drivers/hwspinlock/hwspinlock_core.c - kernel/common - Git at Google

 /*
  * Hardware spinlock framework
  *
  * Copyright (C) 2010 Texas Instruments Incorporated - http://www.ti.com
  *
  * Contact: Ohad Ben-Cohen <[email protected]>
  *
  * 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 "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 spinlock,
  * as the radix-tree API requires that users provide all synchronisation.
  */
 static DEFINE_SPINLOCK(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->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->ops->relax)
 			hwlock->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->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);

 /**
  * hwspin_lock_register() - register a new hw spinlock
  * @hwlock: hwspinlock to register.
  *
  * This function should be called from the underlying platform-specific
  * implementation, to register a new hwspinlock instance.
  *
  * Can be called from an atomic context (will not sleep) but not from
  * within interrupt context.
  *
  * Returns 0 on success, or an appropriate error code on failure
  */
 int hwspin_lock_register(struct hwspinlock *hwlock)
 {
 	struct hwspinlock *tmp;
 	int ret;

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

 	spin_lock_init(&hwlock->lock);

 	spin_lock(&hwspinlock_tree_lock);

 	ret = radix_tree_insert(&hwspinlock_tree, hwlock->id, hwlock);
 	if (ret)
 		goto out;

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

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

 out:
 	spin_unlock(&hwspinlock_tree_lock);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(hwspin_lock_register);

 /**
  * hwspin_lock_unregister() - unregister an hw spinlock
  * @id: index of the specific hwspinlock to unregister
  *
  * This function should be called from the underlying platform-specific
  * implementation, to unregister an existing (and unused) hwspinlock.
  *
  * Can be called from an atomic context (will not sleep) but not from
  * within interrupt context.
  *
  * Returns the address of hwspinlock @id on success, or NULL on failure
  */
 struct hwspinlock *hwspin_lock_unregister(unsigned int id)
 {
 	struct hwspinlock *hwlock = NULL;
 	int ret;

 	spin_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:
 	spin_unlock(&hwspinlock_tree_lock);
 	return hwlock;
 }
 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 hwspinlock *tmp;
 	int ret;

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

 	/* notify PM core that power is now needed */
 	ret = pm_runtime_get_sync(hwlock->dev);
 	if (ret < 0) {
 		dev_err(hwlock->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->id,
 							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->id;
 }
 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()).
  *
  * Can be called from an atomic context (will not sleep) but not from
  * within interrupt context (simply because there is no use case for
  * that yet).
  *
  * Returns the address of the assigned hwspinlock, or NULL on error
  */
 struct hwspinlock *hwspin_lock_request(void)
 {
 	struct hwspinlock *hwlock;
 	int ret;

 	spin_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:
 	spin_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.
  *
  * Can be called from an atomic context (will not sleep) but not from
  * within interrupt context (simply because there is no use case for
  * that yet).
  *
  * 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;

 	spin_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->id != 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:
 	spin_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}.
  *
  * Can be called from an atomic context (will not sleep) but not from
  * within interrupt context (simply because there is no use case for
  * that yet).
  *
  * Returns 0 on success, or an appropriate error code on failure
  */
 int hwspin_lock_free(struct hwspinlock *hwlock)
 {
 	struct hwspinlock *tmp;
 	int ret;

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

 	spin_lock(&hwspinlock_tree_lock);

 	/* make sure the hwspinlock is used */
 	ret = radix_tree_tag_get(&hwspinlock_tree, hwlock->id,
 							HWSPINLOCK_UNUSED);
 	if (ret == 1) {
 		dev_err(hwlock->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(hwlock->dev);
 	if (ret < 0)
 		goto out;

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

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

 	module_put(hwlock->owner);

 out:
 	spin_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 <[email protected]>");
	/*
	* Hardware spinlock framework
	*
	* Copyright (C) 2010 Texas Instruments Incorporated - http://www.ti.com
	*
	* Contact: Ohad Ben-Cohen <[email protected]>
	*
	* 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 "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 spinlock,
	* as the radix-tree API requires that users provide all synchronisation.
	*/
	static DEFINE_SPINLOCK(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->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->ops->relax)
	hwlock->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->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);

	/**
	* hwspin_lock_register() - register a new hw spinlock
	* @hwlock: hwspinlock to register.
	*
	* This function should be called from the underlying platform-specific
	* implementation, to register a new hwspinlock instance.
	*
	* Can be called from an atomic context (will not sleep) but not from
	* within interrupt context.
	*
	* Returns 0 on success, or an appropriate error code on failure
	*/
	int hwspin_lock_register(struct hwspinlock *hwlock)
	{
	struct hwspinlock *tmp;
	int ret;

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

	spin_lock_init(&hwlock->lock);

	spin_lock(&hwspinlock_tree_lock);

	ret = radix_tree_insert(&hwspinlock_tree, hwlock->id, hwlock);
	if (ret)
	goto out;

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

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

	out:
	spin_unlock(&hwspinlock_tree_lock);
	return ret;
	}
	EXPORT_SYMBOL_GPL(hwspin_lock_register);

	/**
	* hwspin_lock_unregister() - unregister an hw spinlock
	* @id: index of the specific hwspinlock to unregister
	*
	* This function should be called from the underlying platform-specific
	* implementation, to unregister an existing (and unused) hwspinlock.
	*
	* Can be called from an atomic context (will not sleep) but not from
	* within interrupt context.
	*
	* Returns the address of hwspinlock @id on success, or NULL on failure
	*/
	struct hwspinlock *hwspin_lock_unregister(unsigned int id)
	{
	struct hwspinlock *hwlock = NULL;
	int ret;

	spin_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:
	spin_unlock(&hwspinlock_tree_lock);
	return hwlock;
	}
	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 hwspinlock *tmp;
	int ret;

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

	/* notify PM core that power is now needed */
	ret = pm_runtime_get_sync(hwlock->dev);
	if (ret < 0) {
	dev_err(hwlock->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->id,
	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->id;
	}
	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()).
	*
	* Can be called from an atomic context (will not sleep) but not from
	* within interrupt context (simply because there is no use case for
	* that yet).
	*
	* Returns the address of the assigned hwspinlock, or NULL on error
	*/
	struct hwspinlock *hwspin_lock_request(void)
	{
	struct hwspinlock *hwlock;
	int ret;

	spin_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:
	spin_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.
	*
	* Can be called from an atomic context (will not sleep) but not from
	* within interrupt context (simply because there is no use case for
	* that yet).
	*
	* 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;

	spin_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->id != 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:
	spin_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}.
	*
	* Can be called from an atomic context (will not sleep) but not from
	* within interrupt context (simply because there is no use case for
	* that yet).
	*
	* Returns 0 on success, or an appropriate error code on failure
	*/
	int hwspin_lock_free(struct hwspinlock *hwlock)
	{
	struct hwspinlock *tmp;
	int ret;

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

	spin_lock(&hwspinlock_tree_lock);

	/* make sure the hwspinlock is used */
	ret = radix_tree_tag_get(&hwspinlock_tree, hwlock->id,
	HWSPINLOCK_UNUSED);
	if (ret == 1) {
	dev_err(hwlock->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(hwlock->dev);
	if (ret < 0)
	goto out;

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

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

	module_put(hwlock->owner);

	out:
	spin_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 <[email protected]>");