drm/nouveau: fix kernel-doc comments

[drm/drm-misc.git] / drivers / hwspinlock / hwspinlock_core.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Hardware spinlock framework
 *
 * Copyright (C) 2010 Texas Instruments Incorporated - http://www.ti.com
 *
 * Contact: Ohad Ben-Cohen <ohad@wizery.com>
 */

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

#include <linux/delay.h>
#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 <linux/of.h>

#include "hwspinlock_internal.h"

/* retry delay used in atomic context */
#define HWSPINLOCK_RETRY_DELAY_US       100

/* 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.
 *
 * Caution: If the mode is HWLOCK_RAW, that means user must protect the routine
 * of getting hardware lock with mutex or spinlock. Since in some scenarios,
 * user need some time-consuming or sleepable operations under the hardware
 * lock, they need one sleepable lock (like mutex) to protect the operations.
 *
 * If the mode is neither HWLOCK_IN_ATOMIC nor HWLOCK_RAW, 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;

        if (WARN_ON(!hwlock || (!flags && mode == HWLOCK_IRQSTATE)))
                return -EINVAL;

        /*
         * 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.)
         */
        switch (mode) {
        case HWLOCK_IRQSTATE:
                ret = spin_trylock_irqsave(&hwlock->lock, *flags);
                break;
        case HWLOCK_IRQ:
                ret = spin_trylock_irq(&hwlock->lock);
                break;
        case HWLOCK_RAW:
        case HWLOCK_IN_ATOMIC:
                ret = 1;
                break;
        default:
                ret = spin_trylock(&hwlock->lock);
                break;
        }

        /* 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) {
                switch (mode) {
                case HWLOCK_IRQSTATE:
                        spin_unlock_irqrestore(&hwlock->lock, *flags);
                        break;
                case HWLOCK_IRQ:
                        spin_unlock_irq(&hwlock->lock);
                        break;
                case HWLOCK_RAW:
                case HWLOCK_IN_ATOMIC:
                        /* Nothing to do */
                        break;
                default:
                        spin_unlock(&hwlock->lock);
                        break;
                }

                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
 * @to: 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.
 *
 * Caution: If the mode is HWLOCK_RAW, that means user must protect the routine
 * of getting hardware lock with mutex or spinlock. Since in some scenarios,
 * user need some time-consuming or sleepable operations under the hardware
 * lock, they need one sleepable lock (like mutex) to protect the operations.
 *
 * If the mode is HWLOCK_IN_ATOMIC (called from an atomic context) the timeout
 * is handled with busy-waiting delays, hence shall not exceed few msecs.
 *
 * If the mode is neither HWLOCK_IN_ATOMIC nor HWLOCK_RAW, 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_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, atomic_delay = 0;

        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 (mode == HWLOCK_IN_ATOMIC) {
                        udelay(HWSPINLOCK_RETRY_DELAY_US);
                        atomic_delay += HWSPINLOCK_RETRY_DELAY_US;
                        if (atomic_delay > to * 1000)
                                return -ETIMEDOUT;
                } else {
                        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)
{
        if (WARN_ON(!hwlock || (!flags && mode == HWLOCK_IRQSTATE)))
                return;

        /*
         * 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 */
        switch (mode) {
        case HWLOCK_IRQSTATE:
                spin_unlock_irqrestore(&hwlock->lock, *flags);
                break;
        case HWLOCK_IRQ:
                spin_unlock_irq(&hwlock->lock);
                break;
        case HWLOCK_RAW:
        case HWLOCK_IN_ATOMIC:
                /* Nothing to do */
                break;
        default:
                spin_unlock(&hwlock->lock);
                break;
        }
}
EXPORT_SYMBOL_GPL(__hwspin_unlock);

/**
 * hwspin_lock_bust() - bust a specific hwspinlock
 * @hwlock: a previously-acquired hwspinlock which we want to bust
 * @id: identifier of the remote lock holder, if applicable
 *
 * This function will bust a hwspinlock that was previously acquired as
 * long as the current owner of the lock matches the id given by the caller.
 *
 * Context: Process context.
 *
 * Returns: 0 on success, or -EINVAL if the hwspinlock does not exist, or
 * the bust operation fails, and -EOPNOTSUPP if the bust operation is not
 * defined for the hwspinlock.
 */
int hwspin_lock_bust(struct hwspinlock *hwlock, unsigned int id)
{
        if (WARN_ON(!hwlock))
                return -EINVAL;

        if (!hwlock->bank->ops->bust) {
                pr_err("bust operation not defined\n");
                return -EOPNOTSUPP;
        }

        return hwlock->bank->ops->bust(hwlock, id);
}
EXPORT_SYMBOL_GPL(hwspin_lock_bust);

/**
 * of_hwspin_lock_simple_xlate - translate hwlock_spec to return a lock id
 * @hwlock_spec: hwlock specifier as found in the device tree
 *
 * This is a simple translation function, suitable for hwspinlock platform
 * drivers that only has a lock specifier length of 1.
 *
 * Returns: a relative index of the lock within a specified bank on success,
 * or -EINVAL on invalid specifier cell count.
 */
static inline int
of_hwspin_lock_simple_xlate(const struct of_phandle_args *hwlock_spec)
{
        if (WARN_ON(hwlock_spec->args_count != 1))
                return -EINVAL;

        return hwlock_spec->args[0];
}

/**
 * of_hwspin_lock_get_id() - get lock id for an OF phandle-based specific lock
 * @np: device node from which to request the specific hwlock
 * @index: index of the hwlock in the list of values
 *
 * This function provides a means for DT users of the hwspinlock module to
 * get the global lock id of a specific hwspinlock using the phandle of the
 * hwspinlock device, so that it can be requested using the normal
 * hwspin_lock_request_specific() API.
 *
 * Returns: the global lock id number on success, -EPROBE_DEFER if the
 * hwspinlock device is not yet registered, -EINVAL on invalid args
 * specifier value or an appropriate error as returned from the OF parsing
 * of the DT client node.
 */
int of_hwspin_lock_get_id(struct device_node *np, int index)
{
        struct of_phandle_args args;
        struct hwspinlock *hwlock;
        struct radix_tree_iter iter;
        void **slot;
        int id;
        int ret;

        ret = of_parse_phandle_with_args(np, "hwlocks", "#hwlock-cells", index,
                                         &args);
        if (ret)
                return ret;

        if (!of_device_is_available(args.np)) {
                ret = -ENOENT;
                goto out;
        }

        /* Find the hwspinlock device: we need its base_id */
        ret = -EPROBE_DEFER;
        rcu_read_lock();
        radix_tree_for_each_slot(slot, &hwspinlock_tree, &iter, 0) {
                hwlock = radix_tree_deref_slot(slot);
                if (unlikely(!hwlock))
                        continue;
                if (radix_tree_deref_retry(hwlock)) {
                        slot = radix_tree_iter_retry(&iter);
                        continue;
                }

                if (device_match_of_node(hwlock->bank->dev, args.np)) {
                        ret = 0;
                        break;
                }
        }
        rcu_read_unlock();
        if (ret < 0)
                goto out;

        id = of_hwspin_lock_simple_xlate(&args);
        if (id < 0 || id >= hwlock->bank->num_locks) {
                ret = -EINVAL;
                goto out;
        }
        id += hwlock->bank->base_id;

out:
        of_node_put(args.np);
        return ret ? ret : id;
}
EXPORT_SYMBOL_GPL(of_hwspin_lock_get_id);

/**
 * of_hwspin_lock_get_id_byname() - get lock id for an specified hwlock name
 * @np: device node from which to request the specific hwlock
 * @name: hwlock name
 *
 * This function provides a means for DT users of the hwspinlock module to
 * get the global lock id of a specific hwspinlock using the specified name of
 * the hwspinlock device, so that it can be requested using the normal
 * hwspin_lock_request_specific() API.
 *
 * Returns: the global lock id number on success, -EPROBE_DEFER if the
 * hwspinlock device is not yet registered, -EINVAL on invalid args
 * specifier value or an appropriate error as returned from the OF parsing
 * of the DT client node.
 */
int of_hwspin_lock_get_id_byname(struct device_node *np, const char *name)
{
        int index;

        if (!name)
                return -EINVAL;

        index = of_property_match_string(np, "hwlock-names", name);
        if (index < 0)
                return index;

        return of_hwspin_lock_get_id(np, index);
}
EXPORT_SYMBOL_GPL(of_hwspin_lock_get_id_byname);

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);

static void devm_hwspin_lock_unreg(struct device *dev, void *res)
{
        hwspin_lock_unregister(*(struct hwspinlock_device **)res);
}

static int devm_hwspin_lock_device_match(struct device *dev, void *res,
                                         void *data)
{
        struct hwspinlock_device **bank = res;

        if (WARN_ON(!bank || !*bank))
                return 0;

        return *bank == data;
}

/**
 * devm_hwspin_lock_unregister() - unregister an hw spinlock device for
 *                                 a managed device
 * @dev: the backing 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 devm_hwspin_lock_unregister(struct device *dev,
                                struct hwspinlock_device *bank)
{
        int ret;

        ret = devres_release(dev, devm_hwspin_lock_unreg,
                             devm_hwspin_lock_device_match, bank);
        WARN_ON(ret);

        return ret;
}
EXPORT_SYMBOL_GPL(devm_hwspin_lock_unregister);

/**
 * devm_hwspin_lock_register() - register a new hw spinlock device for
 *                               a managed device
 * @dev: the backing device
 * @bank: the hwspinlock device, which usually provides numerous hw locks
 * @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 devm_hwspin_lock_register(struct device *dev,
                              struct hwspinlock_device *bank,
                              const struct hwspinlock_ops *ops,
                              int base_id, int num_locks)
{
        struct hwspinlock_device **ptr;
        int ret;

        ptr = devres_alloc(devm_hwspin_lock_unreg, sizeof(*ptr), GFP_KERNEL);
        if (!ptr)
                return -ENOMEM;

        ret = hwspin_lock_register(bank, dev, ops, base_id, num_locks);
        if (!ret) {
                *ptr = bank;
                devres_add(dev, ptr);
        } else {
                devres_free(ptr);
        }

        return ret;
}
EXPORT_SYMBOL_GPL(devm_hwspin_lock_register);

/**
 * __hwspin_lock_request() - tag an hwspinlock as used and power it up
 * @hwlock: the target hwspinlock
 *
 * 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 && ret != -EACCES) {
                dev_err(dev, "%s: can't power on device\n", __func__);
                pm_runtime_put_noidle(dev);
                module_put(dev->driver->owner);
                return ret;
        }

        ret = 0;

        /* 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 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 */
        pm_runtime_put(dev);

        /* 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);

static int devm_hwspin_lock_match(struct device *dev, void *res, void *data)
{
        struct hwspinlock **hwlock = res;

        if (WARN_ON(!hwlock || !*hwlock))
                return 0;

        return *hwlock == data;
}

static void devm_hwspin_lock_release(struct device *dev, void *res)
{
        hwspin_lock_free(*(struct hwspinlock **)res);
}

/**
 * devm_hwspin_lock_free() - free a specific hwspinlock for a managed device
 * @dev: the device to free the 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 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 devm_hwspin_lock_free(struct device *dev, struct hwspinlock *hwlock)
{
        int ret;

        ret = devres_release(dev, devm_hwspin_lock_release,
                             devm_hwspin_lock_match, hwlock);
        WARN_ON(ret);

        return ret;
}
EXPORT_SYMBOL_GPL(devm_hwspin_lock_free);

/**
 * devm_hwspin_lock_request() - request an hwspinlock for a managed device
 * @dev: the device to 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 *devm_hwspin_lock_request(struct device *dev)
{
        struct hwspinlock **ptr, *hwlock;

        ptr = devres_alloc(devm_hwspin_lock_release, sizeof(*ptr), GFP_KERNEL);
        if (!ptr)
                return NULL;

        hwlock = hwspin_lock_request();
        if (hwlock) {
                *ptr = hwlock;
                devres_add(dev, ptr);
        } else {
                devres_free(ptr);
        }

        return hwlock;
}
EXPORT_SYMBOL_GPL(devm_hwspin_lock_request);

/**
 * devm_hwspin_lock_request_specific() - request for a specific hwspinlock for
 *                                       a managed device
 * @dev: the device to request the 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 *devm_hwspin_lock_request_specific(struct device *dev,
                                                     unsigned int id)
{
        struct hwspinlock **ptr, *hwlock;

        ptr = devres_alloc(devm_hwspin_lock_release, sizeof(*ptr), GFP_KERNEL);
        if (!ptr)
                return NULL;

        hwlock = hwspin_lock_request_specific(id);
        if (hwlock) {
                *ptr = hwlock;
                devres_add(dev, ptr);
        } else {
                devres_free(ptr);
        }

        return hwlock;
}
EXPORT_SYMBOL_GPL(devm_hwspin_lock_request_specific);

MODULE_DESCRIPTION("Hardware spinlock interface");
MODULE_AUTHOR("Ohad Ben-Cohen <ohad@wizery.com>");