interface.c

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/*
 * RTC subsystem, interface functions
 *
 * Copyright (C) 2005 Tower Technologies
 * Author: Alessandro Zummo <[email protected]>
 *
 * based on arch/arm/common/rtctime.c
 *
 * 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/rtc.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/log2.h>
#include <linux/workqueue.h>

static int rtc_timer_enqueue(struct rtc_device *rtc, struct rtc_timer *timer);
static void rtc_timer_remove(struct rtc_device *rtc, struct rtc_timer *timer);

static int __rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
{
    int err;
    if (!rtc->ops)
        err = -ENODEV;
    else if (!rtc->ops->read_time)
        err = -EINVAL;
    else {
        memset(tm, 0, sizeof(struct rtc_time));
        err = rtc->ops->read_time(rtc->dev.parent, tm);
    }
    return err;
}

int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
{
    int err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    err = __rtc_read_time(rtc, tm);
    mutex_unlock(&rtc->ops_lock);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_read_time);

int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
{
    int err;

    err = rtc_valid_tm(tm);
    if (err != 0)
        return err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    if (!rtc->ops)
        err = -ENODEV;
    else if (rtc->ops->set_time)
        err = rtc->ops->set_time(rtc->dev.parent, tm);
    else if (rtc->ops->set_mmss) {
        unsigned long secs;
        err = rtc_tm_to_time(tm, &secs);
        if (err == 0)
            err = rtc->ops->set_mmss(rtc->dev.parent, secs);
    } else
        err = -EINVAL;

    mutex_unlock(&rtc->ops_lock);
    /* A timer might have just expired */
    schedule_work(&rtc->irqwork);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_set_time);

int rtc_set_mmss(struct rtc_device *rtc, unsigned long secs)
{
    int err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    if (!rtc->ops)
        err = -ENODEV;
    else if (rtc->ops->set_mmss)
        err = rtc->ops->set_mmss(rtc->dev.parent, secs);
    else if (rtc->ops->read_time && rtc->ops->set_time) {
        struct rtc_time new, old;

        err = rtc->ops->read_time(rtc->dev.parent, &old);
        if (err == 0) {
            rtc_time_to_tm(secs, &new);

            /*
             * avoid writing when we're going to change the day of
             * the month. We will retry in the next minute. This
             * basically means that if the RTC must not drift
             * by more than 1 minute in 11 minutes.
             */
            if (!((old.tm_hour == 23 && old.tm_min == 59) ||
                (new.tm_hour == 23 && new.tm_min == 59)))
                err = rtc->ops->set_time(rtc->dev.parent,
                        &new);
        }
    }
    else
        err = -EINVAL;

    mutex_unlock(&rtc->ops_lock);
    /* A timer might have just expired */
    schedule_work(&rtc->irqwork);

    return err;
}
EXPORT_SYMBOL_GPL(rtc_set_mmss);

static int rtc_read_alarm_internal(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
    int err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    if (rtc->ops == NULL)
        err = -ENODEV;
    else if (!rtc->ops->read_alarm)
        err = -EINVAL;
    else {
        memset(alarm, 0, sizeof(struct rtc_wkalrm));
        err = rtc->ops->read_alarm(rtc->dev.parent, alarm);
    }

    mutex_unlock(&rtc->ops_lock);
    return err;
}

int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
    int err;
    struct rtc_time before, now;
    int first_time = 1;
    unsigned long t_now, t_alm;
    enum { none, day, month, year } missing = none;
    unsigned days;

    /* The lower level RTC driver may return -1 in some fields,
     * creating invalid alarm->time values, for reasons like:
     *
     *   - The hardware may not be capable of filling them in;
     *     many alarms match only on time-of-day fields, not
     *     day/month/year calendar data.
     *
     *   - Some hardware uses illegal values as "wildcard" match
     *     values, which non-Linux firmware (like a BIOS) may try
     *     to set up as e.g. "alarm 15 minutes after each hour".
     *     Linux uses only oneshot alarms.
     *
     * When we see that here, we deal with it by using values from
     * a current RTC timestamp for any missing (-1) values.  The
     * RTC driver prevents "periodic alarm" modes.
     *
     * But this can be racey, because some fields of the RTC timestamp
     * may have wrapped in the interval since we read the RTC alarm,
     * which would lead to us inserting inconsistent values in place
     * of the -1 fields.
     *
     * Reading the alarm and timestamp in the reverse sequence
     * would have the same race condition, and not solve the issue.
     *
     * So, we must first read the RTC timestamp,
     * then read the RTC alarm value,
     * and then read a second RTC timestamp.
     *
     * If any fields of the second timestamp have changed
     * when compared with the first timestamp, then we know
     * our timestamp may be inconsistent with that used by
     * the low-level rtc_read_alarm_internal() function.
     *
     * So, when the two timestamps disagree, we just loop and do
     * the process again to get a fully consistent set of values.
     *
     * This could all instead be done in the lower level driver,
     * but since more than one lower level RTC implementation needs it,
     * then it's probably best best to do it here instead of there..
     */

    /* Get the "before" timestamp */
    err = rtc_read_time(rtc, &before);
    if (err < 0)
        return err;
    do {
        if (!first_time)
            memcpy(&before, &now, sizeof(struct rtc_time));
        first_time = 0;

        /* get the RTC alarm values, which may be incomplete */
        err = rtc_read_alarm_internal(rtc, alarm);
        if (err)
            return err;

        /* full-function RTCs won't have such missing fields */
        if (rtc_valid_tm(&alarm->time) == 0)
            return 0;

        /* get the "after" timestamp, to detect wrapped fields */
        err = rtc_read_time(rtc, &now);
        if (err < 0)
            return err;

        /* note that tm_sec is a "don't care" value here: */
    } while (   before.tm_min   != now.tm_min
         || before.tm_hour  != now.tm_hour
         || before.tm_mon   != now.tm_mon
         || before.tm_year  != now.tm_year);

    /* Fill in the missing alarm fields using the timestamp; we
     * know there's at least one since alarm->time is invalid.
     */
    if (alarm->time.tm_sec == -1)
        alarm->time.tm_sec = now.tm_sec;
    if (alarm->time.tm_min == -1)
        alarm->time.tm_min = now.tm_min;
    if (alarm->time.tm_hour == -1)
        alarm->time.tm_hour = now.tm_hour;

    /* For simplicity, only support date rollover for now */
    if (alarm->time.tm_mday < 1 || alarm->time.tm_mday > 31) {
        alarm->time.tm_mday = now.tm_mday;
        missing = day;
    }
    if ((unsigned)alarm->time.tm_mon >= 12) {
        alarm->time.tm_mon = now.tm_mon;
        if (missing == none)
            missing = month;
    }
    if (alarm->time.tm_year == -1) {
        alarm->time.tm_year = now.tm_year;
        if (missing == none)
            missing = year;
    }

    /* with luck, no rollover is needed */
    rtc_tm_to_time(&now, &t_now);
    rtc_tm_to_time(&alarm->time, &t_alm);
    if (t_now < t_alm)
        goto done;

    switch (missing) {

    /* 24 hour rollover ... if it's now 10am Monday, an alarm that
     * that will trigger at 5am will do so at 5am Tuesday, which
     * could also be in the next month or year.  This is a common
     * case, especially for PCs.
     */
    case day:
        dev_dbg(&rtc->dev, "alarm rollover: %s\n", "day");
        t_alm += 24 * 60 * 60;
        rtc_time_to_tm(t_alm, &alarm->time);
        break;

    /* Month rollover ... if it's the 31th, an alarm on the 3rd will
     * be next month.  An alarm matching on the 30th, 29th, or 28th
     * may end up in the month after that!  Many newer PCs support
     * this type of alarm.
     */
    case month:
        dev_dbg(&rtc->dev, "alarm rollover: %s\n", "month");
        do {
            if (alarm->time.tm_mon < 11)
                alarm->time.tm_mon++;
            else {
                alarm->time.tm_mon = 0;
                alarm->time.tm_year++;
            }
            days = rtc_month_days(alarm->time.tm_mon,
                    alarm->time.tm_year);
        } while (days < alarm->time.tm_mday);
        break;

    /* Year rollover ... easy except for leap years! */
    case year:
        dev_dbg(&rtc->dev, "alarm rollover: %s\n", "year");
        do {
            alarm->time.tm_year++;
        } while (rtc_valid_tm(&alarm->time) != 0);
        break;

    default:
        dev_warn(&rtc->dev, "alarm rollover not handled\n");
    }

done:
    return 0;
}

int rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
    int err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;
    if (rtc->ops == NULL)
        err = -ENODEV;
    else if (!rtc->ops->read_alarm)
        err = -EINVAL;
    else {
        memset(alarm, 0, sizeof(struct rtc_wkalrm));
        alarm->enabled = rtc->aie_timer.enabled;
        alarm->time = rtc_ktime_to_tm(rtc->aie_timer.node.expires);
    }
    mutex_unlock(&rtc->ops_lock);

    return err;
}
EXPORT_SYMBOL_GPL(rtc_read_alarm);

static int __rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
    struct rtc_time tm;
    long now, scheduled;
    int err;

    err = rtc_valid_tm(&alarm->time);
    if (err)
        return err;
    rtc_tm_to_time(&alarm->time, &scheduled);

    /* Make sure we're not setting alarms in the past */
    err = __rtc_read_time(rtc, &tm);
    rtc_tm_to_time(&tm, &now);
    if (scheduled <= now)
        return -ETIME;
    /*
     * XXX - We just checked to make sure the alarm time is not
     * in the past, but there is still a race window where if
     * the is alarm set for the next second and the second ticks
     * over right here, before we set the alarm.
     */

    if (!rtc->ops)
        err = -ENODEV;
    else if (!rtc->ops->set_alarm)
        err = -EINVAL;
    else
        err = rtc->ops->set_alarm(rtc->dev.parent, alarm);

    return err;
}

int rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
    int err;

    err = rtc_valid_tm(&alarm->time);
    if (err != 0)
        return err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;
    if (rtc->aie_timer.enabled) {
        rtc_timer_remove(rtc, &rtc->aie_timer);
    }
    rtc->aie_timer.node.expires = rtc_tm_to_ktime(alarm->time);
    rtc->aie_timer.period = ktime_set(0, 0);
    if (alarm->enabled) {
        err = rtc_timer_enqueue(rtc, &rtc->aie_timer);
    }
    mutex_unlock(&rtc->ops_lock);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_set_alarm);

/* Called once per device from rtc_device_register */
int rtc_initialize_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
    int err;
    struct rtc_time now;

    err = rtc_valid_tm(&alarm->time);
    if (err != 0)
        return err;

    err = rtc_read_time(rtc, &now);
    if (err)
        return err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    rtc->aie_timer.node.expires = rtc_tm_to_ktime(alarm->time);
    rtc->aie_timer.period = ktime_set(0, 0);

    /* Alarm has to be enabled & in the futrure for us to enqueue it */
    if (alarm->enabled && (rtc_tm_to_ktime(now).tv64 <
             rtc->aie_timer.node.expires.tv64)) {

        rtc->aie_timer.enabled = 1;
        timerqueue_add(&rtc->timerqueue, &rtc->aie_timer.node);
    }
    mutex_unlock(&rtc->ops_lock);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_initialize_alarm);



int rtc_alarm_irq_enable(struct rtc_device *rtc, unsigned int enabled)
{
    int err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    if (rtc->aie_timer.enabled != enabled) {
        if (enabled)
            err = rtc_timer_enqueue(rtc, &rtc->aie_timer);
        else
            rtc_timer_remove(rtc, &rtc->aie_timer);
    }

    if (err)
        /* nothing */;
    else if (!rtc->ops)
        err = -ENODEV;
    else if (!rtc->ops->alarm_irq_enable)
        err = -EINVAL;
    else
        err = rtc->ops->alarm_irq_enable(rtc->dev.parent, enabled);

    mutex_unlock(&rtc->ops_lock);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_alarm_irq_enable);

int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
{
    int err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
    if (enabled == 0 && rtc->uie_irq_active) {
        mutex_unlock(&rtc->ops_lock);
        return rtc_dev_update_irq_enable_emul(rtc, 0);
    }
#endif
    /* make sure we're changing state */
    if (rtc->uie_rtctimer.enabled == enabled)
        goto out;

    if (rtc->uie_unsupported) {
        err = -EINVAL;
        goto out;
    }

    if (enabled) {
        struct rtc_time tm;
        ktime_t now, onesec;

        __rtc_read_time(rtc, &tm);
        onesec = ktime_set(1, 0);
        now = rtc_tm_to_ktime(tm);
        rtc->uie_rtctimer.node.expires = ktime_add(now, onesec);
        rtc->uie_rtctimer.period = ktime_set(1, 0);
        err = rtc_timer_enqueue(rtc, &rtc->uie_rtctimer);
    } else
        rtc_timer_remove(rtc, &rtc->uie_rtctimer);

out:
    mutex_unlock(&rtc->ops_lock);
#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
    /*
     * Enable emulation if the driver did not provide
     * the update_irq_enable function pointer or if returned
     * -EINVAL to signal that it has been configured without
     * interrupts or that are not available at the moment.
     */
    if (err == -EINVAL)
        err = rtc_dev_update_irq_enable_emul(rtc, enabled);
#endif
    return err;

}
EXPORT_SYMBOL_GPL(rtc_update_irq_enable);


void rtc_handle_legacy_irq(struct rtc_device *rtc, int num, int mode)
{
    unsigned long flags;

    /* mark one irq of the appropriate mode */
    spin_lock_irqsave(&rtc->irq_lock, flags);
    rtc->irq_data = (rtc->irq_data + (num << 8)) | (RTC_IRQF|mode);
    spin_unlock_irqrestore(&rtc->irq_lock, flags);

    /* call the task func */
    spin_lock_irqsave(&rtc->irq_task_lock, flags);
    if (rtc->irq_task)
        rtc->irq_task->func(rtc->irq_task->private_data);
    spin_unlock_irqrestore(&rtc->irq_task_lock, flags);

    wake_up_interruptible(&rtc->irq_queue);
    kill_fasync(&rtc->async_queue, SIGIO, POLL_IN);
}


void rtc_aie_update_irq(void *private)
{
    struct rtc_device *rtc = (struct rtc_device *)private;
    rtc_handle_legacy_irq(rtc, 1, RTC_AF);
}


void rtc_uie_update_irq(void *private)
{
    struct rtc_device *rtc = (struct rtc_device *)private;
    rtc_handle_legacy_irq(rtc, 1,  RTC_UF);
}


enum hrtimer_restart rtc_pie_update_irq(struct hrtimer *timer)
{
    struct rtc_device *rtc;
    ktime_t period;
    int count;
    rtc = container_of(timer, struct rtc_device, pie_timer);

    period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq);
    count = hrtimer_forward_now(timer, period);

    rtc_handle_legacy_irq(rtc, count, RTC_PF);

    return HRTIMER_RESTART;
}

void rtc_update_irq(struct rtc_device *rtc,
        unsigned long num, unsigned long events)
{
    pm_stay_awake(rtc->dev.parent);
    schedule_work(&rtc->irqwork);
}
EXPORT_SYMBOL_GPL(rtc_update_irq);

static int __rtc_match(struct device *dev, void *data)
{
    char *name = (char *)data;

    if (strcmp(dev_name(dev), name) == 0)
        return 1;
    return 0;
}

struct rtc_device *rtc_class_open(char *name)
{
    struct device *dev;
    struct rtc_device *rtc = NULL;

    dev = class_find_device(rtc_class, NULL, name, __rtc_match);
    if (dev)
        rtc = to_rtc_device(dev);

    if (rtc) {
        if (!try_module_get(rtc->owner)) {
            put_device(dev);
            rtc = NULL;
        }
    }

    return rtc;
}
EXPORT_SYMBOL_GPL(rtc_class_open);

void rtc_class_close(struct rtc_device *rtc)
{
    module_put(rtc->owner);
    put_device(&rtc->dev);
}
EXPORT_SYMBOL_GPL(rtc_class_close);

int rtc_irq_register(struct rtc_device *rtc, struct rtc_task *task)
{
    int retval = -EBUSY;

    if (task == NULL || task->func == NULL)
        return -EINVAL;

    /* Cannot register while the char dev is in use */
    if (test_and_set_bit_lock(RTC_DEV_BUSY, &rtc->flags))
        return -EBUSY;

    spin_lock_irq(&rtc->irq_task_lock);
    if (rtc->irq_task == NULL) {
        rtc->irq_task = task;
        retval = 0;
    }
    spin_unlock_irq(&rtc->irq_task_lock);

    clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);

    return retval;
}
EXPORT_SYMBOL_GPL(rtc_irq_register);

void rtc_irq_unregister(struct rtc_device *rtc, struct rtc_task *task)
{
    spin_lock_irq(&rtc->irq_task_lock);
    if (rtc->irq_task == task)
        rtc->irq_task = NULL;
    spin_unlock_irq(&rtc->irq_task_lock);
}
EXPORT_SYMBOL_GPL(rtc_irq_unregister);

static int rtc_update_hrtimer(struct rtc_device *rtc, int enabled)
{
    /*
     * We always cancel the timer here first, because otherwise
     * we could run into BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
     * when we manage to start the timer before the callback
     * returns HRTIMER_RESTART.
     *
     * We cannot use hrtimer_cancel() here as a running callback
     * could be blocked on rtc->irq_task_lock and hrtimer_cancel()
     * would spin forever.
     */
    if (hrtimer_try_to_cancel(&rtc->pie_timer) < 0)
        return -1;

    if (enabled) {
        ktime_t period = ktime_set(0, NSEC_PER_SEC / rtc->irq_freq);

        hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL);
    }
    return 0;
}

int rtc_irq_set_state(struct rtc_device *rtc, struct rtc_task *task, int enabled)
{
    int err = 0;
    unsigned long flags;

retry:
    spin_lock_irqsave(&rtc->irq_task_lock, flags);
    if (rtc->irq_task != NULL && task == NULL)
        err = -EBUSY;
    if (rtc->irq_task != task)
        err = -EACCES;
    if (!err) {
        if (rtc_update_hrtimer(rtc, enabled) < 0) {
            spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
            cpu_relax();
            goto retry;
        }
        rtc->pie_enabled = enabled;
    }
    spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_irq_set_state);

int rtc_irq_set_freq(struct rtc_device *rtc, struct rtc_task *task, int freq)
{
    int err = 0;
    unsigned long flags;

    if (freq <= 0 || freq > RTC_MAX_FREQ)
        return -EINVAL;
retry:
    spin_lock_irqsave(&rtc->irq_task_lock, flags);
    if (rtc->irq_task != NULL && task == NULL)
        err = -EBUSY;
    if (rtc->irq_task != task)
        err = -EACCES;
    if (!err) {
        rtc->irq_freq = freq;
        if (rtc->pie_enabled && rtc_update_hrtimer(rtc, 1) < 0) {
            spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
            cpu_relax();
            goto retry;
        }
    }
    spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_irq_set_freq);

static int rtc_timer_enqueue(struct rtc_device *rtc, struct rtc_timer *timer)
{
    timer->enabled = 1;
    timerqueue_add(&rtc->timerqueue, &timer->node);
    if (&timer->node == timerqueue_getnext(&rtc->timerqueue)) {
        struct rtc_wkalrm alarm;
        int err;
        alarm.time = rtc_ktime_to_tm(timer->node.expires);
        alarm.enabled = 1;
        err = __rtc_set_alarm(rtc, &alarm);
        if (err == -ETIME)
            schedule_work(&rtc->irqwork);
        else if (err) {
            timerqueue_del(&rtc->timerqueue, &timer->node);
            timer->enabled = 0;
            return err;
        }
    }
    return 0;
}

static void rtc_alarm_disable(struct rtc_device *rtc)
{
    if (!rtc->ops || !rtc->ops->alarm_irq_enable)
        return;

    rtc->ops->alarm_irq_enable(rtc->dev.parent, false);
}

static void rtc_timer_remove(struct rtc_device *rtc, struct rtc_timer *timer)
{
    struct timerqueue_node *next = timerqueue_getnext(&rtc->timerqueue);
    timerqueue_del(&rtc->timerqueue, &timer->node);
    timer->enabled = 0;
    if (next == &timer->node) {
        struct rtc_wkalrm alarm;
        int err;
        next = timerqueue_getnext(&rtc->timerqueue);
        if (!next) {
            rtc_alarm_disable(rtc);
            return;
        }
        alarm.time = rtc_ktime_to_tm(next->expires);
        alarm.enabled = 1;
        err = __rtc_set_alarm(rtc, &alarm);
        if (err == -ETIME)
            schedule_work(&rtc->irqwork);
    }
}

void rtc_timer_do_work(struct work_struct *work)
{
    struct rtc_timer *timer;
    struct timerqueue_node *next;
    ktime_t now;
    struct rtc_time tm;

    struct rtc_device *rtc =
        container_of(work, struct rtc_device, irqwork);

    mutex_lock(&rtc->ops_lock);
again:
    pm_relax(rtc->dev.parent);
    __rtc_read_time(rtc, &tm);
    now = rtc_tm_to_ktime(tm);
    while ((next = timerqueue_getnext(&rtc->timerqueue))) {
        if (next->expires.tv64 > now.tv64)
            break;

        /* expire timer */
        timer = container_of(next, struct rtc_timer, node);
        timerqueue_del(&rtc->timerqueue, &timer->node);
        timer->enabled = 0;
        if (timer->task.func)
            timer->task.func(timer->task.private_data);

        /* Re-add/fwd periodic timers */
        if (ktime_to_ns(timer->period)) {
            timer->node.expires = ktime_add(timer->node.expires,
                            timer->period);
            timer->enabled = 1;
            timerqueue_add(&rtc->timerqueue, &timer->node);
        }
    }

    /* Set next alarm */
    if (next) {
        struct rtc_wkalrm alarm;
        int err;
        alarm.time = rtc_ktime_to_tm(next->expires);
        alarm.enabled = 1;
        err = __rtc_set_alarm(rtc, &alarm);
        if (err == -ETIME)
            goto again;
    } else
        rtc_alarm_disable(rtc);

    mutex_unlock(&rtc->ops_lock);
}


/* rtc_timer_init - Initializes an rtc_timer
 * @timer: timer to be intiialized
 * @f: function pointer to be called when timer fires
 * @data: private data passed to function pointer
 *
 * Kernel interface to initializing an rtc_timer.
 */
void rtc_timer_init(struct rtc_timer *timer, void (*f)(void* p), void* data)
{
    timerqueue_init(&timer->node);
    timer->enabled = 0;
    timer->task.func = f;
    timer->task.private_data = data;
}

/* rtc_timer_start - Sets an rtc_timer to fire in the future
 * @ rtc: rtc device to be used
 * @ timer: timer being set
 * @ expires: time at which to expire the timer
 * @ period: period that the timer will recur
 *
 * Kernel interface to set an rtc_timer
 */
int rtc_timer_start(struct rtc_device *rtc, struct rtc_timer* timer,
            ktime_t expires, ktime_t period)
{
    int ret = 0;
    mutex_lock(&rtc->ops_lock);
    if (timer->enabled)
        rtc_timer_remove(rtc, timer);

    timer->node.expires = expires;
    timer->period = period;

    ret = rtc_timer_enqueue(rtc, timer);

    mutex_unlock(&rtc->ops_lock);
    return ret;
}

/* rtc_timer_cancel - Stops an rtc_timer
 * @ rtc: rtc device to be used
 * @ timer: timer being set
 *
 * Kernel interface to cancel an rtc_timer
 */
int rtc_timer_cancel(struct rtc_device *rtc, struct rtc_timer* timer)
{
    int ret = 0;
    mutex_lock(&rtc->ops_lock);
    if (timer->enabled)
        rtc_timer_remove(rtc, timer);
    mutex_unlock(&rtc->ops_lock);
    return ret;
}