/*
* include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
* in lib/rwsem.c.
*/

#ifndef _ASM_SH_RWSEM_H
#define _ASM_SH_RWSEM_H

#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif

#ifdef __KERNEL__

#define RWSEM_UNLOCKED_VALUE 0x00000000
#define RWSEM_ACTIVE_BIAS 0x00000001
#define RWSEM_ACTIVE_MASK 0x0000ffff
#define RWSEM_WAITING_BIAS (-0x00010000)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

/*
* lock for reading
*/
static inline void __down_read(struct rw_semaphore *sem)
{
if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
smp_wmb();
else
rwsem_down_read_failed(sem);
}

static inline int __down_read_trylock(struct rw_semaphore *sem)
{
int tmp;

while ((tmp = sem->count) >= 0) {
if (tmp == cmpxchg(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
smp_wmb();
return 1;
}
}
return 0;
}

/*
* lock for writing
*/
static inline void __down_write(struct rw_semaphore *sem)
{
int tmp;

tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic_t *)(&sem->count));
if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
smp_wmb();
else
rwsem_down_write_failed(sem);
}

static inline int __down_write_trylock(struct rw_semaphore *sem)
{
int tmp;

tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
smp_wmb();
return tmp == RWSEM_UNLOCKED_VALUE;
}

/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
int tmp;

smp_wmb();
tmp = atomic_dec_return((atomic_t *)(&sem->count));
if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}

/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
smp_wmb();
if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic_t *)(&sem->count)) < 0)
rwsem_wake(sem);
}

/*
* implement atomic add functionality
*/
static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
{
atomic_add(delta, (atomic_t *)(&sem->count));
}

/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
int tmp;

smp_wmb();
tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
if (tmp < 0)
rwsem_downgrade_wake(sem);
}

static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
__down_write(sem);
}

/*
* implement exchange and add functionality
*/
static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
smp_mb();
return atomic_add_return(delta, (atomic_t *)(&sem->count));
}

#endif /* __KERNEL__ */
#endif /* _ASM_SH_RWSEM_H */