spinlock.h

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#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H

#include <asm/barrier.h>
#include <asm/ldcw.h>
#include <asm/processor.h>
#include <asm/spinlock_types.h>

static inline int arch_spin_is_locked(arch_spinlock_t *x)
{
    volatile unsigned int *a = __ldcw_align(x);
    return *a == 0;
}

#define arch_spin_lock(lock) arch_spin_lock_flags(lock, 0)
#define arch_spin_unlock_wait(x) \
        do { cpu_relax(); } while (arch_spin_is_locked(x))

static inline void arch_spin_lock_flags(arch_spinlock_t *x,
                     unsigned long flags)
{
    volatile unsigned int *a;

    mb();
    a = __ldcw_align(x);
    while (__ldcw(a) == 0)
        while (*a == 0)
            if (flags & PSW_SM_I) {
                local_irq_enable();
                cpu_relax();
                local_irq_disable();
            } else
                cpu_relax();
    mb();
}

static inline void arch_spin_unlock(arch_spinlock_t *x)
{
    volatile unsigned int *a;
    mb();
    a = __ldcw_align(x);
    *a = 1;
    mb();
}

static inline int arch_spin_trylock(arch_spinlock_t *x)
{
    volatile unsigned int *a;
    int ret;

    mb();
    a = __ldcw_align(x);
        ret = __ldcw(a) != 0;
    mb();

    return ret;
}

/*
 * Read-write spinlocks, allowing multiple readers but only one writer.
 * Linux rwlocks are unfair to writers; they can be starved for an indefinite
 * time by readers.  With care, they can also be taken in interrupt context.
 *
 * In the PA-RISC implementation, we have a spinlock and a counter.
 * Readers use the lock to serialise their access to the counter (which
 * records how many readers currently hold the lock).
 * Writers hold the spinlock, preventing any readers or other writers from
 * grabbing the rwlock.
 */

/* Note that we have to ensure interrupts are disabled in case we're
 * interrupted by some other code that wants to grab the same read lock */
static  __inline__ void arch_read_lock(arch_rwlock_t *rw)
{
    unsigned long flags;
    local_irq_save(flags);
    arch_spin_lock_flags(&rw->lock, flags);
    rw->counter++;
    arch_spin_unlock(&rw->lock);
    local_irq_restore(flags);
}

/* Note that we have to ensure interrupts are disabled in case we're
 * interrupted by some other code that wants to grab the same read lock */
static  __inline__ void arch_read_unlock(arch_rwlock_t *rw)
{
    unsigned long flags;
    local_irq_save(flags);
    arch_spin_lock_flags(&rw->lock, flags);
    rw->counter--;
    arch_spin_unlock(&rw->lock);
    local_irq_restore(flags);
}

/* Note that we have to ensure interrupts are disabled in case we're
 * interrupted by some other code that wants to grab the same read lock */
static __inline__ int arch_read_trylock(arch_rwlock_t *rw)
{
    unsigned long flags;
 retry:
    local_irq_save(flags);
    if (arch_spin_trylock(&rw->lock)) {
        rw->counter++;
        arch_spin_unlock(&rw->lock);
        local_irq_restore(flags);
        return 1;
    }

    local_irq_restore(flags);
    /* If write-locked, we fail to acquire the lock */
    if (rw->counter < 0)
        return 0;

    /* Wait until we have a realistic chance at the lock */
    while (arch_spin_is_locked(&rw->lock) && rw->counter >= 0)
        cpu_relax();

    goto retry;
}

/* Note that we have to ensure interrupts are disabled in case we're
 * interrupted by some other code that wants to read_trylock() this lock */
static __inline__ void arch_write_lock(arch_rwlock_t *rw)
{
    unsigned long flags;
retry:
    local_irq_save(flags);
    arch_spin_lock_flags(&rw->lock, flags);

    if (rw->counter != 0) {
        arch_spin_unlock(&rw->lock);
        local_irq_restore(flags);

        while (rw->counter != 0)
            cpu_relax();

        goto retry;
    }

    rw->counter = -1; /* mark as write-locked */
    mb();
    local_irq_restore(flags);
}

static __inline__ void arch_write_unlock(arch_rwlock_t *rw)
{
    rw->counter = 0;
    arch_spin_unlock(&rw->lock);
}

/* Note that we have to ensure interrupts are disabled in case we're
 * interrupted by some other code that wants to read_trylock() this lock */
static __inline__ int arch_write_trylock(arch_rwlock_t *rw)
{
    unsigned long flags;
    int result = 0;

    local_irq_save(flags);
    if (arch_spin_trylock(&rw->lock)) {
        if (rw->counter == 0) {
            rw->counter = -1;
            result = 1;
        } else {
            /* Read-locked.  Oh well. */
            arch_spin_unlock(&rw->lock);
        }
    }
    local_irq_restore(flags);

    return result;
}

/*
 * read_can_lock - would read_trylock() succeed?
 * @lock: the rwlock in question.
 */
static __inline__ int arch_read_can_lock(arch_rwlock_t *rw)
{
    return rw->counter >= 0;
}

/*
 * write_can_lock - would write_trylock() succeed?
 * @lock: the rwlock in question.
 */
static __inline__ int arch_write_can_lock(arch_rwlock_t *rw)
{
    return !rw->counter;
}

#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)

#define arch_spin_relax(lock)   cpu_relax()
#define arch_read_relax(lock)   cpu_relax()
#define arch_write_relax(lock)  cpu_relax()

#endif /* __ASM_SPINLOCK_H */