summaryrefslogtreecommitdiff
path: root/arch/arm/common/bL_switcher.c
blob: 37dc0fe1093fb24bb26b1c852c568bd8fcd3f6d2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
/*
 * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
 *
 * Created by:	Nicolas Pitre, March 2012
 * Copyright:	(C) 2012-2013  Linaro Limited
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/atomic.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/cpu_pm.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/time.h>
#include <linux/clockchips.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/notifier.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/irqchip/arm-gic.h>
#include <linux/moduleparam.h>

#include <asm/smp_plat.h>
#include <asm/cputype.h>
#include <asm/suspend.h>
#include <asm/mcpm.h>
#include <asm/bL_switcher.h>

#define CREATE_TRACE_POINTS
#include <trace/events/power_cpu_migrate.h>


/*
 * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
 * __attribute_const__ and we don't want the compiler to assume any
 * constness here as the value _does_ change along some code paths.
 */

static int read_mpidr(void)
{
	unsigned int id;
	asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
	return id & MPIDR_HWID_BITMASK;
}

/*
 * bL switcher core code.
 */

static void bL_do_switch(void *_arg)
{
	unsigned ib_mpidr, ib_cpu, ib_cluster;
	long volatile handshake, **handshake_ptr = _arg;

	pr_debug("%s\n", __func__);

	ib_mpidr = cpu_logical_map(smp_processor_id());
	ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
	ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);

	/* Advertise our handshake location */
	if (handshake_ptr) {
		handshake = 0;
		*handshake_ptr = &handshake;
	} else
		handshake = -1;

	/*
	 * Our state has been saved at this point.  Let's release our
	 * inbound CPU.
	 */
	mcpm_set_entry_vector(ib_cpu, ib_cluster, cpu_resume);
	sev();

	/*
	 * From this point, we must assume that our counterpart CPU might
	 * have taken over in its parallel world already, as if execution
	 * just returned from cpu_suspend().  It is therefore important to
	 * be very careful not to make any change the other guy is not
	 * expecting.  This is why we need stack isolation.
	 *
	 * Fancy under cover tasks could be performed here.  For now
	 * we have none.
	 */

	/*
	 * Let's wait until our inbound is alive.
	 */
	while (!handshake) {
		wfe();
		smp_mb();
	}

	/* Let's put ourself down. */
	mcpm_cpu_power_down();

	/* should never get here */
	BUG();
}

/*
 * Stack isolation.  To ensure 'current' remains valid, we just use another
 * piece of our thread's stack space which should be fairly lightly used.
 * The selected area starts just above the thread_info structure located
 * at the very bottom of the stack, aligned to a cache line, and indexed
 * with the cluster number.
 */
#define STACK_SIZE 512
extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
static int bL_switchpoint(unsigned long _arg)
{
	unsigned int mpidr = read_mpidr();
	unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
	void *stack = current_thread_info() + 1;
	stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
	stack += clusterid * STACK_SIZE + STACK_SIZE;
	call_with_stack(bL_do_switch, (void *)_arg, stack);
	BUG();
}

/*
 * Generic switcher interface
 */

static unsigned int bL_gic_id[MAX_CPUS_PER_CLUSTER][MAX_NR_CLUSTERS];
static int bL_switcher_cpu_pairing[NR_CPUS];

/*
 * bL_switch_to - Switch to a specific cluster for the current CPU
 * @new_cluster_id: the ID of the cluster to switch to.
 *
 * This function must be called on the CPU to be switched.
 * Returns 0 on success, else a negative status code.
 */
static int bL_switch_to(unsigned int new_cluster_id)
{
	unsigned int mpidr, this_cpu, that_cpu;
	unsigned int ob_mpidr, ob_cpu, ob_cluster, ib_mpidr, ib_cpu, ib_cluster;
	struct completion inbound_alive;
	long volatile *handshake_ptr;
	int ipi_nr, ret;

	this_cpu = smp_processor_id();
	ob_mpidr = read_mpidr();
	ob_cpu = MPIDR_AFFINITY_LEVEL(ob_mpidr, 0);
	ob_cluster = MPIDR_AFFINITY_LEVEL(ob_mpidr, 1);
	BUG_ON(cpu_logical_map(this_cpu) != ob_mpidr);

	if (new_cluster_id == ob_cluster)
		return 0;

	that_cpu = bL_switcher_cpu_pairing[this_cpu];
	ib_mpidr = cpu_logical_map(that_cpu);
	ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
	ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);

	pr_debug("before switch: CPU %d MPIDR %#x -> %#x\n",
		 this_cpu, ob_mpidr, ib_mpidr);

	this_cpu = smp_processor_id();

	/* Close the gate for our entry vectors */
	mcpm_set_entry_vector(ob_cpu, ob_cluster, NULL);
	mcpm_set_entry_vector(ib_cpu, ib_cluster, NULL);

	/* Install our "inbound alive" notifier. */
	init_completion(&inbound_alive);
	ipi_nr = register_ipi_completion(&inbound_alive, this_cpu);
	ipi_nr |= ((1 << 16) << bL_gic_id[ob_cpu][ob_cluster]);
	mcpm_set_early_poke(ib_cpu, ib_cluster, gic_get_sgir_physaddr(), ipi_nr);

	/*
	 * Let's wake up the inbound CPU now in case it requires some delay
	 * to come online, but leave it gated in our entry vector code.
	 */
	ret = mcpm_cpu_power_up(ib_cpu, ib_cluster);
	if (ret) {
		pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
		return ret;
	}

	/*
	 * Raise a SGI on the inbound CPU to make sure it doesn't stall
	 * in a possible WFI, such as in bL_power_down().
	 */
	gic_send_sgi(bL_gic_id[ib_cpu][ib_cluster], 0);

	/*
	 * Wait for the inbound to come up.  This allows for other
	 * tasks to be scheduled in the mean time.
	 */
	wait_for_completion(&inbound_alive);
	mcpm_set_early_poke(ib_cpu, ib_cluster, 0, 0);

	/*
	 * From this point we are entering the switch critical zone
	 * and can't take any interrupts anymore.
	 */
	local_irq_disable();
	local_fiq_disable();
	trace_cpu_migrate_begin(ktime_get_real_ns(), ob_mpidr);

	/* redirect GIC's SGIs to our counterpart */
	gic_migrate_target(bL_gic_id[ib_cpu][ib_cluster]);

	tick_suspend_local();

	ret = cpu_pm_enter();

	/* we can not tolerate errors at this point */
	if (ret)
		panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);

	/* Swap the physical CPUs in the logical map for this logical CPU. */
	cpu_logical_map(this_cpu) = ib_mpidr;
	cpu_logical_map(that_cpu) = ob_mpidr;

	/* Let's do the actual CPU switch. */
	ret = cpu_suspend((unsigned long)&handshake_ptr, bL_switchpoint);
	if (ret > 0)
		panic("%s: cpu_suspend() returned %d\n", __func__, ret);

	/* We are executing on the inbound CPU at this point */
	mpidr = read_mpidr();
	pr_debug("after switch: CPU %d MPIDR %#x\n", this_cpu, mpidr);
	BUG_ON(mpidr != ib_mpidr);

	mcpm_cpu_powered_up();

	ret = cpu_pm_exit();

	tick_resume_local();

	trace_cpu_migrate_finish(ktime_get_real_ns(), ib_mpidr);
	local_fiq_enable();
	local_irq_enable();

	*handshake_ptr = 1;
	dsb_sev();

	if (ret)
		pr_err("%s exiting with error %d\n", __func__, ret);
	return ret;
}

struct bL_thread {
	spinlock_t lock;
	struct task_struct *task;
	wait_queue_head_t wq;
	int wanted_cluster;
	struct completion started;
	bL_switch_completion_handler completer;
	void *completer_cookie;
};

static struct bL_thread bL_threads[NR_CPUS];

static int bL_switcher_thread(void *arg)
{
	struct bL_thread *t = arg;
	struct sched_param param = { .sched_priority = 1 };
	int cluster;
	bL_switch_completion_handler completer;
	void *completer_cookie;

	sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
	complete(&t->started);

	do {
		if (signal_pending(current))
			flush_signals(current);
		wait_event_interruptible(t->wq,
				t->wanted_cluster != -1 ||
				kthread_should_stop());

		spin_lock(&t->lock);
		cluster = t->wanted_cluster;
		completer = t->completer;
		completer_cookie = t->completer_cookie;
		t->wanted_cluster = -1;
		t->completer = NULL;
		spin_unlock(&t->lock);

		if (cluster != -1) {
			bL_switch_to(cluster);

			if (completer)
				completer(completer_cookie);
		}
	} while (!kthread_should_stop());

	return 0;
}

static struct task_struct *bL_switcher_thread_create(int cpu, void *arg)
{
	struct task_struct *task;

	task = kthread_create_on_node(bL_switcher_thread, arg,
				      cpu_to_node(cpu), "kswitcher_%d", cpu);
	if (!IS_ERR(task)) {
		kthread_bind(task, cpu);
		wake_up_process(task);
	} else
		pr_err("%s failed for CPU %d\n", __func__, cpu);
	return task;
}

/*
 * bL_switch_request_cb - Switch to a specific cluster for the given CPU,
 *      with completion notification via a callback
 *
 * @cpu: the CPU to switch
 * @new_cluster_id: the ID of the cluster to switch to.
 * @completer: switch completion callback.  if non-NULL,
 *	@completer(@completer_cookie) will be called on completion of
 *	the switch, in non-atomic context.
 * @completer_cookie: opaque context argument for @completer.
 *
 * This function causes a cluster switch on the given CPU by waking up
 * the appropriate switcher thread.  This function may or may not return
 * before the switch has occurred.
 *
 * If a @completer callback function is supplied, it will be called when
 * the switch is complete.  This can be used to determine asynchronously
 * when the switch is complete, regardless of when bL_switch_request()
 * returns.  When @completer is supplied, no new switch request is permitted
 * for the affected CPU until after the switch is complete, and @completer
 * has returned.
 */
int bL_switch_request_cb(unsigned int cpu, unsigned int new_cluster_id,
			 bL_switch_completion_handler completer,
			 void *completer_cookie)
{
	struct bL_thread *t;

	if (cpu >= ARRAY_SIZE(bL_threads)) {
		pr_err("%s: cpu %d out of bounds\n", __func__, cpu);
		return -EINVAL;
	}

	t = &bL_threads[cpu];

	if (IS_ERR(t->task))
		return PTR_ERR(t->task);
	if (!t->task)
		return -ESRCH;

	spin_lock(&t->lock);
	if (t->completer) {
		spin_unlock(&t->lock);
		return -EBUSY;
	}
	t->completer = completer;
	t->completer_cookie = completer_cookie;
	t->wanted_cluster = new_cluster_id;
	spin_unlock(&t->lock);
	wake_up(&t->wq);
	return 0;
}
EXPORT_SYMBOL_GPL(bL_switch_request_cb);

/*
 * Activation and configuration code.
 */

static DEFINE_MUTEX(bL_switcher_activation_lock);
static BLOCKING_NOTIFIER_HEAD(bL_activation_notifier);
static unsigned int bL_switcher_active;
static unsigned int bL_switcher_cpu_original_cluster[NR_CPUS];
static cpumask_t bL_switcher_removed_logical_cpus;

int bL_switcher_register_notifier(struct notifier_block *nb)
{
	return blocking_notifier_chain_register(&bL_activation_notifier, nb);
}
EXPORT_SYMBOL_GPL(bL_switcher_register_notifier);

int bL_switcher_unregister_notifier(struct notifier_block *nb)
{
	return blocking_notifier_chain_unregister(&bL_activation_notifier, nb);
}
EXPORT_SYMBOL_GPL(bL_switcher_unregister_notifier);

static int bL_activation_notify(unsigned long val)
{
	int ret;

	ret = blocking_notifier_call_chain(&bL_activation_notifier, val, NULL);
	if (ret & NOTIFY_STOP_MASK)
		pr_err("%s: notifier chain failed with status 0x%x\n",
			__func__, ret);
	return notifier_to_errno(ret);
}

static void bL_switcher_restore_cpus(void)
{
	int i;

	for_each_cpu(i, &bL_switcher_removed_logical_cpus) {
		struct device *cpu_dev = get_cpu_device(i);
		int ret = device_online(cpu_dev);
		if (ret)
			dev_err(cpu_dev, "switcher: unable to restore CPU\n");
	}
}

static int bL_switcher_halve_cpus(void)
{
	int i, j, cluster_0, gic_id, ret;
	unsigned int cpu, cluster, mask;
	cpumask_t available_cpus;

	/* First pass to validate what we have */
	mask = 0;
	for_each_online_cpu(i) {
		cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
		if (cluster >= 2) {
			pr_err("%s: only dual cluster systems are supported\n", __func__);
			return -EINVAL;
		}
		if (WARN_ON(cpu >= MAX_CPUS_PER_CLUSTER))
			return -EINVAL;
		mask |= (1 << cluster);
	}
	if (mask != 3) {
		pr_err("%s: no CPU pairing possible\n", __func__);
		return -EINVAL;
	}

	/*
	 * Now let's do the pairing.  We match each CPU with another CPU
	 * from a different cluster.  To get a uniform scheduling behavior
	 * without fiddling with CPU topology and compute capacity data,
	 * we'll use logical CPUs initially belonging to the same cluster.
	 */
	memset(bL_switcher_cpu_pairing, -1, sizeof(bL_switcher_cpu_pairing));
	cpumask_copy(&available_cpus, cpu_online_mask);
	cluster_0 = -1;
	for_each_cpu(i, &available_cpus) {
		int match = -1;
		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
		if (cluster_0 == -1)
			cluster_0 = cluster;
		if (cluster != cluster_0)
			continue;
		cpumask_clear_cpu(i, &available_cpus);
		for_each_cpu(j, &available_cpus) {
			cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(j), 1);
			/*
			 * Let's remember the last match to create "odd"
			 * pairings on purpose in order for other code not
			 * to assume any relation between physical and
			 * logical CPU numbers.
			 */
			if (cluster != cluster_0)
				match = j;
		}
		if (match != -1) {
			bL_switcher_cpu_pairing[i] = match;
			cpumask_clear_cpu(match, &available_cpus);
			pr_info("CPU%d paired with CPU%d\n", i, match);
		}
	}

	/*
	 * Now we disable the unwanted CPUs i.e. everything that has no
	 * pairing information (that includes the pairing counterparts).
	 */
	cpumask_clear(&bL_switcher_removed_logical_cpus);
	for_each_online_cpu(i) {
		cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);

		/* Let's take note of the GIC ID for this CPU */
		gic_id = gic_get_cpu_id(i);
		if (gic_id < 0) {
			pr_err("%s: bad GIC ID for CPU %d\n", __func__, i);
			bL_switcher_restore_cpus();
			return -EINVAL;
		}
		bL_gic_id[cpu][cluster] = gic_id;
		pr_info("GIC ID for CPU %u cluster %u is %u\n",
			cpu, cluster, gic_id);

		if (bL_switcher_cpu_pairing[i] != -1) {
			bL_switcher_cpu_original_cluster[i] = cluster;
			continue;
		}

		ret = device_offline(get_cpu_device(i));
		if (ret) {
			bL_switcher_restore_cpus();
			return ret;
		}
		cpumask_set_cpu(i, &bL_switcher_removed_logical_cpus);
	}

	return 0;
}

/* Determine the logical CPU a given physical CPU is grouped on. */
int bL_switcher_get_logical_index(u32 mpidr)
{
	int cpu;

	if (!bL_switcher_active)
		return -EUNATCH;

	mpidr &= MPIDR_HWID_BITMASK;
	for_each_online_cpu(cpu) {
		int pairing = bL_switcher_cpu_pairing[cpu];
		if (pairing == -1)
			continue;
		if ((mpidr == cpu_logical_map(cpu)) ||
		    (mpidr == cpu_logical_map(pairing)))
			return cpu;
	}
	return -EINVAL;
}

static void bL_switcher_trace_trigger_cpu(void *__always_unused info)
{
	trace_cpu_migrate_current(ktime_get_real_ns(), read_mpidr());
}

int bL_switcher_trace_trigger(void)
{
	int ret;

	preempt_disable();

	bL_switcher_trace_trigger_cpu(NULL);
	ret = smp_call_function(bL_switcher_trace_trigger_cpu, NULL, true);

	preempt_enable();

	return ret;
}
EXPORT_SYMBOL_GPL(bL_switcher_trace_trigger);

static int bL_switcher_enable(void)
{
	int cpu, ret;

	mutex_lock(&bL_switcher_activation_lock);
	lock_device_hotplug();
	if (bL_switcher_active) {
		unlock_device_hotplug();
		mutex_unlock(&bL_switcher_activation_lock);
		return 0;
	}

	pr_info("big.LITTLE switcher initializing\n");

	ret = bL_activation_notify(BL_NOTIFY_PRE_ENABLE);
	if (ret)
		goto error;

	ret = bL_switcher_halve_cpus();
	if (ret)
		goto error;

	bL_switcher_trace_trigger();

	for_each_online_cpu(cpu) {
		struct bL_thread *t = &bL_threads[cpu];
		spin_lock_init(&t->lock);
		init_waitqueue_head(&t->wq);
		init_completion(&t->started);
		t->wanted_cluster = -1;
		t->task = bL_switcher_thread_create(cpu, t);
	}

	bL_switcher_active = 1;
	bL_activation_notify(BL_NOTIFY_POST_ENABLE);
	pr_info("big.LITTLE switcher initialized\n");
	goto out;

error:
	pr_warn("big.LITTLE switcher initialization failed\n");
	bL_activation_notify(BL_NOTIFY_POST_DISABLE);

out:
	unlock_device_hotplug();
	mutex_unlock(&bL_switcher_activation_lock);
	return ret;
}

#ifdef CONFIG_SYSFS

static void bL_switcher_disable(void)
{
	unsigned int cpu, cluster;
	struct bL_thread *t;
	struct task_struct *task;

	mutex_lock(&bL_switcher_activation_lock);
	lock_device_hotplug();

	if (!bL_switcher_active)
		goto out;

	if (bL_activation_notify(BL_NOTIFY_PRE_DISABLE) != 0) {
		bL_activation_notify(BL_NOTIFY_POST_ENABLE);
		goto out;
	}

	bL_switcher_active = 0;

	/*
	 * To deactivate the switcher, we must shut down the switcher
	 * threads to prevent any other requests from being accepted.
	 * Then, if the final cluster for given logical CPU is not the
	 * same as the original one, we'll recreate a switcher thread
	 * just for the purpose of switching the CPU back without any
	 * possibility for interference from external requests.
	 */
	for_each_online_cpu(cpu) {
		t = &bL_threads[cpu];
		task = t->task;
		t->task = NULL;
		if (!task || IS_ERR(task))
			continue;
		kthread_stop(task);
		/* no more switch may happen on this CPU at this point */
		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
		if (cluster == bL_switcher_cpu_original_cluster[cpu])
			continue;
		init_completion(&t->started);
		t->wanted_cluster = bL_switcher_cpu_original_cluster[cpu];
		task = bL_switcher_thread_create(cpu, t);
		if (!IS_ERR(task)) {
			wait_for_completion(&t->started);
			kthread_stop(task);
			cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
			if (cluster == bL_switcher_cpu_original_cluster[cpu])
				continue;
		}
		/* If execution gets here, we're in trouble. */
		pr_crit("%s: unable to restore original cluster for CPU %d\n",
			__func__, cpu);
		pr_crit("%s: CPU %d can't be restored\n",
			__func__, bL_switcher_cpu_pairing[cpu]);
		cpumask_clear_cpu(bL_switcher_cpu_pairing[cpu],
				  &bL_switcher_removed_logical_cpus);
	}

	bL_switcher_restore_cpus();
	bL_switcher_trace_trigger();

	bL_activation_notify(BL_NOTIFY_POST_DISABLE);

out:
	unlock_device_hotplug();
	mutex_unlock(&bL_switcher_activation_lock);
}

static ssize_t bL_switcher_active_show(struct kobject *kobj,
		struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%u\n", bL_switcher_active);
}

static ssize_t bL_switcher_active_store(struct kobject *kobj,
		struct kobj_attribute *attr, const char *buf, size_t count)
{
	int ret;

	switch (buf[0]) {
	case '0':
		bL_switcher_disable();
		ret = 0;
		break;
	case '1':
		ret = bL_switcher_enable();
		break;
	default:
		ret = -EINVAL;
	}

	return (ret >= 0) ? count : ret;
}

static ssize_t bL_switcher_trace_trigger_store(struct kobject *kobj,
		struct kobj_attribute *attr, const char *buf, size_t count)
{
	int ret = bL_switcher_trace_trigger();

	return ret ? ret : count;
}

static struct kobj_attribute bL_switcher_active_attr =
	__ATTR(active, 0644, bL_switcher_active_show, bL_switcher_active_store);

static struct kobj_attribute bL_switcher_trace_trigger_attr =
	__ATTR(trace_trigger, 0200, NULL, bL_switcher_trace_trigger_store);

static struct attribute *bL_switcher_attrs[] = {
	&bL_switcher_active_attr.attr,
	&bL_switcher_trace_trigger_attr.attr,
	NULL,
};

static struct attribute_group bL_switcher_attr_group = {
	.attrs = bL_switcher_attrs,
};

static struct kobject *bL_switcher_kobj;

static int __init bL_switcher_sysfs_init(void)
{
	int ret;

	bL_switcher_kobj = kobject_create_and_add("bL_switcher", kernel_kobj);
	if (!bL_switcher_kobj)
		return -ENOMEM;
	ret = sysfs_create_group(bL_switcher_kobj, &bL_switcher_attr_group);
	if (ret)
		kobject_put(bL_switcher_kobj);
	return ret;
}

#endif  /* CONFIG_SYSFS */

bool bL_switcher_get_enabled(void)
{
	mutex_lock(&bL_switcher_activation_lock);

	return bL_switcher_active;
}
EXPORT_SYMBOL_GPL(bL_switcher_get_enabled);

void bL_switcher_put_enabled(void)
{
	mutex_unlock(&bL_switcher_activation_lock);
}
EXPORT_SYMBOL_GPL(bL_switcher_put_enabled);

/*
 * Veto any CPU hotplug operation on those CPUs we've removed
 * while the switcher is active.
 * We're just not ready to deal with that given the trickery involved.
 */
static int bL_switcher_hotplug_callback(struct notifier_block *nfb,
					unsigned long action, void *hcpu)
{
	if (bL_switcher_active) {
		int pairing = bL_switcher_cpu_pairing[(unsigned long)hcpu];
		switch (action & 0xf) {
		case CPU_UP_PREPARE:
		case CPU_DOWN_PREPARE:
			if (pairing == -1)
				return NOTIFY_BAD;
		}
	}
	return NOTIFY_DONE;
}

static bool no_bL_switcher;
core_param(no_bL_switcher, no_bL_switcher, bool, 0644);

static int __init bL_switcher_init(void)
{
	int ret;

	if (!mcpm_is_available())
		return -ENODEV;

	cpu_notifier(bL_switcher_hotplug_callback, 0);

	if (!no_bL_switcher) {
		ret = bL_switcher_enable();
		if (ret)
			return ret;
	}

#ifdef CONFIG_SYSFS
	ret = bL_switcher_sysfs_init();
	if (ret)
		pr_err("%s: unable to create sysfs entry\n", __func__);
#endif

	return 0;
}

late_initcall(bL_switcher_init);