coupled.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * coupled.c - helper functions to enter the same idle state on multiple cpus
  4 *
  5 * Copyright (c) 2011 Google, Inc.
  6 *
  7 * Author: Colin Cross <ccross@android.com>
  8 */
  9
 10#include <linux/kernel.h>
 11#include <linux/cpu.h>
 12#include <linux/cpuidle.h>
 13#include <linux/mutex.h>
 14#include <linux/sched.h>
 15#include <linux/slab.h>
 16#include <linux/spinlock.h>
 17
 18#include "cpuidle.h"
 19
 20/**
 21 * DOC: Coupled cpuidle states
 22 *
 23 * On some ARM SMP SoCs (OMAP4460, Tegra 2, and probably more), the
 24 * cpus cannot be independently powered down, either due to
 25 * sequencing restrictions (on Tegra 2, cpu 0 must be the last to
 26 * power down), or due to HW bugs (on OMAP4460, a cpu powering up
 27 * will corrupt the gic state unless the other cpu runs a work
 28 * around).  Each cpu has a power state that it can enter without
 29 * coordinating with the other cpu (usually Wait For Interrupt, or
 30 * WFI), and one or more "coupled" power states that affect blocks
 31 * shared between the cpus (L2 cache, interrupt controller, and
 32 * sometimes the whole SoC).  Entering a coupled power state must
 33 * be tightly controlled on both cpus.
 34 *
 35 * This file implements a solution, where each cpu will wait in the
 36 * WFI state until all cpus are ready to enter a coupled state, at
 37 * which point the coupled state function will be called on all
 38 * cpus at approximately the same time.
 39 *
 40 * Once all cpus are ready to enter idle, they are woken by an smp
 41 * cross call.  At this point, there is a chance that one of the
 42 * cpus will find work to do, and choose not to enter idle.  A
 43 * final pass is needed to guarantee that all cpus will call the
 44 * power state enter function at the same time.  During this pass,
 45 * each cpu will increment the ready counter, and continue once the
 46 * ready counter matches the number of online coupled cpus.  If any
 47 * cpu exits idle, the other cpus will decrement their counter and
 48 * retry.
 49 *
 50 * requested_state stores the deepest coupled idle state each cpu
 51 * is ready for.  It is assumed that the states are indexed from
 52 * shallowest (highest power, lowest exit latency) to deepest
 53 * (lowest power, highest exit latency).  The requested_state
 54 * variable is not locked.  It is only written from the cpu that
 55 * it stores (or by the on/offlining cpu if that cpu is offline),
 56 * and only read after all the cpus are ready for the coupled idle
 57 * state are no longer updating it.
 58 *
 59 * Three atomic counters are used.  alive_count tracks the number
 60 * of cpus in the coupled set that are currently or soon will be
 61 * online.  waiting_count tracks the number of cpus that are in
 62 * the waiting loop, in the ready loop, or in the coupled idle state.
 63 * ready_count tracks the number of cpus that are in the ready loop
 64 * or in the coupled idle state.
 65 *
 66 * To use coupled cpuidle states, a cpuidle driver must:
 67 *
 68 *    Set struct cpuidle_device.coupled_cpus to the mask of all
 69 *    coupled cpus, usually the same as cpu_possible_mask if all cpus
 70 *    are part of the same cluster.  The coupled_cpus mask must be
 71 *    set in the struct cpuidle_device for each cpu.
 72 *
 73 *    Set struct cpuidle_device.safe_state to a state that is not a
 74 *    coupled state.  This is usually WFI.
 75 *
 76 *    Set CPUIDLE_FLAG_COUPLED in struct cpuidle_state.flags for each
 77 *    state that affects multiple cpus.
 78 *
 79 *    Provide a struct cpuidle_state.enter function for each state
 80 *    that affects multiple cpus.  This function is guaranteed to be
 81 *    called on all cpus at approximately the same time.  The driver
 82 *    should ensure that the cpus all abort together if any cpu tries
 83 *    to abort once the function is called.  The function should return
 84 *    with interrupts still disabled.
 85 */
 86
 87/**
 88 * struct cpuidle_coupled - data for set of cpus that share a coupled idle state
 89 * @coupled_cpus: mask of cpus that are part of the coupled set
 90 * @requested_state: array of requested states for cpus in the coupled set
 91 * @ready_waiting_counts: combined count of cpus  in ready or waiting loops
 92 * @abort_barrier: synchronisation point for abort cases
 93 * @online_count: count of cpus that are online
 94 * @refcnt: reference count of cpuidle devices that are using this struct
 95 * @prevent: flag to prevent coupled idle while a cpu is hotplugging
 96 */
 97struct cpuidle_coupled {
 98	cpumask_t coupled_cpus;
 99	int requested_state[NR_CPUS];
100	atomic_t ready_waiting_counts;
101	atomic_t abort_barrier;
102	int online_count;
103	int refcnt;
104	int prevent;
105};
106
107#define WAITING_BITS 16
108#define MAX_WAITING_CPUS (1 << WAITING_BITS)
109#define WAITING_MASK (MAX_WAITING_CPUS - 1)
110#define READY_MASK (~WAITING_MASK)
111
112#define CPUIDLE_COUPLED_NOT_IDLE	(-1)
113
114static DEFINE_PER_CPU(call_single_data_t, cpuidle_coupled_poke_cb);
115
116/*
117 * The cpuidle_coupled_poke_pending mask is used to avoid calling
118 * __smp_call_function_single with the per cpu call_single_data_t struct already
119 * in use.  This prevents a deadlock where two cpus are waiting for each others
120 * call_single_data_t struct to be available
121 */
122static cpumask_t cpuidle_coupled_poke_pending;
123
124/*
125 * The cpuidle_coupled_poked mask is used to ensure that each cpu has been poked
126 * once to minimize entering the ready loop with a poke pending, which would
127 * require aborting and retrying.
128 */
129static cpumask_t cpuidle_coupled_poked;
130
131/**
132 * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus
133 * @dev: cpuidle_device of the calling cpu
134 * @a:   atomic variable to hold the barrier
135 *
136 * No caller to this function will return from this function until all online
137 * cpus in the same coupled group have called this function.  Once any caller
138 * has returned from this function, the barrier is immediately available for
139 * reuse.
140 *
141 * The atomic variable must be initialized to 0 before any cpu calls
142 * this function, will be reset to 0 before any cpu returns from this function.
143 *
144 * Must only be called from within a coupled idle state handler
145 * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).
146 *
147 * Provides full smp barrier semantics before and after calling.
148 */
149void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)
150{
151	int n = dev->coupled->online_count;
152
153	smp_mb__before_atomic();
154	atomic_inc(a);
155
156	while (atomic_read(a) < n)
157		cpu_relax();
158
159	if (atomic_inc_return(a) == n * 2) {
160		atomic_set(a, 0);
161		return;
162	}
163
164	while (atomic_read(a) > n)
165		cpu_relax();
166}
167
168/**
169 * cpuidle_state_is_coupled - check if a state is part of a coupled set
170 * @drv: struct cpuidle_driver for the platform
171 * @state: index of the target state in drv->states
172 *
173 * Returns true if the target state is coupled with cpus besides this one
174 */
175bool cpuidle_state_is_coupled(struct cpuidle_driver *drv, int state)
176{
177	return drv->states[state].flags & CPUIDLE_FLAG_COUPLED;
178}
179
180/**
181 * cpuidle_coupled_state_verify - check if the coupled states are correctly set.
182 * @drv: struct cpuidle_driver for the platform
183 *
184 * Returns 0 for valid state values, a negative error code otherwise:
185 *  * -EINVAL if any coupled state(safe_state_index) is wrongly set.
186 */
187int cpuidle_coupled_state_verify(struct cpuidle_driver *drv)
188{
189	int i;
190
191	for (i = drv->state_count - 1; i >= 0; i--) {
192		if (cpuidle_state_is_coupled(drv, i) &&
193		    (drv->safe_state_index == i ||
194		     drv->safe_state_index < 0 ||
195		     drv->safe_state_index >= drv->state_count))
196			return -EINVAL;
197	}
198
199	return 0;
200}
201
202/**
203 * cpuidle_coupled_set_ready - mark a cpu as ready
204 * @coupled: the struct coupled that contains the current cpu
205 */
206static inline void cpuidle_coupled_set_ready(struct cpuidle_coupled *coupled)
207{
208	atomic_add(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
209}
210
211/**
212 * cpuidle_coupled_set_not_ready - mark a cpu as not ready
213 * @coupled: the struct coupled that contains the current cpu
214 *
215 * Decrements the ready counter, unless the ready (and thus the waiting) counter
216 * is equal to the number of online cpus.  Prevents a race where one cpu
217 * decrements the waiting counter and then re-increments it just before another
218 * cpu has decremented its ready counter, leading to the ready counter going
219 * down from the number of online cpus without going through the coupled idle
220 * state.
221 *
222 * Returns 0 if the counter was decremented successfully, -EINVAL if the ready
223 * counter was equal to the number of online cpus.
224 */
225static
226inline int cpuidle_coupled_set_not_ready(struct cpuidle_coupled *coupled)
227{
228	int all;
229	int ret;
230
231	all = coupled->online_count | (coupled->online_count << WAITING_BITS);
232	ret = atomic_add_unless(&coupled->ready_waiting_counts,
233		-MAX_WAITING_CPUS, all);
234
235	return ret ? 0 : -EINVAL;
236}
237
238/**
239 * cpuidle_coupled_no_cpus_ready - check if no cpus in a coupled set are ready
240 * @coupled: the struct coupled that contains the current cpu
241 *
242 * Returns true if all of the cpus in a coupled set are out of the ready loop.
243 */
244static inline int cpuidle_coupled_no_cpus_ready(struct cpuidle_coupled *coupled)
245{
246	int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS;
247	return r == 0;
248}
249
250/**
251 * cpuidle_coupled_cpus_ready - check if all cpus in a coupled set are ready
252 * @coupled: the struct coupled that contains the current cpu
253 *
254 * Returns true if all cpus coupled to this target state are in the ready loop
255 */
256static inline bool cpuidle_coupled_cpus_ready(struct cpuidle_coupled *coupled)
257{
258	int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS;
259	return r == coupled->online_count;
260}
261
262/**
263 * cpuidle_coupled_cpus_waiting - check if all cpus in a coupled set are waiting
264 * @coupled: the struct coupled that contains the current cpu
265 *
266 * Returns true if all cpus coupled to this target state are in the wait loop
267 */
268static inline bool cpuidle_coupled_cpus_waiting(struct cpuidle_coupled *coupled)
269{
270	int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK;
271	return w == coupled->online_count;
272}
273
274/**
275 * cpuidle_coupled_no_cpus_waiting - check if no cpus in coupled set are waiting
276 * @coupled: the struct coupled that contains the current cpu
277 *
278 * Returns true if all of the cpus in a coupled set are out of the waiting loop.
279 */
280static inline int cpuidle_coupled_no_cpus_waiting(struct cpuidle_coupled *coupled)
281{
282	int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK;
283	return w == 0;
284}
285
286/**
287 * cpuidle_coupled_get_state - determine the deepest idle state
288 * @dev: struct cpuidle_device for this cpu
289 * @coupled: the struct coupled that contains the current cpu
290 *
291 * Returns the deepest idle state that all coupled cpus can enter
292 */
293static inline int cpuidle_coupled_get_state(struct cpuidle_device *dev,
294		struct cpuidle_coupled *coupled)
295{
296	int i;
297	int state = INT_MAX;
298
299	/*
300	 * Read barrier ensures that read of requested_state is ordered after
301	 * reads of ready_count.  Matches the write barriers
302	 * cpuidle_set_state_waiting.
303	 */
304	smp_rmb();
305
306	for_each_cpu(i, &coupled->coupled_cpus)
307		if (cpu_online(i) && coupled->requested_state[i] < state)
308			state = coupled->requested_state[i];
309
310	return state;
311}
312
313static void cpuidle_coupled_handle_poke(void *info)
314{
315	int cpu = (unsigned long)info;
316	cpumask_set_cpu(cpu, &cpuidle_coupled_poked);
317	cpumask_clear_cpu(cpu, &cpuidle_coupled_poke_pending);
318}
319
320/**
321 * cpuidle_coupled_poke - wake up a cpu that may be waiting
322 * @cpu: target cpu
323 *
324 * Ensures that the target cpu exits it's waiting idle state (if it is in it)
325 * and will see updates to waiting_count before it re-enters it's waiting idle
326 * state.
327 *
328 * If cpuidle_coupled_poked_mask is already set for the target cpu, that cpu
329 * either has or will soon have a pending IPI that will wake it out of idle,
330 * or it is currently processing the IPI and is not in idle.
331 */
332static void cpuidle_coupled_poke(int cpu)
333{
334	call_single_data_t *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu);
335
336	if (!cpumask_test_and_set_cpu(cpu, &cpuidle_coupled_poke_pending))
337		smp_call_function_single_async(cpu, csd);
338}
339
340/**
341 * cpuidle_coupled_poke_others - wake up all other cpus that may be waiting
342 * @this_cpu: target cpu
343 * @coupled: the struct coupled that contains the current cpu
344 *
345 * Calls cpuidle_coupled_poke on all other online cpus.
346 */
347static void cpuidle_coupled_poke_others(int this_cpu,
348		struct cpuidle_coupled *coupled)
349{
350	int cpu;
351
352	for_each_cpu(cpu, &coupled->coupled_cpus)
353		if (cpu != this_cpu && cpu_online(cpu))
354			cpuidle_coupled_poke(cpu);
355}
356
357/**
358 * cpuidle_coupled_set_waiting - mark this cpu as in the wait loop
359 * @cpu: target cpu
360 * @coupled: the struct coupled that contains the current cpu
361 * @next_state: the index in drv->states of the requested state for this cpu
362 *
363 * Updates the requested idle state for the specified cpuidle device.
364 * Returns the number of waiting cpus.
365 */
366static int cpuidle_coupled_set_waiting(int cpu,
367		struct cpuidle_coupled *coupled, int next_state)
368{
369	coupled->requested_state[cpu] = next_state;
370
371	/*
372	 * The atomic_inc_return provides a write barrier to order the write
373	 * to requested_state with the later write that increments ready_count.
374	 */
375	return atomic_inc_return(&coupled->ready_waiting_counts) & WAITING_MASK;
376}
377
378/**
379 * cpuidle_coupled_set_not_waiting - mark this cpu as leaving the wait loop
380 * @cpu: target cpu
381 * @coupled: the struct coupled that contains the current cpu
382 *
383 * Removes the requested idle state for the specified cpuidle device.
384 */
385static void cpuidle_coupled_set_not_waiting(int cpu,
386		struct cpuidle_coupled *coupled)
387{
388	/*
389	 * Decrementing waiting count can race with incrementing it in
390	 * cpuidle_coupled_set_waiting, but that's OK.  Worst case, some
391	 * cpus will increment ready_count and then spin until they
392	 * notice that this cpu has cleared it's requested_state.
393	 */
394	atomic_dec(&coupled->ready_waiting_counts);
395
396	coupled->requested_state[cpu] = CPUIDLE_COUPLED_NOT_IDLE;
397}
398
399/**
400 * cpuidle_coupled_set_done - mark this cpu as leaving the ready loop
401 * @cpu: the current cpu
402 * @coupled: the struct coupled that contains the current cpu
403 *
404 * Marks this cpu as no longer in the ready and waiting loops.  Decrements
405 * the waiting count first to prevent another cpu looping back in and seeing
406 * this cpu as waiting just before it exits idle.
407 */
408static void cpuidle_coupled_set_done(int cpu, struct cpuidle_coupled *coupled)
409{
410	cpuidle_coupled_set_not_waiting(cpu, coupled);
411	atomic_sub(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
412}
413
414/**
415 * cpuidle_coupled_clear_pokes - spin until the poke interrupt is processed
416 * @cpu: this cpu
417 *
418 * Turns on interrupts and spins until any outstanding poke interrupts have
419 * been processed and the poke bit has been cleared.
420 *
421 * Other interrupts may also be processed while interrupts are enabled, so
422 * need_resched() must be tested after this function returns to make sure
423 * the interrupt didn't schedule work that should take the cpu out of idle.
424 *
425 * Returns 0 if no poke was pending, 1 if a poke was cleared.
426 */
427static int cpuidle_coupled_clear_pokes(int cpu)
428{
429	if (!cpumask_test_cpu(cpu, &cpuidle_coupled_poke_pending))
430		return 0;
431
432	local_irq_enable();
433	while (cpumask_test_cpu(cpu, &cpuidle_coupled_poke_pending))
434		cpu_relax();
435	local_irq_disable();
436
437	return 1;
438}
439
440static bool cpuidle_coupled_any_pokes_pending(struct cpuidle_coupled *coupled)
441{
442	return cpumask_first_and_and(cpu_online_mask, &coupled->coupled_cpus,
443				     &cpuidle_coupled_poke_pending) < nr_cpu_ids;
444}
445
446/**
447 * cpuidle_enter_state_coupled - attempt to enter a state with coupled cpus
448 * @dev: struct cpuidle_device for the current cpu
449 * @drv: struct cpuidle_driver for the platform
450 * @next_state: index of the requested state in drv->states
451 *
452 * Coordinate with coupled cpus to enter the target state.  This is a two
453 * stage process.  In the first stage, the cpus are operating independently,
454 * and may call into cpuidle_enter_state_coupled at completely different times.
455 * To save as much power as possible, the first cpus to call this function will
456 * go to an intermediate state (the cpuidle_device's safe state), and wait for
457 * all the other cpus to call this function.  Once all coupled cpus are idle,
458 * the second stage will start.  Each coupled cpu will spin until all cpus have
459 * guaranteed that they will call the target_state.
460 *
461 * This function must be called with interrupts disabled.  It may enable
462 * interrupts while preparing for idle, and it will always return with
463 * interrupts enabled.
464 */
465int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
466		struct cpuidle_driver *drv, int next_state)
467{
468	int entered_state = -1;
469	struct cpuidle_coupled *coupled = dev->coupled;
470	int w;
471
472	if (!coupled)
473		return -EINVAL;
474
475	while (coupled->prevent) {
476		cpuidle_coupled_clear_pokes(dev->cpu);
477		if (need_resched()) {
478			local_irq_enable();
479			return entered_state;
480		}
481		entered_state = cpuidle_enter_state(dev, drv,
482			drv->safe_state_index);
483		local_irq_disable();
484	}
485
486	/* Read barrier ensures online_count is read after prevent is cleared */
487	smp_rmb();
488
489reset:
490	cpumask_clear_cpu(dev->cpu, &cpuidle_coupled_poked);
491
492	w = cpuidle_coupled_set_waiting(dev->cpu, coupled, next_state);
493	/*
494	 * If this is the last cpu to enter the waiting state, poke
495	 * all the other cpus out of their waiting state so they can
496	 * enter a deeper state.  This can race with one of the cpus
497	 * exiting the waiting state due to an interrupt and
498	 * decrementing waiting_count, see comment below.
499	 */
500	if (w == coupled->online_count) {
501		cpumask_set_cpu(dev->cpu, &cpuidle_coupled_poked);
502		cpuidle_coupled_poke_others(dev->cpu, coupled);
503	}
504
505retry:
506	/*
507	 * Wait for all coupled cpus to be idle, using the deepest state
508	 * allowed for a single cpu.  If this was not the poking cpu, wait
509	 * for at least one poke before leaving to avoid a race where
510	 * two cpus could arrive at the waiting loop at the same time,
511	 * but the first of the two to arrive could skip the loop without
512	 * processing the pokes from the last to arrive.
513	 */
514	while (!cpuidle_coupled_cpus_waiting(coupled) ||
515			!cpumask_test_cpu(dev->cpu, &cpuidle_coupled_poked)) {
516		if (cpuidle_coupled_clear_pokes(dev->cpu))
517			continue;
518
519		if (need_resched()) {
520			cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
521			goto out;
522		}
523
524		if (coupled->prevent) {
525			cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
526			goto out;
527		}
528
529		entered_state = cpuidle_enter_state(dev, drv,
530			drv->safe_state_index);
531		local_irq_disable();
532	}
533
534	cpuidle_coupled_clear_pokes(dev->cpu);
535	if (need_resched()) {
536		cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
537		goto out;
538	}
539
540	/*
541	 * Make sure final poke status for this cpu is visible before setting
542	 * cpu as ready.
543	 */
544	smp_wmb();
545
546	/*
547	 * All coupled cpus are probably idle.  There is a small chance that
548	 * one of the other cpus just became active.  Increment the ready count,
549	 * and spin until all coupled cpus have incremented the counter. Once a
550	 * cpu has incremented the ready counter, it cannot abort idle and must
551	 * spin until either all cpus have incremented the ready counter, or
552	 * another cpu leaves idle and decrements the waiting counter.
553	 */
554
555	cpuidle_coupled_set_ready(coupled);
556	while (!cpuidle_coupled_cpus_ready(coupled)) {
557		/* Check if any other cpus bailed out of idle. */
558		if (!cpuidle_coupled_cpus_waiting(coupled))
559			if (!cpuidle_coupled_set_not_ready(coupled))
560				goto retry;
561
562		cpu_relax();
563	}
564
565	/*
566	 * Make sure read of all cpus ready is done before reading pending pokes
567	 */
568	smp_rmb();
569
570	/*
571	 * There is a small chance that a cpu left and reentered idle after this
572	 * cpu saw that all cpus were waiting.  The cpu that reentered idle will
573	 * have sent this cpu a poke, which will still be pending after the
574	 * ready loop.  The pending interrupt may be lost by the interrupt
575	 * controller when entering the deep idle state.  It's not possible to
576	 * clear a pending interrupt without turning interrupts on and handling
577	 * it, and it's too late to turn on interrupts here, so reset the
578	 * coupled idle state of all cpus and retry.
579	 */
580	if (cpuidle_coupled_any_pokes_pending(coupled)) {
581		cpuidle_coupled_set_done(dev->cpu, coupled);
582		/* Wait for all cpus to see the pending pokes */
583		cpuidle_coupled_parallel_barrier(dev, &coupled->abort_barrier);
584		goto reset;
585	}
586
587	/* all cpus have acked the coupled state */
588	next_state = cpuidle_coupled_get_state(dev, coupled);
589
590	entered_state = cpuidle_enter_state(dev, drv, next_state);
591
592	cpuidle_coupled_set_done(dev->cpu, coupled);
593
594out:
595	/*
596	 * Normal cpuidle states are expected to return with irqs enabled.
597	 * That leads to an inefficiency where a cpu receiving an interrupt
598	 * that brings it out of idle will process that interrupt before
599	 * exiting the idle enter function and decrementing ready_count.  All
600	 * other cpus will need to spin waiting for the cpu that is processing
601	 * the interrupt.  If the driver returns with interrupts disabled,
602	 * all other cpus will loop back into the safe idle state instead of
603	 * spinning, saving power.
604	 *
605	 * Calling local_irq_enable here allows coupled states to return with
606	 * interrupts disabled, but won't cause problems for drivers that
607	 * exit with interrupts enabled.
608	 */
609	local_irq_enable();
610
611	/*
612	 * Wait until all coupled cpus have exited idle.  There is no risk that
613	 * a cpu exits and re-enters the ready state because this cpu has
614	 * already decremented its waiting_count.
615	 */
616	while (!cpuidle_coupled_no_cpus_ready(coupled))
617		cpu_relax();
618
619	return entered_state;
620}
621
622static void cpuidle_coupled_update_online_cpus(struct cpuidle_coupled *coupled)
623{
624	coupled->online_count = cpumask_weight_and(cpu_online_mask, &coupled->coupled_cpus);
625}
626
627/**
628 * cpuidle_coupled_register_device - register a coupled cpuidle device
629 * @dev: struct cpuidle_device for the current cpu
630 *
631 * Called from cpuidle_register_device to handle coupled idle init.  Finds the
632 * cpuidle_coupled struct for this set of coupled cpus, or creates one if none
633 * exists yet.
634 */
635int cpuidle_coupled_register_device(struct cpuidle_device *dev)
636{
637	int cpu;
638	struct cpuidle_device *other_dev;
639	call_single_data_t *csd;
640	struct cpuidle_coupled *coupled;
641
642	if (cpumask_empty(&dev->coupled_cpus))
643		return 0;
644
645	for_each_cpu(cpu, &dev->coupled_cpus) {
646		other_dev = per_cpu(cpuidle_devices, cpu);
647		if (other_dev && other_dev->coupled) {
648			coupled = other_dev->coupled;
649			goto have_coupled;
650		}
651	}
652
653	/* No existing coupled info found, create a new one */
654	coupled = kzalloc(sizeof(struct cpuidle_coupled), GFP_KERNEL);
655	if (!coupled)
656		return -ENOMEM;
657
658	coupled->coupled_cpus = dev->coupled_cpus;
659
660have_coupled:
661	dev->coupled = coupled;
662	if (WARN_ON(!cpumask_equal(&dev->coupled_cpus, &coupled->coupled_cpus)))
663		coupled->prevent++;
664
665	cpuidle_coupled_update_online_cpus(coupled);
666
667	coupled->refcnt++;
668
669	csd = &per_cpu(cpuidle_coupled_poke_cb, dev->cpu);
670	INIT_CSD(csd, cpuidle_coupled_handle_poke, (void *)(unsigned long)dev->cpu);
671
672	return 0;
673}
674
675/**
676 * cpuidle_coupled_unregister_device - unregister a coupled cpuidle device
677 * @dev: struct cpuidle_device for the current cpu
678 *
679 * Called from cpuidle_unregister_device to tear down coupled idle.  Removes the
680 * cpu from the coupled idle set, and frees the cpuidle_coupled_info struct if
681 * this was the last cpu in the set.
682 */
683void cpuidle_coupled_unregister_device(struct cpuidle_device *dev)
684{
685	struct cpuidle_coupled *coupled = dev->coupled;
686
687	if (cpumask_empty(&dev->coupled_cpus))
688		return;
689
690	if (--coupled->refcnt)
691		kfree(coupled);
692	dev->coupled = NULL;
693}
694
695/**
696 * cpuidle_coupled_prevent_idle - prevent cpus from entering a coupled state
697 * @coupled: the struct coupled that contains the cpu that is changing state
698 *
699 * Disables coupled cpuidle on a coupled set of cpus.  Used to ensure that
700 * cpu_online_mask doesn't change while cpus are coordinating coupled idle.
701 */
702static void cpuidle_coupled_prevent_idle(struct cpuidle_coupled *coupled)
703{
704	int cpu = get_cpu();
705
706	/* Force all cpus out of the waiting loop. */
707	coupled->prevent++;
708	cpuidle_coupled_poke_others(cpu, coupled);
709	put_cpu();
710	while (!cpuidle_coupled_no_cpus_waiting(coupled))
711		cpu_relax();
712}
713
714/**
715 * cpuidle_coupled_allow_idle - allows cpus to enter a coupled state
716 * @coupled: the struct coupled that contains the cpu that is changing state
717 *
718 * Enables coupled cpuidle on a coupled set of cpus.  Used to ensure that
719 * cpu_online_mask doesn't change while cpus are coordinating coupled idle.
720 */
721static void cpuidle_coupled_allow_idle(struct cpuidle_coupled *coupled)
722{
723	int cpu = get_cpu();
724
725	/*
726	 * Write barrier ensures readers see the new online_count when they
727	 * see prevent == 0.
728	 */
729	smp_wmb();
730	coupled->prevent--;
731	/* Force cpus out of the prevent loop. */
732	cpuidle_coupled_poke_others(cpu, coupled);
733	put_cpu();
734}
735
736static int coupled_cpu_online(unsigned int cpu)
737{
738	struct cpuidle_device *dev;
739
740	mutex_lock(&cpuidle_lock);
741
742	dev = per_cpu(cpuidle_devices, cpu);
743	if (dev && dev->coupled) {
744		cpuidle_coupled_update_online_cpus(dev->coupled);
745		cpuidle_coupled_allow_idle(dev->coupled);
746	}
747
748	mutex_unlock(&cpuidle_lock);
749	return 0;
750}
751
752static int coupled_cpu_up_prepare(unsigned int cpu)
753{
754	struct cpuidle_device *dev;
755
756	mutex_lock(&cpuidle_lock);
757
758	dev = per_cpu(cpuidle_devices, cpu);
759	if (dev && dev->coupled)
760		cpuidle_coupled_prevent_idle(dev->coupled);
761
762	mutex_unlock(&cpuidle_lock);
763	return 0;
764}
765
766static int __init cpuidle_coupled_init(void)
767{
768	int ret;
769
770	ret = cpuhp_setup_state_nocalls(CPUHP_CPUIDLE_COUPLED_PREPARE,
771					"cpuidle/coupled:prepare",
772					coupled_cpu_up_prepare,
773					coupled_cpu_online);
774	if (ret)
775		return ret;
776	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
777					"cpuidle/coupled:online",
778					coupled_cpu_online,
779					coupled_cpu_up_prepare);
780	if (ret < 0)
781		cpuhp_remove_state_nocalls(CPUHP_CPUIDLE_COUPLED_PREPARE);
782	return ret;
783}
784core_initcall(cpuidle_coupled_init);