xref: /openbmc/linux/kernel/time/tick-common.c (revision e23feb16)
1 /*
2  * linux/kernel/time/tick-common.c
3  *
4  * This file contains the base functions to manage periodic tick
5  * related events.
6  *
7  * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
8  * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
9  * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
10  *
11  * This code is licenced under the GPL version 2. For details see
12  * kernel-base/COPYING.
13  */
14 #include <linux/cpu.h>
15 #include <linux/err.h>
16 #include <linux/hrtimer.h>
17 #include <linux/interrupt.h>
18 #include <linux/percpu.h>
19 #include <linux/profile.h>
20 #include <linux/sched.h>
21 #include <linux/module.h>
22 
23 #include <asm/irq_regs.h>
24 
25 #include "tick-internal.h"
26 
27 /*
28  * Tick devices
29  */
30 DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
31 /*
32  * Tick next event: keeps track of the tick time
33  */
34 ktime_t tick_next_period;
35 ktime_t tick_period;
36 int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
37 
38 /*
39  * Debugging: see timer_list.c
40  */
41 struct tick_device *tick_get_device(int cpu)
42 {
43 	return &per_cpu(tick_cpu_device, cpu);
44 }
45 
46 /**
47  * tick_is_oneshot_available - check for a oneshot capable event device
48  */
49 int tick_is_oneshot_available(void)
50 {
51 	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
52 
53 	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
54 		return 0;
55 	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
56 		return 1;
57 	return tick_broadcast_oneshot_available();
58 }
59 
60 /*
61  * Periodic tick
62  */
63 static void tick_periodic(int cpu)
64 {
65 	if (tick_do_timer_cpu == cpu) {
66 		write_seqlock(&jiffies_lock);
67 
68 		/* Keep track of the next tick event */
69 		tick_next_period = ktime_add(tick_next_period, tick_period);
70 
71 		do_timer(1);
72 		write_sequnlock(&jiffies_lock);
73 	}
74 
75 	update_process_times(user_mode(get_irq_regs()));
76 	profile_tick(CPU_PROFILING);
77 }
78 
79 /*
80  * Event handler for periodic ticks
81  */
82 void tick_handle_periodic(struct clock_event_device *dev)
83 {
84 	int cpu = smp_processor_id();
85 	ktime_t next;
86 
87 	tick_periodic(cpu);
88 
89 	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
90 		return;
91 	/*
92 	 * Setup the next period for devices, which do not have
93 	 * periodic mode:
94 	 */
95 	next = ktime_add(dev->next_event, tick_period);
96 	for (;;) {
97 		if (!clockevents_program_event(dev, next, false))
98 			return;
99 		/*
100 		 * Have to be careful here. If we're in oneshot mode,
101 		 * before we call tick_periodic() in a loop, we need
102 		 * to be sure we're using a real hardware clocksource.
103 		 * Otherwise we could get trapped in an infinite
104 		 * loop, as the tick_periodic() increments jiffies,
105 		 * when then will increment time, posibly causing
106 		 * the loop to trigger again and again.
107 		 */
108 		if (timekeeping_valid_for_hres())
109 			tick_periodic(cpu);
110 		next = ktime_add(next, tick_period);
111 	}
112 }
113 
114 /*
115  * Setup the device for a periodic tick
116  */
117 void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
118 {
119 	tick_set_periodic_handler(dev, broadcast);
120 
121 	/* Broadcast setup ? */
122 	if (!tick_device_is_functional(dev))
123 		return;
124 
125 	if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
126 	    !tick_broadcast_oneshot_active()) {
127 		clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
128 	} else {
129 		unsigned long seq;
130 		ktime_t next;
131 
132 		do {
133 			seq = read_seqbegin(&jiffies_lock);
134 			next = tick_next_period;
135 		} while (read_seqretry(&jiffies_lock, seq));
136 
137 		clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
138 
139 		for (;;) {
140 			if (!clockevents_program_event(dev, next, false))
141 				return;
142 			next = ktime_add(next, tick_period);
143 		}
144 	}
145 }
146 
147 /*
148  * Setup the tick device
149  */
150 static void tick_setup_device(struct tick_device *td,
151 			      struct clock_event_device *newdev, int cpu,
152 			      const struct cpumask *cpumask)
153 {
154 	ktime_t next_event;
155 	void (*handler)(struct clock_event_device *) = NULL;
156 
157 	/*
158 	 * First device setup ?
159 	 */
160 	if (!td->evtdev) {
161 		/*
162 		 * If no cpu took the do_timer update, assign it to
163 		 * this cpu:
164 		 */
165 		if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
166 			if (!tick_nohz_full_cpu(cpu))
167 				tick_do_timer_cpu = cpu;
168 			else
169 				tick_do_timer_cpu = TICK_DO_TIMER_NONE;
170 			tick_next_period = ktime_get();
171 			tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
172 		}
173 
174 		/*
175 		 * Startup in periodic mode first.
176 		 */
177 		td->mode = TICKDEV_MODE_PERIODIC;
178 	} else {
179 		handler = td->evtdev->event_handler;
180 		next_event = td->evtdev->next_event;
181 		td->evtdev->event_handler = clockevents_handle_noop;
182 	}
183 
184 	td->evtdev = newdev;
185 
186 	/*
187 	 * When the device is not per cpu, pin the interrupt to the
188 	 * current cpu:
189 	 */
190 	if (!cpumask_equal(newdev->cpumask, cpumask))
191 		irq_set_affinity(newdev->irq, cpumask);
192 
193 	/*
194 	 * When global broadcasting is active, check if the current
195 	 * device is registered as a placeholder for broadcast mode.
196 	 * This allows us to handle this x86 misfeature in a generic
197 	 * way. This function also returns !=0 when we keep the
198 	 * current active broadcast state for this CPU.
199 	 */
200 	if (tick_device_uses_broadcast(newdev, cpu))
201 		return;
202 
203 	if (td->mode == TICKDEV_MODE_PERIODIC)
204 		tick_setup_periodic(newdev, 0);
205 	else
206 		tick_setup_oneshot(newdev, handler, next_event);
207 }
208 
209 void tick_install_replacement(struct clock_event_device *newdev)
210 {
211 	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
212 	int cpu = smp_processor_id();
213 
214 	clockevents_exchange_device(td->evtdev, newdev);
215 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
216 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
217 		tick_oneshot_notify();
218 }
219 
220 static bool tick_check_percpu(struct clock_event_device *curdev,
221 			      struct clock_event_device *newdev, int cpu)
222 {
223 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
224 		return false;
225 	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
226 		return true;
227 	/* Check if irq affinity can be set */
228 	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
229 		return false;
230 	/* Prefer an existing cpu local device */
231 	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
232 		return false;
233 	return true;
234 }
235 
236 static bool tick_check_preferred(struct clock_event_device *curdev,
237 				 struct clock_event_device *newdev)
238 {
239 	/* Prefer oneshot capable device */
240 	if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
241 		if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
242 			return false;
243 		if (tick_oneshot_mode_active())
244 			return false;
245 	}
246 
247 	/*
248 	 * Use the higher rated one, but prefer a CPU local device with a lower
249 	 * rating than a non-CPU local device
250 	 */
251 	return !curdev ||
252 		newdev->rating > curdev->rating ||
253 	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
254 }
255 
256 /*
257  * Check whether the new device is a better fit than curdev. curdev
258  * can be NULL !
259  */
260 bool tick_check_replacement(struct clock_event_device *curdev,
261 			    struct clock_event_device *newdev)
262 {
263 	if (tick_check_percpu(curdev, newdev, smp_processor_id()))
264 		return false;
265 
266 	return tick_check_preferred(curdev, newdev);
267 }
268 
269 /*
270  * Check, if the new registered device should be used. Called with
271  * clockevents_lock held and interrupts disabled.
272  */
273 void tick_check_new_device(struct clock_event_device *newdev)
274 {
275 	struct clock_event_device *curdev;
276 	struct tick_device *td;
277 	int cpu;
278 
279 	cpu = smp_processor_id();
280 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
281 		goto out_bc;
282 
283 	td = &per_cpu(tick_cpu_device, cpu);
284 	curdev = td->evtdev;
285 
286 	/* cpu local device ? */
287 	if (!tick_check_percpu(curdev, newdev, cpu))
288 		goto out_bc;
289 
290 	/* Preference decision */
291 	if (!tick_check_preferred(curdev, newdev))
292 		goto out_bc;
293 
294 	if (!try_module_get(newdev->owner))
295 		return;
296 
297 	/*
298 	 * Replace the eventually existing device by the new
299 	 * device. If the current device is the broadcast device, do
300 	 * not give it back to the clockevents layer !
301 	 */
302 	if (tick_is_broadcast_device(curdev)) {
303 		clockevents_shutdown(curdev);
304 		curdev = NULL;
305 	}
306 	clockevents_exchange_device(curdev, newdev);
307 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
308 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
309 		tick_oneshot_notify();
310 	return;
311 
312 out_bc:
313 	/*
314 	 * Can the new device be used as a broadcast device ?
315 	 */
316 	tick_install_broadcast_device(newdev);
317 }
318 
319 /*
320  * Transfer the do_timer job away from a dying cpu.
321  *
322  * Called with interrupts disabled.
323  */
324 void tick_handover_do_timer(int *cpup)
325 {
326 	if (*cpup == tick_do_timer_cpu) {
327 		int cpu = cpumask_first(cpu_online_mask);
328 
329 		tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
330 			TICK_DO_TIMER_NONE;
331 	}
332 }
333 
334 /*
335  * Shutdown an event device on a given cpu:
336  *
337  * This is called on a life CPU, when a CPU is dead. So we cannot
338  * access the hardware device itself.
339  * We just set the mode and remove it from the lists.
340  */
341 void tick_shutdown(unsigned int *cpup)
342 {
343 	struct tick_device *td = &per_cpu(tick_cpu_device, *cpup);
344 	struct clock_event_device *dev = td->evtdev;
345 
346 	td->mode = TICKDEV_MODE_PERIODIC;
347 	if (dev) {
348 		/*
349 		 * Prevent that the clock events layer tries to call
350 		 * the set mode function!
351 		 */
352 		dev->mode = CLOCK_EVT_MODE_UNUSED;
353 		clockevents_exchange_device(dev, NULL);
354 		dev->event_handler = clockevents_handle_noop;
355 		td->evtdev = NULL;
356 	}
357 }
358 
359 void tick_suspend(void)
360 {
361 	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
362 
363 	clockevents_shutdown(td->evtdev);
364 }
365 
366 void tick_resume(void)
367 {
368 	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
369 	int broadcast = tick_resume_broadcast();
370 
371 	clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_RESUME);
372 
373 	if (!broadcast) {
374 		if (td->mode == TICKDEV_MODE_PERIODIC)
375 			tick_setup_periodic(td->evtdev, 0);
376 		else
377 			tick_resume_oneshot();
378 	}
379 }
380 
381 /**
382  * tick_init - initialize the tick control
383  */
384 void __init tick_init(void)
385 {
386 	tick_broadcast_init();
387 }
388