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/*
* Copyright 2011 Tilera Corporation. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* 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, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*/
#include <linux/spinlock.h>
#include <linux/module.h>
#include <asm/processor.h>
#include "spinlock_common.h"
/*
* Read the spinlock value without allocating in our cache and without
* causing an invalidation to another cpu with a copy of the cacheline.
* This is important when we are spinning waiting for the lock.
*/
static inline u32 arch_spin_read_noalloc(void *lock)
{
return atomic_cmpxchg((atomic_t *)lock, -1, -1);
}
/*
* Wait until the high bits (current) match my ticket.
* If we notice the overflow bit set on entry, we clear it.
*/
void arch_spin_lock_slow(arch_spinlock_t *lock, u32 my_ticket)
{
if (unlikely(my_ticket & __ARCH_SPIN_NEXT_OVERFLOW)) {
__insn_fetchand4(&lock->lock, ~__ARCH_SPIN_NEXT_OVERFLOW);
my_ticket &= ~__ARCH_SPIN_NEXT_OVERFLOW;
}
for (;;) {
u32 val = arch_spin_read_noalloc(lock);
u32 delta = my_ticket - arch_spin_current(val);
if (delta == 0)
return;
relax((128 / CYCLES_PER_RELAX_LOOP) * delta);
}
}
EXPORT_SYMBOL(arch_spin_lock_slow);
/*
* Check the lock to see if it is plausible, and try to get it with cmpxchg().
*/
int arch_spin_trylock(arch_spinlock_t *lock)
{
u32 val = arch_spin_read_noalloc(lock);
if (unlikely(arch_spin_current(val) != arch_spin_next(val)))
return 0;
return cmpxchg(&lock->lock, val, (val + 1) & ~__ARCH_SPIN_NEXT_OVERFLOW)
== val;
}
EXPORT_SYMBOL(arch_spin_trylock);
void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
u32 iterations = 0;
u32 val = READ_ONCE(lock->lock);
u32 curr = arch_spin_current(val);
/* Return immediately if unlocked. */
if (arch_spin_next(val) == curr)
return;
/* Wait until the current locker has released the lock. */
do {
delay_backoff(iterations++);
} while (arch_spin_current(READ_ONCE(lock->lock)) == curr);
}
EXPORT_SYMBOL(arch_spin_unlock_wait);
/*
* If the read lock fails due to a writer, we retry periodically
* until the value is positive and we write our incremented reader count.
*/
void __read_lock_failed(arch_rwlock_t *rw)
{
u32 val;
int iterations = 0;
do {
delay_backoff(iterations++);
val = __insn_fetchaddgez4(&rw->lock, 1);
} while (unlikely(arch_write_val_locked(val)));
}
EXPORT_SYMBOL(__read_lock_failed);
/*
* If we failed because there were readers, clear the "writer" bit
* so we don't block additional readers. Otherwise, there was another
* writer anyway, so our "fetchor" made no difference. Then wait,
* issuing periodic fetchor instructions, till we get the lock.
*/
void __write_lock_failed(arch_rwlock_t *rw, u32 val)
{
int iterations = 0;
do {
if (!arch_write_val_locked(val))
val = __insn_fetchand4(&rw->lock, ~__WRITE_LOCK_BIT);
delay_backoff(iterations++);
val = __insn_fetchor4(&rw->lock, __WRITE_LOCK_BIT);
} while (val != 0);
}
EXPORT_SYMBOL(__write_lock_failed);
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