[mirror_ubuntu-bionic-kernel.git] / drivers / devfreq / devfreq.c

/*
 * 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 <linux/of.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 (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);
}

/**
 * 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_set_freq_table() - Initialize freq_table for the frequency
 * @devfreq:    the devfreq instance
 */
static void devfreq_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;

        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;
        }

        rcu_read_lock();
        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;
                        rcu_read_unlock();
                        return;
                }
                profile->freq_table[i] = freq;
        }
        rcu_read_unlock();
}

/**
 * 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, ret = 0;
        unsigned long cur_time;

        cur_time = jiffies;

        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;
}

/**
 * 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);
}

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;
}

/* 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)
{
        struct devfreq_freqs freqs;
        unsigned long freq, cur_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 and QoS.
         *
         * List from the highest priority
         * max_freq
         * 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 */
        }

        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 = freq;
        devfreq_notify_transition(devfreq, &freqs, DEVFREQ_PRECHANGE);

        err = devfreq->profile->target(devfreq->dev.parent, &freq, flags);
        if (err)
                return err;

        freqs.new = freq;
        devfreq_notify_transition(devfreq, &freqs, DEVFREQ_POSTCHANGE);

        if (devfreq->profile->freq_table)
                if (devfreq_update_status(devfreq, freq))
                        dev_err(&devfreq->dev,
                                "Couldn't update frequency transition information.\n");

        devfreq->previous_freq = freq;
        return err;
}
EXPORT_SYMBOL(update_devfreq);

/**
 * devfreq_monitor() - Periodically poll devfreq objects.
 * @work:       the work struct used to run devfreq_monitor periodically.
 *
 */
static void devfreq_monitor(struct work_struct *work)
{
        int err;
        struct devfreq *devfreq = container_of(work,
                                        struct devfreq, work.work);

        mutex_lock(&devfreq->lock);
        err = update_devfreq(devfreq);
        if (err)
                dev_err(&devfreq->dev, "dvfs failed with (%d) error\n", err);

        queue_delayed_work(devfreq_wq, &devfreq->work,
                                msecs_to_jiffies(devfreq->profile->polling_ms));
        mutex_unlock(&devfreq->lock);
}

/**
 * devfreq_monitor_start() - Start load monitoring of devfreq instance
 * @devfreq:    the devfreq instance.
 *
 * Helper function for starting devfreq device load monitoing. By
 * default delayed work based monitoring is supported. Function
 * to be called from governor in response to DEVFREQ_GOV_START
 * event when device is added to devfreq framework.
 */
void devfreq_monitor_start(struct devfreq *devfreq)
{
        INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
        if (devfreq->profile->polling_ms)
                queue_delayed_work(devfreq_wq, &devfreq->work,
                        msecs_to_jiffies(devfreq->profile->polling_ms));
}
EXPORT_SYMBOL(devfreq_monitor_start);

/**
 * devfreq_monitor_stop() - Stop load monitoring of a devfreq instance
 * @devfreq:    the devfreq instance.
 *
 * Helper function to stop devfreq device load monitoing. Function
 * to be called from governor in response to DEVFREQ_GOV_STOP
 * event when device is removed from devfreq framework.
 */
void devfreq_monitor_stop(struct devfreq *devfreq)
{
        cancel_delayed_work_sync(&devfreq->work);
}
EXPORT_SYMBOL(devfreq_monitor_stop);

/**
 * devfreq_monitor_suspend() - Suspend load monitoring of a devfreq instance
 * @devfreq:    the devfreq instance.
 *
 * Helper function to suspend devfreq device load monitoing. Function
 * to be called from governor in response to DEVFREQ_GOV_SUSPEND
 * event or when polling interval is set to zero.
 *
 * Note: Though this function is same as devfreq_monitor_stop(),
 * intentionally kept separate to provide hooks for collecting
 * transition statistics.
 */
void devfreq_monitor_suspend(struct devfreq *devfreq)
{
        mutex_lock(&devfreq->lock);
        if (devfreq->stop_polling) {
                mutex_unlock(&devfreq->lock);
                return;
        }

        devfreq_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
 */
static void _remove_devfreq(struct devfreq *devfreq)
{
        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->governor)
                devfreq->governor->event_handler(devfreq,
                                                 DEVFREQ_GOV_STOP, NULL);

        if (devfreq->profile->exit)
                devfreq->profile->exit(devfreq->dev.parent);

        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.
 */
static void devfreq_dev_release(struct device *dev)
{
        struct devfreq *devfreq = to_devfreq(dev);

        _remove_devfreq(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;
        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. It already has one.\n", __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\n",
                        __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->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);
                devfreq_set_freq_table(devfreq);
                mutex_lock(&devfreq->lock);
        }

        dev_set_name(&devfreq->dev, "%s", dev_name(dev));
        err = device_register(&devfreq->dev);
        if (err) {
                mutex_unlock(&devfreq->lock);
                goto err_out;
        }

        devfreq->trans_table =  devm_kzalloc(&devfreq->dev, sizeof(unsigned int) *
                                                devfreq->profile->max_state *
                                                devfreq->profile->max_state,
                                                GFP_KERNEL);
        devfreq->time_in_state = devm_kzalloc(&devfreq->dev, sizeof(unsigned long) *
                                                devfreq->profile->max_state,
                                                GFP_KERNEL);
        devfreq->last_stat_updated = jiffies;

        srcu_init_notifier_head(&devfreq->transition_notifier_list);

        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\n",
                        __func__);
                goto err_init;
        }

        return devfreq;

err_init:
        list_del(&devfreq->node);
        device_unregister(&devfreq->dev);
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;

        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 ERR_PTR(-ENOMEM);
        }

        *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);
                        return devfreq;
                }
        }
        mutex_unlock(&devfreq_list_lock);

        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 to add 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)
{
        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.\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_device() - Remove devfreq feature from a device.
 * @governor:   the devfreq governor to be removed
 */
int devfreq_remove_governor(struct devfreq_governor *governor)
{
        struct devfreq_governor *g;
        struct devfreq *devfreq;
        int err = 0;

        if (!governor) {
                pr_err("%s: Invalid parameters.\n", __func__);
                return -EINVAL;
        }

        mutex_lock(&devfreq_list_lock);
        g = find_devfreq_governor(governor->name);
        if (IS_ERR(g)) {
                pr_err("%s: governor %s not registered\n", __func__,
                       governor->name);
                err = PTR_ERR(g);
                goto err_out;
        }
        list_for_each_entry(devfreq, &devfreq_list, node) {
                int ret;
                struct device *dev = devfreq->dev.parent;

                if (!strncmp(devfreq->governor_name, governor->name,
                             DEVFREQ_NAME_LEN)) {
                        /* we should have a devfreq governor! */
                        if (!devfreq->governor) {
                                dev_warn(dev, "%s: Governor %s NOT present\n",
                                         __func__, governor->name);
                                continue;
                                /* Fall through */
                        }
                        ret = devfreq->governor->event_handler(devfreq,
                                                DEVFREQ_GOV_STOP, NULL);
                        if (ret) {
                                dev_warn(dev, "%s: Governor %s stop=%d\n",
                                         __func__, devfreq->governor->name,
                                         ret);
                        }
                        devfreq->governor = NULL;
                }
        }

        list_del(&governor->node);
err_out:
        mutex_unlock(&devfreq_list_lock);

        return err;
}
EXPORT_SYMBOL(devfreq_remove_governor);

static ssize_t 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];
        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) {
                ret = 0;
                goto out;
        }

        if (df->governor) {
                ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
                if (ret) {
                        dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
                                 __func__, df->governor->name, ret);
                        goto out;
                }
        }
        df->governor = governor;
        strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
        ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
        if (ret)
                dev_warn(dev, "%s: Governor %s not started(%d)\n",
                         __func__, df->governor->name, ret);
out:
        mutex_unlock(&devfreq_list_lock);

        if (!ret)
                ret = count;
        return ret;
}
static 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], "\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;
        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 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;
}

#define show_one(name)                                          \
static ssize_t name##_show                                      \
(struct device *dev, struct device_attribute *attr, char *buf)  \
{                                                               \
        return sprintf(buf, "%lu\n", to_devfreq(dev)->name);    \
}
show_one(min_freq);
show_one(max_freq);

static DEVICE_ATTR_RW(min_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], "\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);

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;
}
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)
{
        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;
}
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)
{
        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;
}
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);

MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@samsung.com>");
MODULE_DESCRIPTION("devfreq class support");
MODULE_LICENSE("GPL");