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Colin Cross4126c012012-05-07 17:57:41 -07001/*
2 * coupled.c - helper functions to enter the same idle state on multiple cpus
3 *
4 * Copyright (c) 2011 Google, Inc.
5 *
6 * Author: Colin Cross <ccross@android.com>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful, but WITHOUT
14 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
15 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
16 * more details.
17 */
18
19#include <linux/kernel.h>
20#include <linux/cpu.h>
21#include <linux/cpuidle.h>
22#include <linux/mutex.h>
23#include <linux/sched.h>
24#include <linux/slab.h>
25#include <linux/spinlock.h>
26
27#include "cpuidle.h"
28
29/**
30 * DOC: Coupled cpuidle states
31 *
32 * On some ARM SMP SoCs (OMAP4460, Tegra 2, and probably more), the
33 * cpus cannot be independently powered down, either due to
34 * sequencing restrictions (on Tegra 2, cpu 0 must be the last to
35 * power down), or due to HW bugs (on OMAP4460, a cpu powering up
36 * will corrupt the gic state unless the other cpu runs a work
37 * around). Each cpu has a power state that it can enter without
38 * coordinating with the other cpu (usually Wait For Interrupt, or
39 * WFI), and one or more "coupled" power states that affect blocks
40 * shared between the cpus (L2 cache, interrupt controller, and
41 * sometimes the whole SoC). Entering a coupled power state must
42 * be tightly controlled on both cpus.
43 *
44 * This file implements a solution, where each cpu will wait in the
45 * WFI state until all cpus are ready to enter a coupled state, at
46 * which point the coupled state function will be called on all
47 * cpus at approximately the same time.
48 *
49 * Once all cpus are ready to enter idle, they are woken by an smp
50 * cross call. At this point, there is a chance that one of the
51 * cpus will find work to do, and choose not to enter idle. A
52 * final pass is needed to guarantee that all cpus will call the
53 * power state enter function at the same time. During this pass,
54 * each cpu will increment the ready counter, and continue once the
55 * ready counter matches the number of online coupled cpus. If any
56 * cpu exits idle, the other cpus will decrement their counter and
57 * retry.
58 *
59 * requested_state stores the deepest coupled idle state each cpu
60 * is ready for. It is assumed that the states are indexed from
61 * shallowest (highest power, lowest exit latency) to deepest
62 * (lowest power, highest exit latency). The requested_state
63 * variable is not locked. It is only written from the cpu that
64 * it stores (or by the on/offlining cpu if that cpu is offline),
65 * and only read after all the cpus are ready for the coupled idle
66 * state are are no longer updating it.
67 *
68 * Three atomic counters are used. alive_count tracks the number
69 * of cpus in the coupled set that are currently or soon will be
70 * online. waiting_count tracks the number of cpus that are in
71 * the waiting loop, in the ready loop, or in the coupled idle state.
72 * ready_count tracks the number of cpus that are in the ready loop
73 * or in the coupled idle state.
74 *
75 * To use coupled cpuidle states, a cpuidle driver must:
76 *
77 * Set struct cpuidle_device.coupled_cpus to the mask of all
78 * coupled cpus, usually the same as cpu_possible_mask if all cpus
79 * are part of the same cluster. The coupled_cpus mask must be
80 * set in the struct cpuidle_device for each cpu.
81 *
82 * Set struct cpuidle_device.safe_state to a state that is not a
83 * coupled state. This is usually WFI.
84 *
85 * Set CPUIDLE_FLAG_COUPLED in struct cpuidle_state.flags for each
86 * state that affects multiple cpus.
87 *
88 * Provide a struct cpuidle_state.enter function for each state
89 * that affects multiple cpus. This function is guaranteed to be
90 * called on all cpus at approximately the same time. The driver
91 * should ensure that the cpus all abort together if any cpu tries
92 * to abort once the function is called. The function should return
93 * with interrupts still disabled.
94 */
95
96/**
97 * struct cpuidle_coupled - data for set of cpus that share a coupled idle state
98 * @coupled_cpus: mask of cpus that are part of the coupled set
99 * @requested_state: array of requested states for cpus in the coupled set
100 * @ready_waiting_counts: combined count of cpus in ready or waiting loops
101 * @online_count: count of cpus that are online
102 * @refcnt: reference count of cpuidle devices that are using this struct
103 * @prevent: flag to prevent coupled idle while a cpu is hotplugging
104 */
105struct cpuidle_coupled {
106 cpumask_t coupled_cpus;
107 int requested_state[NR_CPUS];
108 atomic_t ready_waiting_counts;
Colin Crossf9838272013-08-28 18:41:47 -0700109 atomic_t abort_barrier;
Colin Cross4126c012012-05-07 17:57:41 -0700110 int online_count;
111 int refcnt;
112 int prevent;
113};
114
115#define WAITING_BITS 16
116#define MAX_WAITING_CPUS (1 << WAITING_BITS)
117#define WAITING_MASK (MAX_WAITING_CPUS - 1)
118#define READY_MASK (~WAITING_MASK)
119
120#define CPUIDLE_COUPLED_NOT_IDLE (-1)
121
122static DEFINE_MUTEX(cpuidle_coupled_lock);
123static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb);
124
125/*
Colin Crossf9838272013-08-28 18:41:47 -0700126 * The cpuidle_coupled_poke_pending mask is used to avoid calling
Colin Cross4126c012012-05-07 17:57:41 -0700127 * __smp_call_function_single with the per cpu call_single_data struct already
128 * in use. This prevents a deadlock where two cpus are waiting for each others
129 * call_single_data struct to be available
130 */
Colin Crossf9838272013-08-28 18:41:47 -0700131static cpumask_t cpuidle_coupled_poke_pending;
132
133/*
134 * The cpuidle_coupled_poked mask is used to ensure that each cpu has been poked
135 * once to minimize entering the ready loop with a poke pending, which would
136 * require aborting and retrying.
137 */
138static cpumask_t cpuidle_coupled_poked;
Colin Cross4126c012012-05-07 17:57:41 -0700139
140/**
Colin Cross20ff51a2012-05-07 17:57:42 -0700141 * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus
142 * @dev: cpuidle_device of the calling cpu
143 * @a: atomic variable to hold the barrier
144 *
145 * No caller to this function will return from this function until all online
146 * cpus in the same coupled group have called this function. Once any caller
147 * has returned from this function, the barrier is immediately available for
148 * reuse.
149 *
Viresh Kumarcaf4a362013-10-03 21:26:41 +0530150 * The atomic variable must be initialized to 0 before any cpu calls
Colin Cross20ff51a2012-05-07 17:57:42 -0700151 * this function, will be reset to 0 before any cpu returns from this function.
152 *
153 * Must only be called from within a coupled idle state handler
154 * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).
155 *
156 * Provides full smp barrier semantics before and after calling.
157 */
158void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)
159{
160 int n = dev->coupled->online_count;
161
Peter Zijlstra4e857c52014-03-17 18:06:10 +0100162 smp_mb__before_atomic();
Colin Cross20ff51a2012-05-07 17:57:42 -0700163 atomic_inc(a);
164
165 while (atomic_read(a) < n)
166 cpu_relax();
167
168 if (atomic_inc_return(a) == n * 2) {
169 atomic_set(a, 0);
170 return;
171 }
172
173 while (atomic_read(a) > n)
174 cpu_relax();
175}
176
177/**
Colin Cross4126c012012-05-07 17:57:41 -0700178 * cpuidle_state_is_coupled - check if a state is part of a coupled set
179 * @dev: struct cpuidle_device for the current cpu
180 * @drv: struct cpuidle_driver for the platform
181 * @state: index of the target state in drv->states
182 *
183 * Returns true if the target state is coupled with cpus besides this one
184 */
185bool cpuidle_state_is_coupled(struct cpuidle_device *dev,
186 struct cpuidle_driver *drv, int state)
187{
188 return drv->states[state].flags & CPUIDLE_FLAG_COUPLED;
189}
190
191/**
192 * cpuidle_coupled_set_ready - mark a cpu as ready
193 * @coupled: the struct coupled that contains the current cpu
194 */
195static inline void cpuidle_coupled_set_ready(struct cpuidle_coupled *coupled)
196{
197 atomic_add(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
198}
199
200/**
201 * cpuidle_coupled_set_not_ready - mark a cpu as not ready
202 * @coupled: the struct coupled that contains the current cpu
203 *
204 * Decrements the ready counter, unless the ready (and thus the waiting) counter
205 * is equal to the number of online cpus. Prevents a race where one cpu
206 * decrements the waiting counter and then re-increments it just before another
207 * cpu has decremented its ready counter, leading to the ready counter going
208 * down from the number of online cpus without going through the coupled idle
209 * state.
210 *
211 * Returns 0 if the counter was decremented successfully, -EINVAL if the ready
212 * counter was equal to the number of online cpus.
213 */
214static
215inline int cpuidle_coupled_set_not_ready(struct cpuidle_coupled *coupled)
216{
217 int all;
218 int ret;
219
Sivaram Nair92638e22012-12-18 13:52:54 +0100220 all = coupled->online_count | (coupled->online_count << WAITING_BITS);
Colin Cross4126c012012-05-07 17:57:41 -0700221 ret = atomic_add_unless(&coupled->ready_waiting_counts,
222 -MAX_WAITING_CPUS, all);
223
224 return ret ? 0 : -EINVAL;
225}
226
227/**
228 * cpuidle_coupled_no_cpus_ready - check if no cpus in a coupled set are ready
229 * @coupled: the struct coupled that contains the current cpu
230 *
231 * Returns true if all of the cpus in a coupled set are out of the ready loop.
232 */
233static inline int cpuidle_coupled_no_cpus_ready(struct cpuidle_coupled *coupled)
234{
235 int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS;
236 return r == 0;
237}
238
239/**
240 * cpuidle_coupled_cpus_ready - check if all cpus in a coupled set are ready
241 * @coupled: the struct coupled that contains the current cpu
242 *
243 * Returns true if all cpus coupled to this target state are in the ready loop
244 */
245static inline bool cpuidle_coupled_cpus_ready(struct cpuidle_coupled *coupled)
246{
247 int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS;
248 return r == coupled->online_count;
249}
250
251/**
252 * cpuidle_coupled_cpus_waiting - check if all cpus in a coupled set are waiting
253 * @coupled: the struct coupled that contains the current cpu
254 *
255 * Returns true if all cpus coupled to this target state are in the wait loop
256 */
257static inline bool cpuidle_coupled_cpus_waiting(struct cpuidle_coupled *coupled)
258{
259 int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK;
260 return w == coupled->online_count;
261}
262
263/**
264 * cpuidle_coupled_no_cpus_waiting - check if no cpus in coupled set are waiting
265 * @coupled: the struct coupled that contains the current cpu
266 *
267 * Returns true if all of the cpus in a coupled set are out of the waiting loop.
268 */
269static inline int cpuidle_coupled_no_cpus_waiting(struct cpuidle_coupled *coupled)
270{
271 int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK;
272 return w == 0;
273}
274
275/**
276 * cpuidle_coupled_get_state - determine the deepest idle state
277 * @dev: struct cpuidle_device for this cpu
278 * @coupled: the struct coupled that contains the current cpu
279 *
280 * Returns the deepest idle state that all coupled cpus can enter
281 */
282static inline int cpuidle_coupled_get_state(struct cpuidle_device *dev,
283 struct cpuidle_coupled *coupled)
284{
285 int i;
286 int state = INT_MAX;
287
288 /*
289 * Read barrier ensures that read of requested_state is ordered after
290 * reads of ready_count. Matches the write barriers
291 * cpuidle_set_state_waiting.
292 */
293 smp_rmb();
294
295 for_each_cpu_mask(i, coupled->coupled_cpus)
296 if (cpu_online(i) && coupled->requested_state[i] < state)
297 state = coupled->requested_state[i];
298
299 return state;
300}
301
Colin Crossf9838272013-08-28 18:41:47 -0700302static void cpuidle_coupled_handle_poke(void *info)
Colin Cross4126c012012-05-07 17:57:41 -0700303{
304 int cpu = (unsigned long)info;
Colin Crossf9838272013-08-28 18:41:47 -0700305 cpumask_set_cpu(cpu, &cpuidle_coupled_poked);
306 cpumask_clear_cpu(cpu, &cpuidle_coupled_poke_pending);
Colin Cross4126c012012-05-07 17:57:41 -0700307}
308
309/**
310 * cpuidle_coupled_poke - wake up a cpu that may be waiting
311 * @cpu: target cpu
312 *
313 * Ensures that the target cpu exits it's waiting idle state (if it is in it)
314 * and will see updates to waiting_count before it re-enters it's waiting idle
315 * state.
316 *
317 * If cpuidle_coupled_poked_mask is already set for the target cpu, that cpu
318 * either has or will soon have a pending IPI that will wake it out of idle,
319 * or it is currently processing the IPI and is not in idle.
320 */
321static void cpuidle_coupled_poke(int cpu)
322{
323 struct call_single_data *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu);
324
Colin Crossf9838272013-08-28 18:41:47 -0700325 if (!cpumask_test_and_set_cpu(cpu, &cpuidle_coupled_poke_pending))
Frederic Weisbeckerc46fff22014-02-24 16:40:02 +0100326 smp_call_function_single_async(cpu, csd);
Colin Cross4126c012012-05-07 17:57:41 -0700327}
328
329/**
330 * cpuidle_coupled_poke_others - wake up all other cpus that may be waiting
331 * @dev: struct cpuidle_device for this cpu
332 * @coupled: the struct coupled that contains the current cpu
333 *
334 * Calls cpuidle_coupled_poke on all other online cpus.
335 */
336static void cpuidle_coupled_poke_others(int this_cpu,
337 struct cpuidle_coupled *coupled)
338{
339 int cpu;
340
341 for_each_cpu_mask(cpu, coupled->coupled_cpus)
342 if (cpu != this_cpu && cpu_online(cpu))
343 cpuidle_coupled_poke(cpu);
344}
345
346/**
347 * cpuidle_coupled_set_waiting - mark this cpu as in the wait loop
348 * @dev: struct cpuidle_device for this cpu
349 * @coupled: the struct coupled that contains the current cpu
350 * @next_state: the index in drv->states of the requested state for this cpu
351 *
Colin Crossf9838272013-08-28 18:41:47 -0700352 * Updates the requested idle state for the specified cpuidle device.
353 * Returns the number of waiting cpus.
Colin Cross4126c012012-05-07 17:57:41 -0700354 */
Colin Crossf9838272013-08-28 18:41:47 -0700355static int cpuidle_coupled_set_waiting(int cpu,
Colin Cross4126c012012-05-07 17:57:41 -0700356 struct cpuidle_coupled *coupled, int next_state)
357{
Colin Cross4126c012012-05-07 17:57:41 -0700358 coupled->requested_state[cpu] = next_state;
359
360 /*
Colin Cross4126c012012-05-07 17:57:41 -0700361 * The atomic_inc_return provides a write barrier to order the write
362 * to requested_state with the later write that increments ready_count.
363 */
Colin Crossf9838272013-08-28 18:41:47 -0700364 return atomic_inc_return(&coupled->ready_waiting_counts) & WAITING_MASK;
Colin Cross4126c012012-05-07 17:57:41 -0700365}
366
367/**
368 * cpuidle_coupled_set_not_waiting - mark this cpu as leaving the wait loop
369 * @dev: struct cpuidle_device for this cpu
370 * @coupled: the struct coupled that contains the current cpu
371 *
372 * Removes the requested idle state for the specified cpuidle device.
373 */
374static void cpuidle_coupled_set_not_waiting(int cpu,
375 struct cpuidle_coupled *coupled)
376{
377 /*
378 * Decrementing waiting count can race with incrementing it in
379 * cpuidle_coupled_set_waiting, but that's OK. Worst case, some
380 * cpus will increment ready_count and then spin until they
381 * notice that this cpu has cleared it's requested_state.
382 */
383 atomic_dec(&coupled->ready_waiting_counts);
384
385 coupled->requested_state[cpu] = CPUIDLE_COUPLED_NOT_IDLE;
386}
387
388/**
389 * cpuidle_coupled_set_done - mark this cpu as leaving the ready loop
390 * @cpu: the current cpu
391 * @coupled: the struct coupled that contains the current cpu
392 *
393 * Marks this cpu as no longer in the ready and waiting loops. Decrements
394 * the waiting count first to prevent another cpu looping back in and seeing
395 * this cpu as waiting just before it exits idle.
396 */
397static void cpuidle_coupled_set_done(int cpu, struct cpuidle_coupled *coupled)
398{
399 cpuidle_coupled_set_not_waiting(cpu, coupled);
400 atomic_sub(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
401}
402
403/**
404 * cpuidle_coupled_clear_pokes - spin until the poke interrupt is processed
405 * @cpu - this cpu
406 *
407 * Turns on interrupts and spins until any outstanding poke interrupts have
408 * been processed and the poke bit has been cleared.
409 *
410 * Other interrupts may also be processed while interrupts are enabled, so
Colin Cross9e19b732013-08-23 12:45:12 -0700411 * need_resched() must be tested after this function returns to make sure
Colin Cross4126c012012-05-07 17:57:41 -0700412 * the interrupt didn't schedule work that should take the cpu out of idle.
413 *
Colin Cross9e19b732013-08-23 12:45:12 -0700414 * Returns 0 if no poke was pending, 1 if a poke was cleared.
Colin Cross4126c012012-05-07 17:57:41 -0700415 */
416static int cpuidle_coupled_clear_pokes(int cpu)
417{
Colin Cross9e19b732013-08-23 12:45:12 -0700418 if (!cpumask_test_cpu(cpu, &cpuidle_coupled_poke_pending))
419 return 0;
420
Colin Cross4126c012012-05-07 17:57:41 -0700421 local_irq_enable();
Colin Crossf9838272013-08-28 18:41:47 -0700422 while (cpumask_test_cpu(cpu, &cpuidle_coupled_poke_pending))
Colin Cross4126c012012-05-07 17:57:41 -0700423 cpu_relax();
424 local_irq_disable();
425
Colin Cross9e19b732013-08-23 12:45:12 -0700426 return 1;
Colin Cross4126c012012-05-07 17:57:41 -0700427}
428
Colin Crossf9838272013-08-28 18:41:47 -0700429static bool cpuidle_coupled_any_pokes_pending(struct cpuidle_coupled *coupled)
430{
431 cpumask_t cpus;
432 int ret;
433
434 cpumask_and(&cpus, cpu_online_mask, &coupled->coupled_cpus);
435 ret = cpumask_and(&cpus, &cpuidle_coupled_poke_pending, &cpus);
436
437 return ret;
438}
439
Colin Cross4126c012012-05-07 17:57:41 -0700440/**
441 * cpuidle_enter_state_coupled - attempt to enter a state with coupled cpus
442 * @dev: struct cpuidle_device for the current cpu
443 * @drv: struct cpuidle_driver for the platform
444 * @next_state: index of the requested state in drv->states
445 *
446 * Coordinate with coupled cpus to enter the target state. This is a two
447 * stage process. In the first stage, the cpus are operating independently,
448 * and may call into cpuidle_enter_state_coupled at completely different times.
449 * To save as much power as possible, the first cpus to call this function will
450 * go to an intermediate state (the cpuidle_device's safe state), and wait for
451 * all the other cpus to call this function. Once all coupled cpus are idle,
452 * the second stage will start. Each coupled cpu will spin until all cpus have
453 * guaranteed that they will call the target_state.
454 *
455 * This function must be called with interrupts disabled. It may enable
456 * interrupts while preparing for idle, and it will always return with
457 * interrupts enabled.
458 */
459int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
460 struct cpuidle_driver *drv, int next_state)
461{
462 int entered_state = -1;
463 struct cpuidle_coupled *coupled = dev->coupled;
Colin Crossf9838272013-08-28 18:41:47 -0700464 int w;
Colin Cross4126c012012-05-07 17:57:41 -0700465
466 if (!coupled)
467 return -EINVAL;
468
469 while (coupled->prevent) {
Colin Cross9e19b732013-08-23 12:45:12 -0700470 cpuidle_coupled_clear_pokes(dev->cpu);
471 if (need_resched()) {
Colin Cross4126c012012-05-07 17:57:41 -0700472 local_irq_enable();
473 return entered_state;
474 }
475 entered_state = cpuidle_enter_state(dev, drv,
476 dev->safe_state_index);
Colin Cross59e99852013-08-23 12:45:10 -0700477 local_irq_disable();
Colin Cross4126c012012-05-07 17:57:41 -0700478 }
479
480 /* Read barrier ensures online_count is read after prevent is cleared */
481 smp_rmb();
482
Colin Crossf9838272013-08-28 18:41:47 -0700483reset:
484 cpumask_clear_cpu(dev->cpu, &cpuidle_coupled_poked);
485
486 w = cpuidle_coupled_set_waiting(dev->cpu, coupled, next_state);
487 /*
488 * If this is the last cpu to enter the waiting state, poke
489 * all the other cpus out of their waiting state so they can
490 * enter a deeper state. This can race with one of the cpus
491 * exiting the waiting state due to an interrupt and
492 * decrementing waiting_count, see comment below.
493 */
494 if (w == coupled->online_count) {
495 cpumask_set_cpu(dev->cpu, &cpuidle_coupled_poked);
496 cpuidle_coupled_poke_others(dev->cpu, coupled);
497 }
Colin Cross4126c012012-05-07 17:57:41 -0700498
499retry:
500 /*
501 * Wait for all coupled cpus to be idle, using the deepest state
Colin Crossf9838272013-08-28 18:41:47 -0700502 * allowed for a single cpu. If this was not the poking cpu, wait
503 * for at least one poke before leaving to avoid a race where
504 * two cpus could arrive at the waiting loop at the same time,
505 * but the first of the two to arrive could skip the loop without
506 * processing the pokes from the last to arrive.
Colin Cross4126c012012-05-07 17:57:41 -0700507 */
Colin Crossf9838272013-08-28 18:41:47 -0700508 while (!cpuidle_coupled_cpus_waiting(coupled) ||
509 !cpumask_test_cpu(dev->cpu, &cpuidle_coupled_poked)) {
Colin Cross9e19b732013-08-23 12:45:12 -0700510 if (cpuidle_coupled_clear_pokes(dev->cpu))
511 continue;
512
513 if (need_resched()) {
Colin Cross4126c012012-05-07 17:57:41 -0700514 cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
515 goto out;
516 }
517
518 if (coupled->prevent) {
519 cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
520 goto out;
521 }
522
523 entered_state = cpuidle_enter_state(dev, drv,
524 dev->safe_state_index);
Colin Cross59e99852013-08-23 12:45:10 -0700525 local_irq_disable();
Colin Cross4126c012012-05-07 17:57:41 -0700526 }
527
Colin Cross9e19b732013-08-23 12:45:12 -0700528 cpuidle_coupled_clear_pokes(dev->cpu);
529 if (need_resched()) {
Colin Cross4126c012012-05-07 17:57:41 -0700530 cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
531 goto out;
532 }
533
534 /*
Colin Crossf9838272013-08-28 18:41:47 -0700535 * Make sure final poke status for this cpu is visible before setting
536 * cpu as ready.
537 */
538 smp_wmb();
539
540 /*
Colin Cross4126c012012-05-07 17:57:41 -0700541 * All coupled cpus are probably idle. There is a small chance that
542 * one of the other cpus just became active. Increment the ready count,
543 * and spin until all coupled cpus have incremented the counter. Once a
544 * cpu has incremented the ready counter, it cannot abort idle and must
545 * spin until either all cpus have incremented the ready counter, or
546 * another cpu leaves idle and decrements the waiting counter.
547 */
548
549 cpuidle_coupled_set_ready(coupled);
550 while (!cpuidle_coupled_cpus_ready(coupled)) {
551 /* Check if any other cpus bailed out of idle. */
552 if (!cpuidle_coupled_cpus_waiting(coupled))
553 if (!cpuidle_coupled_set_not_ready(coupled))
554 goto retry;
555
556 cpu_relax();
557 }
558
Colin Crossf9838272013-08-28 18:41:47 -0700559 /*
560 * Make sure read of all cpus ready is done before reading pending pokes
561 */
562 smp_rmb();
563
564 /*
565 * There is a small chance that a cpu left and reentered idle after this
566 * cpu saw that all cpus were waiting. The cpu that reentered idle will
567 * have sent this cpu a poke, which will still be pending after the
568 * ready loop. The pending interrupt may be lost by the interrupt
569 * controller when entering the deep idle state. It's not possible to
570 * clear a pending interrupt without turning interrupts on and handling
571 * it, and it's too late to turn on interrupts here, so reset the
572 * coupled idle state of all cpus and retry.
573 */
574 if (cpuidle_coupled_any_pokes_pending(coupled)) {
575 cpuidle_coupled_set_done(dev->cpu, coupled);
576 /* Wait for all cpus to see the pending pokes */
577 cpuidle_coupled_parallel_barrier(dev, &coupled->abort_barrier);
578 goto reset;
579 }
580
Colin Cross4126c012012-05-07 17:57:41 -0700581 /* all cpus have acked the coupled state */
582 next_state = cpuidle_coupled_get_state(dev, coupled);
583
584 entered_state = cpuidle_enter_state(dev, drv, next_state);
585
586 cpuidle_coupled_set_done(dev->cpu, coupled);
587
588out:
589 /*
590 * Normal cpuidle states are expected to return with irqs enabled.
591 * That leads to an inefficiency where a cpu receiving an interrupt
592 * that brings it out of idle will process that interrupt before
593 * exiting the idle enter function and decrementing ready_count. All
594 * other cpus will need to spin waiting for the cpu that is processing
595 * the interrupt. If the driver returns with interrupts disabled,
596 * all other cpus will loop back into the safe idle state instead of
597 * spinning, saving power.
598 *
599 * Calling local_irq_enable here allows coupled states to return with
600 * interrupts disabled, but won't cause problems for drivers that
601 * exit with interrupts enabled.
602 */
603 local_irq_enable();
604
605 /*
606 * Wait until all coupled cpus have exited idle. There is no risk that
607 * a cpu exits and re-enters the ready state because this cpu has
608 * already decremented its waiting_count.
609 */
610 while (!cpuidle_coupled_no_cpus_ready(coupled))
611 cpu_relax();
612
613 return entered_state;
614}
615
616static void cpuidle_coupled_update_online_cpus(struct cpuidle_coupled *coupled)
617{
618 cpumask_t cpus;
619 cpumask_and(&cpus, cpu_online_mask, &coupled->coupled_cpus);
620 coupled->online_count = cpumask_weight(&cpus);
621}
622
623/**
624 * cpuidle_coupled_register_device - register a coupled cpuidle device
625 * @dev: struct cpuidle_device for the current cpu
626 *
627 * Called from cpuidle_register_device to handle coupled idle init. Finds the
628 * cpuidle_coupled struct for this set of coupled cpus, or creates one if none
629 * exists yet.
630 */
631int cpuidle_coupled_register_device(struct cpuidle_device *dev)
632{
633 int cpu;
634 struct cpuidle_device *other_dev;
635 struct call_single_data *csd;
636 struct cpuidle_coupled *coupled;
637
638 if (cpumask_empty(&dev->coupled_cpus))
639 return 0;
640
641 for_each_cpu_mask(cpu, dev->coupled_cpus) {
642 other_dev = per_cpu(cpuidle_devices, cpu);
643 if (other_dev && other_dev->coupled) {
644 coupled = other_dev->coupled;
645 goto have_coupled;
646 }
647 }
648
649 /* No existing coupled info found, create a new one */
650 coupled = kzalloc(sizeof(struct cpuidle_coupled), GFP_KERNEL);
651 if (!coupled)
652 return -ENOMEM;
653
654 coupled->coupled_cpus = dev->coupled_cpus;
655
656have_coupled:
657 dev->coupled = coupled;
658 if (WARN_ON(!cpumask_equal(&dev->coupled_cpus, &coupled->coupled_cpus)))
659 coupled->prevent++;
660
661 cpuidle_coupled_update_online_cpus(coupled);
662
663 coupled->refcnt++;
664
665 csd = &per_cpu(cpuidle_coupled_poke_cb, dev->cpu);
Colin Crossf9838272013-08-28 18:41:47 -0700666 csd->func = cpuidle_coupled_handle_poke;
Colin Cross4126c012012-05-07 17:57:41 -0700667 csd->info = (void *)(unsigned long)dev->cpu;
668
669 return 0;
670}
671
672/**
673 * cpuidle_coupled_unregister_device - unregister a coupled cpuidle device
674 * @dev: struct cpuidle_device for the current cpu
675 *
676 * Called from cpuidle_unregister_device to tear down coupled idle. Removes the
677 * cpu from the coupled idle set, and frees the cpuidle_coupled_info struct if
678 * this was the last cpu in the set.
679 */
680void cpuidle_coupled_unregister_device(struct cpuidle_device *dev)
681{
682 struct cpuidle_coupled *coupled = dev->coupled;
683
684 if (cpumask_empty(&dev->coupled_cpus))
685 return;
686
687 if (--coupled->refcnt)
688 kfree(coupled);
689 dev->coupled = NULL;
690}
691
692/**
693 * cpuidle_coupled_prevent_idle - prevent cpus from entering a coupled state
694 * @coupled: the struct coupled that contains the cpu that is changing state
695 *
696 * Disables coupled cpuidle on a coupled set of cpus. Used to ensure that
697 * cpu_online_mask doesn't change while cpus are coordinating coupled idle.
698 */
699static void cpuidle_coupled_prevent_idle(struct cpuidle_coupled *coupled)
700{
701 int cpu = get_cpu();
702
703 /* Force all cpus out of the waiting loop. */
704 coupled->prevent++;
705 cpuidle_coupled_poke_others(cpu, coupled);
706 put_cpu();
707 while (!cpuidle_coupled_no_cpus_waiting(coupled))
708 cpu_relax();
709}
710
711/**
712 * cpuidle_coupled_allow_idle - allows cpus to enter a coupled state
713 * @coupled: the struct coupled that contains the cpu that is changing state
714 *
715 * Enables coupled cpuidle on a coupled set of cpus. Used to ensure that
716 * cpu_online_mask doesn't change while cpus are coordinating coupled idle.
717 */
718static void cpuidle_coupled_allow_idle(struct cpuidle_coupled *coupled)
719{
720 int cpu = get_cpu();
721
722 /*
723 * Write barrier ensures readers see the new online_count when they
724 * see prevent == 0.
725 */
726 smp_wmb();
727 coupled->prevent--;
728 /* Force cpus out of the prevent loop. */
729 cpuidle_coupled_poke_others(cpu, coupled);
730 put_cpu();
731}
732
733/**
734 * cpuidle_coupled_cpu_notify - notifier called during hotplug transitions
735 * @nb: notifier block
736 * @action: hotplug transition
737 * @hcpu: target cpu number
738 *
739 * Called when a cpu is brought on or offline using hotplug. Updates the
740 * coupled cpu set appropriately
741 */
742static int cpuidle_coupled_cpu_notify(struct notifier_block *nb,
743 unsigned long action, void *hcpu)
744{
745 int cpu = (unsigned long)hcpu;
746 struct cpuidle_device *dev;
747
Colin Cross63c6ba42012-08-15 22:10:50 +0200748 switch (action & ~CPU_TASKS_FROZEN) {
749 case CPU_UP_PREPARE:
750 case CPU_DOWN_PREPARE:
751 case CPU_ONLINE:
752 case CPU_DEAD:
753 case CPU_UP_CANCELED:
754 case CPU_DOWN_FAILED:
755 break;
756 default:
757 return NOTIFY_OK;
758 }
759
Colin Cross4126c012012-05-07 17:57:41 -0700760 mutex_lock(&cpuidle_lock);
761
762 dev = per_cpu(cpuidle_devices, cpu);
Jon Medhurst (Tixy)5fbbb902012-08-15 22:11:00 +0200763 if (!dev || !dev->coupled)
Colin Cross4126c012012-05-07 17:57:41 -0700764 goto out;
765
766 switch (action & ~CPU_TASKS_FROZEN) {
767 case CPU_UP_PREPARE:
768 case CPU_DOWN_PREPARE:
769 cpuidle_coupled_prevent_idle(dev->coupled);
770 break;
771 case CPU_ONLINE:
772 case CPU_DEAD:
773 cpuidle_coupled_update_online_cpus(dev->coupled);
774 /* Fall through */
775 case CPU_UP_CANCELED:
776 case CPU_DOWN_FAILED:
777 cpuidle_coupled_allow_idle(dev->coupled);
778 break;
779 }
780
781out:
782 mutex_unlock(&cpuidle_lock);
783 return NOTIFY_OK;
784}
785
786static struct notifier_block cpuidle_coupled_cpu_notifier = {
787 .notifier_call = cpuidle_coupled_cpu_notify,
788};
789
790static int __init cpuidle_coupled_init(void)
791{
792 return register_cpu_notifier(&cpuidle_coupled_cpu_notifier);
793}
794core_initcall(cpuidle_coupled_init);