2 * Hardware spinlock framework
4 * Copyright (C) 2010 Texas Instruments Incorporated - http://www.ti.com
6 * Contact: Ohad Ben-Cohen <ohad@wizery.com>
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.
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.
18 #define pr_fmt(fmt) "%s: " fmt, __func__
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>
31 #include "hwspinlock_internal.h"
34 #define HWSPINLOCK_UNUSED (0) /* tags an hwspinlock as unused */
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
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).
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.
53 static RADIX_TREE(hwspinlock_tree, GFP_KERNEL);
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.
60 static DEFINE_MUTEX(hwspinlock_tree_lock);
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
70 * This function attempts to lock an hwspinlock, and will immediately
71 * fail if the hwspinlock is already taken.
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.
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.
84 * Returns 0 if we successfully locked the hwspinlock or -EBUSY if
85 * the hwspinlock was already taken.
86 * This function will never sleep.
88 int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
93 BUG_ON(!flags && mode == HWLOCK_IRQSTATE);
96 * This spin_lock{_irq, _irqsave} serves three purposes:
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.)
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);
113 ret = spin_trylock(&hwlock->lock);
115 /* is lock already taken by another context on the local cpu ? */
119 /* try to take the hwspinlock device */
120 ret = hwlock->bank->ops->trylock(hwlock);
122 /* if hwlock is already taken, undo spin_trylock_* and exit */
124 if (mode == HWLOCK_IRQSTATE)
125 spin_unlock_irqrestore(&hwlock->lock, *flags);
126 else if (mode == HWLOCK_IRQ)
127 spin_unlock_irq(&hwlock->lock);
129 spin_unlock(&hwlock->lock);
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.
141 * Note: the implicit memory barrier of the spinlock above is too
142 * early, so we need this additional explicit memory barrier.
148 EXPORT_SYMBOL_GPL(__hwspin_trylock);
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
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.
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.
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.
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.
177 int __hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int to,
178 int mode, unsigned long *flags)
181 unsigned long expire;
183 expire = msecs_to_jiffies(to) + jiffies;
186 /* Try to take the hwspinlock */
187 ret = __hwspin_trylock(hwlock, mode, flags);
192 * The lock is already taken, let's check if the user wants
195 if (time_is_before_eq_jiffies(expire))
199 * Allow platform-specific relax handlers to prevent
200 * hogging the interconnect (no sleeping, though)
202 if (hwlock->bank->ops->relax)
203 hwlock->bank->ops->relax(hwlock);
208 EXPORT_SYMBOL_GPL(__hwspin_lock_timeout);
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)
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.
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.
227 * The function will never sleep.
229 void __hwspin_unlock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
232 BUG_ON(!flags && mode == HWLOCK_IRQSTATE);
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.
239 * That's the purpose of this explicit memory barrier.
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.
248 hwlock->bank->ops->unlock(hwlock);
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);
256 spin_unlock(&hwlock->lock);
258 EXPORT_SYMBOL_GPL(__hwspin_unlock);
260 static int hwspin_lock_register_single(struct hwspinlock *hwlock, int id)
262 struct hwspinlock *tmp;
265 mutex_lock(&hwspinlock_tree_lock);
267 ret = radix_tree_insert(&hwspinlock_tree, id, hwlock);
270 pr_err("hwspinlock id %d already exists!\n", id);
274 /* mark this hwspinlock as available */
275 tmp = radix_tree_tag_set(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
277 /* self-sanity check which should never fail */
278 WARN_ON(tmp != hwlock);
281 mutex_unlock(&hwspinlock_tree_lock);
285 static struct hwspinlock *hwspin_lock_unregister_single(unsigned int id)
287 struct hwspinlock *hwlock = NULL;
290 mutex_lock(&hwspinlock_tree_lock);
292 /* make sure the hwspinlock is not in use (tag is set) */
293 ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
295 pr_err("hwspinlock %d still in use (or not present)\n", id);
299 hwlock = radix_tree_delete(&hwspinlock_tree, id);
301 pr_err("failed to delete hwspinlock %d\n", id);
306 mutex_unlock(&hwspinlock_tree_lock);
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
318 * This function should be called from the underlying platform-specific
319 * implementation, to register a new hwspinlock device instance.
321 * Should be called from a process context (might sleep)
323 * Returns 0 on success, or an appropriate error code on failure
325 int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev,
326 const struct hwspinlock_ops *ops, int base_id, int num_locks)
328 struct hwspinlock *hwlock;
331 if (!bank || !ops || !dev || !num_locks || !ops->trylock ||
333 pr_err("invalid parameters\n");
339 bank->base_id = base_id;
340 bank->num_locks = num_locks;
342 for (i = 0; i < num_locks; i++) {
343 hwlock = &bank->lock[i];
345 spin_lock_init(&hwlock->lock);
348 ret = hwspin_lock_register_single(hwlock, base_id + i);
357 hwspin_lock_unregister_single(base_id + i);
360 EXPORT_SYMBOL_GPL(hwspin_lock_register);
363 * hwspin_lock_unregister() - unregister an hw spinlock device
364 * @bank: the hwspinlock device, which usually provides numerous hw locks
366 * This function should be called from the underlying platform-specific
367 * implementation, to unregister an existing (and unused) hwspinlock.
369 * Should be called from a process context (might sleep)
371 * Returns 0 on success, or an appropriate error code on failure
373 int hwspin_lock_unregister(struct hwspinlock_device *bank)
375 struct hwspinlock *hwlock, *tmp;
378 for (i = 0; i < bank->num_locks; i++) {
379 hwlock = &bank->lock[i];
381 tmp = hwspin_lock_unregister_single(bank->base_id + i);
385 /* self-sanity check that should never fail */
386 WARN_ON(tmp != hwlock);
391 EXPORT_SYMBOL_GPL(hwspin_lock_unregister);
394 * __hwspin_lock_request() - tag an hwspinlock as used and power it up
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.
400 * Returns 0 or positive to indicate success, and a negative value to
401 * indicate an error (with the appropriate error code)
403 static int __hwspin_lock_request(struct hwspinlock *hwlock)
405 struct device *dev = hwlock->bank->dev;
406 struct hwspinlock *tmp;
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__);
415 /* notify PM core that power is now needed */
416 ret = pm_runtime_get_sync(dev);
418 dev_err(dev, "%s: can't power on device\n", __func__);
419 pm_runtime_put_noidle(dev);
420 module_put(dev->driver->owner);
424 /* mark hwspinlock as used, should not fail */
425 tmp = radix_tree_tag_clear(&hwspinlock_tree, hwlock_to_id(hwlock),
428 /* self-sanity check that should never fail */
429 WARN_ON(tmp != hwlock);
435 * hwspin_lock_get_id() - retrieve id number of a given hwspinlock
436 * @hwlock: a valid hwspinlock instance
438 * Returns the id number of a given @hwlock, or -EINVAL if @hwlock is invalid.
440 int hwspin_lock_get_id(struct hwspinlock *hwlock)
443 pr_err("invalid hwlock\n");
447 return hwlock_to_id(hwlock);
449 EXPORT_SYMBOL_GPL(hwspin_lock_get_id);
452 * hwspin_lock_request() - request an hwspinlock
454 * This function should be called by users of the hwspinlock device,
455 * in order to dynamically assign them an unused hwspinlock.
456 * Usually the user of this lock will then have to communicate the lock's id
457 * to the remote core before it can be used for synchronization (to get the
458 * id of a given hwlock, use hwspin_lock_get_id()).
460 * Should be called from a process context (might sleep)
462 * Returns the address of the assigned hwspinlock, or NULL on error
464 struct hwspinlock *hwspin_lock_request(void)
466 struct hwspinlock *hwlock;
469 mutex_lock(&hwspinlock_tree_lock);
471 /* look for an unused lock */
472 ret = radix_tree_gang_lookup_tag(&hwspinlock_tree, (void **)&hwlock,
473 0, 1, HWSPINLOCK_UNUSED);
475 pr_warn("a free hwspinlock is not available\n");
480 /* sanity check that should never fail */
483 /* mark as used and power up */
484 ret = __hwspin_lock_request(hwlock);
489 mutex_unlock(&hwspinlock_tree_lock);
492 EXPORT_SYMBOL_GPL(hwspin_lock_request);
495 * hwspin_lock_request_specific() - request for a specific hwspinlock
496 * @id: index of the specific hwspinlock that is requested
498 * This function should be called by users of the hwspinlock module,
499 * in order to assign them a specific hwspinlock.
500 * Usually early board code will be calling this function in order to
501 * reserve specific hwspinlock ids for predefined purposes.
503 * Should be called from a process context (might sleep)
505 * Returns the address of the assigned hwspinlock, or NULL on error
507 struct hwspinlock *hwspin_lock_request_specific(unsigned int id)
509 struct hwspinlock *hwlock;
512 mutex_lock(&hwspinlock_tree_lock);
514 /* make sure this hwspinlock exists */
515 hwlock = radix_tree_lookup(&hwspinlock_tree, id);
517 pr_warn("hwspinlock %u does not exist\n", id);
521 /* sanity check (this shouldn't happen) */
522 WARN_ON(hwlock_to_id(hwlock) != id);
524 /* make sure this hwspinlock is unused */
525 ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
527 pr_warn("hwspinlock %u is already in use\n", id);
532 /* mark as used and power up */
533 ret = __hwspin_lock_request(hwlock);
538 mutex_unlock(&hwspinlock_tree_lock);
541 EXPORT_SYMBOL_GPL(hwspin_lock_request_specific);
544 * hwspin_lock_free() - free a specific hwspinlock
545 * @hwlock: the specific hwspinlock to free
547 * This function mark @hwlock as free again.
548 * Should only be called with an @hwlock that was retrieved from
549 * an earlier call to omap_hwspin_lock_request{_specific}.
551 * Should be called from a process context (might sleep)
553 * Returns 0 on success, or an appropriate error code on failure
555 int hwspin_lock_free(struct hwspinlock *hwlock)
558 struct hwspinlock *tmp;
562 pr_err("invalid hwlock\n");
566 dev = hwlock->bank->dev;
567 mutex_lock(&hwspinlock_tree_lock);
569 /* make sure the hwspinlock is used */
570 ret = radix_tree_tag_get(&hwspinlock_tree, hwlock_to_id(hwlock),
573 dev_err(dev, "%s: hwlock is already free\n", __func__);
579 /* notify the underlying device that power is not needed */
580 ret = pm_runtime_put(dev);
584 /* mark this hwspinlock as available */
585 tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
588 /* sanity check (this shouldn't happen) */
589 WARN_ON(tmp != hwlock);
591 module_put(dev->driver->owner);
594 mutex_unlock(&hwspinlock_tree_lock);
597 EXPORT_SYMBOL_GPL(hwspin_lock_free);
599 MODULE_LICENSE("GPL v2");
600 MODULE_DESCRIPTION("Hardware spinlock interface");
601 MODULE_AUTHOR("Ohad Ben-Cohen <ohad@wizery.com>");