source: svn/trunk/newcon3bcm2_21bu/toolchain/mips-linux-uclibc/include/asm/semaphore.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.
 *
 * Copyright (C) 1996  Linus Torvalds
 * Copyright (C) 1998, 99, 2000, 01  Ralf Baechle
 * Copyright (C) 1999, 2000, 01  Silicon Graphics, Inc.
 * Copyright (C) 2000, 01 MIPS Technologies, Inc.
 */
#ifndef _ASM_SEMAPHORE_H
#define _ASM_SEMAPHORE_H

#include <asm/atomic.h>
#include <linux/wait.h>

struct semaphore {
#ifdef __MIPSEB__
        atomic_t count;
        atomic_t waking;
#else
        atomic_t waking;
        atomic_t count;
#endif
        wait_queue_head_t wait;
#if WAITQUEUE_DEBUG
        long __magic;
#endif
} __attribute__((aligned(8)));

#if WAITQUEUE_DEBUG
# define __SEM_DEBUG_INIT(name) , .__magic = (long)&(name).__magic
#else
# define __SEM_DEBUG_INIT(name)
#endif

#define __SEMAPHORE_INITIALIZER(name,_count) {                          \
        .count  = ATOMIC_INIT(_count),                                  \
        .waking = ATOMIC_INIT(0),                                       \
        .wait   = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait)            \
        __SEM_DEBUG_INIT(name)                                          \
}

#define __MUTEX_INITIALIZER(name) __SEMAPHORE_INITIALIZER(name, 1)

#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
        struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)

#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1)
#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)

static inline void sema_init (struct semaphore *sem, int val)
{
        atomic_set(&sem->count, val);
        atomic_set(&sem->waking, 0);
        init_waitqueue_head(&sem->wait);
#if WAITQUEUE_DEBUG
        sem->__magic = (long)&sem->__magic;
#endif
}

static inline void init_MUTEX (struct semaphore *sem)
{
        sema_init(sem, 1);
}

static inline void init_MUTEX_LOCKED (struct semaphore *sem)
{
        sema_init(sem, 0);
}

#ifndef CONFIG_CPU_HAS_LLDSCD
/*
 * On machines without lld/scd we need a spinlock to make the manipulation of
 * sem->count and sem->waking atomic.
 */
extern spinlock_t semaphore_lock;
#endif

extern void __down_failed(struct semaphore * sem);
extern int  __down_failed_interruptible(struct semaphore * sem);
extern void __up_wakeup(struct semaphore * sem);

static inline void down(struct semaphore * sem)
{
        int count;

#if WAITQUEUE_DEBUG
        CHECK_MAGIC(sem->__magic);
#endif
        might_sleep();
        count = atomic_dec_return(&sem->count);
        if (unlikely(count < 0))
                __down_failed(sem);
}

/*
 * Interruptible try to acquire a semaphore.  If we obtained
 * it, return zero.  If we were interrupted, returns -EINTR
 */
static inline int down_interruptible(struct semaphore * sem)
{
        int count;

#if WAITQUEUE_DEBUG
        CHECK_MAGIC(sem->__magic);
#endif
        might_sleep();
        count = atomic_dec_return(&sem->count);
        if (unlikely(count < 0))
                return __down_failed_interruptible(sem);

        return 0;
}

#ifdef CONFIG_CPU_HAS_LLDSCD

/*
 * down_trylock returns 0 on success, 1 if we failed to get the lock.
 *
 * We must manipulate count and waking simultaneously and atomically.
 * Here, we do this by using lld/scd on the pair of 32-bit words.
 *
 * Pseudocode:
 *
 *   Decrement(sem->count)
 *   If(sem->count >=0) {
 *      Return(SUCCESS)                 // resource is free
 *   } else {
 *      If(sem->waking <= 0) {          // if no wakeup pending
 *         Increment(sem->count)        // undo decrement
 *         Return(FAILURE)
 *      } else {
 *         Decrement(sem->waking)       // otherwise "steal" wakeup
 *         Return(SUCCESS)
 *      }
 *   }
 */
static inline int down_trylock(struct semaphore * sem)
{
        long ret, tmp, tmp2, sub;

#if WAITQUEUE_DEBUG
        CHECK_MAGIC(sem->__magic);
#endif

        __asm__ __volatile__(
        "       .set    mips3                   # down_trylock          \n"
        "0:     lld     %1, %4                                          \n"
        "       dli     %3, 0x0000000100000000  # count -= 1            \n"
        "       dsubu   %1, %3                                          \n"
        "       li      %0, 0                   # ret = 0               \n"
        "       bgez    %1, 2f                  # if count >= 0         \n"
        "       sll     %2, %1, 0               # extract waking        \n"
        "       blez    %2, 1f                  # if waking < 0 -> 1f   \n"
        "       daddiu  %1, %1, -1              # waking -= 1           \n"
        "       b       2f                                              \n"
        "1:     daddu   %1, %1, %3              # count += 1            \n"
        "       li      %0, 1                   # ret = 1               \n"
        "2:     scd     %1, %4                                          \n"
        "       beqz    %1, 0b                                          \n"
        "       sync                                                    \n"
        "       .set    mips0                                           \n"
        : "=&r"(ret), "=&r"(tmp), "=&r"(tmp2), "=&r"(sub)
        : "m"(*sem)
        : "memory");

        return ret;
}

/*
 * Note! This is subtle. We jump to wake people up only if
 * the semaphore was negative (== somebody was waiting on it).
 */
static inline void up(struct semaphore * sem)
{
        unsigned long tmp, tmp2;
        int count;

#if WAITQUEUE_DEBUG
        CHECK_MAGIC(sem->__magic);
#endif
        /*
         * We must manipulate count and waking simultaneously and atomically.
         * Otherwise we have races between up and __down_failed_interruptible
         * waking up on a signal.
         */

        __asm__ __volatile__(
        "       .set    mips3                                   \n"
        "       sync                    # up                    \n"
        "1:     lld     %1, %3                                  \n"
        "       dsra32  %0, %1, 0       # extract count to %0   \n"
        "       daddiu  %0, 1           # count += 1            \n"
        "       slti    %2, %0, 1       # %3 = (%0 <= 0)        \n"
        "       daddu   %1, %2          # waking += %3          \n"
        "       dsll32 %1, %1, 0        # zero-extend %1        \n"
        "       dsrl32 %1, %1, 0                                \n"
        "       dsll32  %2, %0, 0       # Reassemble union      \n"
        "       or      %1, %2          # from count and waking \n"
        "       scd     %1, %3                                  \n"
        "       beqz    %1, 1b                                  \n"
        "       .set    mips0                                   \n"
        : "=&r"(count), "=&r"(tmp), "=&r"(tmp2), "+m"(*sem)
        :
        : "memory");

        if (unlikely(count <= 0))
                __up_wakeup(sem);
}

#else

/*
 * Non-blockingly attempt to down() a semaphore.
 * Returns zero if we acquired it
 */
static inline int down_trylock(struct semaphore * sem)
{
        unsigned long flags;
        int count, waking;
        int ret = 0;

#if WAITQUEUE_DEBUG
        CHECK_MAGIC(sem->__magic);
#endif

        spin_lock_irqsave(&semaphore_lock, flags);
        count = atomic_read(&sem->count) - 1;
        atomic_set(&sem->count, count);
        if (unlikely(count < 0)) {
                waking = atomic_read(&sem->waking);
                if (waking <= 0) {
                        atomic_set(&sem->count, count + 1);
                        ret = 1;
                } else {
                        atomic_set(&sem->waking, waking - 1);
                        ret = 0;
                }
        }
        spin_unlock_irqrestore(&semaphore_lock, flags);

        return ret;
}

/*
 * Note! This is subtle. We jump to wake people up only if
 * the semaphore was negative (== somebody was waiting on it).
 */
static inline void up(struct semaphore * sem)
{
        unsigned long flags;
        int count, waking;

#if WAITQUEUE_DEBUG
        CHECK_MAGIC(sem->__magic);
#endif
        /*
         * We must manipulate count and waking simultaneously and atomically.
         * Otherwise we have races between up and __down_failed_interruptible
         * waking up on a signal.
         */

        spin_lock_irqsave(&semaphore_lock, flags);
        count = atomic_read(&sem->count) + 1;
        waking = atomic_read(&sem->waking);
        if (count <= 0)
                waking++;
        atomic_set(&sem->count, count);
        atomic_set(&sem->waking, waking);
        spin_unlock_irqrestore(&semaphore_lock, flags);

        if (unlikely(count <= 0))
                __up_wakeup(sem);
}

#endif /* CONFIG_CPU_HAS_LLDSCD */

#endif /* _ASM_SEMAPHORE_H */