x86/bugs, KVM: Extend speculation control for VIRT_SPEC_CTRL

[linux/fpc-iii.git] / drivers / rtc / interface.c

/*
 * RTC subsystem, interface functions
 *
 * Copyright (C) 2005 Tower Technologies
 * Author: Alessandro Zummo <a.zummo@towertech.it>
 *
 * 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);
                if (err < 0) {
                        dev_dbg(&rtc->dev, "read_time: fail to read: %d\n",
                                err);
                        return err;
                }

                err = rtc_valid_tm(tm);
                if (err < 0)
                        dev_dbg(&rtc->dev, "read_time: rtc_time isn't valid\n");
        }
        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_mmss64) {
                time64_t secs64 = rtc_tm_to_time64(tm);

                err = rtc->ops->set_mmss64(rtc->dev.parent, secs64);
        } else if (rtc->ops->set_mmss) {
                time64_t secs64 = rtc_tm_to_time64(tm);
                err = rtc->ops->set_mmss(rtc->dev.parent, secs64);
        } else
                err = -EINVAL;

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

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 {
                alarm->enabled = 0;
                alarm->pending = 0;
                alarm->time.tm_sec = -1;
                alarm->time.tm_min = -1;
                alarm->time.tm_hour = -1;
                alarm->time.tm_mday = -1;
                alarm->time.tm_mon = -1;
                alarm->time.tm_year = -1;
                alarm->time.tm_wday = -1;
                alarm->time.tm_yday = -1;
                alarm->time.tm_isdst = -1;
                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;
        time64_t 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;
        }

        /* Can't proceed if alarm is still invalid after replacing
         * missing fields.
         */
        err = rtc_valid_tm(&alarm->time);
        if (err)
                goto done;

        /* with luck, no rollover is needed */
        t_now = rtc_tm_to_time64(&now);
        t_alm = rtc_tm_to_time64(&alarm->time);
        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_time64_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 (!is_leap_year(alarm->time.tm_year + 1900)
                        && rtc_valid_tm(&alarm->time) != 0);
                break;

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

        err = rtc_valid_tm(&alarm->time);

done:
        if (err) {
                dev_warn(&rtc->dev, "invalid alarm value: %d-%d-%d %d:%d:%d\n",
                        alarm->time.tm_year + 1900, alarm->time.tm_mon + 1,
                        alarm->time.tm_mday, alarm->time.tm_hour, alarm->time.tm_min,
                        alarm->time.tm_sec);
        }

        return err;
}

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;
        time64_t now, scheduled;
        int err;

        err = rtc_valid_tm(&alarm->time);
        if (err)
                return err;
        scheduled = rtc_tm_to_time64(&alarm->time);

        /* Make sure we're not setting alarms in the past */
        err = __rtc_read_time(rtc, &tm);
        if (err)
                return err;
        now = rtc_tm_to_time64(&tm);
        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 future 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);


/**
 * rtc_handle_legacy_irq - AIE, UIE and PIE event hook
 * @rtc: pointer to the rtc device
 *
 * This function is called when an AIE, UIE or PIE mode interrupt
 * has occurred (or been emulated).
 *
 * Triggers the registered irq_task function callback.
 */
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);
}


/**
 * rtc_aie_update_irq - AIE mode rtctimer hook
 * @private: pointer to the rtc_device
 *
 * This functions is called when the aie_timer expires.
 */
void rtc_aie_update_irq(void *private)
{
        struct rtc_device *rtc = (struct rtc_device *)private;
        rtc_handle_legacy_irq(rtc, 1, RTC_AF);
}


/**
 * rtc_uie_update_irq - UIE mode rtctimer hook
 * @private: pointer to the rtc_device
 *
 * This functions is called when the uie_timer expires.
 */
void rtc_uie_update_irq(void *private)
{
        struct rtc_device *rtc = (struct rtc_device *)private;
        rtc_handle_legacy_irq(rtc, 1,  RTC_UF);
}


/**
 * rtc_pie_update_irq - PIE mode hrtimer hook
 * @timer: pointer to the pie mode hrtimer
 *
 * This function is used to emulate PIE mode interrupts
 * using an hrtimer. This function is called when the periodic
 * hrtimer expires.
 */
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;
}

/**
 * rtc_update_irq - Triggered when a RTC interrupt occurs.
 * @rtc: the rtc device
 * @num: how many irqs are being reported (usually one)
 * @events: mask of RTC_IRQF with one or more of RTC_PF, RTC_AF, RTC_UF
 * Context: any
 */
void rtc_update_irq(struct rtc_device *rtc,
                unsigned long num, unsigned long events)
{
        if (IS_ERR_OR_NULL(rtc))
                return;

        pm_stay_awake(rtc->dev.parent);
        schedule_work(&rtc->irqwork);
}
EXPORT_SYMBOL_GPL(rtc_update_irq);

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

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

struct rtc_device *rtc_class_open(const 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;
}

/**
 * rtc_irq_set_state - enable/disable 2^N Hz periodic IRQs
 * @rtc: the rtc device
 * @task: currently registered with rtc_irq_register()
 * @enabled: true to enable periodic IRQs
 * Context: any
 *
 * Note that rtc_irq_set_freq() should previously have been used to
 * specify the desired frequency of periodic IRQ task->func() callbacks.
 */
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;
        else if (rtc->irq_task != task)
                err = -EACCES;
        else {
                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);

/**
 * rtc_irq_set_freq - set 2^N Hz periodic IRQ frequency for IRQ
 * @rtc: the rtc device
 * @task: currently registered with rtc_irq_register()
 * @freq: positive frequency with which task->func() will be called
 * Context: any
 *
 * Note that rtc_irq_set_state() is used to enable or disable the
 * periodic IRQs.
 */
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;
        else if (rtc->irq_task != task)
                err = -EACCES;
        else {
                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);

/**
 * rtc_timer_enqueue - Adds a rtc_timer to the rtc_device timerqueue
 * @rtc rtc device
 * @timer timer being added.
 *
 * Enqueues a timer onto the rtc devices timerqueue and sets
 * the next alarm event appropriately.
 *
 * Sets the enabled bit on the added timer.
 *
 * Must hold ops_lock for proper serialization of timerqueue
 */
static int rtc_timer_enqueue(struct rtc_device *rtc, struct rtc_timer *timer)
{
        struct timerqueue_node *next = timerqueue_getnext(&rtc->timerqueue);
        struct rtc_time tm;
        ktime_t now;

        timer->enabled = 1;
        __rtc_read_time(rtc, &tm);
        now = rtc_tm_to_ktime(tm);

        /* Skip over expired timers */
        while (next) {
                if (next->expires.tv64 >= now.tv64)
                        break;
                next = timerqueue_iterate_next(next);
        }

        timerqueue_add(&rtc->timerqueue, &timer->node);
        if (!next || ktime_before(timer->node.expires, next->expires)) {
                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) {
                        pm_stay_awake(rtc->dev.parent);
                        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);
}

/**
 * rtc_timer_remove - Removes a rtc_timer from the rtc_device timerqueue
 * @rtc rtc device
 * @timer timer being removed.
 *
 * Removes a timer onto the rtc devices timerqueue and sets
 * the next alarm event appropriately.
 *
 * Clears the enabled bit on the removed timer.
 *
 * Must hold ops_lock for proper serialization of timerqueue
 */
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) {
                        pm_stay_awake(rtc->dev.parent);
                        schedule_work(&rtc->irqwork);
                }
        }
}

/**
 * rtc_timer_do_work - Expires rtc timers
 * @rtc rtc device
 * @timer timer being removed.
 *
 * Expires rtc timers. Reprograms next alarm event if needed.
 * Called via worktask.
 *
 * Serializes access to timerqueue via ops_lock mutex
 */
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:
        __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;
                int retry = 3;

                alarm.time = rtc_ktime_to_tm(next->expires);
                alarm.enabled = 1;
reprogram:
                err = __rtc_set_alarm(rtc, &alarm);
                if (err == -ETIME)
                        goto again;
                else if (err) {
                        if (retry-- > 0)
                                goto reprogram;

                        timer = container_of(next, struct rtc_timer, node);
                        timerqueue_del(&rtc->timerqueue, &timer->node);
                        timer->enabled = 0;
                        dev_err(&rtc->dev, "__rtc_set_alarm: err=%d\n", err);
                        goto again;
                }
        } else
                rtc_alarm_disable(rtc);

        pm_relax(rtc->dev.parent);
        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
 */
void rtc_timer_cancel(struct rtc_device *rtc, struct rtc_timer *timer)
{
        mutex_lock(&rtc->ops_lock);
        if (timer->enabled)
                rtc_timer_remove(rtc, timer);
        mutex_unlock(&rtc->ops_lock);
}

/**
 * rtc_read_offset - Read the amount of rtc offset in parts per billion
 * @ rtc: rtc device to be used
 * @ offset: the offset in parts per billion
 *
 * see below for details.
 *
 * Kernel interface to read rtc clock offset
 * Returns 0 on success, or a negative number on error.
 * If read_offset() is not implemented for the rtc, return -EINVAL
 */
int rtc_read_offset(struct rtc_device *rtc, long *offset)
{
        int ret;

        if (!rtc->ops)
                return -ENODEV;

        if (!rtc->ops->read_offset)
                return -EINVAL;

        mutex_lock(&rtc->ops_lock);
        ret = rtc->ops->read_offset(rtc->dev.parent, offset);
        mutex_unlock(&rtc->ops_lock);
        return ret;
}

/**
 * rtc_set_offset - Adjusts the duration of the average second
 * @ rtc: rtc device to be used
 * @ offset: the offset in parts per billion
 *
 * Some rtc's allow an adjustment to the average duration of a second
 * to compensate for differences in the actual clock rate due to temperature,
 * the crystal, capacitor, etc.
 *
 * Kernel interface to adjust an rtc clock offset.
 * Return 0 on success, or a negative number on error.
 * If the rtc offset is not setable (or not implemented), return -EINVAL
 */
int rtc_set_offset(struct rtc_device *rtc, long offset)
{
        int ret;

        if (!rtc->ops)
                return -ENODEV;

        if (!rtc->ops->set_offset)
                return -EINVAL;

        mutex_lock(&rtc->ops_lock);
        ret = rtc->ops->set_offset(rtc->dev.parent, offset);
        mutex_unlock(&rtc->ops_lock);
        return ret;
}