/*
* 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->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.
*
* 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 *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);
mutex_lock(&hwspinlock_tree_lock);
ret = radix_tree_insert(&hwspinlock_tree, hwlock->id, hwlock);
if (ret == -EEXIST)
pr_err("hwspinlock id %d already exists!\n", hwlock->id);
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:
mutex_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.
*
* Should be called from a process context (might sleep)
*
* 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;
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;
}
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->dev->driver->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()).
*
* 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->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:
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 hwspinlock *tmp;
int ret;
if (!hwlock) {
pr_err("invalid hwlock\n");
return -EINVAL;
}
mutex_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->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>");
