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/*
* rwsem.h: R/W semaphores implemented using CAS
*
* Written by David S. Miller (davem@redhat.com), 2001.
* Derived from asm-i386/rwsem.h
*/
#ifndef _SPARC64_RWSEM_H
#define _SPARC64_RWSEM_H
#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif
#ifdef __KERNEL__
struct rw_semaphore {
signed long count;
#define RWSEM_UNLOCKED_VALUE 0x00000000L
#define RWSEM_ACTIVE_BIAS 0x00000001L
#define RWSEM_ACTIVE_MASK 0xffffffffL
#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
spinlock_t wait_lock;
struct list_head wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
};
#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif
#define __RWSEM_INITIALIZER(name) \
{ RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }
#define DECLARE_RWSEM(name) \
struct rw_semaphore name = __RWSEM_INITIALIZER(name)
extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key);
#define init_rwsem(sem) \
do { \
static struct lock_class_key __key; \
\
__init_rwsem((sem), #sem, &__key); \
} while (0)
/*
* lock for reading
*/
static inline void __down_read(struct rw_semaphore *sem)
{
if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
rwsem_down_read_failed(sem);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
long tmp;
while ((tmp = sem->count) >= 0L) {
if (tmp == cmpxchg(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
return 1;
}
}
return 0;
}
/*
* lock for writing
*/
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
long tmp;
tmp = atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic64_t *)(&sem->count));
if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
rwsem_down_write_failed(sem);
}
static inline void __down_write(struct rw_semaphore *sem)
{
__down_write_nested(sem, 0);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
long tmp;
tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
return tmp == RWSEM_UNLOCKED_VALUE;
}
/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
long tmp;
tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
rwsem_wake(sem);
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic64_t *)(&sem->count)) < 0L))
rwsem_wake(sem);
}
/*
* implement atomic add functionality
*/
static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
{
atomic64_add(delta, (atomic64_t *)(&sem->count));
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
long tmp;
tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
if (tmp < 0L)
rwsem_downgrade_wake(sem);
}
/*
* implement exchange and add functionality
*/
static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
{
return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
}
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
return (sem->count != 0);
}
#endif /* __KERNEL__ */
#endif /* _SPARC64_RWSEM_H */
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