clocksource.c

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/*
 * linux/kernel/time/clocksource.c
 *
 * This file contains the functions which manage clocksource drivers.
 *
 * Copyright (C) 2004, 2005 IBM, John Stultz ([email protected])
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * TODO WishList:
 *   o Allow clocksource drivers to be unregistered
 */

#include <linux/device.h>
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
#include <linux/kthread.h>

void timecounter_init(struct timecounter *tc,
              const struct cyclecounter *cc,
              u64 start_tstamp)
{
    tc->cc = cc;
    tc->cycle_last = cc->read(cc);
    tc->nsec = start_tstamp;
}
EXPORT_SYMBOL_GPL(timecounter_init);

static u64 timecounter_read_delta(struct timecounter *tc)
{
    cycle_t cycle_now, cycle_delta;
    u64 ns_offset;

    /* read cycle counter: */
    cycle_now = tc->cc->read(tc->cc);

    /* calculate the delta since the last timecounter_read_delta(): */
    cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;

    /* convert to nanoseconds: */
    ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);

    /* update time stamp of timecounter_read_delta() call: */
    tc->cycle_last = cycle_now;

    return ns_offset;
}

u64 timecounter_read(struct timecounter *tc)
{
    u64 nsec;

    /* increment time by nanoseconds since last call */
    nsec = timecounter_read_delta(tc);
    nsec += tc->nsec;
    tc->nsec = nsec;

    return nsec;
}
EXPORT_SYMBOL_GPL(timecounter_read);

u64 timecounter_cyc2time(struct timecounter *tc,
             cycle_t cycle_tstamp)
{
    u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
    u64 nsec;

    /*
     * Instead of always treating cycle_tstamp as more recent
     * than tc->cycle_last, detect when it is too far in the
     * future and treat it as old time stamp instead.
     */
    if (cycle_delta > tc->cc->mask / 2) {
        cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
        nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
    } else {
        nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
    }

    return nsec;
}
EXPORT_SYMBOL_GPL(timecounter_cyc2time);

void
clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
{
    u64 tmp;
    u32 sft, sftacc= 32;

    /*
     * Calculate the shift factor which is limiting the conversion
     * range:
     */
    tmp = ((u64)maxsec * from) >> 32;
    while (tmp) {
        tmp >>=1;
        sftacc--;
    }

    /*
     * Find the conversion shift/mult pair which has the best
     * accuracy and fits the maxsec conversion range:
     */
    for (sft = 32; sft > 0; sft--) {
        tmp = (u64) to << sft;
        tmp += from / 2;
        do_div(tmp, from);
        if ((tmp >> sftacc) == 0)
            break;
    }
    *mult = tmp;
    *shift = sft;
}

/*[Clocksource internal variables]---------
 * curr_clocksource:
 *  currently selected clocksource.
 * clocksource_list:
 *  linked list with the registered clocksources
 * clocksource_mutex:
 *  protects manipulations to curr_clocksource and the clocksource_list
 * override_name:
 *  Name of the user-specified clocksource.
 */
static struct clocksource *curr_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_MUTEX(clocksource_mutex);
static char override_name[32];
static int finished_booting;

#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static void clocksource_watchdog_work(struct work_struct *work);

static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
static DEFINE_SPINLOCK(watchdog_lock);
static int watchdog_running;
static atomic_t watchdog_reset_pending;

static int clocksource_watchdog_kthread(void *data);
static void __clocksource_change_rating(struct clocksource *cs, int rating);

/*
 * Interval: 0.5sec Threshold: 0.0625s
 */
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)

static void clocksource_watchdog_work(struct work_struct *work)
{
    /*
     * If kthread_run fails the next watchdog scan over the
     * watchdog_list will find the unstable clock again.
     */
    kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
}

static void __clocksource_unstable(struct clocksource *cs)
{
    cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
    cs->flags |= CLOCK_SOURCE_UNSTABLE;
    if (finished_booting)
        schedule_work(&watchdog_work);
}

static void clocksource_unstable(struct clocksource *cs, int64_t delta)
{
    printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
           cs->name, delta);
    __clocksource_unstable(cs);
}

void clocksource_mark_unstable(struct clocksource *cs)
{
    unsigned long flags;

    spin_lock_irqsave(&watchdog_lock, flags);
    if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
        if (list_empty(&cs->wd_list))
            list_add(&cs->wd_list, &watchdog_list);
        __clocksource_unstable(cs);
    }
    spin_unlock_irqrestore(&watchdog_lock, flags);
}

static void clocksource_watchdog(unsigned long data)
{
    struct clocksource *cs;
    cycle_t csnow, wdnow;
    int64_t wd_nsec, cs_nsec;
    int next_cpu, reset_pending;

    spin_lock(&watchdog_lock);
    if (!watchdog_running)
        goto out;

    reset_pending = atomic_read(&watchdog_reset_pending);

    list_for_each_entry(cs, &watchdog_list, wd_list) {

        /* Clocksource already marked unstable? */
        if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
            if (finished_booting)
                schedule_work(&watchdog_work);
            continue;
        }

        local_irq_disable();
        csnow = cs->read(cs);
        wdnow = watchdog->read(watchdog);
        local_irq_enable();

        /* Clocksource initialized ? */
        if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
            atomic_read(&watchdog_reset_pending)) {
            cs->flags |= CLOCK_SOURCE_WATCHDOG;
            cs->wd_last = wdnow;
            cs->cs_last = csnow;
            continue;
        }

        wd_nsec = clocksource_cyc2ns((wdnow - cs->wd_last) & watchdog->mask,
                         watchdog->mult, watchdog->shift);

        cs_nsec = clocksource_cyc2ns((csnow - cs->cs_last) &
                         cs->mask, cs->mult, cs->shift);
        cs->cs_last = csnow;
        cs->wd_last = wdnow;

        if (atomic_read(&watchdog_reset_pending))
            continue;

        /* Check the deviation from the watchdog clocksource. */
        if ((abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD)) {
            clocksource_unstable(cs, cs_nsec - wd_nsec);
            continue;
        }

        if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
            (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
            (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
            cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
            /*
             * We just marked the clocksource as highres-capable,
             * notify the rest of the system as well so that we
             * transition into high-res mode:
             */
            tick_clock_notify();
        }
    }

    /*
     * We only clear the watchdog_reset_pending, when we did a
     * full cycle through all clocksources.
     */
    if (reset_pending)
        atomic_dec(&watchdog_reset_pending);

    /*
     * Cycle through CPUs to check if the CPUs stay synchronized
     * to each other.
     */
    next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
    if (next_cpu >= nr_cpu_ids)
        next_cpu = cpumask_first(cpu_online_mask);
    watchdog_timer.expires += WATCHDOG_INTERVAL;
    add_timer_on(&watchdog_timer, next_cpu);
out:
    spin_unlock(&watchdog_lock);
}

static inline void clocksource_start_watchdog(void)
{
    if (watchdog_running || !watchdog || list_empty(&watchdog_list))
        return;
    init_timer(&watchdog_timer);
    watchdog_timer.function = clocksource_watchdog;
    watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
    add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
    watchdog_running = 1;
}

static inline void clocksource_stop_watchdog(void)
{
    if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
        return;
    del_timer(&watchdog_timer);
    watchdog_running = 0;
}

static inline void clocksource_reset_watchdog(void)
{
    struct clocksource *cs;

    list_for_each_entry(cs, &watchdog_list, wd_list)
        cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
}

static void clocksource_resume_watchdog(void)
{
    atomic_inc(&watchdog_reset_pending);
}

static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
    unsigned long flags;

    spin_lock_irqsave(&watchdog_lock, flags);
    if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
        /* cs is a clocksource to be watched. */
        list_add(&cs->wd_list, &watchdog_list);
        cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
    } else {
        /* cs is a watchdog. */
        if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
            cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
        /* Pick the best watchdog. */
        if (!watchdog || cs->rating > watchdog->rating) {
            watchdog = cs;
            /* Reset watchdog cycles */
            clocksource_reset_watchdog();
        }
    }
    /* Check if the watchdog timer needs to be started. */
    clocksource_start_watchdog();
    spin_unlock_irqrestore(&watchdog_lock, flags);
}

static void clocksource_dequeue_watchdog(struct clocksource *cs)
{
    struct clocksource *tmp;
    unsigned long flags;

    spin_lock_irqsave(&watchdog_lock, flags);
    if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
        /* cs is a watched clocksource. */
        list_del_init(&cs->wd_list);
    } else if (cs == watchdog) {
        /* Reset watchdog cycles */
        clocksource_reset_watchdog();
        /* Current watchdog is removed. Find an alternative. */
        watchdog = NULL;
        list_for_each_entry(tmp, &clocksource_list, list) {
            if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
                continue;
            if (!watchdog || tmp->rating > watchdog->rating)
                watchdog = tmp;
        }
    }
    cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
    /* Check if the watchdog timer needs to be stopped. */
    clocksource_stop_watchdog();
    spin_unlock_irqrestore(&watchdog_lock, flags);
}

static int clocksource_watchdog_kthread(void *data)
{
    struct clocksource *cs, *tmp;
    unsigned long flags;
    LIST_HEAD(unstable);

    mutex_lock(&clocksource_mutex);
    spin_lock_irqsave(&watchdog_lock, flags);
    list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
        if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
            list_del_init(&cs->wd_list);
            list_add(&cs->wd_list, &unstable);
        }
    /* Check if the watchdog timer needs to be stopped. */
    clocksource_stop_watchdog();
    spin_unlock_irqrestore(&watchdog_lock, flags);

    /* Needs to be done outside of watchdog lock */
    list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
        list_del_init(&cs->wd_list);
        __clocksource_change_rating(cs, 0);
    }
    mutex_unlock(&clocksource_mutex);
    return 0;
}

#else /* CONFIG_CLOCKSOURCE_WATCHDOG */

static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
    if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
        cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}

static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
static inline int clocksource_watchdog_kthread(void *data) { return 0; }

#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */

void clocksource_suspend(void)
{
    struct clocksource *cs;

    list_for_each_entry_reverse(cs, &clocksource_list, list)
        if (cs->suspend)
            cs->suspend(cs);
}

void clocksource_resume(void)
{
    struct clocksource *cs;

    list_for_each_entry(cs, &clocksource_list, list)
        if (cs->resume)
            cs->resume(cs);

    clocksource_resume_watchdog();
}

void clocksource_touch_watchdog(void)
{
    clocksource_resume_watchdog();
}

static u32 clocksource_max_adjustment(struct clocksource *cs)
{
    u64 ret;
    /*
     * We won't try to correct for more than 11% adjustments (110,000 ppm),
     */
    ret = (u64)cs->mult * 11;
    do_div(ret,100);
    return (u32)ret;
}

static u64 clocksource_max_deferment(struct clocksource *cs)
{
    u64 max_nsecs, max_cycles;

    /*
     * Calculate the maximum number of cycles that we can pass to the
     * cyc2ns function without overflowing a 64-bit signed result. The
     * maximum number of cycles is equal to ULLONG_MAX/(cs->mult+cs->maxadj)
     * which is equivalent to the below.
     * max_cycles < (2^63)/(cs->mult + cs->maxadj)
     * max_cycles < 2^(log2((2^63)/(cs->mult + cs->maxadj)))
     * max_cycles < 2^(log2(2^63) - log2(cs->mult + cs->maxadj))
     * max_cycles < 2^(63 - log2(cs->mult + cs->maxadj))
     * max_cycles < 1 << (63 - log2(cs->mult + cs->maxadj))
     * Please note that we add 1 to the result of the log2 to account for
     * any rounding errors, ensure the above inequality is satisfied and
     * no overflow will occur.
     */
    max_cycles = 1ULL << (63 - (ilog2(cs->mult + cs->maxadj) + 1));

    /*
     * The actual maximum number of cycles we can defer the clocksource is
     * determined by the minimum of max_cycles and cs->mask.
     * Note: Here we subtract the maxadj to make sure we don't sleep for
     * too long if there's a large negative adjustment.
     */
    max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
    max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult - cs->maxadj,
                    cs->shift);

    /*
     * To ensure that the clocksource does not wrap whilst we are idle,
     * limit the time the clocksource can be deferred by 12.5%. Please
     * note a margin of 12.5% is used because this can be computed with
     * a shift, versus say 10% which would require division.
     */
    return max_nsecs - (max_nsecs >> 3);
}

#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET

static void clocksource_select(void)
{
    struct clocksource *best, *cs;

    if (!finished_booting || list_empty(&clocksource_list))
        return;
    /* First clocksource on the list has the best rating. */
    best = list_first_entry(&clocksource_list, struct clocksource, list);
    /* Check for the override clocksource. */
    list_for_each_entry(cs, &clocksource_list, list) {
        if (strcmp(cs->name, override_name) != 0)
            continue;
        /*
         * Check to make sure we don't switch to a non-highres
         * capable clocksource if the tick code is in oneshot
         * mode (highres or nohz)
         */
        if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
            tick_oneshot_mode_active()) {
            /* Override clocksource cannot be used. */
            printk(KERN_WARNING "Override clocksource %s is not "
                   "HRT compatible. Cannot switch while in "
                   "HRT/NOHZ mode\n", cs->name);
            override_name[0] = 0;
        } else
            /* Override clocksource can be used. */
            best = cs;
        break;
    }
    if (curr_clocksource != best) {
        printk(KERN_INFO "Switching to clocksource %s\n", best->name);
        curr_clocksource = best;
        timekeeping_notify(curr_clocksource);
    }
}

#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */

static inline void clocksource_select(void) { }

#endif

/*
 * clocksource_done_booting - Called near the end of core bootup
 *
 * Hack to avoid lots of clocksource churn at boot time.
 * We use fs_initcall because we want this to start before
 * device_initcall but after subsys_initcall.
 */
static int __init clocksource_done_booting(void)
{
    mutex_lock(&clocksource_mutex);
    curr_clocksource = clocksource_default_clock();
    mutex_unlock(&clocksource_mutex);

    finished_booting = 1;

    /*
     * Run the watchdog first to eliminate unstable clock sources
     */
    clocksource_watchdog_kthread(NULL);

    mutex_lock(&clocksource_mutex);
    clocksource_select();
    mutex_unlock(&clocksource_mutex);
    return 0;
}
fs_initcall(clocksource_done_booting);

/*
 * Enqueue the clocksource sorted by rating
 */
static void clocksource_enqueue(struct clocksource *cs)
{
    struct list_head *entry = &clocksource_list;
    struct clocksource *tmp;

    list_for_each_entry(tmp, &clocksource_list, list)
        /* Keep track of the place, where to insert */
        if (tmp->rating >= cs->rating)
            entry = &tmp->list;
    list_add(&cs->list, entry);
}

void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
{
    u64 sec;
    /*
     * Calc the maximum number of seconds which we can run before
     * wrapping around. For clocksources which have a mask > 32bit
     * we need to limit the max sleep time to have a good
     * conversion precision. 10 minutes is still a reasonable
     * amount. That results in a shift value of 24 for a
     * clocksource with mask >= 40bit and f >= 4GHz. That maps to
     * ~ 0.06ppm granularity for NTP. We apply the same 12.5%
     * margin as we do in clocksource_max_deferment()
     */
    sec = (cs->mask - (cs->mask >> 3));
    do_div(sec, freq);
    do_div(sec, scale);
    if (!sec)
        sec = 1;
    else if (sec > 600 && cs->mask > UINT_MAX)
        sec = 600;

    clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
                   NSEC_PER_SEC / scale, sec * scale);

    /*
     * for clocksources that have large mults, to avoid overflow.
     * Since mult may be adjusted by ntp, add an safety extra margin
     *
     */
    cs->maxadj = clocksource_max_adjustment(cs);
    while ((cs->mult + cs->maxadj < cs->mult)
        || (cs->mult - cs->maxadj > cs->mult)) {
        cs->mult >>= 1;
        cs->shift--;
        cs->maxadj = clocksource_max_adjustment(cs);
    }

    cs->max_idle_ns = clocksource_max_deferment(cs);
}
EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);

int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
{

    /* Initialize mult/shift and max_idle_ns */
    __clocksource_updatefreq_scale(cs, scale, freq);

    /* Add clocksource to the clcoksource list */
    mutex_lock(&clocksource_mutex);
    clocksource_enqueue(cs);
    clocksource_enqueue_watchdog(cs);
    clocksource_select();
    mutex_unlock(&clocksource_mutex);
    return 0;
}
EXPORT_SYMBOL_GPL(__clocksource_register_scale);


int clocksource_register(struct clocksource *cs)
{
    /* calculate max adjustment for given mult/shift */
    cs->maxadj = clocksource_max_adjustment(cs);
    WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
        "Clocksource %s might overflow on 11%% adjustment\n",
        cs->name);

    /* calculate max idle time permitted for this clocksource */
    cs->max_idle_ns = clocksource_max_deferment(cs);

    mutex_lock(&clocksource_mutex);
    clocksource_enqueue(cs);
    clocksource_enqueue_watchdog(cs);
    clocksource_select();
    mutex_unlock(&clocksource_mutex);
    return 0;
}
EXPORT_SYMBOL(clocksource_register);

static void __clocksource_change_rating(struct clocksource *cs, int rating)
{
    list_del(&cs->list);
    cs->rating = rating;
    clocksource_enqueue(cs);
    clocksource_select();
}

void clocksource_change_rating(struct clocksource *cs, int rating)
{
    mutex_lock(&clocksource_mutex);
    __clocksource_change_rating(cs, rating);
    mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_change_rating);

void clocksource_unregister(struct clocksource *cs)
{
    mutex_lock(&clocksource_mutex);
    clocksource_dequeue_watchdog(cs);
    list_del(&cs->list);
    clocksource_select();
    mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_unregister);

#ifdef CONFIG_SYSFS

static ssize_t
sysfs_show_current_clocksources(struct device *dev,
                struct device_attribute *attr, char *buf)
{
    ssize_t count = 0;

    mutex_lock(&clocksource_mutex);
    count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
    mutex_unlock(&clocksource_mutex);

    return count;
}

static ssize_t sysfs_override_clocksource(struct device *dev,
                      struct device_attribute *attr,
                      const char *buf, size_t count)
{
    size_t ret = count;

    /* strings from sysfs write are not 0 terminated! */
    if (count >= sizeof(override_name))
        return -EINVAL;

    /* strip of \n: */
    if (buf[count-1] == '\n')
        count--;

    mutex_lock(&clocksource_mutex);

    if (count > 0)
        memcpy(override_name, buf, count);
    override_name[count] = 0;
    clocksource_select();

    mutex_unlock(&clocksource_mutex);

    return ret;
}

static ssize_t
sysfs_show_available_clocksources(struct device *dev,
                  struct device_attribute *attr,
                  char *buf)
{
    struct clocksource *src;
    ssize_t count = 0;

    mutex_lock(&clocksource_mutex);
    list_for_each_entry(src, &clocksource_list, list) {
        /*
         * Don't show non-HRES clocksource if the tick code is
         * in one shot mode (highres=on or nohz=on)
         */
        if (!tick_oneshot_mode_active() ||
            (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
            count += snprintf(buf + count,
                  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
                  "%s ", src->name);
    }
    mutex_unlock(&clocksource_mutex);

    count += snprintf(buf + count,
              max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");

    return count;
}

/*
 * Sysfs setup bits:
 */
static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
           sysfs_override_clocksource);

static DEVICE_ATTR(available_clocksource, 0444,
           sysfs_show_available_clocksources, NULL);

static struct bus_type clocksource_subsys = {
    .name = "clocksource",
    .dev_name = "clocksource",
};

static struct device device_clocksource = {
    .id = 0,
    .bus    = &clocksource_subsys,
};

static int __init init_clocksource_sysfs(void)
{
    int error = subsys_system_register(&clocksource_subsys, NULL);

    if (!error)
        error = device_register(&device_clocksource);
    if (!error)
        error = device_create_file(
                &device_clocksource,
                &dev_attr_current_clocksource);
    if (!error)
        error = device_create_file(
                &device_clocksource,
                &dev_attr_available_clocksource);
    return error;
}

device_initcall(init_clocksource_sysfs);
#endif /* CONFIG_SYSFS */

static int __init boot_override_clocksource(char* str)
{
    mutex_lock(&clocksource_mutex);
    if (str)
        strlcpy(override_name, str, sizeof(override_name));
    mutex_unlock(&clocksource_mutex);
    return 1;
}

__setup("clocksource=", boot_override_clocksource);

static int __init boot_override_clock(char* str)
{
    if (!strcmp(str, "pmtmr")) {
        printk("Warning: clock=pmtmr is deprecated. "
            "Use clocksource=acpi_pm.\n");
        return boot_override_clocksource("acpi_pm");
    }
    printk("Warning! clock= boot option is deprecated. "
        "Use clocksource=xyz\n");
    return boot_override_clocksource(str);
}

__setup("clock=", boot_override_clock);