cpufreq.c

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/*
 *  linux/drivers/cpufreq/cpufreq.c
 *
 *  Copyright (C) 2001 Russell King
 *            (C) 2002 - 2003 Dominik Brodowski <[email protected]>
 *
 *  Oct 2005 - Ashok Raj <[email protected]>
 *  Added handling for CPU hotplug
 *  Feb 2006 - Jacob Shin <[email protected]>
 *  Fix handling for CPU hotplug -- affected CPUs
 *
 * 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/module.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/cpufreq.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/completion.h>
#include <linux/mutex.h>
#include <linux/syscore_ops.h>

#include <trace/events/power.h>

static struct cpufreq_driver *cpufreq_driver;
static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
#ifdef CONFIG_HOTPLUG_CPU
/* This one keeps track of the previously set governor of a removed CPU */
static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
#endif
static DEFINE_SPINLOCK(cpufreq_driver_lock);

/*
 * cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure
 * all cpufreq/hotplug/workqueue/etc related lock issues.
 *
 * The rules for this semaphore:
 * - Any routine that wants to read from the policy structure will
 *   do a down_read on this semaphore.
 * - Any routine that will write to the policy structure and/or may take away
 *   the policy altogether (eg. CPU hotplug), will hold this lock in write
 *   mode before doing so.
 *
 * Additional rules:
 * - All holders of the lock should check to make sure that the CPU they
 *   are concerned with are online after they get the lock.
 * - Governor routines that can be called in cpufreq hotplug path should not
 *   take this sem as top level hotplug notifier handler takes this.
 * - Lock should not be held across
 *     __cpufreq_governor(data, CPUFREQ_GOV_STOP);
 */
static DEFINE_PER_CPU(int, cpufreq_policy_cpu);
static DEFINE_PER_CPU(struct rw_semaphore, cpu_policy_rwsem);

#define lock_policy_rwsem(mode, cpu)                    \
static int lock_policy_rwsem_##mode                 \
(int cpu)                               \
{                                   \
    int policy_cpu = per_cpu(cpufreq_policy_cpu, cpu);      \
    BUG_ON(policy_cpu == -1);                   \
    down_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu));        \
    if (unlikely(!cpu_online(cpu))) {               \
        up_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu));  \
        return -1;                      \
    }                               \
                                    \
    return 0;                           \
}

lock_policy_rwsem(read, cpu);

lock_policy_rwsem(write, cpu);

static void unlock_policy_rwsem_read(int cpu)
{
    int policy_cpu = per_cpu(cpufreq_policy_cpu, cpu);
    BUG_ON(policy_cpu == -1);
    up_read(&per_cpu(cpu_policy_rwsem, policy_cpu));
}

static void unlock_policy_rwsem_write(int cpu)
{
    int policy_cpu = per_cpu(cpufreq_policy_cpu, cpu);
    BUG_ON(policy_cpu == -1);
    up_write(&per_cpu(cpu_policy_rwsem, policy_cpu));
}


/* internal prototypes */
static int __cpufreq_governor(struct cpufreq_policy *policy,
        unsigned int event);
static unsigned int __cpufreq_get(unsigned int cpu);
static void handle_update(struct work_struct *work);

static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
static struct srcu_notifier_head cpufreq_transition_notifier_list;

static bool init_cpufreq_transition_notifier_list_called;
static int __init init_cpufreq_transition_notifier_list(void)
{
    srcu_init_notifier_head(&cpufreq_transition_notifier_list);
    init_cpufreq_transition_notifier_list_called = true;
    return 0;
}
pure_initcall(init_cpufreq_transition_notifier_list);

static int off __read_mostly;
int cpufreq_disabled(void)
{
    return off;
}
void disable_cpufreq(void)
{
    off = 1;
}
static LIST_HEAD(cpufreq_governor_list);
static DEFINE_MUTEX(cpufreq_governor_mutex);

static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, bool sysfs)
{
    struct cpufreq_policy *data;
    unsigned long flags;

    if (cpu >= nr_cpu_ids)
        goto err_out;

    /* get the cpufreq driver */
    spin_lock_irqsave(&cpufreq_driver_lock, flags);

    if (!cpufreq_driver)
        goto err_out_unlock;

    if (!try_module_get(cpufreq_driver->owner))
        goto err_out_unlock;


    /* get the CPU */
    data = per_cpu(cpufreq_cpu_data, cpu);

    if (!data)
        goto err_out_put_module;

    if (!sysfs && !kobject_get(&data->kobj))
        goto err_out_put_module;

    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
    return data;

err_out_put_module:
    module_put(cpufreq_driver->owner);
err_out_unlock:
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
err_out:
    return NULL;
}

struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
{
    return __cpufreq_cpu_get(cpu, false);
}
EXPORT_SYMBOL_GPL(cpufreq_cpu_get);

static struct cpufreq_policy *cpufreq_cpu_get_sysfs(unsigned int cpu)
{
    return __cpufreq_cpu_get(cpu, true);
}

static void __cpufreq_cpu_put(struct cpufreq_policy *data, bool sysfs)
{
    if (!sysfs)
        kobject_put(&data->kobj);
    module_put(cpufreq_driver->owner);
}

void cpufreq_cpu_put(struct cpufreq_policy *data)
{
    __cpufreq_cpu_put(data, false);
}
EXPORT_SYMBOL_GPL(cpufreq_cpu_put);

static void cpufreq_cpu_put_sysfs(struct cpufreq_policy *data)
{
    __cpufreq_cpu_put(data, true);
}

/*********************************************************************
 *            EXTERNALLY AFFECTING FREQUENCY CHANGES                 *
 *********************************************************************/

#ifndef CONFIG_SMP
static unsigned long l_p_j_ref;
static unsigned int  l_p_j_ref_freq;

static void adjust_jiffies(unsigned long val, struct cpufreq_freqs *ci)
{
    if (ci->flags & CPUFREQ_CONST_LOOPS)
        return;

    if (!l_p_j_ref_freq) {
        l_p_j_ref = loops_per_jiffy;
        l_p_j_ref_freq = ci->old;
        pr_debug("saving %lu as reference value for loops_per_jiffy; "
            "freq is %u kHz\n", l_p_j_ref, l_p_j_ref_freq);
    }
    if ((val == CPUFREQ_POSTCHANGE  && ci->old != ci->new) ||
        (val == CPUFREQ_RESUMECHANGE || val == CPUFREQ_SUSPENDCHANGE)) {
        loops_per_jiffy = cpufreq_scale(l_p_j_ref, l_p_j_ref_freq,
                                ci->new);
        pr_debug("scaling loops_per_jiffy to %lu "
            "for frequency %u kHz\n", loops_per_jiffy, ci->new);
    }
}
#else
static inline void adjust_jiffies(unsigned long val, struct cpufreq_freqs *ci)
{
    return;
}
#endif


void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
{
    struct cpufreq_policy *policy;

    BUG_ON(irqs_disabled());

    freqs->flags = cpufreq_driver->flags;
    pr_debug("notification %u of frequency transition to %u kHz\n",
        state, freqs->new);

    policy = per_cpu(cpufreq_cpu_data, freqs->cpu);
    switch (state) {

    case CPUFREQ_PRECHANGE:
        /* detect if the driver reported a value as "old frequency"
         * which is not equal to what the cpufreq core thinks is
         * "old frequency".
         */
        if (!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
            if ((policy) && (policy->cpu == freqs->cpu) &&
                (policy->cur) && (policy->cur != freqs->old)) {
                pr_debug("Warning: CPU frequency is"
                    " %u, cpufreq assumed %u kHz.\n",
                    freqs->old, policy->cur);
                freqs->old = policy->cur;
            }
        }
        srcu_notifier_call_chain(&cpufreq_transition_notifier_list,
                CPUFREQ_PRECHANGE, freqs);
        adjust_jiffies(CPUFREQ_PRECHANGE, freqs);
        break;

    case CPUFREQ_POSTCHANGE:
        adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
        pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
            (unsigned long)freqs->cpu);
        trace_power_frequency(POWER_PSTATE, freqs->new, freqs->cpu);
        trace_cpu_frequency(freqs->new, freqs->cpu);
        srcu_notifier_call_chain(&cpufreq_transition_notifier_list,
                CPUFREQ_POSTCHANGE, freqs);
        if (likely(policy) && likely(policy->cpu == freqs->cpu))
            policy->cur = freqs->new;
        break;
    }
}
EXPORT_SYMBOL_GPL(cpufreq_notify_transition);



/*********************************************************************
 *                          SYSFS INTERFACE                          *
 *********************************************************************/

static struct cpufreq_governor *__find_governor(const char *str_governor)
{
    struct cpufreq_governor *t;

    list_for_each_entry(t, &cpufreq_governor_list, governor_list)
        if (!strnicmp(str_governor, t->name, CPUFREQ_NAME_LEN))
            return t;

    return NULL;
}

static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
                struct cpufreq_governor **governor)
{
    int err = -EINVAL;

    if (!cpufreq_driver)
        goto out;

    if (cpufreq_driver->setpolicy) {
        if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
            *policy = CPUFREQ_POLICY_PERFORMANCE;
            err = 0;
        } else if (!strnicmp(str_governor, "powersave",
                        CPUFREQ_NAME_LEN)) {
            *policy = CPUFREQ_POLICY_POWERSAVE;
            err = 0;
        }
    } else if (cpufreq_driver->target) {
        struct cpufreq_governor *t;

        mutex_lock(&cpufreq_governor_mutex);

        t = __find_governor(str_governor);

        if (t == NULL) {
            int ret;

            mutex_unlock(&cpufreq_governor_mutex);
            ret = request_module("cpufreq_%s", str_governor);
            mutex_lock(&cpufreq_governor_mutex);

            if (ret == 0)
                t = __find_governor(str_governor);
        }

        if (t != NULL) {
            *governor = t;
            err = 0;
        }

        mutex_unlock(&cpufreq_governor_mutex);
    }
out:
    return err;
}


#define show_one(file_name, object)         \
static ssize_t show_##file_name             \
(struct cpufreq_policy *policy, char *buf)      \
{                           \
    return sprintf(buf, "%u\n", policy->object);    \
}

show_one(cpuinfo_min_freq, cpuinfo.min_freq);
show_one(cpuinfo_max_freq, cpuinfo.max_freq);
show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
show_one(scaling_min_freq, min);
show_one(scaling_max_freq, max);
show_one(scaling_cur_freq, cur);

static int __cpufreq_set_policy(struct cpufreq_policy *data,
                struct cpufreq_policy *policy);

#define store_one(file_name, object)            \
static ssize_t store_##file_name                    \
(struct cpufreq_policy *policy, const char *buf, size_t count)      \
{                                   \
    unsigned int ret = -EINVAL;                 \
    struct cpufreq_policy new_policy;               \
                                    \
    ret = cpufreq_get_policy(&new_policy, policy->cpu);     \
    if (ret)                            \
        return -EINVAL;                     \
                                    \
    ret = sscanf(buf, "%u", &new_policy.object);            \
    if (ret != 1)                           \
        return -EINVAL;                     \
                                    \
    ret = __cpufreq_set_policy(policy, &new_policy);        \
    policy->user_policy.object = policy->object;            \
                                    \
    return ret ? ret : count;                   \
}

store_one(scaling_min_freq, min);
store_one(scaling_max_freq, max);

static ssize_t show_cpuinfo_cur_freq(struct cpufreq_policy *policy,
                    char *buf)
{
    unsigned int cur_freq = __cpufreq_get(policy->cpu);
    if (!cur_freq)
        return sprintf(buf, "<unknown>");
    return sprintf(buf, "%u\n", cur_freq);
}


static ssize_t show_scaling_governor(struct cpufreq_policy *policy, char *buf)
{
    if (policy->policy == CPUFREQ_POLICY_POWERSAVE)
        return sprintf(buf, "powersave\n");
    else if (policy->policy == CPUFREQ_POLICY_PERFORMANCE)
        return sprintf(buf, "performance\n");
    else if (policy->governor)
        return scnprintf(buf, CPUFREQ_NAME_LEN, "%s\n",
                policy->governor->name);
    return -EINVAL;
}


static ssize_t store_scaling_governor(struct cpufreq_policy *policy,
                    const char *buf, size_t count)
{
    unsigned int ret = -EINVAL;
    char    str_governor[16];
    struct cpufreq_policy new_policy;

    ret = cpufreq_get_policy(&new_policy, policy->cpu);
    if (ret)
        return ret;

    ret = sscanf(buf, "%15s", str_governor);
    if (ret != 1)
        return -EINVAL;

    if (cpufreq_parse_governor(str_governor, &new_policy.policy,
                        &new_policy.governor))
        return -EINVAL;

    /* Do not use cpufreq_set_policy here or the user_policy.max
       will be wrongly overridden */
    ret = __cpufreq_set_policy(policy, &new_policy);

    policy->user_policy.policy = policy->policy;
    policy->user_policy.governor = policy->governor;

    if (ret)
        return ret;
    else
        return count;
}

static ssize_t show_scaling_driver(struct cpufreq_policy *policy, char *buf)
{
    return scnprintf(buf, CPUFREQ_NAME_LEN, "%s\n", cpufreq_driver->name);
}

static ssize_t show_scaling_available_governors(struct cpufreq_policy *policy,
                        char *buf)
{
    ssize_t i = 0;
    struct cpufreq_governor *t;

    if (!cpufreq_driver->target) {
        i += sprintf(buf, "performance powersave");
        goto out;
    }

    list_for_each_entry(t, &cpufreq_governor_list, governor_list) {
        if (i >= (ssize_t) ((PAGE_SIZE / sizeof(char))
            - (CPUFREQ_NAME_LEN + 2)))
            goto out;
        i += scnprintf(&buf[i], CPUFREQ_NAME_LEN, "%s ", t->name);
    }
out:
    i += sprintf(&buf[i], "\n");
    return i;
}

static ssize_t show_cpus(const struct cpumask *mask, char *buf)
{
    ssize_t i = 0;
    unsigned int cpu;

    for_each_cpu(cpu, mask) {
        if (i)
            i += scnprintf(&buf[i], (PAGE_SIZE - i - 2), " ");
        i += scnprintf(&buf[i], (PAGE_SIZE - i - 2), "%u", cpu);
        if (i >= (PAGE_SIZE - 5))
            break;
    }
    i += sprintf(&buf[i], "\n");
    return i;
}

static ssize_t show_related_cpus(struct cpufreq_policy *policy, char *buf)
{
    if (cpumask_empty(policy->related_cpus))
        return show_cpus(policy->cpus, buf);
    return show_cpus(policy->related_cpus, buf);
}

static ssize_t show_affected_cpus(struct cpufreq_policy *policy, char *buf)
{
    return show_cpus(policy->cpus, buf);
}

static ssize_t store_scaling_setspeed(struct cpufreq_policy *policy,
                    const char *buf, size_t count)
{
    unsigned int freq = 0;
    unsigned int ret;

    if (!policy->governor || !policy->governor->store_setspeed)
        return -EINVAL;

    ret = sscanf(buf, "%u", &freq);
    if (ret != 1)
        return -EINVAL;

    policy->governor->store_setspeed(policy, freq);

    return count;
}

static ssize_t show_scaling_setspeed(struct cpufreq_policy *policy, char *buf)
{
    if (!policy->governor || !policy->governor->show_setspeed)
        return sprintf(buf, "<unsupported>\n");

    return policy->governor->show_setspeed(policy, buf);
}

static ssize_t show_bios_limit(struct cpufreq_policy *policy, char *buf)
{
    unsigned int limit;
    int ret;
    if (cpufreq_driver->bios_limit) {
        ret = cpufreq_driver->bios_limit(policy->cpu, &limit);
        if (!ret)
            return sprintf(buf, "%u\n", limit);
    }
    return sprintf(buf, "%u\n", policy->cpuinfo.max_freq);
}

cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
cpufreq_freq_attr_ro(cpuinfo_min_freq);
cpufreq_freq_attr_ro(cpuinfo_max_freq);
cpufreq_freq_attr_ro(cpuinfo_transition_latency);
cpufreq_freq_attr_ro(scaling_available_governors);
cpufreq_freq_attr_ro(scaling_driver);
cpufreq_freq_attr_ro(scaling_cur_freq);
cpufreq_freq_attr_ro(bios_limit);
cpufreq_freq_attr_ro(related_cpus);
cpufreq_freq_attr_ro(affected_cpus);
cpufreq_freq_attr_rw(scaling_min_freq);
cpufreq_freq_attr_rw(scaling_max_freq);
cpufreq_freq_attr_rw(scaling_governor);
cpufreq_freq_attr_rw(scaling_setspeed);

static struct attribute *default_attrs[] = {
    &cpuinfo_min_freq.attr,
    &cpuinfo_max_freq.attr,
    &cpuinfo_transition_latency.attr,
    &scaling_min_freq.attr,
    &scaling_max_freq.attr,
    &affected_cpus.attr,
    &related_cpus.attr,
    &scaling_governor.attr,
    &scaling_driver.attr,
    &scaling_available_governors.attr,
    &scaling_setspeed.attr,
    NULL
};

struct kobject *cpufreq_global_kobject;
EXPORT_SYMBOL(cpufreq_global_kobject);

#define to_policy(k) container_of(k, struct cpufreq_policy, kobj)
#define to_attr(a) container_of(a, struct freq_attr, attr)

static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
{
    struct cpufreq_policy *policy = to_policy(kobj);
    struct freq_attr *fattr = to_attr(attr);
    ssize_t ret = -EINVAL;
    policy = cpufreq_cpu_get_sysfs(policy->cpu);
    if (!policy)
        goto no_policy;

    if (lock_policy_rwsem_read(policy->cpu) < 0)
        goto fail;

    if (fattr->show)
        ret = fattr->show(policy, buf);
    else
        ret = -EIO;

    unlock_policy_rwsem_read(policy->cpu);
fail:
    cpufreq_cpu_put_sysfs(policy);
no_policy:
    return ret;
}

static ssize_t store(struct kobject *kobj, struct attribute *attr,
             const char *buf, size_t count)
{
    struct cpufreq_policy *policy = to_policy(kobj);
    struct freq_attr *fattr = to_attr(attr);
    ssize_t ret = -EINVAL;
    policy = cpufreq_cpu_get_sysfs(policy->cpu);
    if (!policy)
        goto no_policy;

    if (lock_policy_rwsem_write(policy->cpu) < 0)
        goto fail;

    if (fattr->store)
        ret = fattr->store(policy, buf, count);
    else
        ret = -EIO;

    unlock_policy_rwsem_write(policy->cpu);
fail:
    cpufreq_cpu_put_sysfs(policy);
no_policy:
    return ret;
}

static void cpufreq_sysfs_release(struct kobject *kobj)
{
    struct cpufreq_policy *policy = to_policy(kobj);
    pr_debug("last reference is dropped\n");
    complete(&policy->kobj_unregister);
}

static const struct sysfs_ops sysfs_ops = {
    .show   = show,
    .store  = store,
};

static struct kobj_type ktype_cpufreq = {
    .sysfs_ops  = &sysfs_ops,
    .default_attrs  = default_attrs,
    .release    = cpufreq_sysfs_release,
};

/*
 * Returns:
 *   Negative: Failure
 *   0:        Success
 *   Positive: When we have a managed CPU and the sysfs got symlinked
 */
static int cpufreq_add_dev_policy(unsigned int cpu,
                  struct cpufreq_policy *policy,
                  struct device *dev)
{
    int ret = 0;
#ifdef CONFIG_SMP
    unsigned long flags;
    unsigned int j;
#ifdef CONFIG_HOTPLUG_CPU
    struct cpufreq_governor *gov;

    gov = __find_governor(per_cpu(cpufreq_cpu_governor, cpu));
    if (gov) {
        policy->governor = gov;
        pr_debug("Restoring governor %s for cpu %d\n",
               policy->governor->name, cpu);
    }
#endif

    for_each_cpu(j, policy->cpus) {
        struct cpufreq_policy *managed_policy;

        if (cpu == j)
            continue;

        /* Check for existing affected CPUs.
         * They may not be aware of it due to CPU Hotplug.
         * cpufreq_cpu_put is called when the device is removed
         * in __cpufreq_remove_dev()
         */
        managed_policy = cpufreq_cpu_get(j);
        if (unlikely(managed_policy)) {

            /* Set proper policy_cpu */
            unlock_policy_rwsem_write(cpu);
            per_cpu(cpufreq_policy_cpu, cpu) = managed_policy->cpu;

            if (lock_policy_rwsem_write(cpu) < 0) {
                /* Should not go through policy unlock path */
                if (cpufreq_driver->exit)
                    cpufreq_driver->exit(policy);
                cpufreq_cpu_put(managed_policy);
                return -EBUSY;
            }

            spin_lock_irqsave(&cpufreq_driver_lock, flags);
            cpumask_copy(managed_policy->cpus, policy->cpus);
            per_cpu(cpufreq_cpu_data, cpu) = managed_policy;
            spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

            pr_debug("CPU already managed, adding link\n");
            ret = sysfs_create_link(&dev->kobj,
                        &managed_policy->kobj,
                        "cpufreq");
            if (ret)
                cpufreq_cpu_put(managed_policy);
            /*
             * Success. We only needed to be added to the mask.
             * Call driver->exit() because only the cpu parent of
             * the kobj needed to call init().
             */
            if (cpufreq_driver->exit)
                cpufreq_driver->exit(policy);

            if (!ret)
                return 1;
            else
                return ret;
        }
    }
#endif
    return ret;
}


/* symlink affected CPUs */
static int cpufreq_add_dev_symlink(unsigned int cpu,
                   struct cpufreq_policy *policy)
{
    unsigned int j;
    int ret = 0;

    for_each_cpu(j, policy->cpus) {
        struct cpufreq_policy *managed_policy;
        struct device *cpu_dev;

        if (j == cpu)
            continue;
        if (!cpu_online(j))
            continue;

        pr_debug("CPU %u already managed, adding link\n", j);
        managed_policy = cpufreq_cpu_get(cpu);
        cpu_dev = get_cpu_device(j);
        ret = sysfs_create_link(&cpu_dev->kobj, &policy->kobj,
                    "cpufreq");
        if (ret) {
            cpufreq_cpu_put(managed_policy);
            return ret;
        }
    }
    return ret;
}

static int cpufreq_add_dev_interface(unsigned int cpu,
                     struct cpufreq_policy *policy,
                     struct device *dev)
{
    struct cpufreq_policy new_policy;
    struct freq_attr **drv_attr;
    unsigned long flags;
    int ret = 0;
    unsigned int j;

    /* prepare interface data */
    ret = kobject_init_and_add(&policy->kobj, &ktype_cpufreq,
                   &dev->kobj, "cpufreq");
    if (ret)
        return ret;

    /* set up files for this cpu device */
    drv_attr = cpufreq_driver->attr;
    while ((drv_attr) && (*drv_attr)) {
        ret = sysfs_create_file(&policy->kobj, &((*drv_attr)->attr));
        if (ret)
            goto err_out_kobj_put;
        drv_attr++;
    }
    if (cpufreq_driver->get) {
        ret = sysfs_create_file(&policy->kobj, &cpuinfo_cur_freq.attr);
        if (ret)
            goto err_out_kobj_put;
    }
    if (cpufreq_driver->target) {
        ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
        if (ret)
            goto err_out_kobj_put;
    }
    if (cpufreq_driver->bios_limit) {
        ret = sysfs_create_file(&policy->kobj, &bios_limit.attr);
        if (ret)
            goto err_out_kobj_put;
    }

    spin_lock_irqsave(&cpufreq_driver_lock, flags);
    for_each_cpu(j, policy->cpus) {
        if (!cpu_online(j))
            continue;
        per_cpu(cpufreq_cpu_data, j) = policy;
        per_cpu(cpufreq_policy_cpu, j) = policy->cpu;
    }
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

    ret = cpufreq_add_dev_symlink(cpu, policy);
    if (ret)
        goto err_out_kobj_put;

    memcpy(&new_policy, policy, sizeof(struct cpufreq_policy));
    /* assure that the starting sequence is run in __cpufreq_set_policy */
    policy->governor = NULL;

    /* set default policy */
    ret = __cpufreq_set_policy(policy, &new_policy);
    policy->user_policy.policy = policy->policy;
    policy->user_policy.governor = policy->governor;

    if (ret) {
        pr_debug("setting policy failed\n");
        if (cpufreq_driver->exit)
            cpufreq_driver->exit(policy);
    }
    return ret;

err_out_kobj_put:
    kobject_put(&policy->kobj);
    wait_for_completion(&policy->kobj_unregister);
    return ret;
}


static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
{
    unsigned int cpu = dev->id;
    int ret = 0, found = 0;
    struct cpufreq_policy *policy;
    unsigned long flags;
    unsigned int j;
#ifdef CONFIG_HOTPLUG_CPU
    int sibling;
#endif

    if (cpu_is_offline(cpu))
        return 0;

    pr_debug("adding CPU %u\n", cpu);

#ifdef CONFIG_SMP
    /* check whether a different CPU already registered this
     * CPU because it is in the same boat. */
    policy = cpufreq_cpu_get(cpu);
    if (unlikely(policy)) {
        cpufreq_cpu_put(policy);
        return 0;
    }
#endif

    if (!try_module_get(cpufreq_driver->owner)) {
        ret = -EINVAL;
        goto module_out;
    }

    ret = -ENOMEM;
    policy = kzalloc(sizeof(struct cpufreq_policy), GFP_KERNEL);
    if (!policy)
        goto nomem_out;

    if (!alloc_cpumask_var(&policy->cpus, GFP_KERNEL))
        goto err_free_policy;

    if (!zalloc_cpumask_var(&policy->related_cpus, GFP_KERNEL))
        goto err_free_cpumask;

    policy->cpu = cpu;
    cpumask_copy(policy->cpus, cpumask_of(cpu));

    /* Initially set CPU itself as the policy_cpu */
    per_cpu(cpufreq_policy_cpu, cpu) = cpu;
    ret = (lock_policy_rwsem_write(cpu) < 0);
    WARN_ON(ret);

    init_completion(&policy->kobj_unregister);
    INIT_WORK(&policy->update, handle_update);

    /* Set governor before ->init, so that driver could check it */
#ifdef CONFIG_HOTPLUG_CPU
    for_each_online_cpu(sibling) {
        struct cpufreq_policy *cp = per_cpu(cpufreq_cpu_data, sibling);
        if (cp && cp->governor &&
            (cpumask_test_cpu(cpu, cp->related_cpus))) {
            policy->governor = cp->governor;
            found = 1;
            break;
        }
    }
#endif
    if (!found)
        policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
    /* call driver. From then on the cpufreq must be able
     * to accept all calls to ->verify and ->setpolicy for this CPU
     */
    ret = cpufreq_driver->init(policy);
    if (ret) {
        pr_debug("initialization failed\n");
        goto err_unlock_policy;
    }
    policy->user_policy.min = policy->min;
    policy->user_policy.max = policy->max;

    blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
                     CPUFREQ_START, policy);

    ret = cpufreq_add_dev_policy(cpu, policy, dev);
    if (ret) {
        if (ret > 0)
            /* This is a managed cpu, symlink created,
               exit with 0 */
            ret = 0;
        goto err_unlock_policy;
    }

    ret = cpufreq_add_dev_interface(cpu, policy, dev);
    if (ret)
        goto err_out_unregister;

    unlock_policy_rwsem_write(cpu);

    kobject_uevent(&policy->kobj, KOBJ_ADD);
    module_put(cpufreq_driver->owner);
    pr_debug("initialization complete\n");

    return 0;


err_out_unregister:
    spin_lock_irqsave(&cpufreq_driver_lock, flags);
    for_each_cpu(j, policy->cpus)
        per_cpu(cpufreq_cpu_data, j) = NULL;
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

    kobject_put(&policy->kobj);
    wait_for_completion(&policy->kobj_unregister);

err_unlock_policy:
    unlock_policy_rwsem_write(cpu);
    free_cpumask_var(policy->related_cpus);
err_free_cpumask:
    free_cpumask_var(policy->cpus);
err_free_policy:
    kfree(policy);
nomem_out:
    module_put(cpufreq_driver->owner);
module_out:
    return ret;
}


static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
{
    unsigned int cpu = dev->id;
    unsigned long flags;
    struct cpufreq_policy *data;
    struct kobject *kobj;
    struct completion *cmp;
#ifdef CONFIG_SMP
    struct device *cpu_dev;
    unsigned int j;
#endif

    pr_debug("unregistering CPU %u\n", cpu);

    spin_lock_irqsave(&cpufreq_driver_lock, flags);
    data = per_cpu(cpufreq_cpu_data, cpu);

    if (!data) {
        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
        unlock_policy_rwsem_write(cpu);
        return -EINVAL;
    }
    per_cpu(cpufreq_cpu_data, cpu) = NULL;


#ifdef CONFIG_SMP
    /* if this isn't the CPU which is the parent of the kobj, we
     * only need to unlink, put and exit
     */
    if (unlikely(cpu != data->cpu)) {
        pr_debug("removing link\n");
        cpumask_clear_cpu(cpu, data->cpus);
        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
        kobj = &dev->kobj;
        cpufreq_cpu_put(data);
        unlock_policy_rwsem_write(cpu);
        sysfs_remove_link(kobj, "cpufreq");
        return 0;
    }
#endif

#ifdef CONFIG_SMP

#ifdef CONFIG_HOTPLUG_CPU
    strncpy(per_cpu(cpufreq_cpu_governor, cpu), data->governor->name,
            CPUFREQ_NAME_LEN);
#endif

    /* if we have other CPUs still registered, we need to unlink them,
     * or else wait_for_completion below will lock up. Clean the
     * per_cpu(cpufreq_cpu_data) while holding the lock, and remove
     * the sysfs links afterwards.
     */
    if (unlikely(cpumask_weight(data->cpus) > 1)) {
        for_each_cpu(j, data->cpus) {
            if (j == cpu)
                continue;
            per_cpu(cpufreq_cpu_data, j) = NULL;
        }
    }

    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

    if (unlikely(cpumask_weight(data->cpus) > 1)) {
        for_each_cpu(j, data->cpus) {
            if (j == cpu)
                continue;
            pr_debug("removing link for cpu %u\n", j);
#ifdef CONFIG_HOTPLUG_CPU
            strncpy(per_cpu(cpufreq_cpu_governor, j),
                data->governor->name, CPUFREQ_NAME_LEN);
#endif
            cpu_dev = get_cpu_device(j);
            kobj = &cpu_dev->kobj;
            unlock_policy_rwsem_write(cpu);
            sysfs_remove_link(kobj, "cpufreq");
            lock_policy_rwsem_write(cpu);
            cpufreq_cpu_put(data);
        }
    }
#else
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif

    if (cpufreq_driver->target)
        __cpufreq_governor(data, CPUFREQ_GOV_STOP);

    kobj = &data->kobj;
    cmp = &data->kobj_unregister;
    unlock_policy_rwsem_write(cpu);
    kobject_put(kobj);

    /* we need to make sure that the underlying kobj is actually
     * not referenced anymore by anybody before we proceed with
     * unloading.
     */
    pr_debug("waiting for dropping of refcount\n");
    wait_for_completion(cmp);
    pr_debug("wait complete\n");

    lock_policy_rwsem_write(cpu);
    if (cpufreq_driver->exit)
        cpufreq_driver->exit(data);
    unlock_policy_rwsem_write(cpu);

#ifdef CONFIG_HOTPLUG_CPU
    /* when the CPU which is the parent of the kobj is hotplugged
     * offline, check for siblings, and create cpufreq sysfs interface
     * and symlinks
     */
    if (unlikely(cpumask_weight(data->cpus) > 1)) {
        /* first sibling now owns the new sysfs dir */
        cpumask_clear_cpu(cpu, data->cpus);
        cpufreq_add_dev(get_cpu_device(cpumask_first(data->cpus)), NULL);

        /* finally remove our own symlink */
        lock_policy_rwsem_write(cpu);
        __cpufreq_remove_dev(dev, sif);
    }
#endif

    free_cpumask_var(data->related_cpus);
    free_cpumask_var(data->cpus);
    kfree(data);

    return 0;
}


static int cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
{
    unsigned int cpu = dev->id;
    int retval;

    if (cpu_is_offline(cpu))
        return 0;

    if (unlikely(lock_policy_rwsem_write(cpu)))
        BUG();

    retval = __cpufreq_remove_dev(dev, sif);
    return retval;
}


static void handle_update(struct work_struct *work)
{
    struct cpufreq_policy *policy =
        container_of(work, struct cpufreq_policy, update);
    unsigned int cpu = policy->cpu;
    pr_debug("handle_update for cpu %u called\n", cpu);
    cpufreq_update_policy(cpu);
}

static void cpufreq_out_of_sync(unsigned int cpu, unsigned int old_freq,
                unsigned int new_freq)
{
    struct cpufreq_freqs freqs;

    pr_debug("Warning: CPU frequency out of sync: cpufreq and timing "
           "core thinks of %u, is %u kHz.\n", old_freq, new_freq);

    freqs.cpu = cpu;
    freqs.old = old_freq;
    freqs.new = new_freq;
    cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
    cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
}


unsigned int cpufreq_quick_get(unsigned int cpu)
{
    struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
    unsigned int ret_freq = 0;

    if (policy) {
        ret_freq = policy->cur;
        cpufreq_cpu_put(policy);
    }

    return ret_freq;
}
EXPORT_SYMBOL(cpufreq_quick_get);

unsigned int cpufreq_quick_get_max(unsigned int cpu)
{
    struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
    unsigned int ret_freq = 0;

    if (policy) {
        ret_freq = policy->max;
        cpufreq_cpu_put(policy);
    }

    return ret_freq;
}
EXPORT_SYMBOL(cpufreq_quick_get_max);


static unsigned int __cpufreq_get(unsigned int cpu)
{
    struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
    unsigned int ret_freq = 0;

    if (!cpufreq_driver->get)
        return ret_freq;

    ret_freq = cpufreq_driver->get(cpu);

    if (ret_freq && policy->cur &&
        !(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
        /* verify no discrepancy between actual and
                    saved value exists */
        if (unlikely(ret_freq != policy->cur)) {
            cpufreq_out_of_sync(cpu, policy->cur, ret_freq);
            schedule_work(&policy->update);
        }
    }

    return ret_freq;
}

unsigned int cpufreq_get(unsigned int cpu)
{
    unsigned int ret_freq = 0;
    struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);

    if (!policy)
        goto out;

    if (unlikely(lock_policy_rwsem_read(cpu)))
        goto out_policy;

    ret_freq = __cpufreq_get(cpu);

    unlock_policy_rwsem_read(cpu);

out_policy:
    cpufreq_cpu_put(policy);
out:
    return ret_freq;
}
EXPORT_SYMBOL(cpufreq_get);

static struct subsys_interface cpufreq_interface = {
    .name       = "cpufreq",
    .subsys     = &cpu_subsys,
    .add_dev    = cpufreq_add_dev,
    .remove_dev = cpufreq_remove_dev,
};


static int cpufreq_bp_suspend(void)
{
    int ret = 0;

    int cpu = smp_processor_id();
    struct cpufreq_policy *cpu_policy;

    pr_debug("suspending cpu %u\n", cpu);

    /* If there's no policy for the boot CPU, we have nothing to do. */
    cpu_policy = cpufreq_cpu_get(cpu);
    if (!cpu_policy)
        return 0;

    if (cpufreq_driver->suspend) {
        ret = cpufreq_driver->suspend(cpu_policy);
        if (ret)
            printk(KERN_ERR "cpufreq: suspend failed in ->suspend "
                    "step on CPU %u\n", cpu_policy->cpu);
    }

    cpufreq_cpu_put(cpu_policy);
    return ret;
}

static void cpufreq_bp_resume(void)
{
    int ret = 0;

    int cpu = smp_processor_id();
    struct cpufreq_policy *cpu_policy;

    pr_debug("resuming cpu %u\n", cpu);

    /* If there's no policy for the boot CPU, we have nothing to do. */
    cpu_policy = cpufreq_cpu_get(cpu);
    if (!cpu_policy)
        return;

    if (cpufreq_driver->resume) {
        ret = cpufreq_driver->resume(cpu_policy);
        if (ret) {
            printk(KERN_ERR "cpufreq: resume failed in ->resume "
                    "step on CPU %u\n", cpu_policy->cpu);
            goto fail;
        }
    }

    schedule_work(&cpu_policy->update);

fail:
    cpufreq_cpu_put(cpu_policy);
}

static struct syscore_ops cpufreq_syscore_ops = {
    .suspend    = cpufreq_bp_suspend,
    .resume     = cpufreq_bp_resume,
};


/*********************************************************************
 *                     NOTIFIER LISTS INTERFACE                      *
 *********************************************************************/

int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list)
{
    int ret;

    WARN_ON(!init_cpufreq_transition_notifier_list_called);

    switch (list) {
    case CPUFREQ_TRANSITION_NOTIFIER:
        ret = srcu_notifier_chain_register(
                &cpufreq_transition_notifier_list, nb);
        break;
    case CPUFREQ_POLICY_NOTIFIER:
        ret = blocking_notifier_chain_register(
                &cpufreq_policy_notifier_list, nb);
        break;
    default:
        ret = -EINVAL;
    }

    return ret;
}
EXPORT_SYMBOL(cpufreq_register_notifier);


int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list)
{
    int ret;

    switch (list) {
    case CPUFREQ_TRANSITION_NOTIFIER:
        ret = srcu_notifier_chain_unregister(
                &cpufreq_transition_notifier_list, nb);
        break;
    case CPUFREQ_POLICY_NOTIFIER:
        ret = blocking_notifier_chain_unregister(
                &cpufreq_policy_notifier_list, nb);
        break;
    default:
        ret = -EINVAL;
    }

    return ret;
}
EXPORT_SYMBOL(cpufreq_unregister_notifier);


/*********************************************************************
 *                              GOVERNORS                            *
 *********************************************************************/


int __cpufreq_driver_target(struct cpufreq_policy *policy,
                unsigned int target_freq,
                unsigned int relation)
{
    int retval = -EINVAL;

    if (cpufreq_disabled())
        return -ENODEV;

    pr_debug("target for CPU %u: %u kHz, relation %u\n", policy->cpu,
        target_freq, relation);
    if (cpu_online(policy->cpu) && cpufreq_driver->target)
        retval = cpufreq_driver->target(policy, target_freq, relation);

    return retval;
}
EXPORT_SYMBOL_GPL(__cpufreq_driver_target);

int cpufreq_driver_target(struct cpufreq_policy *policy,
              unsigned int target_freq,
              unsigned int relation)
{
    int ret = -EINVAL;

    policy = cpufreq_cpu_get(policy->cpu);
    if (!policy)
        goto no_policy;

    if (unlikely(lock_policy_rwsem_write(policy->cpu)))
        goto fail;

    ret = __cpufreq_driver_target(policy, target_freq, relation);

    unlock_policy_rwsem_write(policy->cpu);

fail:
    cpufreq_cpu_put(policy);
no_policy:
    return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_driver_target);

int __cpufreq_driver_getavg(struct cpufreq_policy *policy, unsigned int cpu)
{
    int ret = 0;

    policy = cpufreq_cpu_get(policy->cpu);
    if (!policy)
        return -EINVAL;

    if (cpu_online(cpu) && cpufreq_driver->getavg)
        ret = cpufreq_driver->getavg(policy, cpu);

    cpufreq_cpu_put(policy);
    return ret;
}
EXPORT_SYMBOL_GPL(__cpufreq_driver_getavg);

/*
 * when "event" is CPUFREQ_GOV_LIMITS
 */

static int __cpufreq_governor(struct cpufreq_policy *policy,
                    unsigned int event)
{
    int ret;

    /* Only must be defined when default governor is known to have latency
       restrictions, like e.g. conservative or ondemand.
       That this is the case is already ensured in Kconfig
    */
#ifdef CONFIG_CPU_FREQ_GOV_PERFORMANCE
    struct cpufreq_governor *gov = &cpufreq_gov_performance;
#else
    struct cpufreq_governor *gov = NULL;
#endif

    if (policy->governor->max_transition_latency &&
        policy->cpuinfo.transition_latency >
        policy->governor->max_transition_latency) {
        if (!gov)
            return -EINVAL;
        else {
            printk(KERN_WARNING "%s governor failed, too long"
                   " transition latency of HW, fallback"
                   " to %s governor\n",
                   policy->governor->name,
                   gov->name);
            policy->governor = gov;
        }
    }

    if (!try_module_get(policy->governor->owner))
        return -EINVAL;

    pr_debug("__cpufreq_governor for CPU %u, event %u\n",
                        policy->cpu, event);
    ret = policy->governor->governor(policy, event);

    /* we keep one module reference alive for
            each CPU governed by this CPU */
    if ((event != CPUFREQ_GOV_START) || ret)
        module_put(policy->governor->owner);
    if ((event == CPUFREQ_GOV_STOP) && !ret)
        module_put(policy->governor->owner);

    return ret;
}


int cpufreq_register_governor(struct cpufreq_governor *governor)
{
    int err;

    if (!governor)
        return -EINVAL;

    if (cpufreq_disabled())
        return -ENODEV;

    mutex_lock(&cpufreq_governor_mutex);

    err = -EBUSY;
    if (__find_governor(governor->name) == NULL) {
        err = 0;
        list_add(&governor->governor_list, &cpufreq_governor_list);
    }

    mutex_unlock(&cpufreq_governor_mutex);
    return err;
}
EXPORT_SYMBOL_GPL(cpufreq_register_governor);


void cpufreq_unregister_governor(struct cpufreq_governor *governor)
{
#ifdef CONFIG_HOTPLUG_CPU
    int cpu;
#endif

    if (!governor)
        return;

    if (cpufreq_disabled())
        return;

#ifdef CONFIG_HOTPLUG_CPU
    for_each_present_cpu(cpu) {
        if (cpu_online(cpu))
            continue;
        if (!strcmp(per_cpu(cpufreq_cpu_governor, cpu), governor->name))
            strcpy(per_cpu(cpufreq_cpu_governor, cpu), "\0");
    }
#endif

    mutex_lock(&cpufreq_governor_mutex);
    list_del(&governor->governor_list);
    mutex_unlock(&cpufreq_governor_mutex);
    return;
}
EXPORT_SYMBOL_GPL(cpufreq_unregister_governor);



/*********************************************************************
 *                          POLICY INTERFACE                         *
 *********************************************************************/

int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
{
    struct cpufreq_policy *cpu_policy;
    if (!policy)
        return -EINVAL;

    cpu_policy = cpufreq_cpu_get(cpu);
    if (!cpu_policy)
        return -EINVAL;

    memcpy(policy, cpu_policy, sizeof(struct cpufreq_policy));

    cpufreq_cpu_put(cpu_policy);
    return 0;
}
EXPORT_SYMBOL(cpufreq_get_policy);


/*
 * data   : current policy.
 * policy : policy to be set.
 */
static int __cpufreq_set_policy(struct cpufreq_policy *data,
                struct cpufreq_policy *policy)
{
    int ret = 0;

    pr_debug("setting new policy for CPU %u: %u - %u kHz\n", policy->cpu,
        policy->min, policy->max);

    memcpy(&policy->cpuinfo, &data->cpuinfo,
                sizeof(struct cpufreq_cpuinfo));

    if (policy->min > data->max || policy->max < data->min) {
        ret = -EINVAL;
        goto error_out;
    }

    /* verify the cpu speed can be set within this limit */
    ret = cpufreq_driver->verify(policy);
    if (ret)
        goto error_out;

    /* adjust if necessary - all reasons */
    blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
            CPUFREQ_ADJUST, policy);

    /* adjust if necessary - hardware incompatibility*/
    blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
            CPUFREQ_INCOMPATIBLE, policy);

    /* verify the cpu speed can be set within this limit,
       which might be different to the first one */
    ret = cpufreq_driver->verify(policy);
    if (ret)
        goto error_out;

    /* notification of the new policy */
    blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
            CPUFREQ_NOTIFY, policy);

    data->min = policy->min;
    data->max = policy->max;

    pr_debug("new min and max freqs are %u - %u kHz\n",
                    data->min, data->max);

    if (cpufreq_driver->setpolicy) {
        data->policy = policy->policy;
        pr_debug("setting range\n");
        ret = cpufreq_driver->setpolicy(policy);
    } else {
        if (policy->governor != data->governor) {
            /* save old, working values */
            struct cpufreq_governor *old_gov = data->governor;

            pr_debug("governor switch\n");

            /* end old governor */
            if (data->governor)
                __cpufreq_governor(data, CPUFREQ_GOV_STOP);

            /* start new governor */
            data->governor = policy->governor;
            if (__cpufreq_governor(data, CPUFREQ_GOV_START)) {
                /* new governor failed, so re-start old one */
                pr_debug("starting governor %s failed\n",
                            data->governor->name);
                if (old_gov) {
                    data->governor = old_gov;
                    __cpufreq_governor(data,
                               CPUFREQ_GOV_START);
                }
                ret = -EINVAL;
                goto error_out;
            }
            /* might be a policy change, too, so fall through */
        }
        pr_debug("governor: change or update limits\n");
        __cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
    }

error_out:
    return ret;
}

int cpufreq_update_policy(unsigned int cpu)
{
    struct cpufreq_policy *data = cpufreq_cpu_get(cpu);
    struct cpufreq_policy policy;
    int ret;

    if (!data) {
        ret = -ENODEV;
        goto no_policy;
    }

    if (unlikely(lock_policy_rwsem_write(cpu))) {
        ret = -EINVAL;
        goto fail;
    }

    pr_debug("updating policy for CPU %u\n", cpu);
    memcpy(&policy, data, sizeof(struct cpufreq_policy));
    policy.min = data->user_policy.min;
    policy.max = data->user_policy.max;
    policy.policy = data->user_policy.policy;
    policy.governor = data->user_policy.governor;

    /* BIOS might change freq behind our back
      -> ask driver for current freq and notify governors about a change */
    if (cpufreq_driver->get) {
        policy.cur = cpufreq_driver->get(cpu);
        if (!data->cur) {
            pr_debug("Driver did not initialize current freq");
            data->cur = policy.cur;
        } else {
            if (data->cur != policy.cur)
                cpufreq_out_of_sync(cpu, data->cur,
                                policy.cur);
        }
    }

    ret = __cpufreq_set_policy(data, &policy);

    unlock_policy_rwsem_write(cpu);

fail:
    cpufreq_cpu_put(data);
no_policy:
    return ret;
}
EXPORT_SYMBOL(cpufreq_update_policy);

static int __cpuinit cpufreq_cpu_callback(struct notifier_block *nfb,
                    unsigned long action, void *hcpu)
{
    unsigned int cpu = (unsigned long)hcpu;
    struct device *dev;

    dev = get_cpu_device(cpu);
    if (dev) {
        switch (action) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
            cpufreq_add_dev(dev, NULL);
            break;
        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
            if (unlikely(lock_policy_rwsem_write(cpu)))
                BUG();

            __cpufreq_remove_dev(dev, NULL);
            break;
        case CPU_DOWN_FAILED:
        case CPU_DOWN_FAILED_FROZEN:
            cpufreq_add_dev(dev, NULL);
            break;
        }
    }
    return NOTIFY_OK;
}

static struct notifier_block __refdata cpufreq_cpu_notifier = {
    .notifier_call = cpufreq_cpu_callback,
};

/*********************************************************************
 *               REGISTER / UNREGISTER CPUFREQ DRIVER                *
 *********************************************************************/

int cpufreq_register_driver(struct cpufreq_driver *driver_data)
{
    unsigned long flags;
    int ret;

    if (cpufreq_disabled())
        return -ENODEV;

    if (!driver_data || !driver_data->verify || !driver_data->init ||
        ((!driver_data->setpolicy) && (!driver_data->target)))
        return -EINVAL;

    pr_debug("trying to register driver %s\n", driver_data->name);

    if (driver_data->setpolicy)
        driver_data->flags |= CPUFREQ_CONST_LOOPS;

    spin_lock_irqsave(&cpufreq_driver_lock, flags);
    if (cpufreq_driver) {
        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
        return -EBUSY;
    }
    cpufreq_driver = driver_data;
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

    ret = subsys_interface_register(&cpufreq_interface);
    if (ret)
        goto err_null_driver;

    if (!(cpufreq_driver->flags & CPUFREQ_STICKY)) {
        int i;
        ret = -ENODEV;

        /* check for at least one working CPU */
        for (i = 0; i < nr_cpu_ids; i++)
            if (cpu_possible(i) && per_cpu(cpufreq_cpu_data, i)) {
                ret = 0;
                break;
            }

        /* if all ->init() calls failed, unregister */
        if (ret) {
            pr_debug("no CPU initialized for driver %s\n",
                            driver_data->name);
            goto err_if_unreg;
        }
    }

    register_hotcpu_notifier(&cpufreq_cpu_notifier);
    pr_debug("driver %s up and running\n", driver_data->name);

    return 0;
err_if_unreg:
    subsys_interface_unregister(&cpufreq_interface);
err_null_driver:
    spin_lock_irqsave(&cpufreq_driver_lock, flags);
    cpufreq_driver = NULL;
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
    return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_register_driver);


int cpufreq_unregister_driver(struct cpufreq_driver *driver)
{
    unsigned long flags;

    if (!cpufreq_driver || (driver != cpufreq_driver))
        return -EINVAL;

    pr_debug("unregistering driver %s\n", driver->name);

    subsys_interface_unregister(&cpufreq_interface);
    unregister_hotcpu_notifier(&cpufreq_cpu_notifier);

    spin_lock_irqsave(&cpufreq_driver_lock, flags);
    cpufreq_driver = NULL;
    spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

    return 0;
}
EXPORT_SYMBOL_GPL(cpufreq_unregister_driver);

static int __init cpufreq_core_init(void)
{
    int cpu;

    if (cpufreq_disabled())
        return -ENODEV;

    for_each_possible_cpu(cpu) {
        per_cpu(cpufreq_policy_cpu, cpu) = -1;
        init_rwsem(&per_cpu(cpu_policy_rwsem, cpu));
    }

    cpufreq_global_kobject = kobject_create_and_add("cpufreq", &cpu_subsys.dev_root->kobj);
    BUG_ON(!cpufreq_global_kobject);
    register_syscore_ops(&cpufreq_syscore_ops);

    return 0;
}
core_initcall(cpufreq_core_init);