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spinlock.h

#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 */

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