Merge remote-tracking branch 'driver-core/driver-core-next'

[linux-2.6/next.git] / drivers / cpufreq / cpufreq.c

/*
 *  linux/drivers/cpufreq/cpufreq.c
 *
 *  Copyright (C) 2001 Russell King
 *            (C) 2002 - 2003 Dominik Brodowski <linux@brodo.de>
 *
 *  Oct 2005 - Ashok Raj <ashok.raj@intel.com>
 *      Added handling for CPU hotplug
 *  Feb 2006 - Jacob Shin <jacob.shin@amd.com>
 *      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>

/**
 * The "cpufreq driver" - the arch- or hardware-dependent low
 * level driver of CPUFreq support, and its spinlock. This lock
 * also protects the cpufreq_cpu_data array.
 */
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);

/**
 * Two notifier lists: the "policy" list is involved in the
 * validation process for a new CPU frequency policy; the
 * "transition" list for kernel code that needs to handle
 * changes to devices when the CPU clock speed changes.
 * The mutex locks both lists.
 */
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 LIST_HEAD(cpufreq_governor_list);
static DEFINE_MUTEX(cpufreq_governor_mutex);

struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
{
        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 (!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;
}
EXPORT_SYMBOL_GPL(cpufreq_cpu_get);


void cpufreq_cpu_put(struct cpufreq_policy *data)
{
        kobject_put(&data->kobj);
        module_put(cpufreq_driver->owner);
}
EXPORT_SYMBOL_GPL(cpufreq_cpu_put);


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

/**
 * adjust_jiffies - adjust the system "loops_per_jiffy"
 *
 * This function alters the system "loops_per_jiffy" for the clock
 * speed change. Note that loops_per_jiffy cannot be updated on SMP
 * systems as each CPU might be scaled differently. So, use the arch
 * per-CPU loops_per_jiffy value wherever possible.
 */
#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_PRECHANGE  && ci->old < ci->new) ||
            (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


/**
 * cpufreq_notify_transition - call notifier chain and adjust_jiffies
 * on frequency transition.
 *
 * This function calls the transition notifiers and the "adjust_jiffies"
 * function. It is called twice on all CPU frequency changes that have
 * external effects.
 */
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;
}

/**
 * cpufreq_parse_governor - parse a governor string
 */
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;
}


/**
 * cpufreq_per_cpu_attr_read() / show_##file_name() -
 * print out cpufreq information
 *
 * Write out information from cpufreq_driver->policy[cpu]; object must be
 * "unsigned int".
 */

#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);

/**
 * cpufreq_per_cpu_attr_write() / store_##file_name() - sysfs write access
 */
#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);

/**
 * show_cpuinfo_cur_freq - current CPU frequency as detected by hardware
 */
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);
}


/**
 * show_scaling_governor - show the current policy for the specified CPU
 */
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;
}


/**
 * store_scaling_governor - store policy for the specified CPU
 */
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;
}

/**
 * show_scaling_driver - show the cpufreq driver currently loaded
 */
static ssize_t show_scaling_driver(struct cpufreq_policy *policy, char *buf)
{
        return scnprintf(buf, CPUFREQ_NAME_LEN, "%s\n", cpufreq_driver->name);
}

/**
 * show_scaling_available_governors - show the available CPUfreq governors
 */
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;
}

/**
 * show_related_cpus - show the CPUs affected by each transition even if
 * hw coordination is in use
 */
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);
}

/**
 * show_affected_cpus - show the CPUs affected by each transition
 */
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);
}

/**
 * show_scaling_driver - show the current cpufreq HW/BIOS limitation
 */
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(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(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(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(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 sys_device *sys_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(&sys_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 sys_device *cpu_sys_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_sys_dev = get_cpu_sysdev(j);
                ret = sysfs_create_link(&cpu_sys_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 sys_device *sys_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,
                                   &sys_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;
}


/**
 * cpufreq_add_dev - add a CPU device
 *
 * Adds the cpufreq interface for a CPU device.
 *
 * The Oracle says: try running cpufreq registration/unregistration concurrently
 * with with cpu hotplugging and all hell will break loose. Tried to clean this
 * mess up, but more thorough testing is needed. - Mathieu
 */
static int cpufreq_add_dev(struct sys_device *sys_dev)
{
        unsigned int cpu = sys_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, sys_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, sys_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;
}


/**
 * __cpufreq_remove_dev - remove a CPU device
 *
 * Removes the cpufreq interface for a CPU device.
 * Caller should already have policy_rwsem in write mode for this CPU.
 * This routine frees the rwsem before returning.
 */
static int __cpufreq_remove_dev(struct sys_device *sys_dev)
{
        unsigned int cpu = sys_dev->id;
        unsigned long flags;
        struct cpufreq_policy *data;
        struct kobject *kobj;
        struct completion *cmp;
#ifdef CONFIG_SMP
        struct sys_device *cpu_sys_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 = &sys_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_sys_dev = get_cpu_sysdev(j);
                        kobj = &cpu_sys_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_sysdev(cpumask_first(data->cpus)));

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

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

        return 0;
}


static int cpufreq_remove_dev(struct sys_device *sys_dev)
{
        unsigned int cpu = sys_dev->id;
        int retval;

        if (cpu_is_offline(cpu))
                return 0;

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

        retval = __cpufreq_remove_dev(sys_dev);
        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);
}

/**
 *      cpufreq_out_of_sync - If actual and saved CPU frequency differs, we're in deep trouble.
 *      @cpu: cpu number
 *      @old_freq: CPU frequency the kernel thinks the CPU runs at
 *      @new_freq: CPU frequency the CPU actually runs at
 *
 *      We adjust to current frequency first, and need to clean up later.
 *      So either call to cpufreq_update_policy() or schedule handle_update()).
 */
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);
}


/**
 * cpufreq_quick_get - get the CPU frequency (in kHz) from policy->cur
 * @cpu: CPU number
 *
 * This is the last known freq, without actually getting it from the driver.
 * Return value will be same as what is shown in scaling_cur_freq in sysfs.
 */
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);

/**
 * cpufreq_quick_get_max - get the max reported CPU frequency for this CPU
 * @cpu: CPU number
 *
 * Just return the max possible frequency for a given CPU.
 */
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;
}

/**
 * cpufreq_get - get the current CPU frequency (in kHz)
 * @cpu: CPU number
 *
 * Get the CPU current (static) CPU frequency
 */
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 sysdev_driver cpufreq_sysdev_driver = {
        .add            = cpufreq_add_dev,
        .remove         = cpufreq_remove_dev,
};


/**
 * cpufreq_bp_suspend - Prepare the boot CPU for system suspend.
 *
 * This function is only executed for the boot processor.  The other CPUs
 * have been put offline by means of CPU hotplug.
 */
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;
}

/**
 * cpufreq_bp_resume - Restore proper frequency handling of the boot CPU.
 *
 *      1.) resume CPUfreq hardware support (cpufreq_driver->resume())
 *      2.) schedule call cpufreq_update_policy() ASAP as interrupts are
 *          restored. It will verify that the current freq is in sync with
 *          what we believe it to be. This is a bit later than when it
 *          should be, but nonethteless it's better than calling
 *          cpufreq_driver->get() here which might re-enable interrupts...
 *
 * This function is only executed for the boot CPU.  The other CPUs have not
 * been turned on yet.
 */
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                      *
 *********************************************************************/

/**
 *      cpufreq_register_notifier - register a driver with cpufreq
 *      @nb: notifier function to register
 *      @list: CPUFREQ_TRANSITION_NOTIFIER or CPUFREQ_POLICY_NOTIFIER
 *
 *      Add a driver to one of two lists: either a list of drivers that
 *      are notified about clock rate changes (once before and once after
 *      the transition), or a list of drivers that are notified about
 *      changes in cpufreq policy.
 *
 *      This function may sleep, and has the same return conditions as
 *      blocking_notifier_chain_register.
 */
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);


/**
 *      cpufreq_unregister_notifier - unregister a driver with cpufreq
 *      @nb: notifier block to be unregistered
 *      @list: CPUFREQ_TRANSITION_NOTIFIER or CPUFREQ_POLICY_NOTIFIER
 *
 *      Remove a driver from the CPU frequency notifier list.
 *
 *      This function may sleep, and has the same return conditions as
 *      blocking_notifier_chain_unregister.
 */
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;

        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;

        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;

#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                         *
 *********************************************************************/

/**
 * cpufreq_get_policy - get the current cpufreq_policy
 * @policy: struct cpufreq_policy into which the current cpufreq_policy
 *      is written
 *
 * Reads the current cpufreq policy.
 */
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;
}

/**
 *      cpufreq_update_policy - re-evaluate an existing cpufreq policy
 *      @cpu: CPU which shall be re-evaluated
 *
 *      Useful for policy notifiers which have different necessities
 *      at different times.
 */
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 sys_device *sys_dev;

        sys_dev = get_cpu_sysdev(cpu);
        if (sys_dev) {
                switch (action) {
                case CPU_ONLINE:
                case CPU_ONLINE_FROZEN:
                        cpufreq_add_dev(sys_dev);
                        break;
                case CPU_DOWN_PREPARE:
                case CPU_DOWN_PREPARE_FROZEN:
                        if (unlikely(lock_policy_rwsem_write(cpu)))
                                BUG();

                        __cpufreq_remove_dev(sys_dev);
                        break;
                case CPU_DOWN_FAILED:
                case CPU_DOWN_FAILED_FROZEN:
                        cpufreq_add_dev(sys_dev);
                        break;
                }
        }
        return NOTIFY_OK;
}

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

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

/**
 * cpufreq_register_driver - register a CPU Frequency driver
 * @driver_data: A struct cpufreq_driver containing the values#
 * submitted by the CPU Frequency driver.
 *
 *   Registers a CPU Frequency driver to this core code. This code
 * returns zero on success, -EBUSY when another driver got here first
 * (and isn't unregistered in the meantime).
 *
 */
int cpufreq_register_driver(struct cpufreq_driver *driver_data)
{
        unsigned long flags;
        int ret;

        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 = sysdev_driver_register(&cpu_sysdev_class,
                                        &cpufreq_sysdev_driver);
        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_sysdev_unreg;
                }
        }

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

        return 0;
err_sysdev_unreg:
        sysdev_driver_unregister(&cpu_sysdev_class,
                        &cpufreq_sysdev_driver);
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);


/**
 * cpufreq_unregister_driver - unregister the current CPUFreq driver
 *
 *    Unregister the current CPUFreq driver. Only call this if you have
 * the right to do so, i.e. if you have succeeded in initialising before!
 * Returns zero if successful, and -EINVAL if the cpufreq_driver is
 * currently not initialised.
 */
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);

        sysdev_driver_unregister(&cpu_sysdev_class, &cpufreq_sysdev_driver);
        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;

        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_sysdev_class.kset.kobj);
        BUG_ON(!cpufreq_global_kobject);
        register_syscore_ops(&cpufreq_syscore_ops);

        return 0;
}
core_initcall(cpufreq_core_init);