1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This file contains the base functions to manage periodic tick
4 * related events.
5 *
6 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
7 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
8 * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
9 */
10#include <linux/compiler.h>
11#include <linux/cpu.h>
12#include <linux/err.h>
13#include <linux/hrtimer.h>
14#include <linux/interrupt.h>
15#include <linux/nmi.h>
16#include <linux/percpu.h>
17#include <linux/profile.h>
18#include <linux/sched.h>
19#include <linux/module.h>
20#include <trace/events/power.h>
21
22#include <asm/irq_regs.h>
23
24#include "tick-internal.h"
25
26/*
27 * Tick devices
28 */
29DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
30/*
31 * Tick next event: keeps track of the tick time. It's updated by the
32 * CPU which handles the tick and protected by jiffies_lock. There is
33 * no requirement to write hold the jiffies seqcount for it.
34 */
35ktime_t tick_next_period;
36
37/*
38 * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
39 * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
40 * variable has two functions:
41 *
42 * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
43 *    timekeeping lock all at once. Only the CPU which is assigned to do the
44 *    update is handling it.
45 *
46 * 2) Hand off the duty in the NOHZ idle case by setting the value to
47 *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
48 *    at it will take over and keep the time keeping alive.  The handover
49 *    procedure also covers cpu hotplug.
50 */
51int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
52#ifdef CONFIG_NO_HZ_FULL
53/*
54 * tick_do_timer_boot_cpu indicates the boot CPU temporarily owns
55 * tick_do_timer_cpu and it should be taken over by an eligible secondary
56 * when one comes online.
57 */
58static int tick_do_timer_boot_cpu __read_mostly = -1;
59#endif
60
61/*
62 * Debugging: see timer_list.c
63 */
64struct tick_device *tick_get_device(int cpu)
65{
66	return &per_cpu(tick_cpu_device, cpu);
67}
68
69/**
70 * tick_is_oneshot_available - check for a oneshot capable event device
71 */
72int tick_is_oneshot_available(void)
73{
74	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
75
76	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
77		return 0;
78	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
79		return 1;
80	return tick_broadcast_oneshot_available();
81}
82
83/*
84 * Periodic tick
85 */
86static void tick_periodic(int cpu)
87{
88	if (READ_ONCE(tick_do_timer_cpu) == cpu) {
89		raw_spin_lock(&jiffies_lock);
90		write_seqcount_begin(&jiffies_seq);
91
92		/* Keep track of the next tick event */
93		tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);
94
95		do_timer(1);
96		write_seqcount_end(&jiffies_seq);
97		raw_spin_unlock(&jiffies_lock);
98		update_wall_time();
99	}
100
101	update_process_times(user_mode(get_irq_regs()));
102	profile_tick(CPU_PROFILING);
103}
104
105/*
106 * Event handler for periodic ticks
107 */
108void tick_handle_periodic(struct clock_event_device *dev)
109{
110	int cpu = smp_processor_id();
111	ktime_t next = dev->next_event;
112
113	tick_periodic(cpu);
114
115	/*
116	 * The cpu might have transitioned to HIGHRES or NOHZ mode via
117	 * update_process_times() -> run_local_timers() ->
118	 * hrtimer_run_queues().
119	 */
120	if (IS_ENABLED(CONFIG_TICK_ONESHOT) && dev->event_handler != tick_handle_periodic)
121		return;
122
123	if (!clockevent_state_oneshot(dev))
124		return;
125	for (;;) {
126		/*
127		 * Setup the next period for devices, which do not have
128		 * periodic mode:
129		 */
130		next = ktime_add_ns(next, TICK_NSEC);
131
132		if (!clockevents_program_event(dev, next, false))
133			return;
134		/*
135		 * Have to be careful here. If we're in oneshot mode,
136		 * before we call tick_periodic() in a loop, we need
137		 * to be sure we're using a real hardware clocksource.
138		 * Otherwise we could get trapped in an infinite
139		 * loop, as the tick_periodic() increments jiffies,
140		 * which then will increment time, possibly causing
141		 * the loop to trigger again and again.
142		 */
143		if (timekeeping_valid_for_hres())
144			tick_periodic(cpu);
145	}
146}
147
148/*
149 * Setup the device for a periodic tick
150 */
151void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
152{
153	tick_set_periodic_handler(dev, broadcast);
154
155	/* Broadcast setup ? */
156	if (!tick_device_is_functional(dev))
157		return;
158
159	if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
160	    !tick_broadcast_oneshot_active()) {
161		clockevents_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);
162	} else {
163		unsigned int seq;
164		ktime_t next;
165
166		do {
167			seq = read_seqcount_begin(&jiffies_seq);
168			next = tick_next_period;
169		} while (read_seqcount_retry(&jiffies_seq, seq));
170
171		clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
172
173		for (;;) {
174			if (!clockevents_program_event(dev, next, false))
175				return;
176			next = ktime_add_ns(next, TICK_NSEC);
177		}
178	}
179}
180
181#ifdef CONFIG_NO_HZ_FULL
182static void giveup_do_timer(void *info)
183{
184	int cpu = *(unsigned int *)info;
185
186	WARN_ON(tick_do_timer_cpu != smp_processor_id());
187
188	tick_do_timer_cpu = cpu;
189}
190
191static void tick_take_do_timer_from_boot(void)
192{
193	int cpu = smp_processor_id();
194	int from = tick_do_timer_boot_cpu;
195
196	if (from >= 0 && from != cpu)
197		smp_call_function_single(from, giveup_do_timer, &cpu, 1);
198}
199#endif
200
201/*
202 * Setup the tick device
203 */
204static void tick_setup_device(struct tick_device *td,
205			      struct clock_event_device *newdev, int cpu,
206			      const struct cpumask *cpumask)
207{
208	void (*handler)(struct clock_event_device *) = NULL;
209	ktime_t next_event = 0;
210
211	/*
212	 * First device setup ?
213	 */
214	if (!td->evtdev) {
215		/*
216		 * If no cpu took the do_timer update, assign it to
217		 * this cpu:
218		 */
219		if (READ_ONCE(tick_do_timer_cpu) == TICK_DO_TIMER_BOOT) {
220			WRITE_ONCE(tick_do_timer_cpu, cpu);
221			tick_next_period = ktime_get();
222#ifdef CONFIG_NO_HZ_FULL
223			/*
224			 * The boot CPU may be nohz_full, in which case set
225			 * tick_do_timer_boot_cpu so the first housekeeping
226			 * secondary that comes up will take do_timer from
227			 * us.
228			 */
229			if (tick_nohz_full_cpu(cpu))
230				tick_do_timer_boot_cpu = cpu;
231
232		} else if (tick_do_timer_boot_cpu != -1 &&
233						!tick_nohz_full_cpu(cpu)) {
234			tick_take_do_timer_from_boot();
235			tick_do_timer_boot_cpu = -1;
236			WARN_ON(READ_ONCE(tick_do_timer_cpu) != cpu);
237#endif
238		}
239
240		/*
241		 * Startup in periodic mode first.
242		 */
243		td->mode = TICKDEV_MODE_PERIODIC;
244	} else {
245		handler = td->evtdev->event_handler;
246		next_event = td->evtdev->next_event;
247		td->evtdev->event_handler = clockevents_handle_noop;
248	}
249
250	td->evtdev = newdev;
251
252	/*
253	 * When the device is not per cpu, pin the interrupt to the
254	 * current cpu:
255	 */
256	if (!cpumask_equal(newdev->cpumask, cpumask))
257		irq_set_affinity(newdev->irq, cpumask);
258
259	/*
260	 * When global broadcasting is active, check if the current
261	 * device is registered as a placeholder for broadcast mode.
262	 * This allows us to handle this x86 misfeature in a generic
263	 * way. This function also returns !=0 when we keep the
264	 * current active broadcast state for this CPU.
265	 */
266	if (tick_device_uses_broadcast(newdev, cpu))
267		return;
268
269	if (td->mode == TICKDEV_MODE_PERIODIC)
270		tick_setup_periodic(newdev, 0);
271	else
272		tick_setup_oneshot(newdev, handler, next_event);
273}
274
275void tick_install_replacement(struct clock_event_device *newdev)
276{
277	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
278	int cpu = smp_processor_id();
279
280	clockevents_exchange_device(td->evtdev, newdev);
281	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
282	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
283		tick_oneshot_notify();
284}
285
286static bool tick_check_percpu(struct clock_event_device *curdev,
287			      struct clock_event_device *newdev, int cpu)
288{
289	if (!cpumask_test_cpu(cpu, newdev->cpumask))
290		return false;
291	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
292		return true;
293	/* Check if irq affinity can be set */
294	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
295		return false;
296	/* Prefer an existing cpu local device */
297	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
298		return false;
299	return true;
300}
301
302static bool tick_check_preferred(struct clock_event_device *curdev,
303				 struct clock_event_device *newdev)
304{
305	/* Prefer oneshot capable device */
306	if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
307		if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
308			return false;
309		if (tick_oneshot_mode_active())
310			return false;
311	}
312
313	/*
314	 * Use the higher rated one, but prefer a CPU local device with a lower
315	 * rating than a non-CPU local device
316	 */
317	return !curdev ||
318		newdev->rating > curdev->rating ||
319	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
320}
321
322/*
323 * Check whether the new device is a better fit than curdev. curdev
324 * can be NULL !
325 */
326bool tick_check_replacement(struct clock_event_device *curdev,
327			    struct clock_event_device *newdev)
328{
329	if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
330		return false;
331
332	return tick_check_preferred(curdev, newdev);
333}
334
335/*
336 * Check, if the new registered device should be used. Called with
337 * clockevents_lock held and interrupts disabled.
338 */
339void tick_check_new_device(struct clock_event_device *newdev)
340{
341	struct clock_event_device *curdev;
342	struct tick_device *td;
343	int cpu;
344
345	cpu = smp_processor_id();
346	td = &per_cpu(tick_cpu_device, cpu);
347	curdev = td->evtdev;
348
349	if (!tick_check_replacement(curdev, newdev))
350		goto out_bc;
351
352	if (!try_module_get(newdev->owner))
353		return;
354
355	/*
356	 * Replace the eventually existing device by the new
357	 * device. If the current device is the broadcast device, do
358	 * not give it back to the clockevents layer !
359	 */
360	if (tick_is_broadcast_device(curdev)) {
361		clockevents_shutdown(curdev);
362		curdev = NULL;
363	}
364	clockevents_exchange_device(curdev, newdev);
365	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
366	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
367		tick_oneshot_notify();
368	return;
369
370out_bc:
371	/*
372	 * Can the new device be used as a broadcast device ?
373	 */
374	tick_install_broadcast_device(newdev, cpu);
375}
376
377/**
378 * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
379 * @state:	The target state (enter/exit)
380 *
381 * The system enters/leaves a state, where affected devices might stop
382 * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
383 *
384 * Called with interrupts disabled, so clockevents_lock is not
385 * required here because the local clock event device cannot go away
386 * under us.
387 */
388int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
389{
390	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
391
392	if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
393		return 0;
394
395	return __tick_broadcast_oneshot_control(state);
396}
397EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);
398
399#ifdef CONFIG_HOTPLUG_CPU
400void tick_assert_timekeeping_handover(void)
401{
402	WARN_ON_ONCE(tick_do_timer_cpu == smp_processor_id());
403}
404/*
405 * Stop the tick and transfer the timekeeping job away from a dying cpu.
406 */
407int tick_cpu_dying(unsigned int dying_cpu)
408{
409	/*
410	 * If the current CPU is the timekeeper, it's the only one that can
411	 * safely hand over its duty. Also all online CPUs are in stop
412	 * machine, guaranteed not to be idle, therefore there is no
413	 * concurrency and it's safe to pick any online successor.
414	 */
415	if (tick_do_timer_cpu == dying_cpu)
416		tick_do_timer_cpu = cpumask_first(cpu_online_mask);
417
418	/* Make sure the CPU won't try to retake the timekeeping duty */
419	tick_sched_timer_dying(dying_cpu);
420
421	/* Remove CPU from timer broadcasting */
422	tick_offline_cpu(dying_cpu);
423
424	return 0;
425}
426
427/*
428 * Shutdown an event device on a given cpu:
429 *
430 * This is called on a life CPU, when a CPU is dead. So we cannot
431 * access the hardware device itself.
432 * We just set the mode and remove it from the lists.
433 */
434void tick_shutdown(unsigned int cpu)
435{
436	struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
437	struct clock_event_device *dev = td->evtdev;
438
439	td->mode = TICKDEV_MODE_PERIODIC;
440	if (dev) {
441		/*
442		 * Prevent that the clock events layer tries to call
443		 * the set mode function!
444		 */
445		clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
446		clockevents_exchange_device(dev, NULL);
447		dev->event_handler = clockevents_handle_noop;
448		td->evtdev = NULL;
449	}
450}
451#endif
452
453/**
454 * tick_suspend_local - Suspend the local tick device
455 *
456 * Called from the local cpu for freeze with interrupts disabled.
457 *
458 * No locks required. Nothing can change the per cpu device.
459 */
460void tick_suspend_local(void)
461{
462	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
463
464	clockevents_shutdown(td->evtdev);
465}
466
467/**
468 * tick_resume_local - Resume the local tick device
469 *
470 * Called from the local CPU for unfreeze or XEN resume magic.
471 *
472 * No locks required. Nothing can change the per cpu device.
473 */
474void tick_resume_local(void)
475{
476	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
477	bool broadcast = tick_resume_check_broadcast();
478
479	clockevents_tick_resume(td->evtdev);
480	if (!broadcast) {
481		if (td->mode == TICKDEV_MODE_PERIODIC)
482			tick_setup_periodic(td->evtdev, 0);
483		else
484			tick_resume_oneshot();
485	}
486
487	/*
488	 * Ensure that hrtimers are up to date and the clockevents device
489	 * is reprogrammed correctly when high resolution timers are
490	 * enabled.
491	 */
492	hrtimers_resume_local();
493}
494
495/**
496 * tick_suspend - Suspend the tick and the broadcast device
497 *
498 * Called from syscore_suspend() via timekeeping_suspend with only one
499 * CPU online and interrupts disabled or from tick_unfreeze() under
500 * tick_freeze_lock.
501 *
502 * No locks required. Nothing can change the per cpu device.
503 */
504void tick_suspend(void)
505{
506	tick_suspend_local();
507	tick_suspend_broadcast();
508}
509
510/**
511 * tick_resume - Resume the tick and the broadcast device
512 *
513 * Called from syscore_resume() via timekeeping_resume with only one
514 * CPU online and interrupts disabled.
515 *
516 * No locks required. Nothing can change the per cpu device.
517 */
518void tick_resume(void)
519{
520	tick_resume_broadcast();
521	tick_resume_local();
522}
523
524#ifdef CONFIG_SUSPEND
525static DEFINE_RAW_SPINLOCK(tick_freeze_lock);
526static unsigned int tick_freeze_depth;
527
528/**
529 * tick_freeze - Suspend the local tick and (possibly) timekeeping.
530 *
531 * Check if this is the last online CPU executing the function and if so,
532 * suspend timekeeping.  Otherwise suspend the local tick.
533 *
534 * Call with interrupts disabled.  Must be balanced with %tick_unfreeze().
535 * Interrupts must not be enabled before the subsequent %tick_unfreeze().
536 */
537void tick_freeze(void)
538{
539	raw_spin_lock(&tick_freeze_lock);
540
541	tick_freeze_depth++;
542	if (tick_freeze_depth == num_online_cpus()) {
543		trace_suspend_resume(TPS("timekeeping_freeze"),
544				     smp_processor_id(), true);
545		system_state = SYSTEM_SUSPEND;
546		sched_clock_suspend();
547		timekeeping_suspend();
548	} else {
549		tick_suspend_local();
550	}
551
552	raw_spin_unlock(&tick_freeze_lock);
553}
554
555/**
556 * tick_unfreeze - Resume the local tick and (possibly) timekeeping.
557 *
558 * Check if this is the first CPU executing the function and if so, resume
559 * timekeeping.  Otherwise resume the local tick.
560 *
561 * Call with interrupts disabled.  Must be balanced with %tick_freeze().
562 * Interrupts must not be enabled after the preceding %tick_freeze().
563 */
564void tick_unfreeze(void)
565{
566	raw_spin_lock(&tick_freeze_lock);
567
568	if (tick_freeze_depth == num_online_cpus()) {
569		timekeeping_resume();
570		sched_clock_resume();
571		system_state = SYSTEM_RUNNING;
572		trace_suspend_resume(TPS("timekeeping_freeze"),
573				     smp_processor_id(), false);
574	} else {
575		touch_softlockup_watchdog();
576		tick_resume_local();
577	}
578
579	tick_freeze_depth--;
580
581	raw_spin_unlock(&tick_freeze_lock);
582}
583#endif /* CONFIG_SUSPEND */
584
585/**
586 * tick_init - initialize the tick control
587 */
588void __init tick_init(void)
589{
590	tick_broadcast_init();
591	tick_nohz_init();
592}
593