[deliverable/linux.git] / drivers / base / power / domain.c

/*
 * drivers/base/power/domain.c - Common code related to device power domains.
 *
 * Copyright (C) 2011 Rafael J. Wysocki <rjw@sisk.pl>, Renesas Electronics Corp.
 *
 * This file is released under the GPLv2.
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/io.h>
#include <linux/pm_runtime.h>
#include <linux/pm_domain.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/suspend.h>
#include <linux/export.h>

#define GENPD_DEV_CALLBACK(genpd, type, callback, dev)          \
({                                                              \
        type (*__routine)(struct device *__d);                  \
        type __ret = (type)0;                                   \
                                                                \
        __routine = genpd->dev_ops.callback;                    \
        if (__routine) {                                        \
                __ret = __routine(dev);                         \
        } else {                                                \
                __routine = dev_gpd_data(dev)->ops.callback;    \
                if (__routine)                                  \
                        __ret = __routine(dev);                 \
        }                                                       \
        __ret;                                                  \
})

#define GENPD_DEV_TIMED_CALLBACK(genpd, type, callback, dev, field, name)       \
({                                                                              \
        ktime_t __start = ktime_get();                                          \
        type __retval = GENPD_DEV_CALLBACK(genpd, type, callback, dev);         \
        s64 __elapsed = ktime_to_ns(ktime_sub(ktime_get(), __start));           \
        struct generic_pm_domain_data *__gpd_data = dev_gpd_data(dev);          \
        if (__elapsed > __gpd_data->td.field) {                                 \
                __gpd_data->td.field = __elapsed;                               \
                dev_warn(dev, name " latency exceeded, new value %lld ns\n",    \
                        __elapsed);                                             \
        }                                                                       \
        __retval;                                                               \
})

static LIST_HEAD(gpd_list);
static DEFINE_MUTEX(gpd_list_lock);

#ifdef CONFIG_PM

struct generic_pm_domain *dev_to_genpd(struct device *dev)
{
        if (IS_ERR_OR_NULL(dev->pm_domain))
                return ERR_PTR(-EINVAL);

        return pd_to_genpd(dev->pm_domain);
}

static int genpd_stop_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_TIMED_CALLBACK(genpd, int, stop, dev,
                                        stop_latency_ns, "stop");
}

static int genpd_start_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_TIMED_CALLBACK(genpd, int, start, dev,
                                        start_latency_ns, "start");
}

static int genpd_save_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_TIMED_CALLBACK(genpd, int, save_state, dev,
                                        save_state_latency_ns, "state save");
}

static int genpd_restore_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_TIMED_CALLBACK(genpd, int, restore_state, dev,
                                        restore_state_latency_ns,
                                        "state restore");
}

static bool genpd_sd_counter_dec(struct generic_pm_domain *genpd)
{
        bool ret = false;

        if (!WARN_ON(atomic_read(&genpd->sd_count) == 0))
                ret = !!atomic_dec_and_test(&genpd->sd_count);

        return ret;
}

static void genpd_sd_counter_inc(struct generic_pm_domain *genpd)
{
        atomic_inc(&genpd->sd_count);
        smp_mb__after_atomic_inc();
}

static void genpd_acquire_lock(struct generic_pm_domain *genpd)
{
        DEFINE_WAIT(wait);

        mutex_lock(&genpd->lock);
        /*
         * Wait for the domain to transition into either the active,
         * or the power off state.
         */
        for (;;) {
                prepare_to_wait(&genpd->status_wait_queue, &wait,
                                TASK_UNINTERRUPTIBLE);
                if (genpd->status == GPD_STATE_ACTIVE
                    || genpd->status == GPD_STATE_POWER_OFF)
                        break;
                mutex_unlock(&genpd->lock);

                schedule();

                mutex_lock(&genpd->lock);
        }
        finish_wait(&genpd->status_wait_queue, &wait);
}

static void genpd_release_lock(struct generic_pm_domain *genpd)
{
        mutex_unlock(&genpd->lock);
}

static void genpd_set_active(struct generic_pm_domain *genpd)
{
        if (genpd->resume_count == 0)
                genpd->status = GPD_STATE_ACTIVE;
}

/**
 * __pm_genpd_poweron - Restore power to a given PM domain and its masters.
 * @genpd: PM domain to power up.
 *
 * Restore power to @genpd and all of its masters so that it is possible to
 * resume a device belonging to it.
 */
int __pm_genpd_poweron(struct generic_pm_domain *genpd)
        __releases(&genpd->lock) __acquires(&genpd->lock)
{
        struct gpd_link *link;
        DEFINE_WAIT(wait);
        int ret = 0;

        /* If the domain's master is being waited for, we have to wait too. */
        for (;;) {
                prepare_to_wait(&genpd->status_wait_queue, &wait,
                                TASK_UNINTERRUPTIBLE);
                if (genpd->status != GPD_STATE_WAIT_MASTER)
                        break;
                mutex_unlock(&genpd->lock);

                schedule();

                mutex_lock(&genpd->lock);
        }
        finish_wait(&genpd->status_wait_queue, &wait);

        if (genpd->status == GPD_STATE_ACTIVE
            || (genpd->prepared_count > 0 && genpd->suspend_power_off))
                return 0;

        if (genpd->status != GPD_STATE_POWER_OFF) {
                genpd_set_active(genpd);
                return 0;
        }

        /*
         * The list is guaranteed not to change while the loop below is being
         * executed, unless one of the masters' .power_on() callbacks fiddles
         * with it.
         */
        list_for_each_entry(link, &genpd->slave_links, slave_node) {
                genpd_sd_counter_inc(link->master);
                genpd->status = GPD_STATE_WAIT_MASTER;

                mutex_unlock(&genpd->lock);

                ret = pm_genpd_poweron(link->master);

                mutex_lock(&genpd->lock);

                /*
                 * The "wait for parent" status is guaranteed not to change
                 * while the master is powering on.
                 */
                genpd->status = GPD_STATE_POWER_OFF;
                wake_up_all(&genpd->status_wait_queue);
                if (ret) {
                        genpd_sd_counter_dec(link->master);
                        goto err;
                }
        }

        if (genpd->power_on) {
                ktime_t time_start = ktime_get();
                s64 elapsed_ns;

                ret = genpd->power_on(genpd);
                if (ret)
                        goto err;

                elapsed_ns = ktime_to_ns(ktime_sub(ktime_get(), time_start));
                if (elapsed_ns > genpd->power_on_latency_ns) {
                        genpd->power_on_latency_ns = elapsed_ns;
                        if (genpd->name)
                                pr_warning("%s: Power-on latency exceeded, "
                                        "new value %lld ns\n", genpd->name,
                                        elapsed_ns);
                }
        }

        genpd_set_active(genpd);

        return 0;

 err:
        list_for_each_entry_continue_reverse(link, &genpd->slave_links, slave_node)
                genpd_sd_counter_dec(link->master);

        return ret;
}

/**
 * pm_genpd_poweron - Restore power to a given PM domain and its masters.
 * @genpd: PM domain to power up.
 */
int pm_genpd_poweron(struct generic_pm_domain *genpd)
{
        int ret;

        mutex_lock(&genpd->lock);
        ret = __pm_genpd_poweron(genpd);
        mutex_unlock(&genpd->lock);
        return ret;
}

#endif /* CONFIG_PM */

#ifdef CONFIG_PM_RUNTIME

/**
 * __pm_genpd_save_device - Save the pre-suspend state of a device.
 * @pdd: Domain data of the device to save the state of.
 * @genpd: PM domain the device belongs to.
 */
static int __pm_genpd_save_device(struct pm_domain_data *pdd,
                                  struct generic_pm_domain *genpd)
        __releases(&genpd->lock) __acquires(&genpd->lock)
{
        struct generic_pm_domain_data *gpd_data = to_gpd_data(pdd);
        struct device *dev = pdd->dev;
        int ret = 0;

        if (gpd_data->need_restore)
                return 0;

        mutex_unlock(&genpd->lock);

        genpd_start_dev(genpd, dev);
        ret = genpd_save_dev(genpd, dev);
        genpd_stop_dev(genpd, dev);

        mutex_lock(&genpd->lock);

        if (!ret)
                gpd_data->need_restore = true;

        return ret;
}

/**
 * __pm_genpd_restore_device - Restore the pre-suspend state of a device.
 * @pdd: Domain data of the device to restore the state of.
 * @genpd: PM domain the device belongs to.
 */
static void __pm_genpd_restore_device(struct pm_domain_data *pdd,
                                      struct generic_pm_domain *genpd)
        __releases(&genpd->lock) __acquires(&genpd->lock)
{
        struct generic_pm_domain_data *gpd_data = to_gpd_data(pdd);
        struct device *dev = pdd->dev;

        if (!gpd_data->need_restore)
                return;

        mutex_unlock(&genpd->lock);

        genpd_start_dev(genpd, dev);
        genpd_restore_dev(genpd, dev);
        genpd_stop_dev(genpd, dev);

        mutex_lock(&genpd->lock);

        gpd_data->need_restore = false;
}

/**
 * genpd_abort_poweroff - Check if a PM domain power off should be aborted.
 * @genpd: PM domain to check.
 *
 * Return true if a PM domain's status changed to GPD_STATE_ACTIVE during
 * a "power off" operation, which means that a "power on" has occured in the
 * meantime, or if its resume_count field is different from zero, which means
 * that one of its devices has been resumed in the meantime.
 */
static bool genpd_abort_poweroff(struct generic_pm_domain *genpd)
{
        return genpd->status == GPD_STATE_WAIT_MASTER
                || genpd->status == GPD_STATE_ACTIVE || genpd->resume_count > 0;
}

/**
 * genpd_queue_power_off_work - Queue up the execution of pm_genpd_poweroff().
 * @genpd: PM domait to power off.
 *
 * Queue up the execution of pm_genpd_poweroff() unless it's already been done
 * before.
 */
void genpd_queue_power_off_work(struct generic_pm_domain *genpd)
{
        if (!work_pending(&genpd->power_off_work))
                queue_work(pm_wq, &genpd->power_off_work);
}

/**
 * pm_genpd_poweroff - Remove power from a given PM domain.
 * @genpd: PM domain to power down.
 *
 * If all of the @genpd's devices have been suspended and all of its subdomains
 * have been powered down, run the runtime suspend callbacks provided by all of
 * the @genpd's devices' drivers and remove power from @genpd.
 */
static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
        __releases(&genpd->lock) __acquires(&genpd->lock)
{
        struct pm_domain_data *pdd;
        struct gpd_link *link;
        unsigned int not_suspended;
        int ret = 0;

 start:
        /*
         * Do not try to power off the domain in the following situations:
         * (1) The domain is already in the "power off" state.
         * (2) The domain is waiting for its master to power up.
         * (3) One of the domain's devices is being resumed right now.
         * (4) System suspend is in progress.
         */
        if (genpd->status == GPD_STATE_POWER_OFF
            || genpd->status == GPD_STATE_WAIT_MASTER
            || genpd->resume_count > 0 || genpd->prepared_count > 0)
                return 0;

        if (atomic_read(&genpd->sd_count) > 0)
                return -EBUSY;

        not_suspended = 0;
        list_for_each_entry(pdd, &genpd->dev_list, list_node)
                if (pdd->dev->driver && (!pm_runtime_suspended(pdd->dev)
                    || pdd->dev->power.irq_safe))
                        not_suspended++;

        if (not_suspended > genpd->in_progress)
                return -EBUSY;

        if (genpd->poweroff_task) {
                /*
                 * Another instance of pm_genpd_poweroff() is executing
                 * callbacks, so tell it to start over and return.
                 */
                genpd->status = GPD_STATE_REPEAT;
                return 0;
        }

        if (genpd->gov && genpd->gov->power_down_ok) {
                if (!genpd->gov->power_down_ok(&genpd->domain))
                        return -EAGAIN;
        }

        genpd->status = GPD_STATE_BUSY;
        genpd->poweroff_task = current;

        list_for_each_entry_reverse(pdd, &genpd->dev_list, list_node) {
                ret = atomic_read(&genpd->sd_count) == 0 ?
                        __pm_genpd_save_device(pdd, genpd) : -EBUSY;

                if (genpd_abort_poweroff(genpd))
                        goto out;

                if (ret) {
                        genpd_set_active(genpd);
                        goto out;
                }

                if (genpd->status == GPD_STATE_REPEAT) {
                        genpd->poweroff_task = NULL;
                        goto start;
                }
        }

        if (genpd->power_off) {
                ktime_t time_start;
                s64 elapsed_ns;

                if (atomic_read(&genpd->sd_count) > 0) {
                        ret = -EBUSY;
                        goto out;
                }

                time_start = ktime_get();

                /*
                 * If sd_count > 0 at this point, one of the subdomains hasn't
                 * managed to call pm_genpd_poweron() for the master yet after
                 * incrementing it.  In that case pm_genpd_poweron() will wait
                 * for us to drop the lock, so we can call .power_off() and let
                 * the pm_genpd_poweron() restore power for us (this shouldn't
                 * happen very often).
                 */
                ret = genpd->power_off(genpd);
                if (ret == -EBUSY) {
                        genpd_set_active(genpd);
                        goto out;
                }

                elapsed_ns = ktime_to_ns(ktime_sub(ktime_get(), time_start));
                if (elapsed_ns > genpd->power_off_latency_ns) {
                        genpd->power_off_latency_ns = elapsed_ns;
                        if (genpd->name)
                                pr_warning("%s: Power-off latency exceeded, "
                                        "new value %lld ns\n", genpd->name,
                                        elapsed_ns);
                }
        }

        genpd->status = GPD_STATE_POWER_OFF;
        genpd->power_off_time = ktime_get();

        /* Update PM QoS information for devices in the domain. */
        list_for_each_entry_reverse(pdd, &genpd->dev_list, list_node) {
                struct gpd_timing_data *td = &to_gpd_data(pdd)->td;

                pm_runtime_update_max_time_suspended(pdd->dev,
                                        td->start_latency_ns +
                                        td->restore_state_latency_ns +
                                        genpd->power_on_latency_ns);
        }

        list_for_each_entry(link, &genpd->slave_links, slave_node) {
                genpd_sd_counter_dec(link->master);
                genpd_queue_power_off_work(link->master);
        }

 out:
        genpd->poweroff_task = NULL;
        wake_up_all(&genpd->status_wait_queue);
        return ret;
}

/**
 * genpd_power_off_work_fn - Power off PM domain whose subdomain count is 0.
 * @work: Work structure used for scheduling the execution of this function.
 */
static void genpd_power_off_work_fn(struct work_struct *work)
{
        struct generic_pm_domain *genpd;

        genpd = container_of(work, struct generic_pm_domain, power_off_work);

        genpd_acquire_lock(genpd);
        pm_genpd_poweroff(genpd);
        genpd_release_lock(genpd);
}

/**
 * pm_genpd_runtime_suspend - Suspend a device belonging to I/O PM domain.
 * @dev: Device to suspend.
 *
 * Carry out a runtime suspend of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a PM domain consisting of I/O devices.
 */
static int pm_genpd_runtime_suspend(struct device *dev)
{
        struct generic_pm_domain *genpd;
        bool (*stop_ok)(struct device *__dev);
        int ret;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        might_sleep_if(!genpd->dev_irq_safe);

        stop_ok = genpd->gov ? genpd->gov->stop_ok : NULL;
        if (stop_ok && !stop_ok(dev))
                return -EBUSY;

        ret = genpd_stop_dev(genpd, dev);
        if (ret)
                return ret;

        pm_runtime_update_max_time_suspended(dev,
                                dev_gpd_data(dev)->td.start_latency_ns);

        /*
         * If power.irq_safe is set, this routine will be run with interrupts
         * off, so it can't use mutexes.
         */
        if (dev->power.irq_safe)
                return 0;

        mutex_lock(&genpd->lock);
        genpd->in_progress++;
        pm_genpd_poweroff(genpd);
        genpd->in_progress--;
        mutex_unlock(&genpd->lock);

        return 0;
}

/**
 * pm_genpd_runtime_resume - Resume a device belonging to I/O PM domain.
 * @dev: Device to resume.
 *
 * Carry out a runtime resume of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a PM domain consisting of I/O devices.
 */
static int pm_genpd_runtime_resume(struct device *dev)
{
        struct generic_pm_domain *genpd;
        DEFINE_WAIT(wait);
        int ret;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        might_sleep_if(!genpd->dev_irq_safe);

        /* If power.irq_safe, the PM domain is never powered off. */
        if (dev->power.irq_safe)
                goto out;

        mutex_lock(&genpd->lock);
        ret = __pm_genpd_poweron(genpd);
        if (ret) {
                mutex_unlock(&genpd->lock);
                return ret;
        }
        genpd->status = GPD_STATE_BUSY;
        genpd->resume_count++;
        for (;;) {
                prepare_to_wait(&genpd->status_wait_queue, &wait,
                                TASK_UNINTERRUPTIBLE);
                /*
                 * If current is the powering off task, we have been called
                 * reentrantly from one of the device callbacks, so we should
                 * not wait.
                 */
                if (!genpd->poweroff_task || genpd->poweroff_task == current)
                        break;
                mutex_unlock(&genpd->lock);

                schedule();

                mutex_lock(&genpd->lock);
        }
        finish_wait(&genpd->status_wait_queue, &wait);
        __pm_genpd_restore_device(dev->power.subsys_data->domain_data, genpd);
        genpd->resume_count--;
        genpd_set_active(genpd);
        wake_up_all(&genpd->status_wait_queue);
        mutex_unlock(&genpd->lock);

 out:
        genpd_start_dev(genpd, dev);

        return 0;
}

/**
 * pm_genpd_poweroff_unused - Power off all PM domains with no devices in use.
 */
void pm_genpd_poweroff_unused(void)
{
        struct generic_pm_domain *genpd;

        mutex_lock(&gpd_list_lock);

        list_for_each_entry(genpd, &gpd_list, gpd_list_node)
                genpd_queue_power_off_work(genpd);

        mutex_unlock(&gpd_list_lock);
}

#else

static inline void genpd_power_off_work_fn(struct work_struct *work) {}

#define pm_genpd_runtime_suspend        NULL
#define pm_genpd_runtime_resume         NULL

#endif /* CONFIG_PM_RUNTIME */

#ifdef CONFIG_PM_SLEEP

static bool genpd_dev_active_wakeup(struct generic_pm_domain *genpd,
                                    struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, bool, active_wakeup, dev);
}

static int genpd_suspend_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, suspend, dev);
}

static int genpd_suspend_late(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, suspend_late, dev);
}

static int genpd_resume_early(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, resume_early, dev);
}

static int genpd_resume_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, resume, dev);
}

static int genpd_freeze_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, freeze, dev);
}

static int genpd_freeze_late(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, freeze_late, dev);
}

static int genpd_thaw_early(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, thaw_early, dev);
}

static int genpd_thaw_dev(struct generic_pm_domain *genpd, struct device *dev)
{
        return GENPD_DEV_CALLBACK(genpd, int, thaw, dev);
}

/**
 * pm_genpd_sync_poweroff - Synchronously power off a PM domain and its masters.
 * @genpd: PM domain to power off, if possible.
 *
 * Check if the given PM domain can be powered off (during system suspend or
 * hibernation) and do that if so.  Also, in that case propagate to its masters.
 *
 * This function is only called in "noirq" stages of system power transitions,
 * so it need not acquire locks (all of the "noirq" callbacks are executed
 * sequentially, so it is guaranteed that it will never run twice in parallel).
 */
static void pm_genpd_sync_poweroff(struct generic_pm_domain *genpd)
{
        struct gpd_link *link;

        if (genpd->status == GPD_STATE_POWER_OFF)
                return;

        if (genpd->suspended_count != genpd->device_count
            || atomic_read(&genpd->sd_count) > 0)
                return;

        if (genpd->power_off)
                genpd->power_off(genpd);

        genpd->status = GPD_STATE_POWER_OFF;

        list_for_each_entry(link, &genpd->slave_links, slave_node) {
                genpd_sd_counter_dec(link->master);
                pm_genpd_sync_poweroff(link->master);
        }
}

/**
 * resume_needed - Check whether to resume a device before system suspend.
 * @dev: Device to check.
 * @genpd: PM domain the device belongs to.
 *
 * There are two cases in which a device that can wake up the system from sleep
 * states should be resumed by pm_genpd_prepare(): (1) if the device is enabled
 * to wake up the system and it has to remain active for this purpose while the
 * system is in the sleep state and (2) if the device is not enabled to wake up
 * the system from sleep states and it generally doesn't generate wakeup signals
 * by itself (those signals are generated on its behalf by other parts of the
 * system).  In the latter case it may be necessary to reconfigure the device's
 * wakeup settings during system suspend, because it may have been set up to
 * signal remote wakeup from the system's working state as needed by runtime PM.
 * Return 'true' in either of the above cases.
 */
static bool resume_needed(struct device *dev, struct generic_pm_domain *genpd)
{
        bool active_wakeup;

        if (!device_can_wakeup(dev))
                return false;

        active_wakeup = genpd_dev_active_wakeup(genpd, dev);
        return device_may_wakeup(dev) ? active_wakeup : !active_wakeup;
}

/**
 * pm_genpd_prepare - Start power transition of a device in a PM domain.
 * @dev: Device to start the transition of.
 *
 * Start a power transition of a device (during a system-wide power transition)
 * under the assumption that its pm_domain field points to the domain member of
 * an object of type struct generic_pm_domain representing a PM domain
 * consisting of I/O devices.
 */
static int pm_genpd_prepare(struct device *dev)
{
        struct generic_pm_domain *genpd;
        int ret;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        /*
         * If a wakeup request is pending for the device, it should be woken up
         * at this point and a system wakeup event should be reported if it's
         * set up to wake up the system from sleep states.
         */
        pm_runtime_get_noresume(dev);
        if (pm_runtime_barrier(dev) && device_may_wakeup(dev))
                pm_wakeup_event(dev, 0);

        if (pm_wakeup_pending()) {
                pm_runtime_put_sync(dev);
                return -EBUSY;
        }

        if (resume_needed(dev, genpd))
                pm_runtime_resume(dev);

        genpd_acquire_lock(genpd);

        if (genpd->prepared_count++ == 0)
                genpd->suspend_power_off = genpd->status == GPD_STATE_POWER_OFF;

        genpd_release_lock(genpd);

        if (genpd->suspend_power_off) {
                pm_runtime_put_noidle(dev);
                return 0;
        }

        /*
         * The PM domain must be in the GPD_STATE_ACTIVE state at this point,
         * so pm_genpd_poweron() will return immediately, but if the device
         * is suspended (e.g. it's been stopped by genpd_stop_dev()), we need
         * to make it operational.
         */
        pm_runtime_resume(dev);
        __pm_runtime_disable(dev, false);

        ret = pm_generic_prepare(dev);
        if (ret) {
                mutex_lock(&genpd->lock);

                if (--genpd->prepared_count == 0)
                        genpd->suspend_power_off = false;

                mutex_unlock(&genpd->lock);
                pm_runtime_enable(dev);
        }

        pm_runtime_put_sync(dev);
        return ret;
}

/**
 * pm_genpd_suspend - Suspend a device belonging to an I/O PM domain.
 * @dev: Device to suspend.
 *
 * Suspend a device under the assumption that its pm_domain field points to the
 * domain member of an object of type struct generic_pm_domain representing
 * a PM domain consisting of I/O devices.
 */
static int pm_genpd_suspend(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        return genpd->suspend_power_off ? 0 : genpd_suspend_dev(genpd, dev);
}

/**
 * pm_genpd_suspend_noirq - Late suspend of a device from an I/O PM domain.
 * @dev: Device to suspend.
 *
 * Carry out a late suspend of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a PM domain consisting of I/O devices.
 */
static int pm_genpd_suspend_noirq(struct device *dev)
{
        struct generic_pm_domain *genpd;
        int ret;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        if (genpd->suspend_power_off)
                return 0;

        ret = genpd_suspend_late(genpd, dev);
        if (ret)
                return ret;

        if (dev->power.wakeup_path && genpd_dev_active_wakeup(genpd, dev))
                return 0;

        genpd_stop_dev(genpd, dev);

        /*
         * Since all of the "noirq" callbacks are executed sequentially, it is
         * guaranteed that this function will never run twice in parallel for
         * the same PM domain, so it is not necessary to use locking here.
         */
        genpd->suspended_count++;
        pm_genpd_sync_poweroff(genpd);

        return 0;
}

/**
 * pm_genpd_resume_noirq - Early resume of a device from an I/O power domain.
 * @dev: Device to resume.
 *
 * Carry out an early resume of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a power domain consisting of I/O
 * devices.
 */
static int pm_genpd_resume_noirq(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        if (genpd->suspend_power_off)
                return 0;

        /*
         * Since all of the "noirq" callbacks are executed sequentially, it is
         * guaranteed that this function will never run twice in parallel for
         * the same PM domain, so it is not necessary to use locking here.
         */
        pm_genpd_poweron(genpd);
        genpd->suspended_count--;
        genpd_start_dev(genpd, dev);

        return genpd_resume_early(genpd, dev);
}

/**
 * pm_genpd_resume - Resume a device belonging to an I/O power domain.
 * @dev: Device to resume.
 *
 * Resume a device under the assumption that its pm_domain field points to the
 * domain member of an object of type struct generic_pm_domain representing
 * a power domain consisting of I/O devices.
 */
static int pm_genpd_resume(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        return genpd->suspend_power_off ? 0 : genpd_resume_dev(genpd, dev);
}

/**
 * pm_genpd_freeze - Freeze a device belonging to an I/O power domain.
 * @dev: Device to freeze.
 *
 * Freeze a device under the assumption that its pm_domain field points to the
 * domain member of an object of type struct generic_pm_domain representing
 * a power domain consisting of I/O devices.
 */
static int pm_genpd_freeze(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        return genpd->suspend_power_off ? 0 : genpd_freeze_dev(genpd, dev);
}

/**
 * pm_genpd_freeze_noirq - Late freeze of a device from an I/O power domain.
 * @dev: Device to freeze.
 *
 * Carry out a late freeze of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a power domain consisting of I/O
 * devices.
 */
static int pm_genpd_freeze_noirq(struct device *dev)
{
        struct generic_pm_domain *genpd;
        int ret;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        if (genpd->suspend_power_off)
                return 0;

        ret = genpd_freeze_late(genpd, dev);
        if (ret)
                return ret;

        genpd_stop_dev(genpd, dev);

        return 0;
}

/**
 * pm_genpd_thaw_noirq - Early thaw of a device from an I/O power domain.
 * @dev: Device to thaw.
 *
 * Carry out an early thaw of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a power domain consisting of I/O
 * devices.
 */
static int pm_genpd_thaw_noirq(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        if (genpd->suspend_power_off)
                return 0;

        genpd_start_dev(genpd, dev);

        return genpd_thaw_early(genpd, dev);
}

/**
 * pm_genpd_thaw - Thaw a device belonging to an I/O power domain.
 * @dev: Device to thaw.
 *
 * Thaw a device under the assumption that its pm_domain field points to the
 * domain member of an object of type struct generic_pm_domain representing
 * a power domain consisting of I/O devices.
 */
static int pm_genpd_thaw(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        return genpd->suspend_power_off ? 0 : genpd_thaw_dev(genpd, dev);
}

/**
 * pm_genpd_restore_noirq - Early restore of a device from an I/O power domain.
 * @dev: Device to resume.
 *
 * Carry out an early restore of a device under the assumption that its
 * pm_domain field points to the domain member of an object of type
 * struct generic_pm_domain representing a power domain consisting of I/O
 * devices.
 */
static int pm_genpd_restore_noirq(struct device *dev)
{
        struct generic_pm_domain *genpd;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return -EINVAL;

        /*
         * Since all of the "noirq" callbacks are executed sequentially, it is
         * guaranteed that this function will never run twice in parallel for
         * the same PM domain, so it is not necessary to use locking here.
         */
        genpd->status = GPD_STATE_POWER_OFF;
        if (genpd->suspend_power_off) {
                /*
                 * The boot kernel might put the domain into the power on state,
                 * so make sure it really is powered off.
                 */
                if (genpd->power_off)
                        genpd->power_off(genpd);
                return 0;
        }

        pm_genpd_poweron(genpd);
        genpd->suspended_count--;
        genpd_start_dev(genpd, dev);

        return genpd_resume_early(genpd, dev);
}

/**
 * pm_genpd_complete - Complete power transition of a device in a power domain.
 * @dev: Device to complete the transition of.
 *
 * Complete a power transition of a device (during a system-wide power
 * transition) under the assumption that its pm_domain field points to the
 * domain member of an object of type struct generic_pm_domain representing
 * a power domain consisting of I/O devices.
 */
static void pm_genpd_complete(struct device *dev)
{
        struct generic_pm_domain *genpd;
        bool run_complete;

        dev_dbg(dev, "%s()\n", __func__);

        genpd = dev_to_genpd(dev);
        if (IS_ERR(genpd))
                return;

        mutex_lock(&genpd->lock);

        run_complete = !genpd->suspend_power_off;
        if (--genpd->prepared_count == 0)
                genpd->suspend_power_off = false;

        mutex_unlock(&genpd->lock);

        if (run_complete) {
                pm_generic_complete(dev);
                pm_runtime_set_active(dev);
                pm_runtime_enable(dev);
                pm_runtime_idle(dev);
        }
}

#else

#define pm_genpd_prepare                NULL
#define pm_genpd_suspend                NULL
#define pm_genpd_suspend_noirq          NULL
#define pm_genpd_resume_noirq           NULL
#define pm_genpd_resume                 NULL
#define pm_genpd_freeze                 NULL
#define pm_genpd_freeze_noirq           NULL
#define pm_genpd_thaw_noirq             NULL
#define pm_genpd_thaw                   NULL
#define pm_genpd_restore_noirq          NULL
#define pm_genpd_complete               NULL

#endif /* CONFIG_PM_SLEEP */

/**
 * __pm_genpd_add_device - Add a device to an I/O PM domain.
 * @genpd: PM domain to add the device to.
 * @dev: Device to be added.
 * @td: Set of PM QoS timing parameters to attach to the device.
 */
int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
                          struct gpd_timing_data *td)
{
        struct generic_pm_domain_data *gpd_data;
        struct pm_domain_data *pdd;
        int ret = 0;

        dev_dbg(dev, "%s()\n", __func__);

        if (IS_ERR_OR_NULL(genpd) || IS_ERR_OR_NULL(dev))
                return -EINVAL;

        genpd_acquire_lock(genpd);

        if (genpd->status == GPD_STATE_POWER_OFF) {
                ret = -EINVAL;
                goto out;
        }

        if (genpd->prepared_count > 0) {
                ret = -EAGAIN;
                goto out;
        }

        list_for_each_entry(pdd, &genpd->dev_list, list_node)
                if (pdd->dev == dev) {
                        ret = -EINVAL;
                        goto out;
                }

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

        genpd->device_count++;

        dev->pm_domain = &genpd->domain;
        dev_pm_get_subsys_data(dev);
        dev->power.subsys_data->domain_data = &gpd_data->base;
        gpd_data->base.dev = dev;
        gpd_data->need_restore = false;
        list_add_tail(&gpd_data->base.list_node, &genpd->dev_list);
        if (td)
                gpd_data->td = *td;

 out:
        genpd_release_lock(genpd);

        return ret;
}

/**
 * pm_genpd_remove_device - Remove a device from an I/O PM domain.
 * @genpd: PM domain to remove the device from.
 * @dev: Device to be removed.
 */
int pm_genpd_remove_device(struct generic_pm_domain *genpd,
                           struct device *dev)
{
        struct pm_domain_data *pdd;
        int ret = -EINVAL;

        dev_dbg(dev, "%s()\n", __func__);

        if (IS_ERR_OR_NULL(genpd) || IS_ERR_OR_NULL(dev))
                return -EINVAL;

        genpd_acquire_lock(genpd);

        if (genpd->prepared_count > 0) {
                ret = -EAGAIN;
                goto out;
        }

        list_for_each_entry(pdd, &genpd->dev_list, list_node) {
                if (pdd->dev != dev)
                        continue;

                list_del_init(&pdd->list_node);
                pdd->dev = NULL;
                dev_pm_put_subsys_data(dev);
                dev->pm_domain = NULL;
                kfree(to_gpd_data(pdd));

                genpd->device_count--;

                ret = 0;
                break;
        }

 out:
        genpd_release_lock(genpd);

        return ret;
}

/**
 * pm_genpd_add_subdomain - Add a subdomain to an I/O PM domain.
 * @genpd: Master PM domain to add the subdomain to.
 * @subdomain: Subdomain to be added.
 */
int pm_genpd_add_subdomain(struct generic_pm_domain *genpd,
                           struct generic_pm_domain *subdomain)
{
        struct gpd_link *link;
        int ret = 0;

        if (IS_ERR_OR_NULL(genpd) || IS_ERR_OR_NULL(subdomain))
                return -EINVAL;

 start:
        genpd_acquire_lock(genpd);
        mutex_lock_nested(&subdomain->lock, SINGLE_DEPTH_NESTING);

        if (subdomain->status != GPD_STATE_POWER_OFF
            && subdomain->status != GPD_STATE_ACTIVE) {
                mutex_unlock(&subdomain->lock);
                genpd_release_lock(genpd);
                goto start;
        }

        if (genpd->status == GPD_STATE_POWER_OFF
            &&  subdomain->status != GPD_STATE_POWER_OFF) {
                ret = -EINVAL;
                goto out;
        }

        list_for_each_entry(link, &genpd->slave_links, slave_node) {
                if (link->slave == subdomain && link->master == genpd) {
                        ret = -EINVAL;
                        goto out;
                }
        }

        link = kzalloc(sizeof(*link), GFP_KERNEL);
        if (!link) {
                ret = -ENOMEM;
                goto out;
        }
        link->master = genpd;
        list_add_tail(&link->master_node, &genpd->master_links);
        link->slave = subdomain;
        list_add_tail(&link->slave_node, &subdomain->slave_links);
        if (subdomain->status != GPD_STATE_POWER_OFF)
                genpd_sd_counter_inc(genpd);

 out:
        mutex_unlock(&subdomain->lock);
        genpd_release_lock(genpd);

        return ret;
}

/**
 * pm_genpd_remove_subdomain - Remove a subdomain from an I/O PM domain.
 * @genpd: Master PM domain to remove the subdomain from.
 * @subdomain: Subdomain to be removed.
 */
int pm_genpd_remove_subdomain(struct generic_pm_domain *genpd,
                              struct generic_pm_domain *subdomain)
{
        struct gpd_link *link;
        int ret = -EINVAL;

        if (IS_ERR_OR_NULL(genpd) || IS_ERR_OR_NULL(subdomain))
                return -EINVAL;

 start:
        genpd_acquire_lock(genpd);

        list_for_each_entry(link, &genpd->master_links, master_node) {
                if (link->slave != subdomain)
                        continue;

                mutex_lock_nested(&subdomain->lock, SINGLE_DEPTH_NESTING);

                if (subdomain->status != GPD_STATE_POWER_OFF
                    && subdomain->status != GPD_STATE_ACTIVE) {
                        mutex_unlock(&subdomain->lock);
                        genpd_release_lock(genpd);
                        goto start;
                }

                list_del(&link->master_node);
                list_del(&link->slave_node);
                kfree(link);
                if (subdomain->status != GPD_STATE_POWER_OFF)
                        genpd_sd_counter_dec(genpd);

                mutex_unlock(&subdomain->lock);

                ret = 0;
                break;
        }

        genpd_release_lock(genpd);

        return ret;
}

/**
 * pm_genpd_add_callbacks - Add PM domain callbacks to a given device.
 * @dev: Device to add the callbacks to.
 * @ops: Set of callbacks to add.
 * @td: Timing data to add to the device along with the callbacks (optional).
 */
int pm_genpd_add_callbacks(struct device *dev, struct gpd_dev_ops *ops,
                           struct gpd_timing_data *td)
{
        struct pm_domain_data *pdd;
        int ret = 0;

        if (!(dev && dev->power.subsys_data && ops))
                return -EINVAL;

        pm_runtime_disable(dev);
        device_pm_lock();

        pdd = dev->power.subsys_data->domain_data;
        if (pdd) {
                struct generic_pm_domain_data *gpd_data = to_gpd_data(pdd);

                gpd_data->ops = *ops;
                if (td)
                        gpd_data->td = *td;
        } else {
                ret = -EINVAL;
        }

        device_pm_unlock();
        pm_runtime_enable(dev);

        return ret;
}
EXPORT_SYMBOL_GPL(pm_genpd_add_callbacks);

/**
 * __pm_genpd_remove_callbacks - Remove PM domain callbacks from a given device.
 * @dev: Device to remove the callbacks from.
 * @clear_td: If set, clear the device's timing data too.
 */
int __pm_genpd_remove_callbacks(struct device *dev, bool clear_td)
{
        struct pm_domain_data *pdd;
        int ret = 0;

        if (!(dev && dev->power.subsys_data))
                return -EINVAL;

        pm_runtime_disable(dev);
        device_pm_lock();

        pdd = dev->power.subsys_data->domain_data;
        if (pdd) {
                struct generic_pm_domain_data *gpd_data = to_gpd_data(pdd);

                gpd_data->ops = (struct gpd_dev_ops){ 0 };
                if (clear_td)
                        gpd_data->td = (struct gpd_timing_data){ 0 };
        } else {
                ret = -EINVAL;
        }

        device_pm_unlock();
        pm_runtime_enable(dev);

        return ret;
}
EXPORT_SYMBOL_GPL(__pm_genpd_remove_callbacks);

/* Default device callbacks for generic PM domains. */

/**
 * pm_genpd_default_save_state - Default "save device state" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_save_state(struct device *dev)
{
        int (*cb)(struct device *__dev);
        struct device_driver *drv = dev->driver;

        cb = dev_gpd_data(dev)->ops.save_state;
        if (cb)
                return cb(dev);

        if (drv && drv->pm && drv->pm->runtime_suspend)
                return drv->pm->runtime_suspend(dev);

        return 0;
}

/**
 * pm_genpd_default_restore_state - Default PM domians "restore device state".
 * @dev: Device to handle.
 */
static int pm_genpd_default_restore_state(struct device *dev)
{
        int (*cb)(struct device *__dev);
        struct device_driver *drv = dev->driver;

        cb = dev_gpd_data(dev)->ops.restore_state;
        if (cb)
                return cb(dev);

        if (drv && drv->pm && drv->pm->runtime_resume)
                return drv->pm->runtime_resume(dev);

        return 0;
}

#ifdef CONFIG_PM_SLEEP

/**
 * pm_genpd_default_suspend - Default "device suspend" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_suspend(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.suspend;

        return cb ? cb(dev) : pm_generic_suspend(dev);
}

/**
 * pm_genpd_default_suspend_late - Default "late device suspend" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_suspend_late(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.suspend_late;

        return cb ? cb(dev) : pm_generic_suspend_noirq(dev);
}

/**
 * pm_genpd_default_resume_early - Default "early device resume" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_resume_early(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.resume_early;

        return cb ? cb(dev) : pm_generic_resume_noirq(dev);
}

/**
 * pm_genpd_default_resume - Default "device resume" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_resume(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.resume;

        return cb ? cb(dev) : pm_generic_resume(dev);
}

/**
 * pm_genpd_default_freeze - Default "device freeze" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_freeze(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.freeze;

        return cb ? cb(dev) : pm_generic_freeze(dev);
}

/**
 * pm_genpd_default_freeze_late - Default "late device freeze" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_freeze_late(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.freeze_late;

        return cb ? cb(dev) : pm_generic_freeze_noirq(dev);
}

/**
 * pm_genpd_default_thaw_early - Default "early device thaw" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_thaw_early(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.thaw_early;

        return cb ? cb(dev) : pm_generic_thaw_noirq(dev);
}

/**
 * pm_genpd_default_thaw - Default "device thaw" for PM domians.
 * @dev: Device to handle.
 */
static int pm_genpd_default_thaw(struct device *dev)
{
        int (*cb)(struct device *__dev) = dev_gpd_data(dev)->ops.thaw;

        return cb ? cb(dev) : pm_generic_thaw(dev);
}

#else /* !CONFIG_PM_SLEEP */

#define pm_genpd_default_suspend        NULL
#define pm_genpd_default_suspend_late   NULL
#define pm_genpd_default_resume_early   NULL
#define pm_genpd_default_resume         NULL
#define pm_genpd_default_freeze         NULL
#define pm_genpd_default_freeze_late    NULL
#define pm_genpd_default_thaw_early     NULL
#define pm_genpd_default_thaw           NULL

#endif /* !CONFIG_PM_SLEEP */

/**
 * pm_genpd_init - Initialize a generic I/O PM domain object.
 * @genpd: PM domain object to initialize.
 * @gov: PM domain governor to associate with the domain (may be NULL).
 * @is_off: Initial value of the domain's power_is_off field.
 */
void pm_genpd_init(struct generic_pm_domain *genpd,
                   struct dev_power_governor *gov, bool is_off)
{
        if (IS_ERR_OR_NULL(genpd))
                return;

        INIT_LIST_HEAD(&genpd->master_links);
        INIT_LIST_HEAD(&genpd->slave_links);
        INIT_LIST_HEAD(&genpd->dev_list);
        mutex_init(&genpd->lock);
        genpd->gov = gov;
        INIT_WORK(&genpd->power_off_work, genpd_power_off_work_fn);
        genpd->in_progress = 0;
        atomic_set(&genpd->sd_count, 0);
        genpd->status = is_off ? GPD_STATE_POWER_OFF : GPD_STATE_ACTIVE;
        init_waitqueue_head(&genpd->status_wait_queue);
        genpd->poweroff_task = NULL;
        genpd->resume_count = 0;
        genpd->device_count = 0;
        genpd->suspended_count = 0;
        genpd->max_off_time_ns = -1;
        genpd->domain.ops.runtime_suspend = pm_genpd_runtime_suspend;
        genpd->domain.ops.runtime_resume = pm_genpd_runtime_resume;
        genpd->domain.ops.runtime_idle = pm_generic_runtime_idle;
        genpd->domain.ops.prepare = pm_genpd_prepare;
        genpd->domain.ops.suspend = pm_genpd_suspend;
        genpd->domain.ops.suspend_noirq = pm_genpd_suspend_noirq;
        genpd->domain.ops.resume_noirq = pm_genpd_resume_noirq;
        genpd->domain.ops.resume = pm_genpd_resume;
        genpd->domain.ops.freeze = pm_genpd_freeze;
        genpd->domain.ops.freeze_noirq = pm_genpd_freeze_noirq;
        genpd->domain.ops.thaw_noirq = pm_genpd_thaw_noirq;
        genpd->domain.ops.thaw = pm_genpd_thaw;
        genpd->domain.ops.poweroff = pm_genpd_suspend;
        genpd->domain.ops.poweroff_noirq = pm_genpd_suspend_noirq;
        genpd->domain.ops.restore_noirq = pm_genpd_restore_noirq;
        genpd->domain.ops.restore = pm_genpd_resume;
        genpd->domain.ops.complete = pm_genpd_complete;
        genpd->dev_ops.save_state = pm_genpd_default_save_state;
        genpd->dev_ops.restore_state = pm_genpd_default_restore_state;
        genpd->dev_ops.suspend = pm_genpd_default_suspend;
        genpd->dev_ops.suspend_late = pm_genpd_default_suspend_late;
        genpd->dev_ops.resume_early = pm_genpd_default_resume_early;
        genpd->dev_ops.resume = pm_genpd_default_resume;
        genpd->dev_ops.freeze = pm_genpd_default_freeze;
        genpd->dev_ops.freeze_late = pm_genpd_default_freeze_late;
        genpd->dev_ops.thaw_early = pm_genpd_default_thaw_early;
        genpd->dev_ops.thaw = pm_genpd_default_thaw;
        mutex_lock(&gpd_list_lock);
        list_add(&genpd->gpd_list_node, &gpd_list);
        mutex_unlock(&gpd_list_lock);
}