rwsem.h

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#ifndef _ASM_POWERPC_RWSEM_H
#define _ASM_POWERPC_RWSEM_H

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

#ifdef __KERNEL__

/*
 * R/W semaphores for PPC using the stuff in lib/rwsem.c.
 * Adapted largely from include/asm-i386/rwsem.h
 * by Paul Mackerras <[email protected]>.
 */

/*
 * the semaphore definition
 */
#ifdef CONFIG_PPC64
# define RWSEM_ACTIVE_MASK      0xffffffffL
#else
# define RWSEM_ACTIVE_MASK      0x0000ffffL
#endif

#define RWSEM_UNLOCKED_VALUE        0x00000000L
#define RWSEM_ACTIVE_BIAS       0x00000001L
#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)

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
    if (unlikely(atomic_long_inc_return((atomic_long_t *)&sem->count) <= 0))
        rwsem_down_read_failed(sem);
}

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

    while ((tmp = sem->count) >= 0) {
        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 = atomic_long_add_return(RWSEM_ACTIVE_WRITE_BIAS,
                     (atomic_long_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 = atomic_long_dec_return((atomic_long_t *)&sem->count);
    if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
        rwsem_wake(sem);
}

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

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

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

    tmp = atomic_long_add_return(-RWSEM_WAITING_BIAS,
                     (atomic_long_t *)&sem->count);
    if (tmp < 0)
        rwsem_downgrade_wake(sem);
}

/*
 * implement exchange and add functionality
 */
static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
{
    return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);
}

#endif  /* __KERNEL__ */
#endif  /* _ASM_POWERPC_RWSEM_H */