linux-next/drivers/hwspinlock/hwspinlock_core.c

/*
 * 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 "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 <ohad@wizery.com>");