Root/drivers/hwspinlock/hwspinlock_core.c

1/*
2 * Hardware spinlock framework
3 *
4 * Copyright (C) 2010 Texas Instruments Incorporated - http://www.ti.com
5 *
6 * Contact: Ohad Ben-Cohen <ohad@wizery.com>
7 *
8 * This program is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 as published
10 * by the Free Software Foundation.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 */
17
18#define pr_fmt(fmt) "%s: " fmt, __func__
19
20#include <linux/kernel.h>
21#include <linux/module.h>
22#include <linux/spinlock.h>
23#include <linux/types.h>
24#include <linux/err.h>
25#include <linux/jiffies.h>
26#include <linux/radix-tree.h>
27#include <linux/hwspinlock.h>
28#include <linux/pm_runtime.h>
29#include <linux/mutex.h>
30
31#include "hwspinlock_internal.h"
32
33/* radix tree tags */
34#define HWSPINLOCK_UNUSED (0) /* tags an hwspinlock as unused */
35
36/*
37 * A radix tree is used to maintain the available hwspinlock instances.
38 * The tree associates hwspinlock pointers with their integer key id,
39 * and provides easy-to-use API which makes the hwspinlock core code simple
40 * and easy to read.
41 *
42 * Radix trees are quick on lookups, and reasonably efficient in terms of
43 * storage, especially with high density usages such as this framework
44 * requires (a continuous range of integer keys, beginning with zero, is
45 * used as the ID's of the hwspinlock instances).
46 *
47 * The radix tree API supports tagging items in the tree, which this
48 * framework uses to mark unused hwspinlock instances (see the
49 * HWSPINLOCK_UNUSED tag above). As a result, the process of querying the
50 * tree, looking for an unused hwspinlock instance, is now reduced to a
51 * single radix tree API call.
52 */
53static RADIX_TREE(hwspinlock_tree, GFP_KERNEL);
54
55/*
56 * Synchronization of access to the tree is achieved using this mutex,
57 * as the radix-tree API requires that users provide all synchronisation.
58 * A mutex is needed because we're using non-atomic radix tree allocations.
59 */
60static DEFINE_MUTEX(hwspinlock_tree_lock);
61
62
63/**
64 * __hwspin_trylock() - attempt to lock a specific hwspinlock
65 * @hwlock: an hwspinlock which we want to trylock
66 * @mode: controls whether local interrupts are disabled or not
67 * @flags: a pointer where the caller's interrupt state will be saved at (if
68 * requested)
69 *
70 * This function attempts to lock an hwspinlock, and will immediately
71 * fail if the hwspinlock is already taken.
72 *
73 * Upon a successful return from this function, preemption (and possibly
74 * interrupts) is disabled, so the caller must not sleep, and is advised to
75 * release the hwspinlock as soon as possible. This is required in order to
76 * minimize remote cores polling on the hardware interconnect.
77 *
78 * The user decides whether local interrupts are disabled or not, and if yes,
79 * whether he wants their previous state to be saved. It is up to the user
80 * to choose the appropriate @mode of operation, exactly the same way users
81 * should decide between spin_trylock, spin_trylock_irq and
82 * spin_trylock_irqsave.
83 *
84 * Returns 0 if we successfully locked the hwspinlock or -EBUSY if
85 * the hwspinlock was already taken.
86 * This function will never sleep.
87 */
88int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
89{
90    int ret;
91
92    BUG_ON(!hwlock);
93    BUG_ON(!flags && mode == HWLOCK_IRQSTATE);
94
95    /*
96     * This spin_lock{_irq, _irqsave} serves three purposes:
97     *
98     * 1. Disable preemption, in order to minimize the period of time
99     * in which the hwspinlock is taken. This is important in order
100     * to minimize the possible polling on the hardware interconnect
101     * by a remote user of this lock.
102     * 2. Make the hwspinlock SMP-safe (so we can take it from
103     * additional contexts on the local host).
104     * 3. Ensure that in_atomic/might_sleep checks catch potential
105     * problems with hwspinlock usage (e.g. scheduler checks like
106     * 'scheduling while atomic' etc.)
107     */
108    if (mode == HWLOCK_IRQSTATE)
109        ret = spin_trylock_irqsave(&hwlock->lock, *flags);
110    else if (mode == HWLOCK_IRQ)
111        ret = spin_trylock_irq(&hwlock->lock);
112    else
113        ret = spin_trylock(&hwlock->lock);
114
115    /* is lock already taken by another context on the local cpu ? */
116    if (!ret)
117        return -EBUSY;
118
119    /* try to take the hwspinlock device */
120    ret = hwlock->bank->ops->trylock(hwlock);
121
122    /* if hwlock is already taken, undo spin_trylock_* and exit */
123    if (!ret) {
124        if (mode == HWLOCK_IRQSTATE)
125            spin_unlock_irqrestore(&hwlock->lock, *flags);
126        else if (mode == HWLOCK_IRQ)
127            spin_unlock_irq(&hwlock->lock);
128        else
129            spin_unlock(&hwlock->lock);
130
131        return -EBUSY;
132    }
133
134    /*
135     * We can be sure the other core's memory operations
136     * are observable to us only _after_ we successfully take
137     * the hwspinlock, and we must make sure that subsequent memory
138     * operations (both reads and writes) will not be reordered before
139     * we actually took the hwspinlock.
140     *
141     * Note: the implicit memory barrier of the spinlock above is too
142     * early, so we need this additional explicit memory barrier.
143     */
144    mb();
145
146    return 0;
147}
148EXPORT_SYMBOL_GPL(__hwspin_trylock);
149
150/**
151 * __hwspin_lock_timeout() - lock an hwspinlock with timeout limit
152 * @hwlock: the hwspinlock to be locked
153 * @timeout: timeout value in msecs
154 * @mode: mode which controls whether local interrupts are disabled or not
155 * @flags: a pointer to where the caller's interrupt state will be saved at (if
156 * requested)
157 *
158 * This function locks the given @hwlock. If the @hwlock
159 * is already taken, the function will busy loop waiting for it to
160 * be released, but give up after @timeout msecs have elapsed.
161 *
162 * Upon a successful return from this function, preemption is disabled
163 * (and possibly local interrupts, too), so the caller must not sleep,
164 * and is advised to release the hwspinlock as soon as possible.
165 * This is required in order to minimize remote cores polling on the
166 * hardware interconnect.
167 *
168 * The user decides whether local interrupts are disabled or not, and if yes,
169 * whether he wants their previous state to be saved. It is up to the user
170 * to choose the appropriate @mode of operation, exactly the same way users
171 * should decide between spin_lock, spin_lock_irq and spin_lock_irqsave.
172 *
173 * Returns 0 when the @hwlock was successfully taken, and an appropriate
174 * error code otherwise (most notably -ETIMEDOUT if the @hwlock is still
175 * busy after @timeout msecs). The function will never sleep.
176 */
177int __hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int to,
178                    int mode, unsigned long *flags)
179{
180    int ret;
181    unsigned long expire;
182
183    expire = msecs_to_jiffies(to) + jiffies;
184
185    for (;;) {
186        /* Try to take the hwspinlock */
187        ret = __hwspin_trylock(hwlock, mode, flags);
188        if (ret != -EBUSY)
189            break;
190
191        /*
192         * The lock is already taken, let's check if the user wants
193         * us to try again
194         */
195        if (time_is_before_eq_jiffies(expire))
196            return -ETIMEDOUT;
197
198        /*
199         * Allow platform-specific relax handlers to prevent
200         * hogging the interconnect (no sleeping, though)
201         */
202        if (hwlock->bank->ops->relax)
203            hwlock->bank->ops->relax(hwlock);
204    }
205
206    return ret;
207}
208EXPORT_SYMBOL_GPL(__hwspin_lock_timeout);
209
210/**
211 * __hwspin_unlock() - unlock a specific hwspinlock
212 * @hwlock: a previously-acquired hwspinlock which we want to unlock
213 * @mode: controls whether local interrupts needs to be restored or not
214 * @flags: previous caller's interrupt state to restore (if requested)
215 *
216 * This function will unlock a specific hwspinlock, enable preemption and
217 * (possibly) enable interrupts or restore their previous state.
218 * @hwlock must be already locked before calling this function: it is a bug
219 * to call unlock on a @hwlock that is already unlocked.
220 *
221 * The user decides whether local interrupts should be enabled or not, and
222 * if yes, whether he wants their previous state to be restored. It is up
223 * to the user to choose the appropriate @mode of operation, exactly the
224 * same way users decide between spin_unlock, spin_unlock_irq and
225 * spin_unlock_irqrestore.
226 *
227 * The function will never sleep.
228 */
229void __hwspin_unlock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
230{
231    BUG_ON(!hwlock);
232    BUG_ON(!flags && mode == HWLOCK_IRQSTATE);
233
234    /*
235     * We must make sure that memory operations (both reads and writes),
236     * done before unlocking the hwspinlock, will not be reordered
237     * after the lock is released.
238     *
239     * That's the purpose of this explicit memory barrier.
240     *
241     * Note: the memory barrier induced by the spin_unlock below is too
242     * late; the other core is going to access memory soon after it will
243     * take the hwspinlock, and by then we want to be sure our memory
244     * operations are already observable.
245     */
246    mb();
247
248    hwlock->bank->ops->unlock(hwlock);
249
250    /* Undo the spin_trylock{_irq, _irqsave} called while locking */
251    if (mode == HWLOCK_IRQSTATE)
252        spin_unlock_irqrestore(&hwlock->lock, *flags);
253    else if (mode == HWLOCK_IRQ)
254        spin_unlock_irq(&hwlock->lock);
255    else
256        spin_unlock(&hwlock->lock);
257}
258EXPORT_SYMBOL_GPL(__hwspin_unlock);
259
260static int hwspin_lock_register_single(struct hwspinlock *hwlock, int id)
261{
262    struct hwspinlock *tmp;
263    int ret;
264
265    mutex_lock(&hwspinlock_tree_lock);
266
267    ret = radix_tree_insert(&hwspinlock_tree, id, hwlock);
268    if (ret) {
269        if (ret == -EEXIST)
270            pr_err("hwspinlock id %d already exists!\n", id);
271        goto out;
272    }
273
274    /* mark this hwspinlock as available */
275    tmp = radix_tree_tag_set(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
276
277    /* self-sanity check which should never fail */
278    WARN_ON(tmp != hwlock);
279
280out:
281    mutex_unlock(&hwspinlock_tree_lock);
282    return 0;
283}
284
285static struct hwspinlock *hwspin_lock_unregister_single(unsigned int id)
286{
287    struct hwspinlock *hwlock = NULL;
288    int ret;
289
290    mutex_lock(&hwspinlock_tree_lock);
291
292    /* make sure the hwspinlock is not in use (tag is set) */
293    ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
294    if (ret == 0) {
295        pr_err("hwspinlock %d still in use (or not present)\n", id);
296        goto out;
297    }
298
299    hwlock = radix_tree_delete(&hwspinlock_tree, id);
300    if (!hwlock) {
301        pr_err("failed to delete hwspinlock %d\n", id);
302        goto out;
303    }
304
305out:
306    mutex_unlock(&hwspinlock_tree_lock);
307    return hwlock;
308}
309
310/**
311 * hwspin_lock_register() - register a new hw spinlock device
312 * @bank: the hwspinlock device, which usually provides numerous hw locks
313 * @dev: the backing device
314 * @ops: hwspinlock handlers for this device
315 * @base_id: id of the first hardware spinlock in this bank
316 * @num_locks: number of hwspinlocks provided by this device
317 *
318 * This function should be called from the underlying platform-specific
319 * implementation, to register a new hwspinlock device instance.
320 *
321 * Should be called from a process context (might sleep)
322 *
323 * Returns 0 on success, or an appropriate error code on failure
324 */
325int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev,
326        const struct hwspinlock_ops *ops, int base_id, int num_locks)
327{
328    struct hwspinlock *hwlock;
329    int ret = 0, i;
330
331    if (!bank || !ops || !dev || !num_locks || !ops->trylock ||
332                            !ops->unlock) {
333        pr_err("invalid parameters\n");
334        return -EINVAL;
335    }
336
337    bank->dev = dev;
338    bank->ops = ops;
339    bank->base_id = base_id;
340    bank->num_locks = num_locks;
341
342    for (i = 0; i < num_locks; i++) {
343        hwlock = &bank->lock[i];
344
345        spin_lock_init(&hwlock->lock);
346        hwlock->bank = bank;
347
348        ret = hwspin_lock_register_single(hwlock, base_id + i);
349        if (ret)
350            goto reg_failed;
351    }
352
353    return 0;
354
355reg_failed:
356    while (--i >= 0)
357        hwspin_lock_unregister_single(base_id + i);
358    return ret;
359}
360EXPORT_SYMBOL_GPL(hwspin_lock_register);
361
362/**
363 * hwspin_lock_unregister() - unregister an hw spinlock device
364 * @bank: the hwspinlock device, which usually provides numerous hw locks
365 *
366 * This function should be called from the underlying platform-specific
367 * implementation, to unregister an existing (and unused) hwspinlock.
368 *
369 * Should be called from a process context (might sleep)
370 *
371 * Returns 0 on success, or an appropriate error code on failure
372 */
373int hwspin_lock_unregister(struct hwspinlock_device *bank)
374{
375    struct hwspinlock *hwlock, *tmp;
376    int i;
377
378    for (i = 0; i < bank->num_locks; i++) {
379        hwlock = &bank->lock[i];
380
381        tmp = hwspin_lock_unregister_single(bank->base_id + i);
382        if (!tmp)
383            return -EBUSY;
384
385        /* self-sanity check that should never fail */
386        WARN_ON(tmp != hwlock);
387    }
388
389    return 0;
390}
391EXPORT_SYMBOL_GPL(hwspin_lock_unregister);
392
393/**
394 * __hwspin_lock_request() - tag an hwspinlock as used and power it up
395 *
396 * This is an internal function that prepares an hwspinlock instance
397 * before it is given to the user. The function assumes that
398 * hwspinlock_tree_lock is taken.
399 *
400 * Returns 0 or positive to indicate success, and a negative value to
401 * indicate an error (with the appropriate error code)
402 */
403static int __hwspin_lock_request(struct hwspinlock *hwlock)
404{
405    struct device *dev = hwlock->bank->dev;
406    struct hwspinlock *tmp;
407    int ret;
408
409    /* prevent underlying implementation from being removed */
410    if (!try_module_get(dev->driver->owner)) {
411        dev_err(dev, "%s: can't get owner\n", __func__);
412        return -EINVAL;
413    }
414
415    /* notify PM core that power is now needed */
416    ret = pm_runtime_get_sync(dev);
417    if (ret < 0) {
418        dev_err(dev, "%s: can't power on device\n", __func__);
419        return ret;
420    }
421
422    /* mark hwspinlock as used, should not fail */
423    tmp = radix_tree_tag_clear(&hwspinlock_tree, hwlock_to_id(hwlock),
424                            HWSPINLOCK_UNUSED);
425
426    /* self-sanity check that should never fail */
427    WARN_ON(tmp != hwlock);
428
429    return ret;
430}
431
432/**
433 * hwspin_lock_get_id() - retrieve id number of a given hwspinlock
434 * @hwlock: a valid hwspinlock instance
435 *
436 * Returns the id number of a given @hwlock, or -EINVAL if @hwlock is invalid.
437 */
438int hwspin_lock_get_id(struct hwspinlock *hwlock)
439{
440    if (!hwlock) {
441        pr_err("invalid hwlock\n");
442        return -EINVAL;
443    }
444
445    return hwlock_to_id(hwlock);
446}
447EXPORT_SYMBOL_GPL(hwspin_lock_get_id);
448
449/**
450 * hwspin_lock_request() - request an hwspinlock
451 *
452 * This function should be called by users of the hwspinlock device,
453 * in order to dynamically assign them an unused hwspinlock.
454 * Usually the user of this lock will then have to communicate the lock's id
455 * to the remote core before it can be used for synchronization (to get the
456 * id of a given hwlock, use hwspin_lock_get_id()).
457 *
458 * Should be called from a process context (might sleep)
459 *
460 * Returns the address of the assigned hwspinlock, or NULL on error
461 */
462struct hwspinlock *hwspin_lock_request(void)
463{
464    struct hwspinlock *hwlock;
465    int ret;
466
467    mutex_lock(&hwspinlock_tree_lock);
468
469    /* look for an unused lock */
470    ret = radix_tree_gang_lookup_tag(&hwspinlock_tree, (void **)&hwlock,
471                        0, 1, HWSPINLOCK_UNUSED);
472    if (ret == 0) {
473        pr_warn("a free hwspinlock is not available\n");
474        hwlock = NULL;
475        goto out;
476    }
477
478    /* sanity check that should never fail */
479    WARN_ON(ret > 1);
480
481    /* mark as used and power up */
482    ret = __hwspin_lock_request(hwlock);
483    if (ret < 0)
484        hwlock = NULL;
485
486out:
487    mutex_unlock(&hwspinlock_tree_lock);
488    return hwlock;
489}
490EXPORT_SYMBOL_GPL(hwspin_lock_request);
491
492/**
493 * hwspin_lock_request_specific() - request for a specific hwspinlock
494 * @id: index of the specific hwspinlock that is requested
495 *
496 * This function should be called by users of the hwspinlock module,
497 * in order to assign them a specific hwspinlock.
498 * Usually early board code will be calling this function in order to
499 * reserve specific hwspinlock ids for predefined purposes.
500 *
501 * Should be called from a process context (might sleep)
502 *
503 * Returns the address of the assigned hwspinlock, or NULL on error
504 */
505struct hwspinlock *hwspin_lock_request_specific(unsigned int id)
506{
507    struct hwspinlock *hwlock;
508    int ret;
509
510    mutex_lock(&hwspinlock_tree_lock);
511
512    /* make sure this hwspinlock exists */
513    hwlock = radix_tree_lookup(&hwspinlock_tree, id);
514    if (!hwlock) {
515        pr_warn("hwspinlock %u does not exist\n", id);
516        goto out;
517    }
518
519    /* sanity check (this shouldn't happen) */
520    WARN_ON(hwlock_to_id(hwlock) != id);
521
522    /* make sure this hwspinlock is unused */
523    ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
524    if (ret == 0) {
525        pr_warn("hwspinlock %u is already in use\n", id);
526        hwlock = NULL;
527        goto out;
528    }
529
530    /* mark as used and power up */
531    ret = __hwspin_lock_request(hwlock);
532    if (ret < 0)
533        hwlock = NULL;
534
535out:
536    mutex_unlock(&hwspinlock_tree_lock);
537    return hwlock;
538}
539EXPORT_SYMBOL_GPL(hwspin_lock_request_specific);
540
541/**
542 * hwspin_lock_free() - free a specific hwspinlock
543 * @hwlock: the specific hwspinlock to free
544 *
545 * This function mark @hwlock as free again.
546 * Should only be called with an @hwlock that was retrieved from
547 * an earlier call to omap_hwspin_lock_request{_specific}.
548 *
549 * Should be called from a process context (might sleep)
550 *
551 * Returns 0 on success, or an appropriate error code on failure
552 */
553int hwspin_lock_free(struct hwspinlock *hwlock)
554{
555    struct device *dev;
556    struct hwspinlock *tmp;
557    int ret;
558
559    if (!hwlock) {
560        pr_err("invalid hwlock\n");
561        return -EINVAL;
562    }
563
564    dev = hwlock->bank->dev;
565    mutex_lock(&hwspinlock_tree_lock);
566
567    /* make sure the hwspinlock is used */
568    ret = radix_tree_tag_get(&hwspinlock_tree, hwlock_to_id(hwlock),
569                            HWSPINLOCK_UNUSED);
570    if (ret == 1) {
571        dev_err(dev, "%s: hwlock is already free\n", __func__);
572        dump_stack();
573        ret = -EINVAL;
574        goto out;
575    }
576
577    /* notify the underlying device that power is not needed */
578    ret = pm_runtime_put(dev);
579    if (ret < 0)
580        goto out;
581
582    /* mark this hwspinlock as available */
583    tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
584                            HWSPINLOCK_UNUSED);
585
586    /* sanity check (this shouldn't happen) */
587    WARN_ON(tmp != hwlock);
588
589    module_put(dev->driver->owner);
590
591out:
592    mutex_unlock(&hwspinlock_tree_lock);
593    return ret;
594}
595EXPORT_SYMBOL_GPL(hwspin_lock_free);
596
597MODULE_LICENSE("GPL v2");
598MODULE_DESCRIPTION("Hardware spinlock interface");
599MODULE_AUTHOR("Ohad Ben-Cohen <ohad@wizery.com>");
600

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