[SPARC64]: Rate limited kernel unaligned trap logging, ala IA64.

[linux-2.6/verdex.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/config.h>
#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>

#define dprintk(msg...) cpufreq_debug_printk(CPUFREQ_DEBUG_CORE, "cpufreq-core", msg)

/**
 * The "cpufreq driver" - the arch- or hardware-dependend 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 struct cpufreq_policy *cpufreq_cpu_data[NR_CPUS];
static DEFINE_SPINLOCK(cpufreq_driver_lock);

/* internal prototypes */
static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event);
static void handle_update(void *data);

/**
 * 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 BLOCKING_NOTIFIER_HEAD(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_CPUS)
                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 = 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);


/*********************************************************************
 *                     UNIFIED DEBUG HELPERS                         *
 *********************************************************************/
#ifdef CONFIG_CPU_FREQ_DEBUG

/* what part(s) of the CPUfreq subsystem are debugged? */
static unsigned int debug;

/* is the debug output ratelimit'ed using printk_ratelimit? User can
 * set or modify this value.
 */
static unsigned int debug_ratelimit = 1;

/* is the printk_ratelimit'ing enabled? It's enabled after a successful
 * loading of a cpufreq driver, temporarily disabled when a new policy
 * is set, and disabled upon cpufreq driver removal
 */
static unsigned int disable_ratelimit = 1;
static DEFINE_SPINLOCK(disable_ratelimit_lock);

static void cpufreq_debug_enable_ratelimit(void)
{
        unsigned long flags;

        spin_lock_irqsave(&disable_ratelimit_lock, flags);
        if (disable_ratelimit)
                disable_ratelimit--;
        spin_unlock_irqrestore(&disable_ratelimit_lock, flags);
}

static void cpufreq_debug_disable_ratelimit(void)
{
        unsigned long flags;

        spin_lock_irqsave(&disable_ratelimit_lock, flags);
        disable_ratelimit++;
        spin_unlock_irqrestore(&disable_ratelimit_lock, flags);
}

void cpufreq_debug_printk(unsigned int type, const char *prefix, const char *fmt, ...)
{
        char s[256];
        va_list args;
        unsigned int len;
        unsigned long flags;

        WARN_ON(!prefix);
        if (type & debug) {
                spin_lock_irqsave(&disable_ratelimit_lock, flags);
                if (!disable_ratelimit && debug_ratelimit && !printk_ratelimit()) {
                        spin_unlock_irqrestore(&disable_ratelimit_lock, flags);
                        return;
                }
                spin_unlock_irqrestore(&disable_ratelimit_lock, flags);

                len = snprintf(s, 256, KERN_DEBUG "%s: ", prefix);

                va_start(args, fmt);
                len += vsnprintf(&s[len], (256 - len), fmt, args);
                va_end(args);

                printk(s);

                WARN_ON(len < 5);
        }
}
EXPORT_SYMBOL(cpufreq_debug_printk);


module_param(debug, uint, 0644);
MODULE_PARM_DESC(debug, "CPUfreq debugging: add 1 to debug core, 2 to debug drivers, and 4 to debug governors.");

module_param(debug_ratelimit, uint, 0644);
MODULE_PARM_DESC(debug_ratelimit, "CPUfreq debugging: set to 0 to disable ratelimiting.");

#else /* !CONFIG_CPU_FREQ_DEBUG */

static inline void cpufreq_debug_enable_ratelimit(void) { return; }
static inline void cpufreq_debug_disable_ratelimit(void) { return; }

#endif /* CONFIG_CPU_FREQ_DEBUG */


/*********************************************************************
 *            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;
                dprintk("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);
                dprintk("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;
        dprintk("notification %u of frequency transition to %u kHz\n",
                state, freqs->new);

        policy = 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)) {
                                dprintk("Warning: CPU frequency is"
                                        " %u, cpufreq assumed %u kHz.\n",
                                        freqs->old, policy->cur);
                                freqs->old = policy->cur;
                        }
                }
                blocking_notifier_call_chain(&cpufreq_transition_notifier_list,
                                CPUFREQ_PRECHANGE, freqs);
                adjust_jiffies(CPUFREQ_PRECHANGE, freqs);
                break;

        case CPUFREQ_POSTCHANGE:
                adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
                blocking_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                          *
 *********************************************************************/

/**
 * cpufreq_parse_governor - parse a governor string
 */
static int cpufreq_parse_governor (char *str_governor, unsigned int *policy,
                                struct cpufreq_governor **governor)
{
        if (!cpufreq_driver)
                return -EINVAL;
        if (cpufreq_driver->setpolicy) {
                if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
                        *policy = CPUFREQ_POLICY_PERFORMANCE;
                        return 0;
                } else if (!strnicmp(str_governor, "powersave", CPUFREQ_NAME_LEN)) {
                        *policy = CPUFREQ_POLICY_POWERSAVE;
                        return 0;
                }
                return -EINVAL;
        } else {
                struct cpufreq_governor *t;
                mutex_lock(&cpufreq_governor_mutex);
                if (!cpufreq_driver || !cpufreq_driver->target)
                        goto out;
                list_for_each_entry(t, &cpufreq_governor_list, governor_list) {
                        if (!strnicmp(str_governor,t->name,CPUFREQ_NAME_LEN)) {
                                *governor = t;
                                mutex_unlock(&cpufreq_governor_mutex);
                                return 0;
                        }
                }
out:
                mutex_unlock(&cpufreq_governor_mutex);
        }
        return -EINVAL;
}


/* drivers/base/cpu.c */
extern struct sysdev_class cpu_sysdev_class;


/**
 * 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(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;                                         \
                                                                        \
        mutex_lock(&policy->lock);                                      \
        ret = __cpufreq_set_policy(policy, &new_policy);                \
        policy->user_policy.object = policy->object;                    \
        mutex_unlock(&policy->lock);                                    \
                                                                        \
        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 */
        mutex_lock(&policy->lock);
        ret = __cpufreq_set_policy(policy, &new_policy);

        policy->user_policy.policy = policy->policy;
        policy->user_policy.governor = policy->governor;
        mutex_unlock(&policy->lock);

        return ret ? ret : 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;
}
/**
 * show_affected_cpus - show the CPUs affected by each transition
 */
static ssize_t show_affected_cpus (struct cpufreq_policy * policy, char *buf)
{
        ssize_t i = 0;
        unsigned int cpu;

        for_each_cpu_mask(cpu, policy->cpus) {
                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;
}


#define define_one_ro(_name) \
static struct freq_attr _name = \
__ATTR(_name, 0444, show_##_name, NULL)

#define define_one_ro0400(_name) \
static struct freq_attr _name = \
__ATTR(_name, 0400, show_##_name, NULL)

#define define_one_rw(_name) \
static struct freq_attr _name = \
__ATTR(_name, 0644, show_##_name, store_##_name)

define_one_ro0400(cpuinfo_cur_freq);
define_one_ro(cpuinfo_min_freq);
define_one_ro(cpuinfo_max_freq);
define_one_ro(scaling_available_governors);
define_one_ro(scaling_driver);
define_one_ro(scaling_cur_freq);
define_one_ro(affected_cpus);
define_one_rw(scaling_min_freq);
define_one_rw(scaling_max_freq);
define_one_rw(scaling_governor);

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

#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;
        policy = cpufreq_cpu_get(policy->cpu);
        if (!policy)
                return -EINVAL;
        ret = fattr->show ? fattr->show(policy,buf) : -EIO;
        cpufreq_cpu_put(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;
        policy = cpufreq_cpu_get(policy->cpu);
        if (!policy)
                return -EINVAL;
        ret = fattr->store ? fattr->store(policy,buf,count) : -EIO;
        cpufreq_cpu_put(policy);
        return ret;
}

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

static 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,
};


/**
 * cpufreq_add_dev - add a CPU device
 *
 * Adds the cpufreq interface for a CPU device.
 */
static int cpufreq_add_dev (struct sys_device * sys_dev)
{
        unsigned int cpu = sys_dev->id;
        int ret = 0;
        struct cpufreq_policy new_policy;
        struct cpufreq_policy *policy;
        struct freq_attr **drv_attr;
        struct sys_device *cpu_sys_dev;
        unsigned long flags;
        unsigned int j;
#ifdef CONFIG_SMP
        struct cpufreq_policy *managed_policy;
#endif

        if (cpu_is_offline(cpu))
                return 0;

        cpufreq_debug_disable_ratelimit();
        dprintk("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);
                cpufreq_debug_enable_ratelimit();
                return 0;
        }
#endif

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

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

        policy->cpu = cpu;
        policy->cpus = cpumask_of_cpu(cpu);

        mutex_init(&policy->lock);
        mutex_lock(&policy->lock);
        init_completion(&policy->kobj_unregister);
        INIT_WORK(&policy->update, handle_update, (void *)(long)cpu);

        /* 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) {
                dprintk("initialization failed\n");
                mutex_unlock(&policy->lock);
                goto err_out;
        }

#ifdef CONFIG_SMP
        for_each_cpu_mask(j, policy->cpus) {
                if (cpu == j)
                        continue;

                /* check for existing affected CPUs.  They may not be aware
                 * of it due to CPU Hotplug.
                 */
                managed_policy = cpufreq_cpu_get(j);
                if (unlikely(managed_policy)) {
                        spin_lock_irqsave(&cpufreq_driver_lock, flags);
                        managed_policy->cpus = policy->cpus;
                        cpufreq_cpu_data[cpu] = managed_policy;
                        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

                        dprintk("CPU already managed, adding link\n");
                        sysfs_create_link(&sys_dev->kobj,
                                          &managed_policy->kobj, "cpufreq");

                        cpufreq_debug_enable_ratelimit();
                        mutex_unlock(&policy->lock);
                        ret = 0;
                        goto err_out_driver_exit; /* call driver->exit() */
                }
        }
#endif
        memcpy(&new_policy, policy, sizeof(struct cpufreq_policy));

        /* prepare interface data */
        policy->kobj.parent = &sys_dev->kobj;
        policy->kobj.ktype = &ktype_cpufreq;
        strlcpy(policy->kobj.name, "cpufreq", KOBJ_NAME_LEN);

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

        spin_lock_irqsave(&cpufreq_driver_lock, flags);
        for_each_cpu_mask(j, policy->cpus)
                cpufreq_cpu_data[j] = policy;
        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

        /* symlink affected CPUs */
        for_each_cpu_mask(j, policy->cpus) {
                if (j == cpu)
                        continue;
                if (!cpu_online(j))
                        continue;

                dprintk("CPU %u already managed, adding link\n", j);
                cpufreq_cpu_get(cpu);
                cpu_sys_dev = get_cpu_sysdev(j);
                sysfs_create_link(&cpu_sys_dev->kobj, &policy->kobj,
                                  "cpufreq");
        }

        policy->governor = NULL; /* to assure that the starting sequence is
                                  * run in cpufreq_set_policy */
        mutex_unlock(&policy->lock);

        /* set default policy */
        ret = cpufreq_set_policy(&new_policy);
        if (ret) {
                dprintk("setting policy failed\n");
                goto err_out_unregister;
        }

        module_put(cpufreq_driver->owner);
        dprintk("initialization complete\n");
        cpufreq_debug_enable_ratelimit();

        return 0;


err_out_unregister:
        spin_lock_irqsave(&cpufreq_driver_lock, flags);
        for_each_cpu_mask(j, policy->cpus)
                cpufreq_cpu_data[j] = NULL;
        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

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

err_out_driver_exit:
        if (cpufreq_driver->exit)
                cpufreq_driver->exit(policy);

err_out:
        kfree(policy);

nomem_out:
        module_put(cpufreq_driver->owner);
module_out:
        cpufreq_debug_enable_ratelimit();
        return ret;
}


/**
 * cpufreq_remove_dev - remove a CPU device
 *
 * Removes the cpufreq interface for a CPU device.
 */
static int cpufreq_remove_dev (struct sys_device * sys_dev)
{
        unsigned int cpu = sys_dev->id;
        unsigned long flags;
        struct cpufreq_policy *data;
#ifdef CONFIG_SMP
        struct sys_device *cpu_sys_dev;
        unsigned int j;
#endif

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

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

        if (!data) {
                spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
                cpufreq_debug_enable_ratelimit();
                return -EINVAL;
        }
        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)) {
                dprintk("removing link\n");
                cpu_clear(cpu, data->cpus);
                spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
                sysfs_remove_link(&sys_dev->kobj, "cpufreq");
                cpufreq_cpu_put(data);
                cpufreq_debug_enable_ratelimit();
                return 0;
        }
#endif


        if (!kobject_get(&data->kobj)) {
                spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
                cpufreq_debug_enable_ratelimit();
                return -EFAULT;
        }

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

        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

        if (unlikely(cpus_weight(data->cpus) > 1)) {
                for_each_cpu_mask(j, data->cpus) {
                        if (j == cpu)
                                continue;
                        dprintk("removing link for cpu %u\n", j);
                        cpu_sys_dev = get_cpu_sysdev(j);
                        sysfs_remove_link(&cpu_sys_dev->kobj, "cpufreq");
                        cpufreq_cpu_put(data);
                }
        }
#else
        spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif

        mutex_lock(&data->lock);
        if (cpufreq_driver->target)
                __cpufreq_governor(data, CPUFREQ_GOV_STOP);
        mutex_unlock(&data->lock);

        kobject_unregister(&data->kobj);

        kobject_put(&data->kobj);

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

        if (cpufreq_driver->exit)
                cpufreq_driver->exit(data);

        kfree(data);

        cpufreq_debug_enable_ratelimit();
        return 0;
}


static void handle_update(void *data)
{
        unsigned int cpu = (unsigned int)(long)data;
        dprintk("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;

        dprintk("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) frpm 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 = 0;

        if (policy) {
                mutex_lock(&policy->lock);
                ret = policy->cur;
                mutex_unlock(&policy->lock);
                cpufreq_cpu_put(policy);
        }

        return (ret);
}
EXPORT_SYMBOL(cpufreq_quick_get);


/**
 * 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)
{
        struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
        unsigned int ret = 0;

        if (!policy)
                return 0;

        if (!cpufreq_driver->get)
                goto out;

        mutex_lock(&policy->lock);

        ret = cpufreq_driver->get(cpu);

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

        mutex_unlock(&policy->lock);

out:
        cpufreq_cpu_put(policy);

        return (ret);
}
EXPORT_SYMBOL(cpufreq_get);


/**
 *      cpufreq_suspend - let the low level driver prepare for suspend
 */

static int cpufreq_suspend(struct sys_device * sysdev, pm_message_t pmsg)
{
        int cpu = sysdev->id;
        unsigned int ret = 0;
        unsigned int cur_freq = 0;
        struct cpufreq_policy *cpu_policy;

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

        if (!cpu_online(cpu))
                return 0;

        /* we may be lax here as interrupts are off. Nonetheless
         * we need to grab the correct cpu policy, as to check
         * whether we really run on this CPU.
         */

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

        /* only handle each CPU group once */
        if (unlikely(cpu_policy->cpu != cpu)) {
                cpufreq_cpu_put(cpu_policy);
                return 0;
        }

        if (cpufreq_driver->suspend) {
                ret = cpufreq_driver->suspend(cpu_policy, pmsg);
                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;
                }
        }


        if (cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)
                goto out;

        if (cpufreq_driver->get)
                cur_freq = cpufreq_driver->get(cpu_policy->cpu);

        if (!cur_freq || !cpu_policy->cur) {
                printk(KERN_ERR "cpufreq: suspend failed to assert current "
                       "frequency is what timing core thinks it is.\n");
                goto out;
        }

        if (unlikely(cur_freq != cpu_policy->cur)) {
                struct cpufreq_freqs freqs;

                if (!(cpufreq_driver->flags & CPUFREQ_PM_NO_WARN))
                        dprintk("Warning: CPU frequency is %u, "
                               "cpufreq assumed %u kHz.\n",
                               cur_freq, cpu_policy->cur);

                freqs.cpu = cpu;
                freqs.old = cpu_policy->cur;
                freqs.new = cur_freq;

                blocking_notifier_call_chain(&cpufreq_transition_notifier_list,
                                    CPUFREQ_SUSPENDCHANGE, &freqs);
                adjust_jiffies(CPUFREQ_SUSPENDCHANGE, &freqs);

                cpu_policy->cur = cur_freq;
        }

out:
        cpufreq_cpu_put(cpu_policy);
        return 0;
}

/**
 *      cpufreq_resume -  restore proper CPU frequency handling after resume
 *
 *      1.) resume CPUfreq hardware support (cpufreq_driver->resume())
 *      2.) if ->target and !CPUFREQ_CONST_LOOPS: verify we're in sync
 *      3.) schedule call cpufreq_update_policy() ASAP as interrupts are
 *          restored.
 */
static int cpufreq_resume(struct sys_device * sysdev)
{
        int cpu = sysdev->id;
        unsigned int ret = 0;
        struct cpufreq_policy *cpu_policy;

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

        if (!cpu_online(cpu))
                return 0;

        /* we may be lax here as interrupts are off. Nonetheless
         * we need to grab the correct cpu policy, as to check
         * whether we really run on this CPU.
         */

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

        /* only handle each CPU group once */
        if (unlikely(cpu_policy->cpu != cpu)) {
                cpufreq_cpu_put(cpu_policy);
                return 0;
        }

        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);
                        cpufreq_cpu_put(cpu_policy);
                        return ret;
                }
        }

        if (!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
                unsigned int cur_freq = 0;

                if (cpufreq_driver->get)
                        cur_freq = cpufreq_driver->get(cpu_policy->cpu);

                if (!cur_freq || !cpu_policy->cur) {
                        printk(KERN_ERR "cpufreq: resume failed to assert "
                                        "current frequency is what timing core "
                                        "thinks it is.\n");
                        goto out;
                }

                if (unlikely(cur_freq != cpu_policy->cur)) {
                        struct cpufreq_freqs freqs;

                        if (!(cpufreq_driver->flags & CPUFREQ_PM_NO_WARN))
                                dprintk("Warning: CPU frequency"
                                       "is %u, cpufreq assumed %u kHz.\n",
                                       cur_freq, cpu_policy->cur);

                        freqs.cpu = cpu;
                        freqs.old = cpu_policy->cur;
                        freqs.new = cur_freq;

                        blocking_notifier_call_chain(
                                        &cpufreq_transition_notifier_list,
                                        CPUFREQ_RESUMECHANGE, &freqs);
                        adjust_jiffies(CPUFREQ_RESUMECHANGE, &freqs);

                        cpu_policy->cur = cur_freq;
                }
        }

out:
        schedule_work(&cpu_policy->update);
        cpufreq_cpu_put(cpu_policy);
        return ret;
}

static struct sysdev_driver cpufreq_sysdev_driver = {
        .add            = cpufreq_add_dev,
        .remove         = cpufreq_remove_dev,
        .suspend        = cpufreq_suspend,
        .resume         = cpufreq_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;

        switch (list) {
        case CPUFREQ_TRANSITION_NOTIFIER:
                ret = blocking_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 = blocking_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;

        lock_cpu_hotplug();
        dprintk("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);

        unlock_cpu_hotplug();

        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;

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

        mutex_lock(&policy->lock);

        ret = __cpufreq_driver_target(policy, target_freq, relation);

        mutex_unlock(&policy->lock);

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


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

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

        dprintk("__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_governor(unsigned int cpu, unsigned int event)
{
        int ret = 0;
        struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);

        if (!policy)
                return -EINVAL;

        mutex_lock(&policy->lock);
        ret = __cpufreq_governor(policy, event);
        mutex_unlock(&policy->lock);

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


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

        if (!governor)
                return -EINVAL;

        mutex_lock(&cpufreq_governor_mutex);

        list_for_each_entry(t, &cpufreq_governor_list, governor_list) {
                if (!strnicmp(governor->name,t->name,CPUFREQ_NAME_LEN)) {
                        mutex_unlock(&cpufreq_governor_mutex);
                        return -EBUSY;
                }
        }
        list_add(&governor->governor_list, &cpufreq_governor_list);

        mutex_unlock(&cpufreq_governor_mutex);
        return 0;
}
EXPORT_SYMBOL_GPL(cpufreq_register_governor);


void cpufreq_unregister_governor(struct cpufreq_governor *governor)
{
        if (!governor)
                return;

        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;

        mutex_lock(&cpu_policy->lock);
        memcpy(policy, cpu_policy, sizeof(struct cpufreq_policy));
        mutex_unlock(&cpu_policy->lock);

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


static int __cpufreq_set_policy(struct cpufreq_policy *data, struct cpufreq_policy *policy)
{
        int ret = 0;

        cpufreq_debug_disable_ratelimit();
        dprintk("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));

        /* 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;

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

        if (cpufreq_driver->setpolicy) {
                data->policy = policy->policy;
                dprintk("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;

                        dprintk("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 */
                                dprintk("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 */
                }
                dprintk("governor: change or update limits\n");
                __cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
        }

error_out:
        cpufreq_debug_enable_ratelimit();
        return ret;
}

/**
 *      cpufreq_set_policy - set a new CPUFreq policy
 *      @policy: policy to be set.
 *
 *      Sets a new CPU frequency and voltage scaling policy.
 */
int cpufreq_set_policy(struct cpufreq_policy *policy)
{
        int ret = 0;
        struct cpufreq_policy *data;

        if (!policy)
                return -EINVAL;

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

        /* lock this CPU */
        mutex_lock(&data->lock);

        ret = __cpufreq_set_policy(data, policy);
        data->user_policy.min = data->min;
        data->user_policy.max = data->max;
        data->user_policy.policy = data->policy;
        data->user_policy.governor = data->governor;

        mutex_unlock(&data->lock);
        cpufreq_cpu_put(data);

        return ret;
}
EXPORT_SYMBOL(cpufreq_set_policy);


/**
 *      cpufreq_update_policy - re-evaluate an existing cpufreq policy
 *      @cpu: CPU which shall be re-evaluated
 *
 *      Usefull 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 = 0;

        if (!data)
                return -ENODEV;

        mutex_lock(&data->lock);

        dprintk("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) {
                        dprintk("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);

        mutex_unlock(&data->lock);

        cpufreq_cpu_put(data);
        return ret;
}
EXPORT_SYMBOL(cpufreq_update_policy);

static int cpufreq_cpu_callback(struct notifier_block *nfb,
                                        unsigned long action, void *hcpu)
{
        unsigned int cpu = (unsigned long)hcpu;
        struct cpufreq_policy *policy;
        struct sys_device *sys_dev;

        sys_dev = get_cpu_sysdev(cpu);

        if (sys_dev) {
                switch (action) {
                case CPU_ONLINE:
                        cpufreq_add_dev(sys_dev);
                        break;
                case CPU_DOWN_PREPARE:
                        /*
                         * We attempt to put this cpu in lowest frequency
                         * possible before going down. This will permit
                         * hardware-managed P-State to switch other related
                         * threads to min or higher speeds if possible.
                         */
                        policy = cpufreq_cpu_data[cpu];
                        if (policy) {
                                cpufreq_driver_target(policy, policy->min,
                                                CPUFREQ_RELATION_H);
                        }
                        break;
                case CPU_DEAD:
                        cpufreq_remove_dev(sys_dev);
                        break;
                }
        }
        return NOTIFY_OK;
}

static struct notifier_block 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;

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

                /* check for at least one working CPU */
                for (i=0; i<NR_CPUS; i++)
                        if (cpufreq_cpu_data[i])
                                ret = 0;

                /* if all ->init() calls failed, unregister */
                if (ret) {
                        dprintk("no CPU initialized for driver %s\n", driver_data->name);
                        sysdev_driver_unregister(&cpu_sysdev_class, &cpufreq_sysdev_driver);

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

        if (!ret) {
                register_cpu_notifier(&cpufreq_cpu_notifier);
                dprintk("driver %s up and running\n", driver_data->name);
                cpufreq_debug_enable_ratelimit();
        }

        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;

        cpufreq_debug_disable_ratelimit();

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

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

        sysdev_driver_unregister(&cpu_sysdev_class, &cpufreq_sysdev_driver);
        unregister_cpu_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);