root/include/asm-xtensa/rwsem.h

INCLUDED FROM

DEFINITIONS

1. init_rwsem
2. __down_read
3. __down_read_trylock
4. __down_write
5. __down_write_trylock
6. __up_read
7. __up_write
8. rwsem_atomic_add
9. __downgrade_write
10. rwsem_atomic_update
11. rwsem_is_locked

/*
 * include/asm-xtensa/rwsem.h
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Largely copied from include/asm-ppc/rwsem.h
 *
 * Copyright (C) 2001 - 2005 Tensilica Inc.
 */

#ifndef _XTENSA_RWSEM_H
#define _XTENSA_RWSEM_H

#include <linux/list.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
#include <asm/system.h>

/*
 * the semaphore definition
 */
struct rw_semaphore {
        signed long             count;
#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)
        spinlock_t              wait_lock;
        struct list_head        wait_list;
};

#define __RWSEM_INITIALIZER(name) \
        { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
          LIST_HEAD_INIT((name).wait_list) }

#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);

static inline void init_rwsem(struct rw_semaphore *sem)
{
        sem->count = RWSEM_UNLOCKED_VALUE;
        spin_lock_init(&sem->wait_lock);
        INIT_LIST_HEAD(&sem->wait_list);
}

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
        if (atomic_add_return(1,(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_sub_return(1,(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);
}

/*
 * 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));
}

static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
        return (sem->count != 0);
}

#endif  /* _XTENSA_RWSEM_H */