// SPDX-License-Identifier: GPL-2.0
/*
 * This file contains the base functions to manage periodic tick
 * related events.
 *
 * Copyright(C) 2005-2006, Linutronix GmbH, Thomas Gleixner <tglx@kernel.org>
 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
 * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
 */
#include <linux/compiler.h>
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/nmi.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <trace/events/power.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. It's updated by the
 * CPU which handles the tick and protected by jiffies_lock. There is
 * no requirement to write hold the jiffies seqcount for it.
 */
ktime_t tick_next_period;

/*
 * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
 * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
 * variable has two functions:
 *
 * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
 *    timekeeping lock all at once. Only the CPU which is assigned to do the
 *    update is handling it.
 *
 * 2) Hand off the duty in the NOHZ idle case by setting the value to
 *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
 *    at it will take over and keep the time keeping alive.  The handover
 *    procedure also covers cpu hotplug.
 */
int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
#ifdef CONFIG_NO_HZ_FULL
/*
 * tick_do_timer_boot_cpu indicates the boot CPU temporarily owns
 * tick_do_timer_cpu and it should be taken over by an eligible secondary
 * when one comes online.
 */
static int tick_do_timer_boot_cpu __read_mostly = -1;
#endif

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

/**
 * tick_is_oneshot_available - check for a oneshot capable event device
 */
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 (READ_ONCE(tick_do_timer_cpu) == cpu) {
                raw_spin_lock(&jiffies_lock);
                write_seqcount_begin(&jiffies_seq);

                /* Keep track of the next tick event */
                tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);

                do_timer(1);
                write_seqcount_end(&jiffies_seq);
                raw_spin_unlock(&jiffies_lock);
                update_wall_time();
        }

        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 = dev->next_event;

        tick_periodic(cpu);

        /*
         * The cpu might have transitioned to HIGHRES or NOHZ mode via
         * update_process_times() -> run_local_timers() ->
         * hrtimer_run_queues().
         */
        if (IS_ENABLED(CONFIG_TICK_ONESHOT) && dev->event_handler != tick_handle_periodic)
                return;

        if (!clockevent_state_oneshot(dev))
                return;
        for (;;) {
                /*
                 * Setup the next period for devices, which do not have
                 * periodic mode:
                 */
                next = ktime_add_ns(next, TICK_NSEC);

                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,
                 * which then will increment time, possibly causing
                 * the loop to trigger again and again.
                 */
                if (timekeeping_valid_for_hres())
                        tick_periodic(cpu);
        }
}

/*
 * 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_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);
        } else {
                unsigned int seq;
                ktime_t next;

                do {
                        seq = read_seqcount_begin(&jiffies_seq);
                        next = tick_next_period;
                } while (read_seqcount_retry(&jiffies_seq, seq));

                clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);

                for (;;) {
                        if (!clockevents_program_event(dev, next, false))
                                return;
                        next = ktime_add_ns(next, TICK_NSEC);
                }
        }
}

/*
 * Setup the tick device
 */
static void tick_setup_device(struct tick_device *td,
                              struct clock_event_device *newdev, int cpu,
                              const struct cpumask *cpumask)
{
        void (*handler)(struct clock_event_device *) = NULL;
        ktime_t next_event = 0;

        /*
         * First device setup ?
         */
        if (!td->evtdev) {
                /*
                 * If no cpu took the do_timer update, assign it to
                 * this cpu:
                 */
                if (READ_ONCE(tick_do_timer_cpu) == TICK_DO_TIMER_BOOT) {
                        WRITE_ONCE(tick_do_timer_cpu, cpu);
                        tick_next_period = ktime_get();
#ifdef CONFIG_NO_HZ_FULL
                        /*
                         * The boot CPU may be nohz_full, in which case the
                         * first housekeeping secondary will take do_timer()
                         * from it.
                         */
                        if (tick_nohz_full_cpu(cpu))
                                tick_do_timer_boot_cpu = cpu;

                } else if (tick_do_timer_boot_cpu != -1 && !tick_nohz_full_cpu(cpu)) {
                        tick_do_timer_boot_cpu = -1;
                        /*
                         * The boot CPU will stay in periodic (NOHZ disabled)
                         * mode until clocksource_done_booting() called after
                         * smp_init() selects a high resolution clocksource and
                         * timekeeping_notify() kicks the NOHZ stuff alive.
                         *
                         * So this WRITE_ONCE can only race with the READ_ONCE
                         * check in tick_periodic() but this race is harmless.
                         */
                        WRITE_ONCE(tick_do_timer_cpu, cpu);
#endif
                }

                /*
                 * 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. This function also returns !=0 when we keep the
         * current active broadcast state for this CPU.
         */
        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);
}

void tick_install_replacement(struct clock_event_device *newdev)
{
        struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
        int cpu = smp_processor_id();

        clockevents_exchange_device(td->evtdev, newdev);
        tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
        if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
                tick_oneshot_notify();
}

static bool tick_check_percpu(struct clock_event_device *curdev,
                              struct clock_event_device *newdev, int cpu)
{
        if (!cpumask_test_cpu(cpu, newdev->cpumask))
                return false;
        if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
                return true;
        /* Check if irq affinity can be set */
        if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
                return false;
        /* Prefer an existing cpu local device */
        if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
                return false;
        return true;
}

static bool tick_check_preferred(struct clock_event_device *curdev,
                                 struct clock_event_device *newdev)
{
        /* Prefer oneshot capable device */
        if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
                if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
                        return false;
                if (tick_oneshot_mode_active())
                        return false;
        }

        /*
         * Use the higher rated one, but prefer a CPU local device with a lower
         * rating than a non-CPU local device
         */
        return !curdev ||
                newdev->rating > curdev->rating ||
               !cpumask_equal(curdev->cpumask, newdev->cpumask);
}

/*
 * Check whether the new device is a better fit than curdev. curdev
 * can be NULL !
 */
bool tick_check_replacement(struct clock_event_device *curdev,
                            struct clock_event_device *newdev)
{
        if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
                return false;

        return tick_check_preferred(curdev, newdev);
}

/*
 * Check, if the new registered device should be used. Called with
 * clockevents_lock held and interrupts disabled.
 */
void tick_check_new_device(struct clock_event_device *newdev)
{
        struct clock_event_device *curdev;
        struct tick_device *td;
        int cpu;

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

        if (!tick_check_replacement(curdev, newdev))
                goto out_bc;

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

        /*
         * 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();
        return;

out_bc:
        /*
         * Can the new device be used as a broadcast device ?
         */
        tick_install_broadcast_device(newdev, cpu);
}

/**
 * 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 tick_device *td = this_cpu_ptr(&tick_cpu_device);

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

        return __tick_broadcast_oneshot_control(state);
}
EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);

#ifdef CONFIG_HOTPLUG_CPU
void tick_assert_timekeeping_handover(void)
{
        WARN_ON_ONCE(tick_do_timer_cpu == smp_processor_id());
}
/*
 * Stop the tick and transfer the timekeeping job away from a dying cpu.
 */
int tick_cpu_dying(unsigned int dying_cpu)
{
        /*
         * If the current CPU is the timekeeper, it's the only one that can
         * safely hand over its duty. Also all online CPUs are in stop
         * machine, guaranteed not to be idle, therefore there is no
         * concurrency and it's safe to pick any online successor.
         */
        if (tick_do_timer_cpu == dying_cpu)
                tick_do_timer_cpu = cpumask_first(cpu_online_mask);

        /* Make sure the CPU won't try to retake the timekeeping duty */
        tick_sched_timer_dying(dying_cpu);

        /* Remove CPU from timer broadcasting */
        tick_offline_cpu(dying_cpu);

        return 0;
}

/*
 * Shutdown an event device on the outgoing CPU:
 *
 * Called by the dying CPU during teardown, with clockevents_lock held
 * and interrupts disabled.
 */
void tick_shutdown(void)
{
        struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
        struct clock_event_device *dev = td->evtdev;

        td->mode = TICKDEV_MODE_PERIODIC;
        if (dev) {
                clockevents_exchange_device(dev, NULL);
                dev->event_handler = clockevents_handle_noop;
                td->evtdev = NULL;
        }
}
#endif

/**
 * tick_suspend_local - Suspend the local tick device
 *
 * Called from the local cpu for freeze with interrupts disabled.
 *
 * No locks required. Nothing can change the per cpu device.
 */
void tick_suspend_local(void)
{
        struct tick_device *td = this_cpu_ptr(&tick_cpu_device);

        clockevents_shutdown(td->evtdev);
}

/**
 * tick_resume_local - Resume the local tick device
 *
 * Called from the local CPU for unfreeze or XEN resume magic.
 *
 * No locks required. Nothing can change the per cpu device.
 */
void tick_resume_local(void)
{
        struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
        bool broadcast = tick_resume_check_broadcast();

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

        /*
         * Ensure that hrtimers are up to date and the clockevents device
         * is reprogrammed correctly when high resolution timers are
         * enabled.
         */
        hrtimers_resume_local();
}

/**
 * tick_suspend - Suspend the tick and the broadcast device
 *
 * Called from syscore_suspend() via timekeeping_suspend with only one
 * CPU online and interrupts disabled or from tick_unfreeze() under
 * tick_freeze_lock.
 *
 * No locks required. Nothing can change the per cpu device.
 */
void tick_suspend(void)
{
        tick_suspend_local();
        tick_suspend_broadcast();
}

/**
 * tick_resume - Resume the tick and the broadcast device
 *
 * Called from syscore_resume() via timekeeping_resume with only one
 * CPU online and interrupts disabled.
 *
 * No locks required. Nothing can change the per cpu device.
 */
void tick_resume(void)
{
        tick_resume_broadcast();
        tick_resume_local();
}

#ifdef CONFIG_SUSPEND
static DEFINE_RAW_SPINLOCK(tick_freeze_lock);
static DEFINE_WAIT_OVERRIDE_MAP(tick_freeze_map, LD_WAIT_SLEEP);
static unsigned int tick_freeze_depth;

/**
 * tick_freeze - Suspend the local tick and (possibly) timekeeping.
 *
 * Check if this is the last online CPU executing the function and if so,
 * suspend timekeeping.  Otherwise suspend the local tick.
 *
 * Call with interrupts disabled.  Must be balanced with %tick_unfreeze().
 * Interrupts must not be enabled before the subsequent %tick_unfreeze().
 */
void tick_freeze(void)
{
        raw_spin_lock(&tick_freeze_lock);

        tick_freeze_depth++;
        if (tick_freeze_depth == num_online_cpus()) {
                trace_suspend_resume(TPS("timekeeping_freeze"),
                                     smp_processor_id(), true);
                /*
                 * All other CPUs have their interrupts disabled and are
                 * suspended to idle. Other tasks have been frozen so there
                 * is no scheduling happening. This means that there is no
                 * concurrency in the system at this point. Therefore it is
                 * okay to acquire a sleeping lock on PREEMPT_RT, such as a
                 * spinlock, because the lock cannot be held by other CPUs
                 * or threads and acquiring it cannot block.
                 *
                 * Inform lockdep about the situation.
                 */
                lock_map_acquire_try(&tick_freeze_map);
                system_state = SYSTEM_SUSPEND;
                sched_clock_suspend();
                timekeeping_suspend();
                lock_map_release(&tick_freeze_map);
        } else {
                tick_suspend_local();
        }

        raw_spin_unlock(&tick_freeze_lock);
}

/**
 * tick_unfreeze - Resume the local tick and (possibly) timekeeping.
 *
 * Check if this is the first CPU executing the function and if so, resume
 * timekeeping.  Otherwise resume the local tick.
 *
 * Call with interrupts disabled.  Must be balanced with %tick_freeze().
 * Interrupts must not be enabled after the preceding %tick_freeze().
 */
void tick_unfreeze(void)
{
        raw_spin_lock(&tick_freeze_lock);

        if (tick_freeze_depth == num_online_cpus()) {
                /*
                 * Similar to tick_freeze(). On resumption the first CPU may
                 * acquire uncontended sleeping locks while other CPUs block on
                 * tick_freeze_lock.
                 */
                lock_map_acquire_try(&tick_freeze_map);
                timekeeping_resume();
                sched_clock_resume();
                lock_map_release(&tick_freeze_map);

                system_state = SYSTEM_RUNNING;
                trace_suspend_resume(TPS("timekeeping_freeze"),
                                     smp_processor_id(), false);
        } else {
                touch_softlockup_watchdog();
                tick_resume_local();
        }

        tick_freeze_depth--;

        raw_spin_unlock(&tick_freeze_lock);
}
#endif /* CONFIG_SUSPEND */

/**
 * tick_init - initialize the tick control
 */
void __init tick_init(void)
{
        tick_broadcast_init();
        tick_nohz_init();
}