tick-common.c

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/*
 * linux/kernel/time/tick-common.c
 *
 * This file contains the base functions to manage periodic tick
 * related events.
 *
 * Copyright(C) 2005-2006, Thomas Gleixner <[email protected]>
 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
 * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
 *
 * This code is licenced under the GPL version 2. For details see
 * kernel-base/COPYING.
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/sched.h>

#include <asm/irq_regs.h>

#include "tick-internal.h"

/*
 * Tick devices
 */
DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
/*
 * Tick next event: keeps track of the tick time
 */
ktime_t tick_next_period;
ktime_t tick_period;
int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
static DEFINE_RAW_SPINLOCK(tick_device_lock);

/*
 * Debugging: see timer_list.c
 */
struct tick_device *tick_get_device(int cpu)
{
    return &per_cpu(tick_cpu_device, cpu);
}

int tick_is_oneshot_available(void)
{
    struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);

    if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
        return 0;
    if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
        return 1;
    return tick_broadcast_oneshot_available();
}

/*
 * Periodic tick
 */
static void tick_periodic(int cpu)
{
    if (tick_do_timer_cpu == cpu) {
        write_seqlock(&xtime_lock);

        /* Keep track of the next tick event */
        tick_next_period = ktime_add(tick_next_period, tick_period);

        do_timer(1);
        write_sequnlock(&xtime_lock);
    }

    update_process_times(user_mode(get_irq_regs()));
    profile_tick(CPU_PROFILING);
}

/*
 * Event handler for periodic ticks
 */
void tick_handle_periodic(struct clock_event_device *dev)
{
    int cpu = smp_processor_id();
    ktime_t next;

    tick_periodic(cpu);

    if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
        return;
    /*
     * Setup the next period for devices, which do not have
     * periodic mode:
     */
    next = ktime_add(dev->next_event, tick_period);
    for (;;) {
        if (!clockevents_program_event(dev, next, false))
            return;
        /*
         * Have to be careful here. If we're in oneshot mode,
         * before we call tick_periodic() in a loop, we need
         * to be sure we're using a real hardware clocksource.
         * Otherwise we could get trapped in an infinite
         * loop, as the tick_periodic() increments jiffies,
         * when then will increment time, posibly causing
         * the loop to trigger again and again.
         */
        if (timekeeping_valid_for_hres())
            tick_periodic(cpu);
        next = ktime_add(next, tick_period);
    }
}

/*
 * Setup the device for a periodic tick
 */
void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
{
    tick_set_periodic_handler(dev, broadcast);

    /* Broadcast setup ? */
    if (!tick_device_is_functional(dev))
        return;

    if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
        !tick_broadcast_oneshot_active()) {
        clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
    } else {
        unsigned long seq;
        ktime_t next;

        do {
            seq = read_seqbegin(&xtime_lock);
            next = tick_next_period;
        } while (read_seqretry(&xtime_lock, seq));

        clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);

        for (;;) {
            if (!clockevents_program_event(dev, next, false))
                return;
            next = ktime_add(next, tick_period);
        }
    }
}

/*
 * Setup the tick device
 */
static void tick_setup_device(struct tick_device *td,
                  struct clock_event_device *newdev, int cpu,
                  const struct cpumask *cpumask)
{
    ktime_t next_event;
    void (*handler)(struct clock_event_device *) = NULL;

    /*
     * First device setup ?
     */
    if (!td->evtdev) {
        /*
         * If no cpu took the do_timer update, assign it to
         * this cpu:
         */
        if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
            tick_do_timer_cpu = cpu;
            tick_next_period = ktime_get();
            tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
        }

        /*
         * Startup in periodic mode first.
         */
        td->mode = TICKDEV_MODE_PERIODIC;
    } else {
        handler = td->evtdev->event_handler;
        next_event = td->evtdev->next_event;
        td->evtdev->event_handler = clockevents_handle_noop;
    }

    td->evtdev = newdev;

    /*
     * When the device is not per cpu, pin the interrupt to the
     * current cpu:
     */
    if (!cpumask_equal(newdev->cpumask, cpumask))
        irq_set_affinity(newdev->irq, cpumask);

    /*
     * When global broadcasting is active, check if the current
     * device is registered as a placeholder for broadcast mode.
     * This allows us to handle this x86 misfeature in a generic
     * way.
     */
    if (tick_device_uses_broadcast(newdev, cpu))
        return;

    if (td->mode == TICKDEV_MODE_PERIODIC)
        tick_setup_periodic(newdev, 0);
    else
        tick_setup_oneshot(newdev, handler, next_event);
}

/*
 * Check, if the new registered device should be used.
 */
static int tick_check_new_device(struct clock_event_device *newdev)
{
    struct clock_event_device *curdev;
    struct tick_device *td;
    int cpu, ret = NOTIFY_OK;
    unsigned long flags;

    raw_spin_lock_irqsave(&tick_device_lock, flags);

    cpu = smp_processor_id();
    if (!cpumask_test_cpu(cpu, newdev->cpumask))
        goto out_bc;

    td = &per_cpu(tick_cpu_device, cpu);
    curdev = td->evtdev;

    /* cpu local device ? */
    if (!cpumask_equal(newdev->cpumask, cpumask_of(cpu))) {

        /*
         * If the cpu affinity of the device interrupt can not
         * be set, ignore it.
         */
        if (!irq_can_set_affinity(newdev->irq))
            goto out_bc;

        /*
         * If we have a cpu local device already, do not replace it
         * by a non cpu local device
         */
        if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
            goto out_bc;
    }

    /*
     * If we have an active device, then check the rating and the oneshot
     * feature.
     */
    if (curdev) {
        /*
         * Prefer one shot capable devices !
         */
        if ((curdev->features & CLOCK_EVT_FEAT_ONESHOT) &&
            !(newdev->features & CLOCK_EVT_FEAT_ONESHOT))
            goto out_bc;
        /*
         * Check the rating
         */
        if (curdev->rating >= newdev->rating)
            goto out_bc;
    }

    /*
     * Replace the eventually existing device by the new
     * device. If the current device is the broadcast device, do
     * not give it back to the clockevents layer !
     */
    if (tick_is_broadcast_device(curdev)) {
        clockevents_shutdown(curdev);
        curdev = NULL;
    }
    clockevents_exchange_device(curdev, newdev);
    tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
    if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
        tick_oneshot_notify();

    raw_spin_unlock_irqrestore(&tick_device_lock, flags);
    return NOTIFY_STOP;

out_bc:
    /*
     * Can the new device be used as a broadcast device ?
     */
    if (tick_check_broadcast_device(newdev))
        ret = NOTIFY_STOP;

    raw_spin_unlock_irqrestore(&tick_device_lock, flags);

    return ret;
}

/*
 * Transfer the do_timer job away from a dying cpu.
 *
 * Called with interrupts disabled.
 */
static void tick_handover_do_timer(int *cpup)
{
    if (*cpup == tick_do_timer_cpu) {
        int cpu = cpumask_first(cpu_online_mask);

        tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
            TICK_DO_TIMER_NONE;
    }
}

/*
 * Shutdown an event device on a given cpu:
 *
 * This is called on a life CPU, when a CPU is dead. So we cannot
 * access the hardware device itself.
 * We just set the mode and remove it from the lists.
 */
static void tick_shutdown(unsigned int *cpup)
{
    struct tick_device *td = &per_cpu(tick_cpu_device, *cpup);
    struct clock_event_device *dev = td->evtdev;
    unsigned long flags;

    raw_spin_lock_irqsave(&tick_device_lock, flags);
    td->mode = TICKDEV_MODE_PERIODIC;
    if (dev) {
        /*
         * Prevent that the clock events layer tries to call
         * the set mode function!
         */
        dev->mode = CLOCK_EVT_MODE_UNUSED;
        clockevents_exchange_device(dev, NULL);
        td->evtdev = NULL;
    }
    raw_spin_unlock_irqrestore(&tick_device_lock, flags);
}

static void tick_suspend(void)
{
    struct tick_device *td = &__get_cpu_var(tick_cpu_device);
    unsigned long flags;

    raw_spin_lock_irqsave(&tick_device_lock, flags);
    clockevents_shutdown(td->evtdev);
    raw_spin_unlock_irqrestore(&tick_device_lock, flags);
}

static void tick_resume(void)
{
    struct tick_device *td = &__get_cpu_var(tick_cpu_device);
    unsigned long flags;
    int broadcast = tick_resume_broadcast();

    raw_spin_lock_irqsave(&tick_device_lock, flags);
    clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_RESUME);

    if (!broadcast) {
        if (td->mode == TICKDEV_MODE_PERIODIC)
            tick_setup_periodic(td->evtdev, 0);
        else
            tick_resume_oneshot();
    }
    raw_spin_unlock_irqrestore(&tick_device_lock, flags);
}

/*
 * Notification about clock event devices
 */
static int tick_notify(struct notifier_block *nb, unsigned long reason,
                   void *dev)
{
    switch (reason) {

    case CLOCK_EVT_NOTIFY_ADD:
        return tick_check_new_device(dev);

    case CLOCK_EVT_NOTIFY_BROADCAST_ON:
    case CLOCK_EVT_NOTIFY_BROADCAST_OFF:
    case CLOCK_EVT_NOTIFY_BROADCAST_FORCE:
        tick_broadcast_on_off(reason, dev);
        break;

    case CLOCK_EVT_NOTIFY_BROADCAST_ENTER:
    case CLOCK_EVT_NOTIFY_BROADCAST_EXIT:
        tick_broadcast_oneshot_control(reason);
        break;

    case CLOCK_EVT_NOTIFY_CPU_DYING:
        tick_handover_do_timer(dev);
        break;

    case CLOCK_EVT_NOTIFY_CPU_DEAD:
        tick_shutdown_broadcast_oneshot(dev);
        tick_shutdown_broadcast(dev);
        tick_shutdown(dev);
        break;

    case CLOCK_EVT_NOTIFY_SUSPEND:
        tick_suspend();
        tick_suspend_broadcast();
        break;

    case CLOCK_EVT_NOTIFY_RESUME:
        tick_resume();
        break;

    default:
        break;
    }

    return NOTIFY_OK;
}

static struct notifier_block tick_notifier = {
    .notifier_call = tick_notify,
};

void __init tick_init(void)
{
    clockevents_register_notifier(&tick_notifier);
}