINVAL;
  
  	profile->max_state = count;
  	profile->freq_table = devm_kcalloc(devfreq->dev.parent,
  					profile->max_state,
  					sizeof(*profile->freq_table),
  					GFP_KERNEL);
  	if (!profile->freq_table) {
  		profile->max_state = 0;
  		return -ENOMEM;
  	}
  
  	for (i = 0, freq = 0; i < profile->max_state; i++, freq++) {
  		opp = dev_pm_opp_find_freq_ceil(devfreq->dev.parent, &freq);
  		if (IS_ERR(opp)) {
  			devm_kfree(devfreq->dev.parent, profile->freq_table);
  			profile->max_state = 0;
  			return PTR_ERR(opp);
  		}
  		dev_pm_opp_put(opp);
  		profile->freq_table[i] = freq;
  	}
  
  	return 0;
  }
  
  /**
   * devfreq_update_status() - Update statistics of devfreq behavior
   * @devfreq:	the devfreq instance
   * @freq:	the update target frequency
   */
  int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
  {
  	int lev, prev_lev, ret = 0;
  	unsigned long cur_time;
  
  	cur_time = jiffies;
  
  	/* Immediately exit if previous_freq is not initialized yet. */
  	if (!devfreq->previous_freq)
  		goto out;
  
  	prev_lev = devfreq_get_freq_level(devfreq, devfreq->previous_freq);
  	if (prev_lev < 0) {
  		ret = prev_lev;
  		goto out;
  	}
  
  	devfreq->time_in_state[prev_lev] +=
  			 cur_time - devfreq->last_stat_updated;
  
  	lev = devfreq_get_freq_level(devfreq, freq);
  	if (lev < 0) {
  		ret = lev;
  		goto out;
  	}
  
  	if (lev != prev_lev) {
  		devfreq->trans_table[(prev_lev *
  				devfreq->profile->max_state) + lev]++;
  		devfreq->total_trans++;
  	}
  
  out:
  	devfreq->last_stat_updated = cur_time;
  	return ret;
  }
  EXPORT_SYMBOL(devfreq_update_status);
  
  /**
   * 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 (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);
  }
  
  /**
   * try_then_request_governor() - Try to find the governor and request the
   *                               module if is not found.
   * @name:	name of the governor
   *
   * Search the list of devfreq governors and request the module and try again
   * if is not found. This can happen when both drivers (the governor driver
   * and the driver that call devfreq_add_device) are built as modules.
   * devfreq_list_lock should be held by the caller. Returns the matched
   * governor's pointer or an error pointer.
   */
  static struct devfreq_governor *try_then_request_governor(const char *name)
  {
  	struct devfreq_governor *governor;
  	int err = 0;
  
  	if (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.");
  
  	governor = find_devfreq_governor(name);
  	if (IS_ERR(governor)) {
  		mutex_unlock(&devfreq_list_lock);
  
  		if (!strncmp(name, DEVFREQ_GOV_SIMPLE_ONDEMAND,
  			     DEVFREQ_NAME_LEN))
  			err = request_module("governor_%s", "simpleondemand");
  		else
  			err = request_module("governor_%s", name);
  		/* Restore previous state before return */
  		mutex_lock(&devfreq_list_lock);
  		if (err)
  			return (err < 0) ? ERR_PTR(err) : ERR_PTR(-EINVAL);
  
  		governor = find_devfreq_governor(name);
  	}
  
  	return governor;
  }
  
  static int devfreq_notify_transition(struct devfreq *devfreq,
  		struct devfreq_freqs *freqs, unsigned int state)
  {
  	if (!devfreq)
  		return -EINVAL;
  
  	switch (state) {
  	case DEVFREQ_PRECHANGE:
  		srcu_notifier_call_chain(&devfreq->transition_notifier_list,
  				DEVFREQ_PRECHANGE, freqs);
  		break;
  
  	case DEVFREQ_POSTCHANGE:
  		srcu_notifier_call_chain(&devfreq->transition_notifier_list,
  				DEVFREQ_POSTCHANGE, freqs);
  		break;
  	default:
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
  			      u32 flags)
  {
  	struct devfreq_freqs freqs;
  	unsigned long cur_freq;
  	int err = 0;
  
  	if (devfreq->profile->get_cur_freq)
  		devfreq->profile->get_cur_freq(devfreq->dev.parent, &cur_freq);
  	else
  		cur_freq = devfreq->previous_freq;
  
  	freqs.old = cur_freq;
  	freqs.new = new_freq;
  	devfreq_notify_transition(devfreq, &freqs, DEVFREQ_PRECHANGE);
  
  	err = devfreq->profile->target(devfreq->dev.parent, &new_freq, flags);
  	if (err) {
  		freqs.new = cur_freq;
  		devfreq_notify_transition(devfreq, &freqs, DEVFREQ_POSTCHANGE);
  		return err;
  	}
  
  	freqs.new = new_freq;
  	devfreq_notify_transition(devfreq, &freqs, DEVFREQ_POSTCHANGE);
  
  	if (devfreq_update_status(devfreq, new_freq))
  		dev_err(&devfreq->dev,
  			"Couldn't update frequency transition information.\n");
  
  	devfreq->previous_freq = new_freq;
  
  	if (devfreq->suspend_freq)
  		devfreq->resume_freq = cur_freq;
  
  	return err;
  }
  
  /* 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, min_freq, max_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;
  	}
  
  	if (!devfreq->governor)
  		return -EINVAL;
  
  	/* Reevaluate the proper frequency */
  	err = devfreq->governor->get_target_freq(devfreq, &freq);
  	if (err)
  		return err;
  
  	/*
  	 * Adjust the frequency with user freq, QoS and available freq.
  	 *
  	 * List from the highest priority
  	 * max_freq
  	 * min_freq
  	 */
  	max_freq = min(devfreq->scaling_max_freq, devfreq->max_freq);
  	min_freq = max(devfreq->scaling_min_freq, devfreq->min_freq);
  
  	if (freq < min_freq) {
  		freq = min_freq;
  		flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use GLB */
  	}
  	if (freq > max_freq) {
  		freq = max_freq;
  		flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use LUB */
  	}
  
  	return devfreq_set_target(devfreq, freq, flags);
  
  }
  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);
  
  	trace_devfreq_monitor(devfreq);
  }
  
  /**
   * devfreq_monitor_start() - Start load monitoring of devfreq instance
   * @devfreq:	the devfreq instance.
   *
   * Helper function for starting devfreq device load monitoring. 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 monitoring. 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 monitoring. 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 monitoring. 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);
  
  	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
  	if (!devfreq->scaling_min_freq) {
  		mutex_unlock(&devfreq->lock);
  		return -EINVAL;
  	}
  
  	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
  	if (!devfreq->scaling_max_freq) {
  		mutex_unlock(&devfreq->lock);
  		return -EINVAL;
  	}
  
  	ret = update_devfreq(devfreq);
  	mutex_unlock(&devfreq->lock);
  
  	return ret;
  }
  
  /**
   * devfreq_dev_release() - Callback for struct device to release the device.
   * @dev:	the devfreq device
   *
   * Remove devfreq from the list and release its resources.
   */
  static void devfreq_dev_release(struct device *dev)
  {
  	struct devfreq *devfreq = to_devfreq(dev);
  
  	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->profile->exit)
  		devfreq->profile->exit(devfreq->dev.parent);
  
  	mutex_destroy(&devfreq->lock);
  	kfree(devfreq);
  }
  
  /**
   * 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;
  	static atomic_t devfreq_no = ATOMIC_INIT(-1);
  	int err = 0;
  
  	if (!dev || !profile || !governor_name) {
  		dev_err(dev, "%s: Invalid parameters.\n", __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.\n",
  			__func__);
  		err = -EINVAL;
  		goto err_out;
  	}
  
  	devfreq = kzalloc(sizeof(struct devfreq), GFP_KERNEL);
  	if (!devfreq) {
  		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->last_status.current_frequency = profile->initial_freq;
  	devfreq->data = data;
  	devfreq->nb.notifier_call = devfreq_notifier_call;
  
  	if (!devfreq->profile->max_state && !devfreq->profile->freq_table) {
  		mutex_unlock(&devfreq->lock);
  		err = set_freq_table(devfreq);
  		if (err < 0)
  			goto err_dev;
  		mutex_lock(&devfreq->lock);
  	}
  
  	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
  	if (!devfreq->scaling_min_freq) {
  		mutex_unlock(&devfreq->lock);
  		err = -EINVAL;
  		goto err_dev;
  	}
  	devfreq->min_freq = devfreq->scaling_min_freq;
  
  	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
  	if (!devfreq->scaling_max_freq) {
  		mutex_unlock(&devfreq->lock);
  		err = -EINVAL;
  		goto err_dev;
  	}
  	devfreq->max_freq = devfreq->scaling_max_freq;
  
  	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
  	atomic_set(&devfreq->suspend_count, 0);
  
  	dev_set_name(&devfreq->dev, "devfreq%d",
  				atomic_inc_return(&devfreq_no));
  	err = device_register(&devfreq->dev);
  	if (err) {
  		mutex_unlock(&devfreq->lock);
  		put_device(&devfreq->dev);
  		goto err_out;
  	}
  
  	devfreq->trans_table = devm_kzalloc(&devfreq->dev,
  			array3_size(sizeof(unsigned int),
  				    devfreq->profile->max_state,
  				    devfreq->profile->max_state),
  			GFP_KERNEL);
  	if (!devfreq->trans_table) {
  		mutex_unlock(&devfreq->lock);
  		err = -ENOMEM;
  		goto err_devfreq;
  	}
  
  	devfreq->time_in_state = devm_kcalloc(&devfreq->dev,
  			devfreq->profile->max_state,
  			sizeof(unsigned long),
  			GFP_KERNEL);
  	if (!devfreq->time_in_state) {
  		mutex_unlock(&devfreq->lock);
  		err = -ENOMEM;
  		goto err_devfreq;
  	}
  
  	devfreq->last_stat_updated = jiffies;
  
  	srcu_init_notifier_head(&devfreq->transition_notifier_list);
  
  	mutex_unlock(&devfreq->lock);
  
  	mutex_lock(&devfreq_list_lock);
  
  	governor = try_then_request_governor(devfreq->governor_name);
  	if (IS_ERR(governor)) {
  		dev_err(dev, "%s: Unable to find governor for the device\n",
  			__func__);
  		err = PTR_ERR(governor);
  		goto err_init;
  	}
  
  	devfreq->governor = governor;
  	err = devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_START,
  						NULL);
  	if (err) {
  		dev_err(dev, "%s: Unable to start governor for the device\n",
  			__func__);
  		goto err_init;
  	}
  
  	list_add(&devfreq->node, &devfreq_list);
  
  	mutex_unlock(&devfreq_list_lock);
  
  	return devfreq;
  
  err_init:
  	mutex_unlock(&devfreq_list_lock);
  err_devfreq:
  	devfreq_remove_device(devfreq);
  	devfreq = NULL;
  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;
  
  	if (devfreq->governor)
  		devfreq->governor->event_handler(devfreq,
  						 DEVFREQ_GOV_STOP, NULL);
  	device_unregister(&devfreq->dev);
  
  	return 0;
  }
  EXPORT_SYMBOL(devfreq_remove_device);
  
  static int devm_devfreq_dev_match(struct device *dev, void *res, void *data)
  {
  	struct devfreq **r = res;
  
  	if (WARN_ON(!r || !*r))
  		return 0;
  
  	return *r == data;
  }
  
  static void devm_devfreq_dev_release(struct device *dev, void *res)
  {
  	devfreq_remove_device(*(struct devfreq **)res);
  }
  
  /**
   * devm_devfreq_add_device() - Resource-managed devfreq_add_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.
   *
   * This function manages automatically the memory of devfreq device using device
   * resource management and simplify the free operation for memory of devfreq
   * device.
   */
  struct devfreq *devm_devfreq_add_device(struct device *dev,
  					struct devfreq_dev_profile *profile,
  					const char *governor_name,
  					void *data)
  {
  	struct devfreq **ptr, *devfreq;
  
  	ptr = devres_alloc(devm_devfreq_dev_release, sizeof(*ptr), GFP_KERNEL);
  	if (!ptr)
  		return ERR_PTR(-ENOMEM);
  
  	devfreq = devfreq_add_device(dev, profile, governor_name, data);
  	if (IS_ERR(devfreq)) {
  		devres_free(ptr);
  		return devfreq;
  	}
  
  	*ptr = devfreq;
  	devres_add(dev, ptr);
  
  	return devfreq;
  }
  EXPORT_SYMBOL(devm_devfreq_add_device);
  
  #ifdef CONFIG_OF
  /*
   * devfreq_get_devfreq_by_phandle - Get the devfreq device from devicetree
   * @dev - instance to the given device
   * @index - index into list of devfreq
   *
   * return the instance of devfreq device
   */
  struct devfreq *devfreq_get_devfreq_by_phandle(struct device *dev, int index)
  {
  	struct device_node *node;
  	struct devfreq *devfreq;
  
  	if (!dev)
  		return ERR_PTR(-EINVAL);
  
  	if (!dev->of_node)
  		return ERR_PTR(-EINVAL);
  
  	node = of_parse_phandle(dev->of_node, "devfreq", index);
  	if (!node)
  		return ERR_PTR(-ENODEV);
  
  	mutex_lock(&devfreq_list_lock);
  	list_for_each_entry(devfreq, &devfreq_list, node) {
  		if (devfreq->dev.parent
  			&& devfreq->dev.parent->of_node == node) {
  			mutex_unlock(&devfreq_list_lock);
  			of_node_put(node);
  			return devfreq;
  		}
  	}
  	mutex_unlock(&devfreq_list_lock);
  	of_node_put(node);
  
  	return ERR_PTR(-EPROBE_DEFER);
  }
  #else
  struct devfreq *devfreq_get_devfreq_by_phandle(struct device *dev, int index)
  {
  	return ERR_PTR(-ENODEV);
  }
  #endif /* CONFIG_OF */
  EXPORT_SYMBOL_GPL(devfreq_get_devfreq_by_phandle);
  
  /**
   * devm_devfreq_remove_device() - Resource-managed devfreq_remove_device()
   * @dev:	the device from which to remove devfreq feature.
   * @devfreq:	the devfreq instance to be removed
   */
  void devm_devfreq_remove_device(struct device *dev, struct devfreq *devfreq)
  {
  	WARN_ON(devres_release(dev, devm_devfreq_dev_release,
  			       devm_devfreq_dev_match, devfreq));
  }
  EXPORT_SYMBOL(devm_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)
  {
  	int ret;
  
  	if (!devfreq)
  		return -EINVAL;
  
  	if (atomic_inc_return(&devfreq->suspend_count) > 1)
  		return 0;
  
  	if (devfreq->governor) {
  		ret = devfreq->governor->event_handler(devfreq,
  					DEVFREQ_GOV_SUSPEND, NULL);
  		if (ret)
  			return ret;
  	}
  
  	if (devfreq->suspend_freq) {
  		ret = devfreq_set_target(devfreq, devfreq->suspend_freq, 0);
  		if (ret)
  			return ret;
  	}
  
  	return 0;
  }
  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)
  {
  	int ret;
  
  	if (!devfreq)
  		return -EINVAL;
  
  	if (atomic_dec_return(&devfreq->suspend_count) >= 1)
  		return 0;
  
  	if (devfreq->resume_freq) {
  		ret = devfreq_set_target(devfreq, devfreq->resume_freq, 0);
  		if (ret)
  			return ret;
  	}
  
  	if (devfreq->governor) {
  		ret = devfreq->governor->event_handler(devfreq,
  					DEVFREQ_GOV_RESUME, NULL);
  		if (ret)
  			return ret;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(devfreq_resume_device);
  
  /**
   * devfreq_suspend() - Suspend devfreq governors and devices
   *
   * Called during system wide Suspend/Hibernate cycles for suspending governors
   * and devices preserving the state for resume. On some platforms the devfreq
   * device must have precise state (frequency) after resume in order to provide
   * fully operating setup.
   */
  void devfreq_suspend(void)
  {
  	struct devfreq *devfreq;
  	int ret;
  
  	mutex_lock(&devfreq_list_lock);
  	list_for_each_entry(devfreq, &devfreq_list, node) {
  		ret = devfreq_suspend_device(devfreq);
  		if (ret)
  			dev_err(&devfreq->dev,
  				"failed to suspend devfreq device\n");
  	}
  	mutex_unlock(&devfreq_list_lock);
  }
  
  /**
   * devfreq_resume() - Resume devfreq governors and devices
   *
   * Called during system wide Suspend/Hibernate cycle for resuming governors and
   * devices that are suspended with devfreq_suspend().
   */
  void devfreq_resume(void)
  {
  	struct devfreq *devfreq;
  	int ret;
  
  	mutex_lock(&devfreq_list_lock);
  	list_for_each_entry(devfreq, &devfreq_list, node) {
  		ret = devfreq_resume_device(devfreq);
  		if (ret)
  			dev_warn(&devfreq->dev,
  				 "failed to resume devfreq device\n");
  	}
  	mutex_unlock(&devfreq_list_lock);
  }
  
  /**
   * 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;
  	}
  
  	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);
  			}
  		}
  	}
  
  err_out:
  	mutex_unlock(&devfreq_list_lock);
  
  	return err;
  }
  EXPORT_SYMBOL(devfreq_add_governor);
  
  /**
   * devfreq_remove_governor() - 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 governor_show(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 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];
  	const struct devfreq_governor *governor, *prev_governor;
  
  	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
  	if (ret != 1)
  		return -EINVAL;
  
  	mutex_lock(&devfreq_list_lock);
  	governor = try_then_request_governor(str_governor);
  	if (IS_ERR(governor)) {
  		ret = PTR_ERR(governor);
  		goto out;
  	}
  	if (df->governor == governor) {
  		ret = 0;
  		goto out;
  	} else if ((df->governor && df->governor->immutable) ||
  					governor->immutable) {
  		ret = -EINVAL;
  		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;
  		}
  	}
  	prev_governor = df->governor;
  	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);
  		df->governor = prev_governor;
  		strncpy(df->governor_name, prev_governor->name,
  			DEVFREQ_NAME_LEN);
  		ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
  		if (ret) {
  			dev_err(dev,
  				"%s: reverting to Governor %s failed (%d)\n",
  				__func__, df->governor_name, ret);
  			df->governor = NULL;
  		}
  	}
  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 *df = to_devfreq(d);
  	ssize_t count = 0;
  
  	mutex_lock(&devfreq_list_lock);
  
  	/*
  	 * The devfreq with immutable governor (e.g., passive) shows
  	 * only own governor.
  	 */
  	if (df->governor->immutable) {
  		count = scnprintf(&buf[count], DEVFREQ_NAME_LEN,
  				  "%s ", df->governor_name);
  	/*
  	 * The devfreq device shows the registered governor except for
  	 * immutable governors such as passive governor .
  	 */
  	} else {
  		struct devfreq_governor *governor;
  
  		list_for_each_entry(governor, &devfreq_governor_list, node) {
  			if (governor->immutable)
  				continue;
  			count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
  					   "%s ", governor->name);
  		}
  	}
  
  	mutex_unlock(&devfreq_list_lock);
  
  	/* Truncate the trailing space */
  	if (count)
  		count--;
  
  	count += sprintf(&buf[count], "\n");
  
  	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\n", freq);
  
  	return sprintf(buf, "%lu\n", 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\n", 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\n", 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;
  
  	ret = sscanf(buf, "%lu", &value);
  	if (ret != 1)
  		return -EINVAL;
  
  	mutex_lock(&df->lock);
  
  	if (value) {
  		if (value > df->max_freq) {
  			ret = -EINVAL;
  			goto unlock;
  		}
  	} else {
  		unsigned long *freq_table = df->profile->freq_table;
  
  		/* Get minimum frequency according to sorting order */
  		if (freq_table[0] < freq_table[df->profile->max_state - 1])
  			value = freq_table[0];
  		else
  			value = freq_table[df->profile->max_state - 1];
  	}
  
  	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)
  {
  	struct devfreq *df = to_devfreq(dev);
  
  	return sprintf(buf, "%lu\n", max(df->scaling_min_freq, df->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;
  
  	ret = sscanf(buf, "%lu", &value);
  	if (ret != 1)
  		return -EINVAL;
  
  	mutex_lock(&df->lock);
  
  	if (value) {
  		if (value < df->min_freq) {
  			ret = -EINVAL;
  			goto unlock;
  		}
  	} else {
  		unsigned long *freq_table = df->profile->freq_table;
  
  		/* Get maximum frequency according to sorting order */
  		if (freq_table[0] < freq_table[df->profile->max_state - 1])
  			value = freq_table[df->profile->max_state - 1];
  		else
  			value = freq_table[0];
  	}
  
  	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)
  {
  	struct devfreq *df = to_devfreq(dev);
  
  	return sprintf(buf, "%lu\n", min(df->scaling_max_freq, df->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);
  	ssize_t count = 0;
  	int i;
  
  	mutex_lock(&df->lock);
  
  	for (i = 0; i < df->profile->max_state; i++)
  		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
  				"%lu ", df->profile->freq_table[i]);
  
  	mutex_unlock(&df->lock);
  	/* Truncate the trailing space */
  	if (count)
  		count--;
  
  	count += sprintf(&buf[count], "\n");
  
  	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;
  	if (max_state == 0)
  		return sprintf(buf, "Not Supported.\n");
  
  	len = sprintf(buf, "     From  :   To\n");
  	len += sprintf(buf + len, "           :");
  	for (i = 0; i < max_state; i++)
  		len += sprintf(buf + len, "%10lu",
  				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, "%10lu:",
  				devfreq->profile->freq_table[i]);
  		for (j = 0; j < max_state; j++)
  			len += sprintf(buf + len, "%10u",
  				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 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\n", __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\n", __FILE__);
  		return -ENOMEM;
  	}
  	devfreq_class->dev_groups = devfreq_groups;
  
  	return 0;
  }
  subsys_initcall(devfreq_init);
  
  /*
   * The following 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.
   *
   * The callers are required to call dev_pm_opp_put() for the returned OPP after
   * use.
   */
  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;
  }
  EXPORT_SYMBOL(devfreq_recommended_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)
  {
  	return dev_pm_opp_register_notifier(dev, &devfreq->nb);
  }
  EXPORT_SYMBOL(devfreq_register_opp_notifier);
  
  /**
   * 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)
  {
  	return dev_pm_opp_unregister_notifier(dev, &devfreq->nb);
  }
  EXPORT_SYMBOL(devfreq_unregister_opp_notifier);
  
  static void devm_devfreq_opp_release(struct device *dev, void *res)
  {
  	devfreq_unregister_opp_notifier(dev, *(struct devfreq **)res);
  }
  
  /**
   * devm_devfreq_register_opp_notifier() - Resource-managed
   *					  devfreq_register_opp_notifier()
   * @dev:	The devfreq user device. (parent of devfreq)
   * @devfreq:	The devfreq object.
   */
  int devm_devfreq_register_opp_notifier(struct device *dev,
  				       struct devfreq *devfreq)
  {
  	struct devfreq **ptr;
  	int ret;
  
  	ptr = devres_alloc(devm_devfreq_opp_release, sizeof(*ptr), GFP_KERNEL);
  	if (!ptr)
  		return -ENOMEM;
  
  	ret = devfreq_register_opp_notifier(dev, devfreq);
  	if (ret) {
  		devres_free(ptr);
  		return ret;
  	}
  
  	*ptr = devfreq;
  	devres_add(dev, ptr);
  
  	return 0;
  }
  EXPORT_SYMBOL(devm_devfreq_register_opp_notifier);
  
  /**
   * devm_devfreq_unregister_opp_notifier() - Resource-managed
   *					    devfreq_unregister_opp_notifier()
   * @dev:	The devfreq user device. (parent of devfreq)
   * @devfreq:	The devfreq object.
   */
  void devm_devfreq_unregister_opp_notifier(struct device *dev,
  					 struct devfreq *devfreq)
  {
  	WARN_ON(devres_release(dev, devm_devfreq_opp_release,
  			       devm_devfreq_dev_match, devfreq));
  }
  EXPORT_SYMBOL(devm_devfreq_unregister_opp_notifier);
  
  /**
   * devfreq_register_notifier() - Register a driver with devfreq
   * @devfreq:	The devfreq object.
   * @nb:		The notifier block to register.
   * @list:	DEVFREQ_TRANSITION_NOTIFIER.
   */
  int devfreq_register_notifier(struct devfreq *devfreq,
  			      struct notifier_block *nb,
  			      unsigned int list)
  {
  	int ret = 0;
  
  	if (!devfreq)
  		return -EINVAL;
  
  	switch (list) {
  	case DEVFREQ_TRANSITION_NOTIFIER:
  		ret = srcu_notifier_chain_register(
  				&devfreq->transition_notifier_list, nb);
  		break;
  	default:
  		ret = -EINVAL;
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL(devfreq_register_notifier);
  
  /*
   * devfreq_unregister_notifier() - Unregister a driver with devfreq
   * @devfreq:	The devfreq object.
   * @nb:		The notifier block to be unregistered.
   * @list:	DEVFREQ_TRANSITION_NOTIFIER.
   */
  int devfreq_unregister_notifier(struct devfreq *devfreq,
  				struct notifier_block *nb,
  				unsigned int list)
  {
  	int ret = 0;
  
  	if (!devfreq)
  		return -EINVAL;
  
  	switch (list) {
  	case DEVFREQ_TRANSITION_NOTIFIER:
  		ret = srcu_notifier_chain_unregister(
  				&devfreq->transition_notifier_list, nb);
  		break;
  	default:
  		ret = -EINVAL;
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL(devfreq_unregister_notifier);
  
  struct devfreq_notifier_devres {
  	struct devfreq *devfreq;
  	struct notifier_block *nb;
  	unsigned int list;
  };
  
  static void devm_devfreq_notifier_release(struct device *dev, void *res)
  {
  	struct devfreq_notifier_devres *this = res;
  
  	devfreq_unregister_notifier(this->devfreq, this->nb, this->list);
  }
  
  /**
   * devm_devfreq_register_notifier()
  	- Resource-managed devfreq_register_notifier()
   * @dev:	The devfreq user device. (parent of devfreq)
   * @devfreq:	The devfreq object.
   * @nb:		The notifier block to be unregistered.
   * @list:	DEVFREQ_TRANSITION_NOTIFIER.
   */
  int devm_devfreq_register_notifier(struct device *dev,
  				struct devfreq *devfreq,
  				struct notifier_block *nb,
  				unsigned int list)
  {
  	struct devfreq_notifier_devres *ptr;
  	int ret;
  
  	ptr = devres_alloc(devm_devfreq_notifier_release, sizeof(*ptr),
  				GFP_KERNEL);
  	if (!ptr)
  		return -ENOMEM;
  
  	ret = devfreq_register_notifier(devfreq, nb, list);
  	if (ret) {
  		devres_free(ptr);
  		return ret;
  	}
  
  	ptr->devfreq = devfreq;
  	ptr->nb = nb;
  	ptr->list = list;
  	devres_add(dev, ptr);
  
  	return 0;
  }
  EXPORT_SYMBOL(devm_devfreq_register_notifier);
  
  /**
   * devm_devfreq_unregister_notifier()
  	- Resource-managed devfreq_unregister_notifier()
   * @dev:	The devfreq user device. (parent of devfreq)
   * @devfreq:	The devfreq object.
   * @nb:		The notifier block to be unregistered.
   * @list:	DEVFREQ_TRANSITION_NOTIFIER.
   */
  void devm_devfreq_unregister_notifier(struct device *dev,
  				      struct devfreq *devfreq,
  				      struct notifier_block *nb,
  				      unsigned int list)
  {
  	WARN_ON(devres_release(dev, devm_devfreq_notifier_release,
  			       devm_devfreq_dev_match, devfreq));
  }
  EXPORT_SYMBOL(devm_devfreq_unregister_notifier);
  