/*
 * drivers/cpufreq/cpufreq_governor.c
 *
 * CPUFREQ governors common code
 *
 * Copyright    (C) 2001 Russell King
 *              (C) 2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
 *              (C) 2003 Jun Nakajima <jun.nakajima@intel.com>
 *              (C) 2009 Alexander Clouter <alex@digriz.org.uk>
 *              (c) 2012 Viresh Kumar <viresh.kumar@linaro.org>
 *
 * 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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/export.h>
#include <linux/kernel_stat.h>
#include <linux/slab.h>

#include "cpufreq_governor.h"

#define CPUFREQ_DBS_MIN_SAMPLING_INTERVAL       (2 * TICK_NSEC / NSEC_PER_USEC)

static DEFINE_PER_CPU(struct cpu_dbs_info, cpu_dbs);

static DEFINE_MUTEX(gov_dbs_data_mutex);

/* Common sysfs tunables */
/**
 * store_sampling_rate - update sampling rate effective immediately if needed.
 *
 * If new rate is smaller than the old, simply updating
 * dbs.sampling_rate might not be appropriate. For example, if the
 * original sampling_rate was 1 second and the requested new sampling rate is 10
 * ms because the user needs immediate reaction from ondemand governor, but not
 * sure if higher frequency will be required or not, then, the governor may
 * change the sampling rate too late; up to 1 second later. Thus, if we are
 * reducing the sampling rate, we need to make the new value effective
 * immediately.
 *
 * This must be called with dbs_data->mutex held, otherwise traversing
 * policy_dbs_list isn't safe.
 */
ssize_t store_sampling_rate(struct gov_attr_set *attr_set, const char *buf,
                            size_t count)
{
        struct dbs_data *dbs_data = to_dbs_data(attr_set);
        struct policy_dbs_info *policy_dbs;
        unsigned int sampling_interval;
        int ret;

        ret = sscanf(buf, "%u", &sampling_interval);
        if (ret != 1 || sampling_interval < CPUFREQ_DBS_MIN_SAMPLING_INTERVAL)
                return -EINVAL;

        dbs_data->sampling_rate = sampling_interval;

        /*
         * We are operating under dbs_data->mutex and so the list and its
         * entries can't be freed concurrently.
         */
        list_for_each_entry(policy_dbs, &attr_set->policy_list, list) {
                mutex_lock(&policy_dbs->update_mutex);
                /*
                 * On 32-bit architectures this may race with the
                 * sample_delay_ns read in dbs_update_util_handler(), but that
                 * really doesn't matter.  If the read returns a value that's
                 * too big, the sample will be skipped, but the next invocation
                 * of dbs_update_util_handler() (when the update has been
                 * completed) will take a sample.
                 *
                 * If this runs in parallel with dbs_work_handler(), we may end
                 * up overwriting the sample_delay_ns value that it has just
                 * written, but it will be corrected next time a sample is
                 * taken, so it shouldn't be significant.
                 */
                gov_update_sample_delay(policy_dbs, 0);
                mutex_unlock(&policy_dbs->update_mutex);
        }

        return count;
}
EXPORT_SYMBOL_GPL(store_sampling_rate);

/**
 * gov_update_cpu_data - Update CPU load data.
 * @dbs_data: Top-level governor data pointer.
 *
 * Update CPU load data for all CPUs in the domain governed by @dbs_data
 * (that may be a single policy or a bunch of them if governor tunables are
 * system-wide).
 *
 * Call under the @dbs_data mutex.
 */
void gov_update_cpu_data(struct dbs_data *dbs_data)
{
        struct policy_dbs_info *policy_dbs;

        list_for_each_entry(policy_dbs, &dbs_data->attr_set.policy_list, list) {
                unsigned int j;

                for_each_cpu(j, policy_dbs->policy->cpus) {
                        struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);

                        j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time,
                                                                  dbs_data->io_is_busy);
                        if (dbs_data->ignore_nice_load)
                                j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
                }
        }
}
EXPORT_SYMBOL_GPL(gov_update_cpu_data);

unsigned int dbs_update(struct cpufreq_policy *policy)
{
        struct policy_dbs_info *policy_dbs = policy->governor_data;
        struct dbs_data *dbs_data = policy_dbs->dbs_data;
        unsigned int ignore_nice = dbs_data->ignore_nice_load;
        unsigned int max_load = 0, idle_periods = UINT_MAX;
        unsigned int sampling_rate, io_busy, j;

        /*
         * Sometimes governors may use an additional multiplier to increase
         * sample delays temporarily.  Apply that multiplier to sampling_rate
         * so as to keep the wake-up-from-idle detection logic a bit
         * conservative.
         */
        sampling_rate = dbs_data->sampling_rate * policy_dbs->rate_mult;
        /*
         * For the purpose of ondemand, waiting for disk IO is an indication
         * that you're performance critical, and not that the system is actually
         * idle, so do not add the iowait time to the CPU idle time then.
         */
        io_busy = dbs_data->io_is_busy;

        /* Get Absolute Load */
        for_each_cpu(j, policy->cpus) {
                struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
                u64 update_time, cur_idle_time;
                unsigned int idle_time, time_elapsed;
                unsigned int load;

                cur_idle_time = get_cpu_idle_time(j, &update_time, io_busy);

                time_elapsed = update_time - j_cdbs->prev_update_time;
                j_cdbs->prev_update_time = update_time;

                idle_time = cur_idle_time - j_cdbs->prev_cpu_idle;
                j_cdbs->prev_cpu_idle = cur_idle_time;

                if (ignore_nice) {
                        u64 cur_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];

                        idle_time += div_u64(cur_nice - j_cdbs->prev_cpu_nice, NSEC_PER_USEC);
                        j_cdbs->prev_cpu_nice = cur_nice;
                }

                if (unlikely(!time_elapsed)) {
                        /*
                         * That can only happen when this function is called
                         * twice in a row with a very short interval between the
                         * calls, so the previous load value can be used then.
                         */
                        load = j_cdbs->prev_load;
                } else if (unlikely((int)idle_time > 2 * sampling_rate &&
                                    j_cdbs->prev_load)) {
                        /*
                         * If the CPU had gone completely idle and a task has
                         * just woken up on this CPU now, it would be unfair to
                         * calculate 'load' the usual way for this elapsed
                         * time-window, because it would show near-zero load,
                         * irrespective of how CPU intensive that task actually
                         * was. This is undesirable for latency-sensitive bursty
                         * workloads.
                         *
                         * To avoid this, reuse the 'load' from the previous
                         * time-window and give this task a chance to start with
                         * a reasonably high CPU frequency. However, that
                         * shouldn't be over-done, lest we get stuck at a high
                         * load (high frequency) for too long, even when the
                         * current system load has actually dropped down, so
                         * clear prev_load to guarantee that the load will be
                         * computed again next time.
                         *
                         * Detecting this situation is easy: an unusually large
                         * 'idle_time' (as compared to the sampling rate)
                         * indicates this scenario.
                         */
                        load = j_cdbs->prev_load;
                        j_cdbs->prev_load = 0;
                } else {
                        if (time_elapsed >= idle_time) {
                                load = 100 * (time_elapsed - idle_time) / time_elapsed;
                        } else {
                                /*
                                 * That can happen if idle_time is returned by
                                 * get_cpu_idle_time_jiffy().  In that case
                                 * idle_time is roughly equal to the difference
                                 * between time_elapsed and "busy time" obtained
                                 * from CPU statistics.  Then, the "busy time"
                                 * can end up being greater than time_elapsed
                                 * (for example, if jiffies_64 and the CPU
                                 * statistics are updated by different CPUs),
                                 * so idle_time may in fact be negative.  That
                                 * means, though, that the CPU was busy all
                                 * the time (on the rough average) during the
                                 * last sampling interval and 100 can be
                                 * returned as the load.
                                 */
                                load = (int)idle_time < 0 ? 100 : 0;
                        }
                        j_cdbs->prev_load = load;
                }

                if (unlikely((int)idle_time > 2 * sampling_rate)) {
                        unsigned int periods = idle_time / sampling_rate;

                        if (periods < idle_periods)
                                idle_periods = periods;
                }

                if (load > max_load)
                        max_load = load;
        }

        policy_dbs->idle_periods = idle_periods;

        return max_load;
}
EXPORT_SYMBOL_GPL(dbs_update);

static void dbs_work_handler(struct work_struct *work)
{
        struct policy_dbs_info *policy_dbs;
        struct cpufreq_policy *policy;
        struct dbs_governor *gov;

        policy_dbs = container_of(work, struct policy_dbs_info, work);
        policy = policy_dbs->policy;
        gov = dbs_governor_of(policy);

        /*
         * Make sure cpufreq_governor_limits() isn't evaluating load or the
         * ondemand governor isn't updating the sampling rate in parallel.
         */
        mutex_lock(&policy_dbs->update_mutex);
        gov_update_sample_delay(policy_dbs, gov->gov_dbs_update(policy));
        mutex_unlock(&policy_dbs->update_mutex);

        /* Allow the utilization update handler to queue up more work. */
        atomic_set(&policy_dbs->work_count, 0);
        /*
         * If the update below is reordered with respect to the sample delay
         * modification, the utilization update handler may end up using a stale
         * sample delay value.
         */
        smp_wmb();
        policy_dbs->work_in_progress = false;
}

static void dbs_irq_work(struct irq_work *irq_work)
{
        struct policy_dbs_info *policy_dbs;

        policy_dbs = container_of(irq_work, struct policy_dbs_info, irq_work);
        schedule_work_on(smp_processor_id(), &policy_dbs->work);
}

static void dbs_update_util_handler(struct update_util_data *data, u64 time,
                                    unsigned int flags)
{
        struct cpu_dbs_info *cdbs = container_of(data, struct cpu_dbs_info, update_util);
        struct policy_dbs_info *policy_dbs = cdbs->policy_dbs;
        u64 delta_ns, lst;

        if (!cpufreq_this_cpu_can_update(policy_dbs->policy))
                return;

        /*
         * The work may not be allowed to be queued up right now.
         * Possible reasons:
         * - Work has already been queued up or is in progress.
         * - It is too early (too little time from the previous sample).
         */
        if (policy_dbs->work_in_progress)
                return;

        /*
         * If the reads below are reordered before the check above, the value
         * of sample_delay_ns used in the computation may be stale.
         */
        smp_rmb();
        lst = READ_ONCE(policy_dbs->last_sample_time);
        delta_ns = time - lst;
        if ((s64)delta_ns < policy_dbs->sample_delay_ns)
                return;

        /*
         * If the policy is not shared, the irq_work may be queued up right away
         * at this point.  Otherwise, we need to ensure that only one of the
         * CPUs sharing the policy will do that.
         */
        if (policy_dbs->is_shared) {
                if (!atomic_add_unless(&policy_dbs->work_count, 1, 1))
                        return;

                /*
                 * If another CPU updated last_sample_time in the meantime, we
                 * shouldn't be here, so clear the work counter and bail out.
                 */
                if (unlikely(lst != READ_ONCE(policy_dbs->last_sample_time))) {
                        atomic_set(&policy_dbs->work_count, 0);
                        return;
                }
        }

        policy_dbs->last_sample_time = time;
        policy_dbs->work_in_progress = true;
        irq_work_queue(&policy_dbs->irq_work);
}

static void gov_set_update_util(struct policy_dbs_info *policy_dbs,
                                unsigned int delay_us)
{
        struct cpufreq_policy *policy = policy_dbs->policy;
        int cpu;

        gov_update_sample_delay(policy_dbs, delay_us);
        policy_dbs->last_sample_time = 0;

        for_each_cpu(cpu, policy->cpus) {
                struct cpu_dbs_info *cdbs = &per_cpu(cpu_dbs, cpu);

                cpufreq_add_update_util_hook(cpu, &cdbs->update_util,
                                             dbs_update_util_handler);
        }
}

static inline void gov_clear_update_util(struct cpufreq_policy *policy)
{
        int i;

        for_each_cpu(i, policy->cpus)
                cpufreq_remove_update_util_hook(i);

        synchronize_rcu();
}

static struct policy_dbs_info *alloc_policy_dbs_info(struct cpufreq_policy *policy,
                                                     struct dbs_governor *gov)
{
        struct policy_dbs_info *policy_dbs;
        int j;

        /* Allocate memory for per-policy governor data. */
        policy_dbs = gov->alloc();
        if (!policy_dbs)
                return NULL;

        policy_dbs->policy = policy;
        mutex_init(&policy_dbs->update_mutex);
        atomic_set(&policy_dbs->work_count, 0);
        init_irq_work(&policy_dbs->irq_work, dbs_irq_work);
        INIT_WORK(&policy_dbs->work, dbs_work_handler);

        /* Set policy_dbs for all CPUs, online+offline */
        for_each_cpu(j, policy->related_cpus) {
                struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);

                j_cdbs->policy_dbs = policy_dbs;
        }
        return policy_dbs;
}

static void free_policy_dbs_info(struct policy_dbs_info *policy_dbs,
                                 struct dbs_governor *gov)
{
        int j;

        mutex_destroy(&policy_dbs->update_mutex);

        for_each_cpu(j, policy_dbs->policy->related_cpus) {
                struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);

                j_cdbs->policy_dbs = NULL;
                j_cdbs->update_util.func = NULL;
        }
        gov->free(policy_dbs);
}

int cpufreq_dbs_governor_init(struct cpufreq_policy *policy)
{
        struct dbs_governor *gov = dbs_governor_of(policy);
        struct dbs_data *dbs_data;
        struct policy_dbs_info *policy_dbs;
        int ret = 0;

        /* State should be equivalent to EXIT */
        if (policy->governor_data)
                return -EBUSY;

        policy_dbs = alloc_policy_dbs_info(policy, gov);
        if (!policy_dbs)
                return -ENOMEM;

        /* Protect gov->gdbs_data against concurrent updates. */
        mutex_lock(&gov_dbs_data_mutex);

        dbs_data = gov->gdbs_data;
        if (dbs_data) {
                if (WARN_ON(have_governor_per_policy())) {
                        ret = -EINVAL;
                        goto free_policy_dbs_info;
                }
                policy_dbs->dbs_data = dbs_data;
                policy->governor_data = policy_dbs;

                gov_attr_set_get(&dbs_data->attr_set, &policy_dbs->list);
                goto out;
        }

        dbs_data = kzalloc(sizeof(*dbs_data), GFP_KERNEL);
        if (!dbs_data) {
                ret = -ENOMEM;
                goto free_policy_dbs_info;
        }

        gov_attr_set_init(&dbs_data->attr_set, &policy_dbs->list);

        ret = gov->init(dbs_data);
        if (ret)
                goto free_policy_dbs_info;

        /*
         * The sampling interval should not be less than the transition latency
         * of the CPU and it also cannot be too small for dbs_update() to work
         * correctly.
         */
        dbs_data->sampling_rate = max_t(unsigned int,
                                        CPUFREQ_DBS_MIN_SAMPLING_INTERVAL,
                                        cpufreq_policy_transition_delay_us(policy));

        if (!have_governor_per_policy())
                gov->gdbs_data = dbs_data;

        policy_dbs->dbs_data = dbs_data;
        policy->governor_data = policy_dbs;

        gov->kobj_type.sysfs_ops = &governor_sysfs_ops;
        ret = kobject_init_and_add(&dbs_data->attr_set.kobj, &gov->kobj_type,
                                   get_governor_parent_kobj(policy),
                                   "%s", gov->gov.name);
        if (!ret)
                goto out;

        /* Failure, so roll back. */
        pr_err("initialization failed (dbs_data kobject init error %d)\n", ret);

        policy->governor_data = NULL;

        if (!have_governor_per_policy())
                gov->gdbs_data = NULL;
        gov->exit(dbs_data);
        kfree(dbs_data);

free_policy_dbs_info:
        free_policy_dbs_info(policy_dbs, gov);

out:
        mutex_unlock(&gov_dbs_data_mutex);
        return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_init);

void cpufreq_dbs_governor_exit(struct cpufreq_policy *policy)
{
        struct dbs_governor *gov = dbs_governor_of(policy);
        struct policy_dbs_info *policy_dbs = policy->governor_data;
        struct dbs_data *dbs_data = policy_dbs->dbs_data;
        unsigned int count;

        /* Protect gov->gdbs_data against concurrent updates. */
        mutex_lock(&gov_dbs_data_mutex);

        count = gov_attr_set_put(&dbs_data->attr_set, &policy_dbs->list);

        policy->governor_data = NULL;

        if (!count) {
                if (!have_governor_per_policy())
                        gov->gdbs_data = NULL;

                gov->exit(dbs_data);
                kfree(dbs_data);
        }

        free_policy_dbs_info(policy_dbs, gov);

        mutex_unlock(&gov_dbs_data_mutex);
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_exit);

int cpufreq_dbs_governor_start(struct cpufreq_policy *policy)
{
        struct dbs_governor *gov = dbs_governor_of(policy);
        struct policy_dbs_info *policy_dbs = policy->governor_data;
        struct dbs_data *dbs_data = policy_dbs->dbs_data;
        unsigned int sampling_rate, ignore_nice, j;
        unsigned int io_busy;

        if (!policy->cur)
                return -EINVAL;

        policy_dbs->is_shared = policy_is_shared(policy);
        policy_dbs->rate_mult = 1;

        sampling_rate = dbs_data->sampling_rate;
        ignore_nice = dbs_data->ignore_nice_load;
        io_busy = dbs_data->io_is_busy;

        for_each_cpu(j, policy->cpus) {
                struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);

                j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time, io_busy);
                /*
                 * Make the first invocation of dbs_update() compute the load.
                 */
                j_cdbs->prev_load = 0;

                if (ignore_nice)
                        j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
        }

        gov->start(policy);

        gov_set_update_util(policy_dbs, sampling_rate);
        return 0;
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_start);

void cpufreq_dbs_governor_stop(struct cpufreq_policy *policy)
{
        struct policy_dbs_info *policy_dbs = policy->governor_data;

        gov_clear_update_util(policy_dbs->policy);
        irq_work_sync(&policy_dbs->irq_work);
        cancel_work_sync(&policy_dbs->work);
        atomic_set(&policy_dbs->work_count, 0);
        policy_dbs->work_in_progress = false;
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_stop);

void cpufreq_dbs_governor_limits(struct cpufreq_policy *policy)
{
        struct policy_dbs_info *policy_dbs;

        /* Protect gov->gdbs_data against cpufreq_dbs_governor_exit() */
        mutex_lock(&gov_dbs_data_mutex);
        policy_dbs = policy->governor_data;
        if (!policy_dbs)
                goto out;

        mutex_lock(&policy_dbs->update_mutex);
        cpufreq_policy_apply_limits(policy);
        gov_update_sample_delay(policy_dbs, 0);
        mutex_unlock(&policy_dbs->update_mutex);

out:
        mutex_unlock(&gov_dbs_data_mutex);
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_limits);