root/include/asm-parisc/spinlock.h

INCLUDED FROM

DEFINITIONS

1. __raw_spin_is_locked
2. __raw_spin_lock_flags
3. __raw_spin_unlock
4. __raw_spin_trylock
5. __raw_read_lock
6. __raw_read_unlock
7. __raw_read_trylock
8. __raw_write_lock
9. __raw_write_unlock
10. __raw_write_trylock
11. __raw_read_can_lock
12. __raw_write_can_lock

#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H

#include <asm/system.h>
#include <asm/processor.h>
#include <asm/spinlock_types.h>

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

#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
#define __raw_spin_unlock_wait(x) \
                do { cpu_relax(); } while (__raw_spin_is_locked(x))

static inline void __raw_spin_lock_flags(raw_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 __raw_spin_unlock(raw_spinlock_t *x)
{
        volatile unsigned int *a;
        mb();
        a = __ldcw_align(x);
        *a = 1;
        mb();
}

static inline int __raw_spin_trylock(raw_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 __raw_read_lock(raw_rwlock_t *rw)
{
        unsigned long flags;
        local_irq_save(flags);
        __raw_spin_lock_flags(&rw->lock, flags);
        rw->counter++;
        __raw_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 __raw_read_unlock(raw_rwlock_t *rw)
{
        unsigned long flags;
        local_irq_save(flags);
        __raw_spin_lock_flags(&rw->lock, flags);
        rw->counter--;
        __raw_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 __raw_read_trylock(raw_rwlock_t *rw)
{
        unsigned long flags;
 retry:
        local_irq_save(flags);
        if (__raw_spin_trylock(&rw->lock)) {
                rw->counter++;
                __raw_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 (__raw_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 __raw_write_lock(raw_rwlock_t *rw)
{
        unsigned long flags;
retry:
        local_irq_save(flags);
        __raw_spin_lock_flags(&rw->lock, flags);

        if (rw->counter != 0) {
                __raw_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 __raw_write_unlock(raw_rwlock_t *rw)
{
        rw->counter = 0;
        __raw_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 __raw_write_trylock(raw_rwlock_t *rw)
{
        unsigned long flags;
        int result = 0;

        local_irq_save(flags);
        if (__raw_spin_trylock(&rw->lock)) {
                if (rw->counter == 0) {
                        rw->counter = -1;
                        result = 1;
                } else {
                        /* Read-locked.  Oh well. */
                        __raw_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 __raw_read_can_lock(raw_rwlock_t *rw)
{
        return rw->counter >= 0;
}

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

#define _raw_spin_relax(lock)   cpu_relax()
#define _raw_read_relax(lock)   cpu_relax()
#define _raw_write_relax(lock)  cpu_relax()

#endif /* __ASM_SPINLOCK_H */