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/*

 * asm-ia64/rwsem.h: R/W semaphores for ia64

 *

 * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>

 * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>

 *

 * Based on asm-i386/rwsem.h and other architecture implementation.

 *

 * The MSW of the count is the negated number of active writers and

 * waiting lockers, and the LSW is the total number of active locks.

 *

 * The lock count is initialized to 0 (no active and no waiting lockers).

 *

 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case

 * of an uncontended lock. Readers increment by 1 and see a positive value

 * when uncontended, negative if there are writers (and maybe) readers

 * waiting (in which case it goes to sleep).

 */

#ifndef _ASM_IA64_RWSEM_H

#define _ASM_IA64_RWSEM_H

#include <linux/list.h>

#include <linux/spinlock.h>

/*

 * the semaphore definition

 */

struct rw_semaphore {

        signed int              count;

        spinlock_t              wait_lock;

        struct list_head        wait_list;

#if RWSEM_DEBUG

        int                     debug;

#endif

};

#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)

/*

 * initialization

 */

#if RWSEM_DEBUG

#define __RWSEM_DEBUG_INIT      , 0

#else

#define __RWSEM_DEBUG_INIT      /* */

#endif

#define __RWSEM_INITIALIZER(name) \

        { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \

          LIST_HEAD_INIT((name).wait_list) \

          __RWSEM_DEBUG_INIT }

#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);

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);

#if RWSEM_DEBUG

        sem->debug = 0;

#endif

}

/*

 * lock for reading

 */

static inline void

__down_read (struct rw_semaphore *sem)

{

        int result;

        __asm__ __volatile__ ("fetchadd4.acq %0=[%1],1" :

                              "=r"(result) : "r"(&sem->count) : "memory");

        if (result < 0)

                rwsem_down_read_failed(sem);

}

/*

 * lock for writing

 */

static inline void

__down_write (struct rw_semaphore *sem)

{

        int old, new;

        do {

                old = sem->count;

                new = old + RWSEM_ACTIVE_WRITE_BIAS;

        } while (cmpxchg_acq(&sem->count, old, new) != old);

        if (old != 0)

                rwsem_down_write_failed(sem);

}

/*

 * unlock after reading

 */

static inline void

__up_read (struct rw_semaphore *sem)

{

        int result;

        __asm__ __volatile__ ("fetchadd4.rel %0=[%1],-1" :

                              "=r"(result) : "r"(&sem->count) : "memory");

        if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)

                rwsem_wake(sem);

}

/*

 * unlock after writing

 */

static inline void

__up_write (struct rw_semaphore *sem)

{

        int old, new;

        do {

                old = sem->count;

                new = old - RWSEM_ACTIVE_WRITE_BIAS;

        } while (cmpxchg_rel(&sem->count, old, new) != old);

        if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)

                rwsem_wake(sem);

}

/*

 * trylock for reading -- returns 1 if successful, 0 if contention

 */

static inline int

__down_read_trylock (struct rw_semaphore *sem)

{

        int tmp;

        while ((tmp = sem->count) >= 0) {

                if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) {

                        return 1;

                }

        }

        return 0;

}

/*

 * trylock for writing -- returns 1 if successful, 0 if contention

 */

static inline int

__down_write_trylock (struct rw_semaphore *sem)

{

        int tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE,

                              RWSEM_ACTIVE_WRITE_BIAS);

        return tmp == RWSEM_UNLOCKED_VALUE;

}

/*

 * downgrade write lock to read lock

 */

static inline void

__downgrade_write (struct rw_semaphore *sem)

{

        int old, new;

        do {

                old = sem->count;

                new = old - RWSEM_WAITING_BIAS;

        } while (cmpxchg_rel(&sem->count, old, new) != old);

        if (old < 0)

                rwsem_downgrade_wake(sem);

}

/*

 * Implement atomic add functionality.  These used to be "inline" functions, but GCC v3.1

 * doesn't quite optimize this stuff right and ends up with bad calls to fetchandadd.

 */

#define rwsem_atomic_add(delta, sem)    atomic_add(delta, (atomic_t *)(&(sem)->count))

#define rwsem_atomic_update(delta, sem) atomic_add_return(delta, (atomic_t *)(&(sem)->count))

#endif /* _ASM_IA64_RWSEM_H */