/* * 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__); pm_runtime_put_noidle(dev); module_put(dev->driver->owner); 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>");