clockevents: Use helpers to check the state of a clockevent device

[linux-2.6/btrfs-unstable.git] / kernel / time / tick-broadcast.c

/*
 * linux/kernel/time/tick-broadcast.c
 *
 * This file contains functions which emulate a local clock-event
 * device via a broadcast event source.
 *
 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
 * 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 <linux/smp.h>
#include <linux/module.h>

#include "tick-internal.h"

/*
 * Broadcast support for broken x86 hardware, where the local apic
 * timer stops in C3 state.
 */

static struct tick_device tick_broadcast_device;
static cpumask_var_t tick_broadcast_mask;
static cpumask_var_t tick_broadcast_on;
static cpumask_var_t tmpmask;
static DEFINE_RAW_SPINLOCK(tick_broadcast_lock);
static int tick_broadcast_forced;

#ifdef CONFIG_TICK_ONESHOT
static void tick_broadcast_clear_oneshot(int cpu);
static void tick_resume_broadcast_oneshot(struct clock_event_device *bc);
#else
static inline void tick_broadcast_clear_oneshot(int cpu) { }
static inline void tick_resume_broadcast_oneshot(struct clock_event_device *bc) { }
#endif

/*
 * Debugging: see timer_list.c
 */
struct tick_device *tick_get_broadcast_device(void)
{
        return &tick_broadcast_device;
}

struct cpumask *tick_get_broadcast_mask(void)
{
        return tick_broadcast_mask;
}

/*
 * Start the device in periodic mode
 */
static void tick_broadcast_start_periodic(struct clock_event_device *bc)
{
        if (bc)
                tick_setup_periodic(bc, 1);
}

/*
 * Check, if the device can be utilized as broadcast device:
 */
static bool tick_check_broadcast_device(struct clock_event_device *curdev,
                                        struct clock_event_device *newdev)
{
        if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) ||
            (newdev->features & CLOCK_EVT_FEAT_PERCPU) ||
            (newdev->features & CLOCK_EVT_FEAT_C3STOP))
                return false;

        if (tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT &&
            !(newdev->features & CLOCK_EVT_FEAT_ONESHOT))
                return false;

        return !curdev || newdev->rating > curdev->rating;
}

/*
 * Conditionally install/replace broadcast device
 */
void tick_install_broadcast_device(struct clock_event_device *dev)
{
        struct clock_event_device *cur = tick_broadcast_device.evtdev;

        if (!tick_check_broadcast_device(cur, dev))
                return;

        if (!try_module_get(dev->owner))
                return;

        clockevents_exchange_device(cur, dev);
        if (cur)
                cur->event_handler = clockevents_handle_noop;
        tick_broadcast_device.evtdev = dev;
        if (!cpumask_empty(tick_broadcast_mask))
                tick_broadcast_start_periodic(dev);
        /*
         * Inform all cpus about this. We might be in a situation
         * where we did not switch to oneshot mode because the per cpu
         * devices are affected by CLOCK_EVT_FEAT_C3STOP and the lack
         * of a oneshot capable broadcast device. Without that
         * notification the systems stays stuck in periodic mode
         * forever.
         */
        if (dev->features & CLOCK_EVT_FEAT_ONESHOT)
                tick_clock_notify();
}

/*
 * Check, if the device is the broadcast device
 */
int tick_is_broadcast_device(struct clock_event_device *dev)
{
        return (dev && tick_broadcast_device.evtdev == dev);
}

int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq)
{
        int ret = -ENODEV;

        if (tick_is_broadcast_device(dev)) {
                raw_spin_lock(&tick_broadcast_lock);
                ret = __clockevents_update_freq(dev, freq);
                raw_spin_unlock(&tick_broadcast_lock);
        }
        return ret;
}


static void err_broadcast(const struct cpumask *mask)
{
        pr_crit_once("Failed to broadcast timer tick. Some CPUs may be unresponsive.\n");
}

static void tick_device_setup_broadcast_func(struct clock_event_device *dev)
{
        if (!dev->broadcast)
                dev->broadcast = tick_broadcast;
        if (!dev->broadcast) {
                pr_warn_once("%s depends on broadcast, but no broadcast function available\n",
                             dev->name);
                dev->broadcast = err_broadcast;
        }
}

/*
 * Check, if the device is disfunctional and a place holder, which
 * needs to be handled by the broadcast device.
 */
int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu)
{
        struct clock_event_device *bc = tick_broadcast_device.evtdev;
        unsigned long flags;
        int ret;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);

        /*
         * Devices might be registered with both periodic and oneshot
         * mode disabled. This signals, that the device needs to be
         * operated from the broadcast device and is a placeholder for
         * the cpu local device.
         */
        if (!tick_device_is_functional(dev)) {
                dev->event_handler = tick_handle_periodic;
                tick_device_setup_broadcast_func(dev);
                cpumask_set_cpu(cpu, tick_broadcast_mask);
                if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
                        tick_broadcast_start_periodic(bc);
                else
                        tick_broadcast_setup_oneshot(bc);
                ret = 1;
        } else {
                /*
                 * Clear the broadcast bit for this cpu if the
                 * device is not power state affected.
                 */
                if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
                        cpumask_clear_cpu(cpu, tick_broadcast_mask);
                else
                        tick_device_setup_broadcast_func(dev);

                /*
                 * Clear the broadcast bit if the CPU is not in
                 * periodic broadcast on state.
                 */
                if (!cpumask_test_cpu(cpu, tick_broadcast_on))
                        cpumask_clear_cpu(cpu, tick_broadcast_mask);

                switch (tick_broadcast_device.mode) {
                case TICKDEV_MODE_ONESHOT:
                        /*
                         * If the system is in oneshot mode we can
                         * unconditionally clear the oneshot mask bit,
                         * because the CPU is running and therefore
                         * not in an idle state which causes the power
                         * state affected device to stop. Let the
                         * caller initialize the device.
                         */
                        tick_broadcast_clear_oneshot(cpu);
                        ret = 0;
                        break;

                case TICKDEV_MODE_PERIODIC:
                        /*
                         * If the system is in periodic mode, check
                         * whether the broadcast device can be
                         * switched off now.
                         */
                        if (cpumask_empty(tick_broadcast_mask) && bc)
                                clockevents_shutdown(bc);
                        /*
                         * If we kept the cpu in the broadcast mask,
                         * tell the caller to leave the per cpu device
                         * in shutdown state. The periodic interrupt
                         * is delivered by the broadcast device.
                         */
                        ret = cpumask_test_cpu(cpu, tick_broadcast_mask);
                        break;
                default:
                        /* Nothing to do */
                        ret = 0;
                        break;
                }
        }
        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
        return ret;
}

#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
int tick_receive_broadcast(void)
{
        struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
        struct clock_event_device *evt = td->evtdev;

        if (!evt)
                return -ENODEV;

        if (!evt->event_handler)
                return -EINVAL;

        evt->event_handler(evt);
        return 0;
}
#endif

/*
 * Broadcast the event to the cpus, which are set in the mask (mangled).
 */
static bool tick_do_broadcast(struct cpumask *mask)
{
        int cpu = smp_processor_id();
        struct tick_device *td;
        bool local = false;

        /*
         * Check, if the current cpu is in the mask
         */
        if (cpumask_test_cpu(cpu, mask)) {
                cpumask_clear_cpu(cpu, mask);
                local = true;
        }

        if (!cpumask_empty(mask)) {
                /*
                 * It might be necessary to actually check whether the devices
                 * have different broadcast functions. For now, just use the
                 * one of the first device. This works as long as we have this
                 * misfeature only on x86 (lapic)
                 */
                td = &per_cpu(tick_cpu_device, cpumask_first(mask));
                td->evtdev->broadcast(mask);
        }
        return local;
}

/*
 * Periodic broadcast:
 * - invoke the broadcast handlers
 */
static bool tick_do_periodic_broadcast(void)
{
        cpumask_and(tmpmask, cpu_online_mask, tick_broadcast_mask);
        return tick_do_broadcast(tmpmask);
}

/*
 * Event handler for periodic broadcast ticks
 */
static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
{
        struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
        bool bc_local;

        raw_spin_lock(&tick_broadcast_lock);
        bc_local = tick_do_periodic_broadcast();

        if (clockevent_state_oneshot(dev)) {
                ktime_t next = ktime_add(dev->next_event, tick_period);

                clockevents_program_event(dev, next, true);
        }
        raw_spin_unlock(&tick_broadcast_lock);

        /*
         * We run the handler of the local cpu after dropping
         * tick_broadcast_lock because the handler might deadlock when
         * trying to switch to oneshot mode.
         */
        if (bc_local)
                td->evtdev->event_handler(td->evtdev);
}

/**
 * tick_broadcast_control - Enable/disable or force broadcast mode
 * @mode:       The selected broadcast mode
 *
 * Called when the system enters a state where affected tick devices
 * might stop. Note: TICK_BROADCAST_FORCE cannot be undone.
 *
 * Called with interrupts disabled, so clockevents_lock is not
 * required here because the local clock event device cannot go away
 * under us.
 */
void tick_broadcast_control(enum tick_broadcast_mode mode)
{
        struct clock_event_device *bc, *dev;
        struct tick_device *td;
        int cpu, bc_stopped;

        td = this_cpu_ptr(&tick_cpu_device);
        dev = td->evtdev;

        /*
         * Is the device not affected by the powerstate ?
         */
        if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP))
                return;

        if (!tick_device_is_functional(dev))
                return;

        raw_spin_lock(&tick_broadcast_lock);
        cpu = smp_processor_id();
        bc = tick_broadcast_device.evtdev;
        bc_stopped = cpumask_empty(tick_broadcast_mask);

        switch (mode) {
        case TICK_BROADCAST_FORCE:
                tick_broadcast_forced = 1;
        case TICK_BROADCAST_ON:
                cpumask_set_cpu(cpu, tick_broadcast_on);
                if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_mask)) {
                        if (tick_broadcast_device.mode ==
                            TICKDEV_MODE_PERIODIC)
                                clockevents_shutdown(dev);
                }
                break;

        case TICK_BROADCAST_OFF:
                if (tick_broadcast_forced)
                        break;
                cpumask_clear_cpu(cpu, tick_broadcast_on);
                if (!tick_device_is_functional(dev))
                        break;
                if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_mask)) {
                        if (tick_broadcast_device.mode ==
                            TICKDEV_MODE_PERIODIC)
                                tick_setup_periodic(dev, 0);
                }
                break;
        }

        if (cpumask_empty(tick_broadcast_mask)) {
                if (!bc_stopped)
                        clockevents_shutdown(bc);
        } else if (bc_stopped) {
                if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
                        tick_broadcast_start_periodic(bc);
                else
                        tick_broadcast_setup_oneshot(bc);
        }
        raw_spin_unlock(&tick_broadcast_lock);
}
EXPORT_SYMBOL_GPL(tick_broadcast_control);

/*
 * Set the periodic handler depending on broadcast on/off
 */
void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast)
{
        if (!broadcast)
                dev->event_handler = tick_handle_periodic;
        else
                dev->event_handler = tick_handle_periodic_broadcast;
}

#ifdef CONFIG_HOTPLUG_CPU
/*
 * Remove a CPU from broadcasting
 */
void tick_shutdown_broadcast(unsigned int cpu)
{
        struct clock_event_device *bc;
        unsigned long flags;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);

        bc = tick_broadcast_device.evtdev;
        cpumask_clear_cpu(cpu, tick_broadcast_mask);
        cpumask_clear_cpu(cpu, tick_broadcast_on);

        if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) {
                if (bc && cpumask_empty(tick_broadcast_mask))
                        clockevents_shutdown(bc);
        }

        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}
#endif

void tick_suspend_broadcast(void)
{
        struct clock_event_device *bc;
        unsigned long flags;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);

        bc = tick_broadcast_device.evtdev;
        if (bc)
                clockevents_shutdown(bc);

        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}

/*
 * This is called from tick_resume_local() on a resuming CPU. That's
 * called from the core resume function, tick_unfreeze() and the magic XEN
 * resume hackery.
 *
 * In none of these cases the broadcast device mode can change and the
 * bit of the resuming CPU in the broadcast mask is safe as well.
 */
bool tick_resume_check_broadcast(void)
{
        if (tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT)
                return false;
        else
                return cpumask_test_cpu(smp_processor_id(), tick_broadcast_mask);
}

void tick_resume_broadcast(void)
{
        struct clock_event_device *bc;
        unsigned long flags;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);

        bc = tick_broadcast_device.evtdev;

        if (bc) {
                clockevents_tick_resume(bc);

                switch (tick_broadcast_device.mode) {
                case TICKDEV_MODE_PERIODIC:
                        if (!cpumask_empty(tick_broadcast_mask))
                                tick_broadcast_start_periodic(bc);
                        break;
                case TICKDEV_MODE_ONESHOT:
                        if (!cpumask_empty(tick_broadcast_mask))
                                tick_resume_broadcast_oneshot(bc);
                        break;
                }
        }
        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}

#ifdef CONFIG_TICK_ONESHOT

static cpumask_var_t tick_broadcast_oneshot_mask;
static cpumask_var_t tick_broadcast_pending_mask;
static cpumask_var_t tick_broadcast_force_mask;

/*
 * Exposed for debugging: see timer_list.c
 */
struct cpumask *tick_get_broadcast_oneshot_mask(void)
{
        return tick_broadcast_oneshot_mask;
}

/*
 * Called before going idle with interrupts disabled. Checks whether a
 * broadcast event from the other core is about to happen. We detected
 * that in tick_broadcast_oneshot_control(). The callsite can use this
 * to avoid a deep idle transition as we are about to get the
 * broadcast IPI right away.
 */
int tick_check_broadcast_expired(void)
{
        return cpumask_test_cpu(smp_processor_id(), tick_broadcast_force_mask);
}

/*
 * Set broadcast interrupt affinity
 */
static void tick_broadcast_set_affinity(struct clock_event_device *bc,
                                        const struct cpumask *cpumask)
{
        if (!(bc->features & CLOCK_EVT_FEAT_DYNIRQ))
                return;

        if (cpumask_equal(bc->cpumask, cpumask))
                return;

        bc->cpumask = cpumask;
        irq_set_affinity(bc->irq, bc->cpumask);
}

static void tick_broadcast_set_event(struct clock_event_device *bc, int cpu,
                                     ktime_t expires)
{
        if (!clockevent_state_oneshot(bc))
                clockevents_set_state(bc, CLOCK_EVT_STATE_ONESHOT);

        clockevents_program_event(bc, expires, 1);
        tick_broadcast_set_affinity(bc, cpumask_of(cpu));
}

static void tick_resume_broadcast_oneshot(struct clock_event_device *bc)
{
        clockevents_set_state(bc, CLOCK_EVT_STATE_ONESHOT);
}

/*
 * Called from irq_enter() when idle was interrupted to reenable the
 * per cpu device.
 */
void tick_check_oneshot_broadcast_this_cpu(void)
{
        if (cpumask_test_cpu(smp_processor_id(), tick_broadcast_oneshot_mask)) {
                struct tick_device *td = this_cpu_ptr(&tick_cpu_device);

                /*
                 * We might be in the middle of switching over from
                 * periodic to oneshot. If the CPU has not yet
                 * switched over, leave the device alone.
                 */
                if (td->mode == TICKDEV_MODE_ONESHOT) {
                        clockevents_set_state(td->evtdev,
                                              CLOCK_EVT_STATE_ONESHOT);
                }
        }
}

/*
 * Handle oneshot mode broadcasting
 */
static void tick_handle_oneshot_broadcast(struct clock_event_device *dev)
{
        struct tick_device *td;
        ktime_t now, next_event;
        int cpu, next_cpu = 0;
        bool bc_local;

        raw_spin_lock(&tick_broadcast_lock);
        dev->next_event.tv64 = KTIME_MAX;
        next_event.tv64 = KTIME_MAX;
        cpumask_clear(tmpmask);
        now = ktime_get();
        /* Find all expired events */
        for_each_cpu(cpu, tick_broadcast_oneshot_mask) {
                td = &per_cpu(tick_cpu_device, cpu);
                if (td->evtdev->next_event.tv64 <= now.tv64) {
                        cpumask_set_cpu(cpu, tmpmask);
                        /*
                         * Mark the remote cpu in the pending mask, so
                         * it can avoid reprogramming the cpu local
                         * timer in tick_broadcast_oneshot_control().
                         */
                        cpumask_set_cpu(cpu, tick_broadcast_pending_mask);
                } else if (td->evtdev->next_event.tv64 < next_event.tv64) {
                        next_event.tv64 = td->evtdev->next_event.tv64;
                        next_cpu = cpu;
                }
        }

        /*
         * Remove the current cpu from the pending mask. The event is
         * delivered immediately in tick_do_broadcast() !
         */
        cpumask_clear_cpu(smp_processor_id(), tick_broadcast_pending_mask);

        /* Take care of enforced broadcast requests */
        cpumask_or(tmpmask, tmpmask, tick_broadcast_force_mask);
        cpumask_clear(tick_broadcast_force_mask);

        /*
         * Sanity check. Catch the case where we try to broadcast to
         * offline cpus.
         */
        if (WARN_ON_ONCE(!cpumask_subset(tmpmask, cpu_online_mask)))
                cpumask_and(tmpmask, tmpmask, cpu_online_mask);

        /*
         * Wakeup the cpus which have an expired event.
         */
        bc_local = tick_do_broadcast(tmpmask);

        /*
         * Two reasons for reprogram:
         *
         * - The global event did not expire any CPU local
         * events. This happens in dyntick mode, as the maximum PIT
         * delta is quite small.
         *
         * - There are pending events on sleeping CPUs which were not
         * in the event mask
         */
        if (next_event.tv64 != KTIME_MAX)
                tick_broadcast_set_event(dev, next_cpu, next_event);

        raw_spin_unlock(&tick_broadcast_lock);

        if (bc_local) {
                td = this_cpu_ptr(&tick_cpu_device);
                td->evtdev->event_handler(td->evtdev);
        }
}

static int broadcast_needs_cpu(struct clock_event_device *bc, int cpu)
{
        if (!(bc->features & CLOCK_EVT_FEAT_HRTIMER))
                return 0;
        if (bc->next_event.tv64 == KTIME_MAX)
                return 0;
        return bc->bound_on == cpu ? -EBUSY : 0;
}

static void broadcast_shutdown_local(struct clock_event_device *bc,
                                     struct clock_event_device *dev)
{
        /*
         * For hrtimer based broadcasting we cannot shutdown the cpu
         * local device if our own event is the first one to expire or
         * if we own the broadcast timer.
         */
        if (bc->features & CLOCK_EVT_FEAT_HRTIMER) {
                if (broadcast_needs_cpu(bc, smp_processor_id()))
                        return;
                if (dev->next_event.tv64 < bc->next_event.tv64)
                        return;
        }
        clockevents_set_state(dev, CLOCK_EVT_STATE_SHUTDOWN);
}

/**
 * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
 * @state:      The target state (enter/exit)
 *
 * The system enters/leaves a state, where affected devices might stop
 * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
 *
 * Called with interrupts disabled, so clockevents_lock is not
 * required here because the local clock event device cannot go away
 * under us.
 */
int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
{
        struct clock_event_device *bc, *dev;
        struct tick_device *td;
        int cpu, ret = 0;
        ktime_t now;

        /*
         * Periodic mode does not care about the enter/exit of power
         * states
         */
        if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
                return 0;

        /*
         * We are called with preemtion disabled from the depth of the
         * idle code, so we can't be moved away.
         */
        td = this_cpu_ptr(&tick_cpu_device);
        dev = td->evtdev;

        if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
                return 0;

        raw_spin_lock(&tick_broadcast_lock);
        bc = tick_broadcast_device.evtdev;
        cpu = smp_processor_id();

        if (state == TICK_BROADCAST_ENTER) {
                if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) {
                        WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask));
                        broadcast_shutdown_local(bc, dev);
                        /*
                         * We only reprogram the broadcast timer if we
                         * did not mark ourself in the force mask and
                         * if the cpu local event is earlier than the
                         * broadcast event. If the current CPU is in
                         * the force mask, then we are going to be
                         * woken by the IPI right away.
                         */
                        if (!cpumask_test_cpu(cpu, tick_broadcast_force_mask) &&
                            dev->next_event.tv64 < bc->next_event.tv64)
                                tick_broadcast_set_event(bc, cpu, dev->next_event);
                }
                /*
                 * If the current CPU owns the hrtimer broadcast
                 * mechanism, it cannot go deep idle and we remove the
                 * CPU from the broadcast mask. We don't have to go
                 * through the EXIT path as the local timer is not
                 * shutdown.
                 */
                ret = broadcast_needs_cpu(bc, cpu);
                if (ret)
                        cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask);
        } else {
                if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) {
                        clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT);
                        /*
                         * The cpu which was handling the broadcast
                         * timer marked this cpu in the broadcast
                         * pending mask and fired the broadcast
                         * IPI. So we are going to handle the expired
                         * event anyway via the broadcast IPI
                         * handler. No need to reprogram the timer
                         * with an already expired event.
                         */
                        if (cpumask_test_and_clear_cpu(cpu,
                                       tick_broadcast_pending_mask))
                                goto out;

                        /*
                         * Bail out if there is no next event.
                         */
                        if (dev->next_event.tv64 == KTIME_MAX)
                                goto out;
                        /*
                         * If the pending bit is not set, then we are
                         * either the CPU handling the broadcast
                         * interrupt or we got woken by something else.
                         *
                         * We are not longer in the broadcast mask, so
                         * if the cpu local expiry time is already
                         * reached, we would reprogram the cpu local
                         * timer with an already expired event.
                         *
                         * This can lead to a ping-pong when we return
                         * to idle and therefor rearm the broadcast
                         * timer before the cpu local timer was able
                         * to fire. This happens because the forced
                         * reprogramming makes sure that the event
                         * will happen in the future and depending on
                         * the min_delta setting this might be far
                         * enough out that the ping-pong starts.
                         *
                         * If the cpu local next_event has expired
                         * then we know that the broadcast timer
                         * next_event has expired as well and
                         * broadcast is about to be handled. So we
                         * avoid reprogramming and enforce that the
                         * broadcast handler, which did not run yet,
                         * will invoke the cpu local handler.
                         *
                         * We cannot call the handler directly from
                         * here, because we might be in a NOHZ phase
                         * and we did not go through the irq_enter()
                         * nohz fixups.
                         */
                        now = ktime_get();
                        if (dev->next_event.tv64 <= now.tv64) {
                                cpumask_set_cpu(cpu, tick_broadcast_force_mask);
                                goto out;
                        }
                        /*
                         * We got woken by something else. Reprogram
                         * the cpu local timer device.
                         */
                        tick_program_event(dev->next_event, 1);
                }
        }
out:
        raw_spin_unlock(&tick_broadcast_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);

/*
 * Reset the one shot broadcast for a cpu
 *
 * Called with tick_broadcast_lock held
 */
static void tick_broadcast_clear_oneshot(int cpu)
{
        cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask);
        cpumask_clear_cpu(cpu, tick_broadcast_pending_mask);
}

static void tick_broadcast_init_next_event(struct cpumask *mask,
                                           ktime_t expires)
{
        struct tick_device *td;
        int cpu;

        for_each_cpu(cpu, mask) {
                td = &per_cpu(tick_cpu_device, cpu);
                if (td->evtdev)
                        td->evtdev->next_event = expires;
        }
}

/**
 * tick_broadcast_setup_oneshot - setup the broadcast device
 */
void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
{
        int cpu = smp_processor_id();

        /* Set it up only once ! */
        if (bc->event_handler != tick_handle_oneshot_broadcast) {
                int was_periodic = clockevent_state_periodic(bc);

                bc->event_handler = tick_handle_oneshot_broadcast;

                /*
                 * We must be careful here. There might be other CPUs
                 * waiting for periodic broadcast. We need to set the
                 * oneshot_mask bits for those and program the
                 * broadcast device to fire.
                 */
                cpumask_copy(tmpmask, tick_broadcast_mask);
                cpumask_clear_cpu(cpu, tmpmask);
                cpumask_or(tick_broadcast_oneshot_mask,
                           tick_broadcast_oneshot_mask, tmpmask);

                if (was_periodic && !cpumask_empty(tmpmask)) {
                        clockevents_set_state(bc, CLOCK_EVT_STATE_ONESHOT);
                        tick_broadcast_init_next_event(tmpmask,
                                                       tick_next_period);
                        tick_broadcast_set_event(bc, cpu, tick_next_period);
                } else
                        bc->next_event.tv64 = KTIME_MAX;
        } else {
                /*
                 * The first cpu which switches to oneshot mode sets
                 * the bit for all other cpus which are in the general
                 * (periodic) broadcast mask. So the bit is set and
                 * would prevent the first broadcast enter after this
                 * to program the bc device.
                 */
                tick_broadcast_clear_oneshot(cpu);
        }
}

/*
 * Select oneshot operating mode for the broadcast device
 */
void tick_broadcast_switch_to_oneshot(void)
{
        struct clock_event_device *bc;
        unsigned long flags;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);

        tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT;
        bc = tick_broadcast_device.evtdev;
        if (bc)
                tick_broadcast_setup_oneshot(bc);

        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}

#ifdef CONFIG_HOTPLUG_CPU
void hotplug_cpu__broadcast_tick_pull(int deadcpu)
{
        struct clock_event_device *bc;
        unsigned long flags;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
        bc = tick_broadcast_device.evtdev;

        if (bc && broadcast_needs_cpu(bc, deadcpu)) {
                /* This moves the broadcast assignment to this CPU: */
                clockevents_program_event(bc, bc->next_event, 1);
        }
        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}

/*
 * Remove a dead CPU from broadcasting
 */
void tick_shutdown_broadcast_oneshot(unsigned int cpu)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&tick_broadcast_lock, flags);

        /*
         * Clear the broadcast masks for the dead cpu, but do not stop
         * the broadcast device!
         */
        cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask);
        cpumask_clear_cpu(cpu, tick_broadcast_pending_mask);
        cpumask_clear_cpu(cpu, tick_broadcast_force_mask);

        raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}
#endif

/*
 * Check, whether the broadcast device is in one shot mode
 */
int tick_broadcast_oneshot_active(void)
{
        return tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT;
}

/*
 * Check whether the broadcast device supports oneshot.
 */
bool tick_broadcast_oneshot_available(void)
{
        struct clock_event_device *bc = tick_broadcast_device.evtdev;

        return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false;
}

#endif

void __init tick_broadcast_init(void)
{
        zalloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT);
        zalloc_cpumask_var(&tick_broadcast_on, GFP_NOWAIT);
        zalloc_cpumask_var(&tmpmask, GFP_NOWAIT);
#ifdef CONFIG_TICK_ONESHOT
        zalloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT);
        zalloc_cpumask_var(&tick_broadcast_pending_mask, GFP_NOWAIT);
        zalloc_cpumask_var(&tick_broadcast_force_mask, GFP_NOWAIT);
#endif
}