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rwsem.h

/*
 * include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
 * in lib/rwsem.c.
 */

#ifndef _ASM_SH_RWSEM_H
#define _ASM_SH_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/list.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
#include <asm/system.h>

/*
 * the semaphore definition
 */
struct rw_semaphore {
      long        count;
#define RWSEM_UNLOCKED_VALUE        0x00000000
#define RWSEM_ACTIVE_BIAS           0x00000001
#define RWSEM_ACTIVE_MASK           0x0000ffff
#define RWSEM_WAITING_BIAS          (-0x00010000)
#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;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
      struct lockdep_map      dep_map;
#endif
};

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif

#define __RWSEM_INITIALIZER(name) \
      { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
        LIST_HEAD_INIT((name).wait_list) \
        __RWSEM_DEP_MAP_INIT(name) }

#define DECLARE_RWSEM(name)         \
      struct rw_semaphore name = __RWSEM_INITIALIZER(name)

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 *sem);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);

extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
                   struct lock_class_key *key);

#define init_rwsem(sem)                   \
do {                                \
      static struct lock_class_key __key; \
                                    \
      __init_rwsem((sem), #sem, &__key);  \
} while (0)

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);
}

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
      if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
            smp_wmb();
      else
            rwsem_down_read_failed(sem);
}

static inline int __down_read_trylock(struct rw_semaphore *sem)
{
      int tmp;

      while ((tmp = sem->count) >= 0) {
            if (tmp == cmpxchg(&sem->count, tmp,
                           tmp + RWSEM_ACTIVE_READ_BIAS)) {
                  smp_wmb();
                  return 1;
            }
      }
      return 0;
}

/*
 * lock for writing
 */
static inline void __down_write(struct rw_semaphore *sem)
{
      int tmp;

      tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
                        (atomic_t *)(&sem->count));
      if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
            smp_wmb();
      else
            rwsem_down_write_failed(sem);
}

static inline int __down_write_trylock(struct rw_semaphore *sem)
{
      int tmp;

      tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
                  RWSEM_ACTIVE_WRITE_BIAS);
      smp_wmb();
      return tmp == RWSEM_UNLOCKED_VALUE;
}

/*
 * unlock after reading
 */
static inline void __up_read(struct rw_semaphore *sem)
{
      int tmp;

      smp_wmb();
      tmp = atomic_dec_return((atomic_t *)(&sem->count));
      if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
            rwsem_wake(sem);
}

/*
 * unlock after writing
 */
static inline void __up_write(struct rw_semaphore *sem)
{
      smp_wmb();
      if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
                        (atomic_t *)(&sem->count)) < 0)
            rwsem_wake(sem);
}

/*
 * implement atomic add functionality
 */
static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
{
      atomic_add(delta, (atomic_t *)(&sem->count));
}

/*
 * downgrade write lock to read lock
 */
static inline void __downgrade_write(struct rw_semaphore *sem)
{
      int tmp;

      smp_wmb();
      tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
      if (tmp < 0)
            rwsem_downgrade_wake(sem);
}

static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
      __down_write(sem);
}

/*
 * implement exchange and add functionality
 */
static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
      smp_mb();
      return atomic_add_return(delta, (atomic_t *)(&sem->count));
}

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

#endif /* __KERNEL__ */
#endif /* _ASM_SH_RWSEM_H */

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