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/*
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.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.
*/
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
#include <asm/spinlock_types.h>
#include <asm/processor.h>
#include <asm/barrier.h>
#define arch_spin_is_locked(x) ((x)->slock != __ARCH_SPIN_LOCK_UNLOCKED__)
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
#define arch_spin_unlock_wait(x) \
do { while (arch_spin_is_locked(x)) cpu_relax(); } while (0)
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
unsigned int tmp = __ARCH_SPIN_LOCK_LOCKED__;
/*
* This smp_mb() is technically superfluous, we only need the one
* after the lock for providing the ACQUIRE semantics.
* However doing the "right" thing was regressing hackbench
* so keeping this, pending further investigation
*/
smp_mb();
__asm__ __volatile__(
"1: ex %0, [%1] \n"
" breq %0, %2, 1b \n"
: "+&r" (tmp)
: "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__)
: "memory");
/*
* ACQUIRE barrier to ensure load/store after taking the lock
* don't "bleed-up" out of the critical section (leak-in is allowed)
* http://www.spinics.net/lists/kernel/msg2010409.html
*
* ARCv2 only has load-load, store-store and all-all barrier
* thus need the full all-all barrier
*/
smp_mb();
}
static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
unsigned int tmp = __ARCH_SPIN_LOCK_LOCKED__;
smp_mb();
__asm__ __volatile__(
"1: ex %0, [%1] \n"
: "+r" (tmp)
: "r"(&(lock->slock))
: "memory");
smp_mb();
return (tmp == __ARCH_SPIN_LOCK_UNLOCKED__);
}
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
unsigned int tmp = __ARCH_SPIN_LOCK_UNLOCKED__;
/*
* RELEASE barrier: given the instructions avail on ARCv2, full barrier
* is the only option
*/
smp_mb();
__asm__ __volatile__(
" ex %0, [%1] \n"
: "+r" (tmp)
: "r"(&(lock->slock))
: "memory");
/*
* superfluous, but keeping for now - see pairing version in
* arch_spin_lock above
*/
smp_mb();
}
/*
* Read-write spinlocks, allowing multiple readers but only one writer.
*
* The spinlock itself is contained in @counter and access to it is
* serialized with @lock_mutex.
*
* Unfair locking as Writers could be starved indefinitely by Reader(s)
*/
/* Would read_trylock() succeed? */
#define arch_read_can_lock(x) ((x)->counter > 0)
/* Would write_trylock() succeed? */
#define arch_write_can_lock(x) ((x)->counter == __ARCH_RW_LOCK_UNLOCKED__)
/* 1 - lock taken successfully */
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
int ret = 0;
arch_spin_lock(&(rw->lock_mutex));
/*
* zero means writer holds the lock exclusively, deny Reader.
* Otherwise grant lock to first/subseq reader
*/
if (rw->counter > 0) {
rw->counter--;
ret = 1;
}
arch_spin_unlock(&(rw->lock_mutex));
smp_mb();
return ret;
}
/* 1 - lock taken successfully */
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
int ret = 0;
arch_spin_lock(&(rw->lock_mutex));
/*
* If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
* deny writer. Otherwise if unlocked grant to writer
* Hence the claim that Linux rwlocks are unfair to writers.
* (can be starved for an indefinite time by readers).
*/
if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
rw->counter = 0;
ret = 1;
}
arch_spin_unlock(&(rw->lock_mutex));
return ret;
}
static inline void arch_read_lock(arch_rwlock_t *rw)
{
while (!arch_read_trylock(rw))
cpu_relax();
}
static inline void arch_write_lock(arch_rwlock_t *rw)
{
while (!arch_write_trylock(rw))
cpu_relax();
}
static inline void arch_read_unlock(arch_rwlock_t *rw)
{
arch_spin_lock(&(rw->lock_mutex));
rw->counter++;
arch_spin_unlock(&(rw->lock_mutex));
}
static inline void arch_write_unlock(arch_rwlock_t *rw)
{
arch_spin_lock(&(rw->lock_mutex));
rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
arch_spin_unlock(&(rw->lock_mutex));
}
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
#define arch_spin_relax(lock) cpu_relax()
#define arch_read_relax(lock) cpu_relax()
#define arch_write_relax(lock) cpu_relax()
#endif /* __ASM_SPINLOCK_H */
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