diff options
Diffstat (limited to 'arch/arc/include/asm/spinlock.h')
| -rw-r--r-- | arch/arc/include/asm/spinlock.h | 144 |
1 files changed, 144 insertions, 0 deletions
diff --git a/arch/arc/include/asm/spinlock.h b/arch/arc/include/asm/spinlock.h new file mode 100644 index 00000000000..f158197ac5b --- /dev/null +++ b/arch/arc/include/asm/spinlock.h @@ -0,0 +1,144 @@ +/* + * 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__; + + __asm__ __volatile__( + "1: ex %0, [%1] \n" + " breq %0, %2, 1b \n" + : "+&r" (tmp) + : "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__) + : "memory"); +} + +static inline int arch_spin_trylock(arch_spinlock_t *lock) +{ + unsigned int tmp = __ARCH_SPIN_LOCK_LOCKED__; + + __asm__ __volatile__( + "1: ex %0, [%1] \n" + : "+r" (tmp) + : "r"(&(lock->slock)) + : "memory"); + + return (tmp == __ARCH_SPIN_LOCK_UNLOCKED__); +} + +static inline void arch_spin_unlock(arch_spinlock_t *lock) +{ + lock->slock = __ARCH_SPIN_LOCK_UNLOCKED__; + 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 */ |