#ifndef _ALPHA_RWSEM_H
  #define _ALPHA_RWSEM_H
  
  /*
   * Written by Ivan Kokshaysky <ink@jurassic.park.msu.ru>, 2001.
   * Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
   */
  
  #ifndef _LINUX_RWSEM_H
  #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
  #endif
  
  #ifdef __KERNEL__
  
  #include <linux/compiler.h>
  #include <linux/list.h>
  #include <linux/spinlock.h>
  
  struct rwsem_waiter;
  
  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 *);
  extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  
  /*
   * the semaphore definition
   */
  struct rw_semaphore {
  	long			count;
  #define RWSEM_UNLOCKED_VALUE		0x0000000000000000L
  #define RWSEM_ACTIVE_BIAS		0x0000000000000001L
  #define RWSEM_ACTIVE_MASK		0x00000000ffffffffL
  #define RWSEM_WAITING_BIAS		(-0x0000000100000000L)
  #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)
  
  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);

  }
  
  static inline void __down_read(struct rw_semaphore *sem)
  {
  	long oldcount;
  #ifndef	CONFIG_SMP
  	oldcount = sem->count;
  	sem->count += RWSEM_ACTIVE_READ_BIAS;
  #else
  	long temp;
  	__asm__ __volatile__(
  	"1:	ldq_l	%0,%1
  "
  	"	addq	%0,%3,%2
  "
  	"	stq_c	%2,%1
  "
  	"	beq	%2,2f
  "
  	"	mb
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
  	:"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");
  #endif
  	if (unlikely(oldcount < 0))
  		rwsem_down_read_failed(sem);
  }
  
  /*
   * trylock for reading -- returns 1 if successful, 0 if contention
   */
  static inline int __down_read_trylock(struct rw_semaphore *sem)
  {
  	long old, new, res;
  
  	res = sem->count;
  	do {
  		new = res + RWSEM_ACTIVE_READ_BIAS;
  		if (new <= 0)
  			break;
  		old = res;
  		res = cmpxchg(&sem->count, old, new);
  	} while (res != old);
  	return res >= 0 ? 1 : 0;
  }
  
  static inline void __down_write(struct rw_semaphore *sem)
  {
  	long oldcount;
  #ifndef	CONFIG_SMP
  	oldcount = sem->count;
  	sem->count += RWSEM_ACTIVE_WRITE_BIAS;
  #else
  	long temp;
  	__asm__ __volatile__(
  	"1:	ldq_l	%0,%1
  "
  	"	addq	%0,%3,%2
  "
  	"	stq_c	%2,%1
  "
  	"	beq	%2,2f
  "
  	"	mb
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
  	:"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");
  #endif
  	if (unlikely(oldcount))
  		rwsem_down_write_failed(sem);
  }
  
  /*
   * trylock for writing -- returns 1 if successful, 0 if contention
   */
  static inline int __down_write_trylock(struct rw_semaphore *sem)
  {
  	long ret = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
  			   RWSEM_ACTIVE_WRITE_BIAS);
  	if (ret == RWSEM_UNLOCKED_VALUE)
  		return 1;
  	return 0;
  }
  
  static inline void __up_read(struct rw_semaphore *sem)
  {
  	long oldcount;
  #ifndef	CONFIG_SMP
  	oldcount = sem->count;
  	sem->count -= RWSEM_ACTIVE_READ_BIAS;
  #else
  	long temp;
  	__asm__ __volatile__(
  	"	mb
  "
  	"1:	ldq_l	%0,%1
  "
  	"	subq	%0,%3,%2
  "
  	"	stq_c	%2,%1
  "
  	"	beq	%2,2f
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
  	:"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");
  #endif
  	if (unlikely(oldcount < 0))
  		if ((int)oldcount - RWSEM_ACTIVE_READ_BIAS == 0)
  			rwsem_wake(sem);
  }
  
  static inline void __up_write(struct rw_semaphore *sem)
  {
  	long count;
  #ifndef	CONFIG_SMP
  	sem->count -= RWSEM_ACTIVE_WRITE_BIAS;
  	count = sem->count;
  #else
  	long temp;
  	__asm__ __volatile__(
  	"	mb
  "
  	"1:	ldq_l	%0,%1
  "
  	"	subq	%0,%3,%2
  "
  	"	stq_c	%2,%1
  "
  	"	beq	%2,2f
  "
  	"	subq	%0,%3,%0
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (count), "=m" (sem->count), "=&r" (temp)
  	:"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");
  #endif
  	if (unlikely(count))
  		if ((int)count == 0)
  			rwsem_wake(sem);
  }
  
  /*
   * downgrade write lock to read lock
   */
  static inline void __downgrade_write(struct rw_semaphore *sem)
  {
  	long oldcount;
  #ifndef	CONFIG_SMP
  	oldcount = sem->count;
  	sem->count -= RWSEM_WAITING_BIAS;
  #else
  	long temp;
  	__asm__ __volatile__(
  	"1:	ldq_l	%0,%1
  "
  	"	addq	%0,%3,%2
  "
  	"	stq_c	%2,%1
  "
  	"	beq	%2,2f
  "
  	"	mb
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
  	:"Ir" (-RWSEM_WAITING_BIAS), "m" (sem->count) : "memory");
  #endif
  	if (unlikely(oldcount < 0))
  		rwsem_downgrade_wake(sem);
  }
  
  static inline void rwsem_atomic_add(long val, struct rw_semaphore *sem)
  {
  #ifndef	CONFIG_SMP
  	sem->count += val;
  #else
  	long temp;
  	__asm__ __volatile__(
  	"1:	ldq_l	%0,%1
  "
  	"	addq	%0,%2,%0
  "
  	"	stq_c	%0,%1
  "
  	"	beq	%0,2f
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (temp), "=m" (sem->count)
  	:"Ir" (val), "m" (sem->count));
  #endif
  }
  
  static inline long rwsem_atomic_update(long val, struct rw_semaphore *sem)
  {
  #ifndef	CONFIG_SMP
  	sem->count += val;
  	return sem->count;
  #else
  	long ret, temp;
  	__asm__ __volatile__(
  	"1:	ldq_l	%0,%1
  "
  	"	addq 	%0,%3,%2
  "
  	"	addq	%0,%3,%0
  "
  	"	stq_c	%2,%1
  "
  	"	beq	%2,2f
  "
  	".subsection 2
  "
  	"2:	br	1b
  "
  	".previous"
  	:"=&r" (ret), "=m" (sem->count), "=&r" (temp)
  	:"Ir" (val), "m" (sem->count));
  
  	return ret;
  #endif
  }

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

  #endif /* __KERNEL__ */
  #endif /* _ALPHA_RWSEM_H */