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 // SPDX-License-Identifier: GPL-2.0
 /*
  * This file contains the base functions to manage periodic tick
  * related events.
  *
  * 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
  */
 #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 (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);
 
 #if defined(CONFIG_HIGH_RES_TIMERS) || defined(CONFIG_NO_HZ_COMMON)
     /*
      * The cpu might have transitioned to HIGHRES or NOHZ mode via
      * update_process_times() -> run_local_timers() ->
      * hrtimer_run_queues().
      */
     if (dev->event_handler != tick_handle_periodic)
         return;
 #endif
 
     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);
         }
     }
 }
 
 #ifdef CONFIG_NO_HZ_FULL
 static void giveup_do_timer(void *info)
 {
     int cpu = *(unsigned int *)info;
 
     WARN_ON(tick_do_timer_cpu != smp_processor_id());
 
     tick_do_timer_cpu = cpu;
 }
 
 static void tick_take_do_timer_from_boot(void)
 {
     int cpu = smp_processor_id();
     int from = tick_do_timer_boot_cpu;
 
     if (from >= 0 && from != cpu)
         smp_call_function_single(from, giveup_do_timer, &cpu, 1);
 }
 #endif
 
 /*
  * 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 (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
             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 set
              * tick_do_timer_boot_cpu so the first housekeeping
              * secondary that comes up will take do_timer from
              * us.
              */
             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_take_do_timer_from_boot();
             tick_do_timer_boot_cpu = -1;
             WARN_ON(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
 /*
  * Transfer the do_timer job away from a dying cpu.
  *
  * Called with interrupts disabled. No locking required. If
  * tick_do_timer_cpu is owned by this cpu, nothing can change it.
  */
 void tick_handover_do_timer(void)
 {
     if (tick_do_timer_cpu == smp_processor_id())
         tick_do_timer_cpu = cpumask_first(cpu_online_mask);
 }
 
 /*
  * 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.
  */
 void tick_shutdown(unsigned int cpu)
 {
     struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
     struct clock_event_device *dev = td->evtdev;
 
     td->mode = TICKDEV_MODE_PERIODIC;
     if (dev) {
         /*
          * Prevent that the clock events layer tries to call
          * the set mode function!
          */
         clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
         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 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);
         system_state = SYSTEM_SUSPEND;
         sched_clock_suspend();
         timekeeping_suspend();
     } 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()) {
         timekeeping_resume();
         sched_clock_resume();
         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();
 }

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