/*
 * 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/opp.h>
#include <linux/devfreq.h>
#include <linux/workqueue.h>
#include <linux/platform_device.h>
#include <linux/list.h>
#include <linux/printk.h>
#include <linux/hrtimer.h>
#include "governor.h"

struct class *devfreq_class;

/*
 * devfreq_work periodically monitors every registered device.
 * The minimum polling interval is one jiffy. The polling interval is
 * determined by the minimum polling period among all polling devfreq
 * devices. The resolution of polling interval is one jiffy.
 */
static bool polling;
static struct workqueue_struct *devfreq_wq;
static struct delayed_work devfreq_work;

/* wait removing if this is to be removed */
static struct devfreq *wait_remove_device;

/* The list of all device-devfreq */
static LIST_HEAD(devfreq_list);
static DEFINE_MUTEX(devfreq_list_lock);

/**
 * find_device_devfreq() - find devfreq struct using device pointer
 * @dev:        device pointer used to lookup device devfreq.
 *
 * Search the list of device devfreqs and return the matched device's
 * devfreq info. devfreq_list_lock should be held by the caller.
 */
static struct devfreq *find_device_devfreq(struct device *dev)
{
        struct devfreq *tmp_devfreq;

        if (unlikely(IS_ERR_OR_NULL(dev))) {
                pr_err("DEVFREQ: %s: Invalid parameters\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);
}

/**
 * update_devfreq() - Reevaluate the device and configure frequency.
 * @devfreq:    the devfreq instance.
 *
 * Note: Lock devfreq->lock before calling update_devfreq
 *       This function is exported for governors.
 */
int update_devfreq(struct devfreq *devfreq)
{
        unsigned long freq;
        int err = 0;

        if (!mutex_is_locked(&devfreq->lock)) {
                WARN(true, "devfreq->lock must be locked by the caller.\n");
                return -EINVAL;
        }

        /* Reevaluate the proper frequency */
        err = devfreq->governor->get_target_freq(devfreq, &freq);
        if (err)
                return err;

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

        devfreq->previous_freq = freq;
        return err;
}

/**
 * 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 device.
 * @devfreq:    the devfreq struct
 * @skip:       skip calling device_unregister().
 *
 * Note that the caller should lock devfreq->lock before calling
 * this. _remove_devfreq() will unlock it and free devfreq
 * internally. devfreq_list_lock should be locked by the caller
 * as well (not relased at return)
 *
 * Lock usage:
 * devfreq->lock: locked before call.
 *                unlocked at return (and freed)
 * devfreq_list_lock: locked before call.
 *                    kept locked at return.
 *                    if devfreq is centrally polled.
 *
 * Freed memory:
 * devfreq
 */
static void _remove_devfreq(struct devfreq *devfreq, bool skip)
{
        if (!mutex_is_locked(&devfreq->lock)) {
                WARN(true, "devfreq->lock must be locked by the caller.\n");
                return;
        }
        if (!devfreq->governor->no_central_polling &&
            !mutex_is_locked(&devfreq_list_lock)) {
                WARN(true, "devfreq_list_lock must be locked by the caller.\n");
                return;
        }

        if (devfreq->being_removed)
                return;

        devfreq->being_removed = true;

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

        if (devfreq->governor->exit)
                devfreq->governor->exit(devfreq);

        if (!skip && get_device(&devfreq->dev)) {
                device_unregister(&devfreq->dev);
                put_device(&devfreq->dev);
        }

        if (!devfreq->governor->no_central_polling)
                list_del(&devfreq->node);

        mutex_unlock(&devfreq->lock);
        mutex_destroy(&devfreq->lock);

        kfree(devfreq);
}

/**
 * devfreq_dev_release() - Callback for struct device to release the device.
 * @dev:        the devfreq device
 *
 * This calls _remove_devfreq() if _remove_devfreq() is not called.
 * Note that devfreq_dev_release() could be called by _remove_devfreq() as
 * well as by others unregistering the device.
 */
static void devfreq_dev_release(struct device *dev)
{
        struct devfreq *devfreq = to_devfreq(dev);
        bool central_polling = !devfreq->governor->no_central_polling;

        /*
         * If devfreq_dev_release() was called by device_unregister() of
         * _remove_devfreq(), we cannot mutex_lock(&devfreq->lock) and
         * being_removed is already set. This also partially checks the case
         * where devfreq_dev_release() is called from a thread other than
         * the one called _remove_devfreq(); however, this case is
         * dealt completely with another following being_removed check.
         *
         * Because being_removed is never being
         * unset, we do not need to worry about race conditions on
         * being_removed.
         */
        if (devfreq->being_removed)
                return;

        if (central_polling)
                mutex_lock(&devfreq_list_lock);

        mutex_lock(&devfreq->lock);

        /*
         * Check being_removed flag again for the case where
         * devfreq_dev_release() was called in a thread other than the one
         * possibly called _remove_devfreq().
         */
        if (devfreq->being_removed) {
                mutex_unlock(&devfreq->lock);
                goto out;
        }

        /* devfreq->lock is unlocked and removed in _removed_devfreq() */
        _remove_devfreq(devfreq, true);

out:
        if (central_polling)
                mutex_unlock(&devfreq_list_lock);
}

/**
 * devfreq_monitor() - Periodically poll devfreq objects.
 * @work: the work struct used to run devfreq_monitor periodically.
 *
 */
static void devfreq_monitor(struct work_struct *work)
{
        static unsigned long last_polled_at;
        struct devfreq *devfreq, *tmp;
        int error;
        unsigned long jiffies_passed;
        unsigned long next_jiffies = ULONG_MAX, now = jiffies;
        struct device *dev;

        /* Initially last_polled_at = 0, polling every device at bootup */
        jiffies_passed = now - last_polled_at;
        last_polled_at = now;
        if (jiffies_passed == 0)
                jiffies_passed = 1;

        mutex_lock(&devfreq_list_lock);
        list_for_each_entry_safe(devfreq, tmp, &devfreq_list, node) {
                mutex_lock(&devfreq->lock);
                dev = devfreq->dev.parent;

                /* Do not remove tmp for a while */
                wait_remove_device = tmp;

                if (devfreq->governor->no_central_polling ||
                    devfreq->next_polling == 0) {
                        mutex_unlock(&devfreq->lock);
                        continue;
                }
                mutex_unlock(&devfreq_list_lock);

                /*
                 * Reduce more next_polling if devfreq_wq took an extra
                 * delay. (i.e., CPU has been idled.)
                 */
                if (devfreq->next_polling <= jiffies_passed) {
                        error = update_devfreq(devfreq);

                        /* Remove a devfreq with an error. */
                        if (error && error != -EAGAIN) {

                                dev_err(dev, "Due to update_devfreq error(%d), devfreq(%s) is removed from the device\n",
                                        error, devfreq->governor->name);

                                /*
                                 * Unlock devfreq before locking the list
                                 * in order to avoid deadlock with
                                 * find_device_devfreq or others
                                 */
                                mutex_unlock(&devfreq->lock);
                                mutex_lock(&devfreq_list_lock);
                                /* Check if devfreq is already removed */
                                if (IS_ERR(find_device_devfreq(dev)))
                                        continue;
                                mutex_lock(&devfreq->lock);
                                /* This unlocks devfreq->lock and free it */
                                _remove_devfreq(devfreq, false);
                                continue;
                        }
                        devfreq->next_polling = devfreq->polling_jiffies;
                } else {
                        devfreq->next_polling -= jiffies_passed;
                }

                if (devfreq->next_polling)
                        next_jiffies = (next_jiffies > devfreq->next_polling) ?
                                        devfreq->next_polling : next_jiffies;

                mutex_unlock(&devfreq->lock);
                mutex_lock(&devfreq_list_lock);
        }
        wait_remove_device = NULL;
        mutex_unlock(&devfreq_list_lock);

        if (next_jiffies > 0 && next_jiffies < ULONG_MAX) {
                polling = true;
                queue_delayed_work(devfreq_wq, &devfreq_work, next_jiffies);
        } else {
                polling = false;
        }
}

/**
 * devfreq_add_device() - Add devfreq feature to the device
 * @dev:        the device to add devfreq feature.
 * @profile:    device-specific profile to run devfreq.
 * @governor:   the policy to choose frequency.
 * @data:       private data for the governor. The devfreq framework does not
 *              touch this value.
 */
struct devfreq *devfreq_add_device(struct device *dev,
                                   struct devfreq_dev_profile *profile,
                                   const struct devfreq_governor *governor,
                                   void *data)
{
        struct devfreq *devfreq;
        int err = 0;

        if (!dev || !profile || !governor) {
                dev_err(dev, "%s: Invalid parameters.\n", __func__);
                return ERR_PTR(-EINVAL);
        }


        if (!governor->no_central_polling) {
                mutex_lock(&devfreq_list_lock);
                devfreq = find_device_devfreq(dev);
                mutex_unlock(&devfreq_list_lock);
                if (!IS_ERR(devfreq)) {
                        dev_err(dev, "%s: Unable to create devfreq for the device. It already has one.\n", __func__);
                        err = -EINVAL;
                        goto err_out;
                }
        }

        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;
        devfreq->governor = governor;
        devfreq->previous_freq = profile->initial_freq;
        devfreq->data = data;
        devfreq->next_polling = devfreq->polling_jiffies
                              = msecs_to_jiffies(devfreq->profile->polling_ms);
        devfreq->nb.notifier_call = devfreq_notifier_call;

        dev_set_name(&devfreq->dev, dev_name(dev));
        err = device_register(&devfreq->dev);
        if (err) {
                put_device(&devfreq->dev);
                goto err_dev;
        }

        if (governor->init)
                err = governor->init(devfreq);
        if (err)
                goto err_init;

        mutex_unlock(&devfreq->lock);

        if (governor->no_central_polling)
                goto out;

        mutex_lock(&devfreq_list_lock);

        list_add(&devfreq->node, &devfreq_list);

        if (devfreq_wq && devfreq->next_polling && !polling) {
                polling = true;
                queue_delayed_work(devfreq_wq, &devfreq_work,
                                   devfreq->next_polling);
        }
        mutex_unlock(&devfreq_list_lock);
out:
        return devfreq;

err_init:
        device_unregister(&devfreq->dev);
err_dev:
        mutex_unlock(&devfreq->lock);
        kfree(devfreq);
err_out:
        return ERR_PTR(err);
}

/**
 * devfreq_remove_device() - Remove devfreq feature from a device.
 * @devfreq     the devfreq instance to be removed
 */
int devfreq_remove_device(struct devfreq *devfreq)
{
        bool central_polling;

        if (!devfreq)
                return -EINVAL;

        central_polling = !devfreq->governor->no_central_polling;

        if (central_polling) {
                mutex_lock(&devfreq_list_lock);
                while (wait_remove_device == devfreq) {
                        mutex_unlock(&devfreq_list_lock);
                        schedule();
                        mutex_lock(&devfreq_list_lock);
                }
        }

        mutex_lock(&devfreq->lock);
        _remove_devfreq(devfreq, false); /* it unlocks devfreq->lock */

        if (central_polling)
                mutex_unlock(&devfreq_list_lock);

        return 0;
}

static ssize_t show_governor(struct device *dev,
                             struct device_attribute *attr, char *buf)
{
        return sprintf(buf, "%s\n", to_devfreq(dev)->governor->name);
}

static ssize_t show_freq(struct device *dev,
                         struct device_attribute *attr, char *buf)
{
        return sprintf(buf, "%lu\n", to_devfreq(dev)->previous_freq);
}

static ssize_t show_polling_interval(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        return sprintf(buf, "%d\n", to_devfreq(dev)->profile->polling_ms);
}

static ssize_t store_polling_interval(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf, size_t count)
{
        struct devfreq *df = to_devfreq(dev);
        unsigned int value;
        int ret;

        ret = sscanf(buf, "%u", &value);
        if (ret != 1)
                goto out;

        mutex_lock(&df->lock);
        df->profile->polling_ms = value;
        df->next_polling = df->polling_jiffies
                         = msecs_to_jiffies(value);
        mutex_unlock(&df->lock);

        ret = count;

        if (df->governor->no_central_polling)
                goto out;

        mutex_lock(&devfreq_list_lock);
        if (df->next_polling > 0 && !polling) {
                polling = true;
                queue_delayed_work(devfreq_wq, &devfreq_work,
                                   df->next_polling);
        }
        mutex_unlock(&devfreq_list_lock);
out:
        return ret;
}

static ssize_t show_central_polling(struct device *dev,
                                    struct device_attribute *attr, char *buf)
{
        return sprintf(buf, "%d\n",
                       !to_devfreq(dev)->governor->no_central_polling);
}

static struct device_attribute devfreq_attrs[] = {
        __ATTR(governor, S_IRUGO, show_governor, NULL),
        __ATTR(cur_freq, S_IRUGO, show_freq, NULL),
        __ATTR(central_polling, S_IRUGO, show_central_polling, NULL),
        __ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
               store_polling_interval),
        { },
};

/**
 * devfreq_start_polling() - Initialize data structure for devfreq framework and
 *                         start polling registered devfreq devices.
 */
static int __init devfreq_start_polling(void)
{
        mutex_lock(&devfreq_list_lock);
        polling = false;
        devfreq_wq = create_freezable_workqueue("devfreq_wq");
        INIT_DELAYED_WORK_DEFERRABLE(&devfreq_work, devfreq_monitor);
        mutex_unlock(&devfreq_list_lock);

        devfreq_monitor(&devfreq_work.work);
        return 0;
}
late_initcall(devfreq_start_polling);

static int __init devfreq_init(void)
{
        devfreq_class = class_create(THIS_MODULE, "devfreq");
        if (IS_ERR(devfreq_class)) {
                pr_err("%s: couldn't create class\n", __FILE__);
                return PTR_ERR(devfreq_class);
        }
        devfreq_class->dev_attrs = devfreq_attrs;
        return 0;
}
subsys_initcall(devfreq_init);

static void __exit devfreq_exit(void)
{
        class_destroy(devfreq_class);
}
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
 *
 */
struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq)
{
        struct opp *opp = opp_find_freq_ceil(dev, freq);

        if (opp == ERR_PTR(-ENODEV))
                opp = opp_find_freq_floor(dev, freq);
        return opp;
}

/**
 * devfreq_register_opp_notifier() - Helper function to get devfreq notified
 *                                 for any changes in the OPP availability
 *                                 changes
 * @dev         The devfreq user device. (parent of devfreq)
 * @devfreq     The devfreq object.
 */
int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
{
        struct srcu_notifier_head *nh = opp_get_notifier(dev);

        if (IS_ERR(nh))
                return PTR_ERR(nh);
        return srcu_notifier_chain_register(nh, &devfreq->nb);
}

/**
 * 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 = opp_get_notifier(dev);

        if (IS_ERR(nh))
                return PTR_ERR(nh);
        return srcu_notifier_chain_unregister(nh, &devfreq->nb);
}

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