summaryrefslogtreecommitdiffstats
path: root/drivers/base/power/opp.c
blob: d24dd614a0bd3208c0d88fd79c35397db5be8a71 (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
/*
 * Generic OPP Interface
 *
 * Copyright (C) 2009-2010 Texas Instruments Incorporated.
 *	Nishanth Menon
 *	Romit Dasgupta
 *	Kevin Hilman
 *
 * 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/kernel.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/list.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/pm_opp.h>
#include <linux/of.h>
#include <linux/export.h>

/*
 * Internal data structure organization with the OPP layer library is as
 * follows:
 * dev_opp_list (root)
 *	|- device 1 (represents voltage domain 1)
 *	|	|- opp 1 (availability, freq, voltage)
 *	|	|- opp 2 ..
 *	...	...
 *	|	`- opp n ..
 *	|- device 2 (represents the next voltage domain)
 *	...
 *	`- device m (represents mth voltage domain)
 * device 1, 2.. are represented by dev_opp structure while each opp
 * is represented by the opp structure.
 */

/**
 * struct dev_pm_opp - Generic OPP description structure
 * @node:	opp list node. The nodes are maintained throughout the lifetime
 *		of boot. It is expected only an optimal set of OPPs are
 *		added to the library by the SoC framework.
 *		RCU usage: opp list is traversed with RCU locks. node
 *		modification is possible realtime, hence the modifications
 *		are protected by the dev_opp_list_lock for integrity.
 *		IMPORTANT: the opp nodes should be maintained in increasing
 *		order.
 * @dynamic:	not-created from static DT entries.
 * @available:	true/false - marks if this OPP as available or not
 * @rate:	Frequency in hertz
 * @u_volt:	Nominal voltage in microvolts corresponding to this OPP
 * @dev_opp:	points back to the device_opp struct this opp belongs to
 * @rcu_head:	RCU callback head used for deferred freeing
 *
 * This structure stores the OPP information for a given device.
 */
struct dev_pm_opp {
	struct list_head node;

	bool available;
	bool dynamic;
	unsigned long rate;
	unsigned long u_volt;

	struct device_opp *dev_opp;
	struct rcu_head rcu_head;
};

/**
 * struct device_opp - Device opp structure
 * @node:	list node - contains the devices with OPPs that
 *		have been registered. Nodes once added are not modified in this
 *		list.
 *		RCU usage: nodes are not modified in the list of device_opp,
 *		however addition is possible and is secured by dev_opp_list_lock
 * @dev:	device pointer
 * @srcu_head:	notifier head to notify the OPP availability changes.
 * @rcu_head:	RCU callback head used for deferred freeing
 * @opp_list:	list of opps
 *
 * This is an internal data structure maintaining the link to opps attached to
 * a device. This structure is not meant to be shared to users as it is
 * meant for book keeping and private to OPP library.
 *
 * Because the opp structures can be used from both rcu and srcu readers, we
 * need to wait for the grace period of both of them before freeing any
 * resources. And so we have used kfree_rcu() from within call_srcu() handlers.
 */
struct device_opp {
	struct list_head node;

	struct device *dev;
	struct srcu_notifier_head srcu_head;
	struct rcu_head rcu_head;
	struct list_head opp_list;
};

/*
 * The root of the list of all devices. All device_opp structures branch off
 * from here, with each device_opp containing the list of opp it supports in
 * various states of availability.
 */
static LIST_HEAD(dev_opp_list);
/* Lock to allow exclusive modification to the device and opp lists */
static DEFINE_MUTEX(dev_opp_list_lock);

/**
 * find_device_opp() - find device_opp struct using device pointer
 * @dev:	device pointer used to lookup device OPPs
 *
 * Search list of device OPPs for one containing matching device. Does a RCU
 * reader operation to grab the pointer needed.
 *
 * Returns pointer to 'struct device_opp' if found, otherwise -ENODEV or
 * -EINVAL based on type of error.
 *
 * Locking: This function must be called under rcu_read_lock(). device_opp
 * is a RCU protected pointer. This means that device_opp is valid as long
 * as we are under RCU lock.
 */
static struct device_opp *find_device_opp(struct device *dev)
{
	struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);

	if (unlikely(IS_ERR_OR_NULL(dev))) {
		pr_err("%s: Invalid parameters\n", __func__);
		return ERR_PTR(-EINVAL);
	}

	list_for_each_entry_rcu(tmp_dev_opp, &dev_opp_list, node) {
		if (tmp_dev_opp->dev == dev) {
			dev_opp = tmp_dev_opp;
			break;
		}
	}

	return dev_opp;
}

/**
 * dev_pm_opp_get_voltage() - Gets the voltage corresponding to an available opp
 * @opp:	opp for which voltage has to be returned for
 *
 * Return voltage in micro volt corresponding to the opp, else
 * return 0
 *
 * Locking: This function must be called under rcu_read_lock(). opp is a rcu
 * protected pointer. This means that opp which could have been fetched by
 * opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
 * under RCU lock. The pointer returned by the opp_find_freq family must be
 * used in the same section as the usage of this function with the pointer
 * prior to unlocking with rcu_read_unlock() to maintain the integrity of the
 * pointer.
 */
unsigned long dev_pm_opp_get_voltage(struct dev_pm_opp *opp)
{
	struct dev_pm_opp *tmp_opp;
	unsigned long v = 0;

	tmp_opp = rcu_dereference(opp);
	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
		pr_err("%s: Invalid parameters\n", __func__);
	else
		v = tmp_opp->u_volt;

	return v;
}
EXPORT_SYMBOL_GPL(dev_pm_opp_get_voltage);

/**
 * dev_pm_opp_get_freq() - Gets the frequency corresponding to an available opp
 * @opp:	opp for which frequency has to be returned for
 *
 * Return frequency in hertz corresponding to the opp, else
 * return 0
 *
 * Locking: This function must be called under rcu_read_lock(). opp is a rcu
 * protected pointer. This means that opp which could have been fetched by
 * opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
 * under RCU lock. The pointer returned by the opp_find_freq family must be
 * used in the same section as the usage of this function with the pointer
 * prior to unlocking with rcu_read_unlock() to maintain the integrity of the
 * pointer.
 */
unsigned long dev_pm_opp_get_freq(struct dev_pm_opp *opp)
{
	struct dev_pm_opp *tmp_opp;
	unsigned long f = 0;

	tmp_opp = rcu_dereference(opp);
	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
		pr_err("%s: Invalid parameters\n", __func__);
	else
		f = tmp_opp->rate;

	return f;
}
EXPORT_SYMBOL_GPL(dev_pm_opp_get_freq);

/**
 * dev_pm_opp_get_opp_count() - Get number of opps available in the opp list
 * @dev:	device for which we do this operation
 *
 * This function returns the number of available opps if there are any,
 * else returns 0 if none or the corresponding error value.
 *
 * Locking: This function must be called under rcu_read_lock(). This function
 * internally references two RCU protected structures: device_opp and opp which
 * are safe as long as we are under a common RCU locked section.
 */
int dev_pm_opp_get_opp_count(struct device *dev)
{
	struct device_opp *dev_opp;
	struct dev_pm_opp *temp_opp;
	int count = 0;

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
		int r = PTR_ERR(dev_opp);
		dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
		return r;
	}

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
		if (temp_opp->available)
			count++;
	}

	return count;
}
EXPORT_SYMBOL_GPL(dev_pm_opp_get_opp_count);

/**
 * dev_pm_opp_find_freq_exact() - search for an exact frequency
 * @dev:		device for which we do this operation
 * @freq:		frequency to search for
 * @available:		true/false - match for available opp
 *
 * Searches for exact match in the opp list and returns pointer to the matching
 * opp if found, else returns ERR_PTR in case of error and should be handled
 * using IS_ERR. Error return values can be:
 * EINVAL:	for bad pointer
 * ERANGE:	no match found for search
 * ENODEV:	if device not found in list of registered devices
 *
 * Note: available is a modifier for the search. if available=true, then the
 * match is for exact matching frequency and is available in the stored OPP
 * table. if false, the match is for exact frequency which is not available.
 *
 * This provides a mechanism to enable an opp which is not available currently
 * or the opposite as well.
 *
 * Locking: This function must be called under rcu_read_lock(). opp is a rcu
 * protected pointer. The reason for the same is that the opp pointer which is
 * returned will remain valid for use with opp_get_{voltage, freq} only while
 * under the locked area. The pointer returned must be used prior to unlocking
 * with rcu_read_unlock() to maintain the integrity of the pointer.
 */
struct dev_pm_opp *dev_pm_opp_find_freq_exact(struct device *dev,
					      unsigned long freq,
					      bool available)
{
	struct device_opp *dev_opp;
	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
		int r = PTR_ERR(dev_opp);
		dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
		return ERR_PTR(r);
	}

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
		if (temp_opp->available == available &&
				temp_opp->rate == freq) {
			opp = temp_opp;
			break;
		}
	}

	return opp;
}
EXPORT_SYMBOL_GPL(dev_pm_opp_find_freq_exact);

/**
 * dev_pm_opp_find_freq_ceil() - Search for an rounded ceil freq
 * @dev:	device for which we do this operation
 * @freq:	Start frequency
 *
 * Search for the matching ceil *available* OPP from a starting freq
 * for a device.
 *
 * Returns matching *opp and refreshes *freq accordingly, else returns
 * ERR_PTR in case of error and should be handled using IS_ERR. Error return
 * values can be:
 * EINVAL:	for bad pointer
 * ERANGE:	no match found for search
 * ENODEV:	if device not found in list of registered devices
 *
 * Locking: This function must be called under rcu_read_lock(). opp is a rcu
 * protected pointer. The reason for the same is that the opp pointer which is
 * returned will remain valid for use with opp_get_{voltage, freq} only while
 * under the locked area. The pointer returned must be used prior to unlocking
 * with rcu_read_unlock() to maintain the integrity of the pointer.
 */
struct dev_pm_opp *dev_pm_opp_find_freq_ceil(struct device *dev,
					     unsigned long *freq)
{
	struct device_opp *dev_opp;
	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);

	if (!dev || !freq) {
		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
		return ERR_PTR(-EINVAL);
	}

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp))
		return ERR_CAST(dev_opp);

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
		if (temp_opp->available && temp_opp->rate >= *freq) {
			opp = temp_opp;
			*freq = opp->rate;
			break;
		}
	}

	return opp;
}
EXPORT_SYMBOL_GPL(dev_pm_opp_find_freq_ceil);

/**
 * dev_pm_opp_find_freq_floor() - Search for a rounded floor freq
 * @dev:	device for which we do this operation
 * @freq:	Start frequency
 *
 * Search for the matching floor *available* OPP from a starting freq
 * for a device.
 *
 * Returns matching *opp and refreshes *freq accordingly, else returns
 * ERR_PTR in case of error and should be handled using IS_ERR. Error return
 * values can be:
 * EINVAL:	for bad pointer
 * ERANGE:	no match found for search
 * ENODEV:	if device not found in list of registered devices
 *
 * Locking: This function must be called under rcu_read_lock(). opp is a rcu
 * protected pointer. The reason for the same is that the opp pointer which is
 * returned will remain valid for use with opp_get_{voltage, freq} only while
 * under the locked area. The pointer returned must be used prior to unlocking
 * with rcu_read_unlock() to maintain the integrity of the pointer.
 */
struct dev_pm_opp *dev_pm_opp_find_freq_floor(struct device *dev,
					      unsigned long *freq)
{
	struct device_opp *dev_opp;
	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);

	if (!dev || !freq) {
		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
		return ERR_PTR(-EINVAL);
	}

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp))
		return ERR_CAST(dev_opp);

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
		if (temp_opp->available) {
			/* go to the next node, before choosing prev */
			if (temp_opp->rate > *freq)
				break;
			else
				opp = temp_opp;
		}
	}
	if (!IS_ERR(opp))
		*freq = opp->rate;

	return opp;
}
EXPORT_SYMBOL_GPL(dev_pm_opp_find_freq_floor);

static struct device_opp *add_device_opp(struct device *dev)
{
	struct device_opp *dev_opp;

	/*
	 * Allocate a new device OPP table. In the infrequent case where a new
	 * device is needed to be added, we pay this penalty.
	 */
	dev_opp = kzalloc(sizeof(*dev_opp), GFP_KERNEL);
	if (!dev_opp)
		return NULL;

	dev_opp->dev = dev;
	srcu_init_notifier_head(&dev_opp->srcu_head);
	INIT_LIST_HEAD(&dev_opp->opp_list);

	/* Secure the device list modification */
	list_add_rcu(&dev_opp->node, &dev_opp_list);
	return dev_opp;
}

static int dev_pm_opp_add_dynamic(struct device *dev, unsigned long freq,
				  unsigned long u_volt, bool dynamic)
{
	struct device_opp *dev_opp = NULL;
	struct dev_pm_opp *opp, *new_opp;
	struct list_head *head;
	int ret;

	/* allocate new OPP node */
	new_opp = kzalloc(sizeof(*new_opp), GFP_KERNEL);
	if (!new_opp) {
		dev_warn(dev, "%s: Unable to create new OPP node\n", __func__);
		return -ENOMEM;
	}

	/* Hold our list modification lock here */
	mutex_lock(&dev_opp_list_lock);

	/* populate the opp table */
	new_opp->rate = freq;
	new_opp->u_volt = u_volt;
	new_opp->available = true;
	new_opp->dynamic = dynamic;

	/* Check for existing list for 'dev' */
	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
		dev_opp = add_device_opp(dev);
		if (!dev_opp) {
			ret = -ENOMEM;
			goto free_opp;
		}

		head = &dev_opp->opp_list;
		goto list_add;
	}

	/*
	 * Insert new OPP in order of increasing frequency
	 * and discard if already present
	 */
	head = &dev_opp->opp_list;
	list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
		if (new_opp->rate <= opp->rate)
			break;
		else
			head = &opp->node;
	}

	/* Duplicate OPPs ? */
	if (new_opp->rate == opp->rate) {
		ret = opp->available && new_opp->u_volt == opp->u_volt ?
			0 : -EEXIST;

		dev_warn(dev, "%s: duplicate OPPs detected. Existing: freq: %lu, volt: %lu, enabled: %d. New: freq: %lu, volt: %lu, enabled: %d\n",
			 __func__, opp->rate, opp->u_volt, opp->available,
			 new_opp->rate, new_opp->u_volt, new_opp->available);
		goto free_opp;
	}

list_add:
	new_opp->dev_opp = dev_opp;
	list_add_rcu(&new_opp->node, head);
	mutex_unlock(&dev_opp_list_lock);

	/*
	 * Notify the changes in the availability of the operable
	 * frequency/voltage list.
	 */
	srcu_notifier_call_chain(&dev_opp->srcu_head, OPP_EVENT_ADD, new_opp);
	return 0;

free_opp:
	mutex_unlock(&dev_opp_list_lock);
	kfree(new_opp);
	return ret;
}

/**
 * dev_pm_opp_add()  - Add an OPP table from a table definitions
 * @dev:	device for which we do this operation
 * @freq:	Frequency in Hz for this OPP
 * @u_volt:	Voltage in uVolts for this OPP
 *
 * This function adds an opp definition to the opp list and returns status.
 * The opp is made available by default and it can be controlled using
 * dev_pm_opp_enable/disable functions.
 *
 * Locking: The internal device_opp and opp structures are RCU protected.
 * Hence this function internally uses RCU updater strategy with mutex locks
 * to keep the integrity of the internal data structures. Callers should ensure
 * that this function is *NOT* called under RCU protection or in contexts where
 * mutex cannot be locked.
 *
 * Return:
 * 0:		On success OR
 *		Duplicate OPPs (both freq and volt are same) and opp->available
 * -EEXIST:	Freq are same and volt are different OR
 *		Duplicate OPPs (both freq and volt are same) and !opp->available
 * -ENOMEM:	Memory allocation failure
 */
int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
{
	return dev_pm_opp_add_dynamic(dev, freq, u_volt, true);
}
EXPORT_SYMBOL_GPL(dev_pm_opp_add);

static void kfree_opp_rcu(struct rcu_head *head)
{
	struct dev_pm_opp *opp = container_of(head, struct dev_pm_opp, rcu_head);

	kfree_rcu(opp, rcu_head);
}

static void kfree_device_rcu(struct rcu_head *head)
{
	struct device_opp *device_opp = container_of(head, struct device_opp, rcu_head);

	kfree_rcu(device_opp, rcu_head);
}

static void __dev_pm_opp_remove(struct device_opp *dev_opp,
				struct dev_pm_opp *opp)
{
	/*
	 * Notify the changes in the availability of the operable
	 * frequency/voltage list.
	 */
	srcu_notifier_call_chain(&dev_opp->srcu_head, OPP_EVENT_REMOVE, opp);
	list_del_rcu(&opp->node);
	call_srcu(&dev_opp->srcu_head.srcu, &opp->rcu_head, kfree_opp_rcu);

	if (list_empty(&dev_opp->opp_list)) {
		list_del_rcu(&dev_opp->node);
		call_srcu(&dev_opp->srcu_head.srcu, &dev_opp->rcu_head,
			  kfree_device_rcu);
	}
}

/**
 * dev_pm_opp_remove()  - Remove an OPP from OPP list
 * @dev:	device for which we do this operation
 * @freq:	OPP to remove with matching 'freq'
 *
 * This function removes an opp from the opp list.
 */
void dev_pm_opp_remove(struct device *dev, unsigned long freq)
{
	struct dev_pm_opp *opp;
	struct device_opp *dev_opp;
	bool found = false;

	/* Hold our list modification lock here */
	mutex_lock(&dev_opp_list_lock);

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp))
		goto unlock;

	list_for_each_entry(opp, &dev_opp->opp_list, node) {
		if (opp->rate == freq) {
			found = true;
			break;
		}
	}

	if (!found) {
		dev_warn(dev, "%s: Couldn't find OPP with freq: %lu\n",
			 __func__, freq);
		goto unlock;
	}

	__dev_pm_opp_remove(dev_opp, opp);
unlock:
	mutex_unlock(&dev_opp_list_lock);
}
EXPORT_SYMBOL_GPL(dev_pm_opp_remove);

/**
 * opp_set_availability() - helper to set the availability of an opp
 * @dev:		device for which we do this operation
 * @freq:		OPP frequency to modify availability
 * @availability_req:	availability status requested for this opp
 *
 * Set the availability of an OPP with an RCU operation, opp_{enable,disable}
 * share a common logic which is isolated here.
 *
 * Returns -EINVAL for bad pointers, -ENOMEM if no memory available for the
 * copy operation, returns 0 if no modifcation was done OR modification was
 * successful.
 *
 * Locking: The internal device_opp and opp structures are RCU protected.
 * Hence this function internally uses RCU updater strategy with mutex locks to
 * keep the integrity of the internal data structures. Callers should ensure
 * that this function is *NOT* called under RCU protection or in contexts where
 * mutex locking or synchronize_rcu() blocking calls cannot be used.
 */
static int opp_set_availability(struct device *dev, unsigned long freq,
		bool availability_req)
{
	struct device_opp *dev_opp;
	struct dev_pm_opp *new_opp, *tmp_opp, *opp = ERR_PTR(-ENODEV);
	int r = 0;

	/* keep the node allocated */
	new_opp = kmalloc(sizeof(*new_opp), GFP_KERNEL);
	if (!new_opp) {
		dev_warn(dev, "%s: Unable to create OPP\n", __func__);
		return -ENOMEM;
	}

	mutex_lock(&dev_opp_list_lock);

	/* Find the device_opp */
	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
		r = PTR_ERR(dev_opp);
		dev_warn(dev, "%s: Device OPP not found (%d)\n", __func__, r);
		goto unlock;
	}

	/* Do we have the frequency? */
	list_for_each_entry(tmp_opp, &dev_opp->opp_list, node) {
		if (tmp_opp->rate == freq) {
			opp = tmp_opp;
			break;
		}
	}
	if (IS_ERR(opp)) {
		r = PTR_ERR(opp);
		goto unlock;
	}

	/* Is update really needed? */
	if (opp->available == availability_req)
		goto unlock;
	/* copy the old data over */
	*new_opp = *opp;

	/* plug in new node */
	new_opp->available = availability_req;

	list_replace_rcu(&opp->node, &new_opp->node);
	mutex_unlock(&dev_opp_list_lock);
	call_srcu(&dev_opp->srcu_head.srcu, &opp->rcu_head, kfree_opp_rcu);

	/* Notify the change of the OPP availability */
	if (availability_req)
		srcu_notifier_call_chain(&dev_opp->srcu_head, OPP_EVENT_ENABLE,
					 new_opp);
	else
		srcu_notifier_call_chain(&dev_opp->srcu_head, OPP_EVENT_DISABLE,
					 new_opp);

	return 0;

unlock:
	mutex_unlock(&dev_opp_list_lock);
	kfree(new_opp);
	return r;
}

/**
 * dev_pm_opp_enable() - Enable a specific OPP
 * @dev:	device for which we do this operation
 * @freq:	OPP frequency to enable
 *
 * Enables a provided opp. If the operation is valid, this returns 0, else the
 * corresponding error value. It is meant to be used for users an OPP available
 * after being temporarily made unavailable with dev_pm_opp_disable.
 *
 * Locking: The internal device_opp and opp structures are RCU protected.
 * Hence this function indirectly uses RCU and mutex locks to keep the
 * integrity of the internal data structures. Callers should ensure that
 * this function is *NOT* called under RCU protection or in contexts where
 * mutex locking or synchronize_rcu() blocking calls cannot be used.
 */
int dev_pm_opp_enable(struct device *dev, unsigned long freq)
{
	return opp_set_availability(dev, freq, true);
}
EXPORT_SYMBOL_GPL(dev_pm_opp_enable);

/**
 * dev_pm_opp_disable() - Disable a specific OPP
 * @dev:	device for which we do this operation
 * @freq:	OPP frequency to disable
 *
 * Disables a provided opp. If the operation is valid, this returns
 * 0, else the corresponding error value. It is meant to be a temporary
 * control by users to make this OPP not available until the circumstances are
 * right to make it available again (with a call to dev_pm_opp_enable).
 *
 * Locking: The internal device_opp and opp structures are RCU protected.
 * Hence this function indirectly uses RCU and mutex locks to keep the
 * integrity of the internal data structures. Callers should ensure that
 * this function is *NOT* called under RCU protection or in contexts where
 * mutex locking or synchronize_rcu() blocking calls cannot be used.
 */
int dev_pm_opp_disable(struct device *dev, unsigned long freq)
{
	return opp_set_availability(dev, freq, false);
}
EXPORT_SYMBOL_GPL(dev_pm_opp_disable);

/**
 * dev_pm_opp_get_notifier() - find notifier_head of the device with opp
 * @dev:	device pointer used to lookup device OPPs.
 */
struct srcu_notifier_head *dev_pm_opp_get_notifier(struct device *dev)
{
	struct device_opp *dev_opp = find_device_opp(dev);

	if (IS_ERR(dev_opp))
		return ERR_CAST(dev_opp); /* matching type */

	return &dev_opp->srcu_head;
}

#ifdef CONFIG_OF
/**
 * of_init_opp_table() - Initialize opp table from device tree
 * @dev:	device pointer used to lookup device OPPs.
 *
 * Register the initial OPP table with the OPP library for given device.
 */
int of_init_opp_table(struct device *dev)
{
	const struct property *prop;
	const __be32 *val;
	int nr;

	prop = of_find_property(dev->of_node, "operating-points", NULL);
	if (!prop)
		return -ENODEV;
	if (!prop->value)
		return -ENODATA;

	/*
	 * Each OPP is a set of tuples consisting of frequency and
	 * voltage like <freq-kHz vol-uV>.
	 */
	nr = prop->length / sizeof(u32);
	if (nr % 2) {
		dev_err(dev, "%s: Invalid OPP list\n", __func__);
		return -EINVAL;
	}

	val = prop->value;
	while (nr) {
		unsigned long freq = be32_to_cpup(val++) * 1000;
		unsigned long volt = be32_to_cpup(val++);

		if (dev_pm_opp_add_dynamic(dev, freq, volt, false))
			dev_warn(dev, "%s: Failed to add OPP %ld\n",
				 __func__, freq);
		nr -= 2;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(of_init_opp_table);

/**
 * of_free_opp_table() - Free OPP table entries created from static DT entries
 * @dev:	device pointer used to lookup device OPPs.
 *
 * Free OPPs created using static entries present in DT.
 */
void of_free_opp_table(struct device *dev)
{
	struct device_opp *dev_opp;
	struct dev_pm_opp *opp, *tmp;

	/* Check for existing list for 'dev' */
	dev_opp = find_device_opp(dev);
	if (WARN(IS_ERR(dev_opp), "%s: dev_opp: %ld\n", dev_name(dev),
		 PTR_ERR(dev_opp)))
		return;

	/* Hold our list modification lock here */
	mutex_lock(&dev_opp_list_lock);

	/* Free static OPPs */
	list_for_each_entry_safe(opp, tmp, &dev_opp->opp_list, node) {
		if (!opp->dynamic)
			__dev_pm_opp_remove(dev_opp, opp);
	}

	mutex_unlock(&dev_opp_list_lock);
}
EXPORT_SYMBOL_GPL(of_free_opp_table);
#endif