summaryrefslogtreecommitdiffstats
path: root/drivers/hwspinlock/hwspinlock_core.c
blob: db713c0dfba4d6c6272ac19c79b793595a9cdad7 (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
/*
 * Hardware spinlock framework
 *
 * Copyright (C) 2010 Texas Instruments Incorporated - http://www.ti.com
 *
 * Contact: Ohad Ben-Cohen <ohad@wizery.com>
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#define pr_fmt(fmt)    "%s: " fmt, __func__

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/err.h>
#include <linux/jiffies.h>
#include <linux/radix-tree.h>
#include <linux/hwspinlock.h>
#include <linux/pm_runtime.h>
#include <linux/mutex.h>

#include "hwspinlock_internal.h"

/* radix tree tags */
#define HWSPINLOCK_UNUSED	(0) /* tags an hwspinlock as unused */

/*
 * A radix tree is used to maintain the available hwspinlock instances.
 * The tree associates hwspinlock pointers with their integer key id,
 * and provides easy-to-use API which makes the hwspinlock core code simple
 * and easy to read.
 *
 * Radix trees are quick on lookups, and reasonably efficient in terms of
 * storage, especially with high density usages such as this framework
 * requires (a continuous range of integer keys, beginning with zero, is
 * used as the ID's of the hwspinlock instances).
 *
 * The radix tree API supports tagging items in the tree, which this
 * framework uses to mark unused hwspinlock instances (see the
 * HWSPINLOCK_UNUSED tag above). As a result, the process of querying the
 * tree, looking for an unused hwspinlock instance, is now reduced to a
 * single radix tree API call.
 */
static RADIX_TREE(hwspinlock_tree, GFP_KERNEL);

/*
 * Synchronization of access to the tree is achieved using this mutex,
 * as the radix-tree API requires that users provide all synchronisation.
 * A mutex is needed because we're using non-atomic radix tree allocations.
 */
static DEFINE_MUTEX(hwspinlock_tree_lock);


/**
 * __hwspin_trylock() - attempt to lock a specific hwspinlock
 * @hwlock: an hwspinlock which we want to trylock
 * @mode: controls whether local interrupts are disabled or not
 * @flags: a pointer where the caller's interrupt state will be saved at (if
 *         requested)
 *
 * This function attempts to lock an hwspinlock, and will immediately
 * fail if the hwspinlock is already taken.
 *
 * Upon a successful return from this function, preemption (and possibly
 * interrupts) is disabled, so the caller must not sleep, and is advised to
 * release the hwspinlock as soon as possible. This is required in order to
 * minimize remote cores polling on the hardware interconnect.
 *
 * The user decides whether local interrupts are disabled or not, and if yes,
 * whether he wants their previous state to be saved. It is up to the user
 * to choose the appropriate @mode of operation, exactly the same way users
 * should decide between spin_trylock, spin_trylock_irq and
 * spin_trylock_irqsave.
 *
 * Returns 0 if we successfully locked the hwspinlock or -EBUSY if
 * the hwspinlock was already taken.
 * This function will never sleep.
 */
int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
{
	int ret;

	BUG_ON(!hwlock);
	BUG_ON(!flags && mode == HWLOCK_IRQSTATE);

	/*
	 * This spin_lock{_irq, _irqsave} serves three purposes:
	 *
	 * 1. Disable preemption, in order to minimize the period of time
	 *    in which the hwspinlock is taken. This is important in order
	 *    to minimize the possible polling on the hardware interconnect
	 *    by a remote user of this lock.
	 * 2. Make the hwspinlock SMP-safe (so we can take it from
	 *    additional contexts on the local host).
	 * 3. Ensure that in_atomic/might_sleep checks catch potential
	 *    problems with hwspinlock usage (e.g. scheduler checks like
	 *    'scheduling while atomic' etc.)
	 */
	if (mode == HWLOCK_IRQSTATE)
		ret = spin_trylock_irqsave(&hwlock->lock, *flags);
	else if (mode == HWLOCK_IRQ)
		ret = spin_trylock_irq(&hwlock->lock);
	else
		ret = spin_trylock(&hwlock->lock);

	/* is lock already taken by another context on the local cpu ? */
	if (!ret)
		return -EBUSY;

	/* try to take the hwspinlock device */
	ret = hwlock->bank->ops->trylock(hwlock);

	/* if hwlock is already taken, undo spin_trylock_* and exit */
	if (!ret) {
		if (mode == HWLOCK_IRQSTATE)
			spin_unlock_irqrestore(&hwlock->lock, *flags);
		else if (mode == HWLOCK_IRQ)
			spin_unlock_irq(&hwlock->lock);
		else
			spin_unlock(&hwlock->lock);

		return -EBUSY;
	}

	/*
	 * We can be sure the other core's memory operations
	 * are observable to us only _after_ we successfully take
	 * the hwspinlock, and we must make sure that subsequent memory
	 * operations (both reads and writes) will not be reordered before
	 * we actually took the hwspinlock.
	 *
	 * Note: the implicit memory barrier of the spinlock above is too
	 * early, so we need this additional explicit memory barrier.
	 */
	mb();

	return 0;
}
EXPORT_SYMBOL_GPL(__hwspin_trylock);

/**
 * __hwspin_lock_timeout() - lock an hwspinlock with timeout limit
 * @hwlock: the hwspinlock to be locked
 * @timeout: timeout value in msecs
 * @mode: mode which controls whether local interrupts are disabled or not
 * @flags: a pointer to where the caller's interrupt state will be saved at (if
 *         requested)
 *
 * This function locks the given @hwlock. If the @hwlock
 * is already taken, the function will busy loop waiting for it to
 * be released, but give up after @timeout msecs have elapsed.
 *
 * Upon a successful return from this function, preemption is disabled
 * (and possibly local interrupts, too), so the caller must not sleep,
 * and is advised to release the hwspinlock as soon as possible.
 * This is required in order to minimize remote cores polling on the
 * hardware interconnect.
 *
 * The user decides whether local interrupts are disabled or not, and if yes,
 * whether he wants their previous state to be saved. It is up to the user
 * to choose the appropriate @mode of operation, exactly the same way users
 * should decide between spin_lock, spin_lock_irq and spin_lock_irqsave.
 *
 * Returns 0 when the @hwlock was successfully taken, and an appropriate
 * error code otherwise (most notably -ETIMEDOUT if the @hwlock is still
 * busy after @timeout msecs). The function will never sleep.
 */
int __hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int to,
					int mode, unsigned long *flags)
{
	int ret;
	unsigned long expire;

	expire = msecs_to_jiffies(to) + jiffies;

	for (;;) {
		/* Try to take the hwspinlock */
		ret = __hwspin_trylock(hwlock, mode, flags);
		if (ret != -EBUSY)
			break;

		/*
		 * The lock is already taken, let's check if the user wants
		 * us to try again
		 */
		if (time_is_before_eq_jiffies(expire))
			return -ETIMEDOUT;

		/*
		 * Allow platform-specific relax handlers to prevent
		 * hogging the interconnect (no sleeping, though)
		 */
		if (hwlock->bank->ops->relax)
			hwlock->bank->ops->relax(hwlock);
	}

	return ret;
}
EXPORT_SYMBOL_GPL(__hwspin_lock_timeout);

/**
 * __hwspin_unlock() - unlock a specific hwspinlock
 * @hwlock: a previously-acquired hwspinlock which we want to unlock
 * @mode: controls whether local interrupts needs to be restored or not
 * @flags: previous caller's interrupt state to restore (if requested)
 *
 * This function will unlock a specific hwspinlock, enable preemption and
 * (possibly) enable interrupts or restore their previous state.
 * @hwlock must be already locked before calling this function: it is a bug
 * to call unlock on a @hwlock that is already unlocked.
 *
 * The user decides whether local interrupts should be enabled or not, and
 * if yes, whether he wants their previous state to be restored. It is up
 * to the user to choose the appropriate @mode of operation, exactly the
 * same way users decide between spin_unlock, spin_unlock_irq and
 * spin_unlock_irqrestore.
 *
 * The function will never sleep.
 */
void __hwspin_unlock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
{
	BUG_ON(!hwlock);
	BUG_ON(!flags && mode == HWLOCK_IRQSTATE);

	/*
	 * We must make sure that memory operations (both reads and writes),
	 * done before unlocking the hwspinlock, will not be reordered
	 * after the lock is released.
	 *
	 * That's the purpose of this explicit memory barrier.
	 *
	 * Note: the memory barrier induced by the spin_unlock below is too
	 * late; the other core is going to access memory soon after it will
	 * take the hwspinlock, and by then we want to be sure our memory
	 * operations are already observable.
	 */
	mb();

	hwlock->bank->ops->unlock(hwlock);

	/* Undo the spin_trylock{_irq, _irqsave} called while locking */
	if (mode == HWLOCK_IRQSTATE)
		spin_unlock_irqrestore(&hwlock->lock, *flags);
	else if (mode == HWLOCK_IRQ)
		spin_unlock_irq(&hwlock->lock);
	else
		spin_unlock(&hwlock->lock);
}
EXPORT_SYMBOL_GPL(__hwspin_unlock);

static int hwspin_lock_register_single(struct hwspinlock *hwlock, int id)
{
	struct hwspinlock *tmp;
	int ret;

	mutex_lock(&hwspinlock_tree_lock);

	ret = radix_tree_insert(&hwspinlock_tree, id, hwlock);
	if (ret) {
		if (ret == -EEXIST)
			pr_err("hwspinlock id %d already exists!\n", id);
		goto out;
	}

	/* mark this hwspinlock as available */
	tmp = radix_tree_tag_set(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);

	/* self-sanity check which should never fail */
	WARN_ON(tmp != hwlock);

out:
	mutex_unlock(&hwspinlock_tree_lock);
	return 0;
}

static struct hwspinlock *hwspin_lock_unregister_single(unsigned int id)
{
	struct hwspinlock *hwlock = NULL;
	int ret;

	mutex_lock(&hwspinlock_tree_lock);

	/* make sure the hwspinlock is not in use (tag is set) */
	ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
	if (ret == 0) {
		pr_err("hwspinlock %d still in use (or not present)\n", id);
		goto out;
	}

	hwlock = radix_tree_delete(&hwspinlock_tree, id);
	if (!hwlock) {
		pr_err("failed to delete hwspinlock %d\n", id);
		goto out;
	}

out:
	mutex_unlock(&hwspinlock_tree_lock);
	return hwlock;
}

/**
 * hwspin_lock_register() - register a new hw spinlock device
 * @bank: the hwspinlock device, which usually provides numerous hw locks
 * @dev: the backing device
 * @ops: hwspinlock handlers for this device
 * @base_id: id of the first hardware spinlock in this bank
 * @num_locks: number of hwspinlocks provided by this device
 *
 * This function should be called from the underlying platform-specific
 * implementation, to register a new hwspinlock device instance.
 *
 * Should be called from a process context (might sleep)
 *
 * Returns 0 on success, or an appropriate error code on failure
 */
int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev,
		const struct hwspinlock_ops *ops, int base_id, int num_locks)
{
	struct hwspinlock *hwlock;
	int ret = 0, i;

	if (!bank || !ops || !dev || !num_locks || !ops->trylock ||
							!ops->unlock) {
		pr_err("invalid parameters\n");
		return -EINVAL;
	}

	bank->dev = dev;
	bank->ops = ops;
	bank->base_id = base_id;
	bank->num_locks = num_locks;

	for (i = 0; i < num_locks; i++) {
		hwlock = &bank->lock[i];

		spin_lock_init(&hwlock->lock);
		hwlock->bank = bank;

		ret = hwspin_lock_register_single(hwlock, base_id + i);
		if (ret)
			goto reg_failed;
	}

	return 0;

reg_failed:
	while (--i >= 0)
		hwspin_lock_unregister_single(base_id + i);
	return ret;
}
EXPORT_SYMBOL_GPL(hwspin_lock_register);

/**
 * hwspin_lock_unregister() - unregister an hw spinlock device
 * @bank: the hwspinlock device, which usually provides numerous hw locks
 *
 * This function should be called from the underlying platform-specific
 * implementation, to unregister an existing (and unused) hwspinlock.
 *
 * Should be called from a process context (might sleep)
 *
 * Returns 0 on success, or an appropriate error code on failure
 */
int hwspin_lock_unregister(struct hwspinlock_device *bank)
{
	struct hwspinlock *hwlock, *tmp;
	int i;

	for (i = 0; i < bank->num_locks; i++) {
		hwlock = &bank->lock[i];

		tmp = hwspin_lock_unregister_single(bank->base_id + i);
		if (!tmp)
			return -EBUSY;

		/* self-sanity check that should never fail */
		WARN_ON(tmp != hwlock);
	}

	return 0;
}
EXPORT_SYMBOL_GPL(hwspin_lock_unregister);

/**
 * __hwspin_lock_request() - tag an hwspinlock as used and power it up
 *
 * This is an internal function that prepares an hwspinlock instance
 * before it is given to the user. The function assumes that
 * hwspinlock_tree_lock is taken.
 *
 * Returns 0 or positive to indicate success, and a negative value to
 * indicate an error (with the appropriate error code)
 */
static int __hwspin_lock_request(struct hwspinlock *hwlock)
{
	struct device *dev = hwlock->bank->dev;
	struct hwspinlock *tmp;
	int ret;

	/* prevent underlying implementation from being removed */
	if (!try_module_get(dev->driver->owner)) {
		dev_err(dev, "%s: can't get owner\n", __func__);
		return -EINVAL;
	}

	/* notify PM core that power is now needed */
	ret = pm_runtime_get_sync(dev);
	if (ret < 0) {
		dev_err(dev, "%s: can't power on device\n", __func__);
		return ret;
	}

	/* mark hwspinlock as used, should not fail */
	tmp = radix_tree_tag_clear(&hwspinlock_tree, hwlock_to_id(hwlock),
							HWSPINLOCK_UNUSED);

	/* self-sanity check that should never fail */
	WARN_ON(tmp != hwlock);

	return ret;
}

/**
 * hwspin_lock_get_id() - retrieve id number of a given hwspinlock
 * @hwlock: a valid hwspinlock instance
 *
 * Returns the id number of a given @hwlock, or -EINVAL if @hwlock is invalid.
 */
int hwspin_lock_get_id(struct hwspinlock *hwlock)
{
	if (!hwlock) {
		pr_err("invalid hwlock\n");
		return -EINVAL;
	}

	return hwlock_to_id(hwlock);
}
EXPORT_SYMBOL_GPL(hwspin_lock_get_id);

/**
 * hwspin_lock_request() - request an hwspinlock
 *
 * This function should be called by users of the hwspinlock device,
 * in order to dynamically assign them an unused hwspinlock.
 * Usually the user of this lock will then have to communicate the lock's id
 * to the remote core before it can be used for synchronization (to get the
 * id of a given hwlock, use hwspin_lock_get_id()).
 *
 * Should be called from a process context (might sleep)
 *
 * Returns the address of the assigned hwspinlock, or NULL on error
 */
struct hwspinlock *hwspin_lock_request(void)
{
	struct hwspinlock *hwlock;
	int ret;

	mutex_lock(&hwspinlock_tree_lock);

	/* look for an unused lock */
	ret = radix_tree_gang_lookup_tag(&hwspinlock_tree, (void **)&hwlock,
						0, 1, HWSPINLOCK_UNUSED);
	if (ret == 0) {
		pr_warn("a free hwspinlock is not available\n");
		hwlock = NULL;
		goto out;
	}

	/* sanity check that should never fail */
	WARN_ON(ret > 1);

	/* mark as used and power up */
	ret = __hwspin_lock_request(hwlock);
	if (ret < 0)
		hwlock = NULL;

out:
	mutex_unlock(&hwspinlock_tree_lock);
	return hwlock;
}
EXPORT_SYMBOL_GPL(hwspin_lock_request);

/**
 * hwspin_lock_request_specific() - request for a specific hwspinlock
 * @id: index of the specific hwspinlock that is requested
 *
 * This function should be called by users of the hwspinlock module,
 * in order to assign them a specific hwspinlock.
 * Usually early board code will be calling this function in order to
 * reserve specific hwspinlock ids for predefined purposes.
 *
 * Should be called from a process context (might sleep)
 *
 * Returns the address of the assigned hwspinlock, or NULL on error
 */
struct hwspinlock *hwspin_lock_request_specific(unsigned int id)
{
	struct hwspinlock *hwlock;
	int ret;

	mutex_lock(&hwspinlock_tree_lock);

	/* make sure this hwspinlock exists */
	hwlock = radix_tree_lookup(&hwspinlock_tree, id);
	if (!hwlock) {
		pr_warn("hwspinlock %u does not exist\n", id);
		goto out;
	}

	/* sanity check (this shouldn't happen) */
	WARN_ON(hwlock_to_id(hwlock) != id);

	/* make sure this hwspinlock is unused */
	ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
	if (ret == 0) {
		pr_warn("hwspinlock %u is already in use\n", id);
		hwlock = NULL;
		goto out;
	}

	/* mark as used and power up */
	ret = __hwspin_lock_request(hwlock);
	if (ret < 0)
		hwlock = NULL;

out:
	mutex_unlock(&hwspinlock_tree_lock);
	return hwlock;
}
EXPORT_SYMBOL_GPL(hwspin_lock_request_specific);

/**
 * hwspin_lock_free() - free a specific hwspinlock
 * @hwlock: the specific hwspinlock to free
 *
 * This function mark @hwlock as free again.
 * Should only be called with an @hwlock that was retrieved from
 * an earlier call to omap_hwspin_lock_request{_specific}.
 *
 * Should be called from a process context (might sleep)
 *
 * Returns 0 on success, or an appropriate error code on failure
 */
int hwspin_lock_free(struct hwspinlock *hwlock)
{
	struct device *dev;
	struct hwspinlock *tmp;
	int ret;

	if (!hwlock) {
		pr_err("invalid hwlock\n");
		return -EINVAL;
	}

	dev = hwlock->bank->dev;
	mutex_lock(&hwspinlock_tree_lock);

	/* make sure the hwspinlock is used */
	ret = radix_tree_tag_get(&hwspinlock_tree, hwlock_to_id(hwlock),
							HWSPINLOCK_UNUSED);
	if (ret == 1) {
		dev_err(dev, "%s: hwlock is already free\n", __func__);
		dump_stack();
		ret = -EINVAL;
		goto out;
	}

	/* notify the underlying device that power is not needed */
	ret = pm_runtime_put(dev);
	if (ret < 0)
		goto out;

	/* mark this hwspinlock as available */
	tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
							HWSPINLOCK_UNUSED);

	/* sanity check (this shouldn't happen) */
	WARN_ON(tmp != hwlock);

	module_put(dev->driver->owner);

out:
	mutex_unlock(&hwspinlock_tree_lock);
	return ret;
}
EXPORT_SYMBOL_GPL(hwspin_lock_free);

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Hardware spinlock interface");
MODULE_AUTHOR("Ohad Ben-Cohen <ohad@wizery.com>");
OpenPOWER on IntegriCloud