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rwsem.h

#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\n"
      "     addq  %0,%3,%2\n"
      "     stq_c %2,%1\n"
      "     beq   %2,2f\n"
      "     mb\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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\n"
      "     addq  %0,%3,%2\n"
      "     stq_c %2,%1\n"
      "     beq   %2,2f\n"
      "     mb\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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\n"
      "1:   ldq_l %0,%1\n"
      "     subq  %0,%3,%2\n"
      "     stq_c %2,%1\n"
      "     beq   %2,2f\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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\n"
      "1:   ldq_l %0,%1\n"
      "     subq  %0,%3,%2\n"
      "     stq_c %2,%1\n"
      "     beq   %2,2f\n"
      "     subq  %0,%3,%0\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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\n"
      "     addq  %0,%3,%2\n"
      "     stq_c %2,%1\n"
      "     beq   %2,2f\n"
      "     mb\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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\n"
      "     addq  %0,%2,%0\n"
      "     stq_c %0,%1\n"
      "     beq   %0,2f\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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\n"
      "     addq  %0,%3,%2\n"
      "     addq  %0,%3,%0\n"
      "     stq_c %2,%1\n"
      "     beq   %2,2f\n"
      ".subsection 2\n"
      "2:   br    1b\n"
      ".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 */

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