LXR linux/arch/xtensa/include/asm/rwsem.h

   1/*
   2 * include/asm-xtensa/rwsem.h
   3 *
   4 * This file is subject to the terms and conditions of the GNU General Public
   5 * License.  See the file "COPYING" in the main directory of this archive
   6 * for more details.
   7 *
   8 * Largely copied from include/asm-ppc/rwsem.h
   9 *
  10 * Copyright (C) 2001 - 2005 Tensilica Inc.
  11 */
  12
  13#ifndef _XTENSA_RWSEM_H
  14#define _XTENSA_RWSEM_H
  15
  16#ifndef _LINUX_RWSEM_H
  17#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  18#endif
  19
  20#define RWSEM_UNLOCKED_VALUE            0x00000000
  21#define RWSEM_ACTIVE_BIAS               0x00000001
  22#define RWSEM_ACTIVE_MASK               0x0000ffff
  23#define RWSEM_WAITING_BIAS              (-0x00010000)
  24#define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  25#define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  26
  27/*
  28 * lock for reading
  29 */
  30static inline void __down_read(struct rw_semaphore *sem)
  31{
  32        if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
  33                smp_wmb();
  34        else
  35                rwsem_down_read_failed(sem);
  36}
  37
  38static inline int __down_read_trylock(struct rw_semaphore *sem)
  39{
  40        int tmp;
  41
  42        while ((tmp = sem->count) >= 0) {
  43                if (tmp == cmpxchg(&sem->count, tmp,
  44                                   tmp + RWSEM_ACTIVE_READ_BIAS)) {
  45                        smp_wmb();
  46                        return 1;
  47                }
  48        }
  49        return 0;
  50}
  51
  52/*
  53 * lock for writing
  54 */
  55static inline void __down_write(struct rw_semaphore *sem)
  56{
  57        int tmp;
  58
  59        tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  60                                (atomic_t *)(&sem->count));
  61        if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
  62                smp_wmb();
  63        else
  64                rwsem_down_write_failed(sem);
  65}
  66
  67static inline int __down_write_trylock(struct rw_semaphore *sem)
  68{
  69        int tmp;
  70
  71        tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
  72                      RWSEM_ACTIVE_WRITE_BIAS);
  73        smp_wmb();
  74        return tmp == RWSEM_UNLOCKED_VALUE;
  75}
  76
  77/*
  78 * unlock after reading
  79 */
  80static inline void __up_read(struct rw_semaphore *sem)
  81{
  82        int tmp;
  83
  84        smp_wmb();
  85        tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
  86        if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
  87                rwsem_wake(sem);
  88}
  89
  90/*
  91 * unlock after writing
  92 */
  93static inline void __up_write(struct rw_semaphore *sem)
  94{
  95        smp_wmb();
  96        if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
  97                              (atomic_t *)(&sem->count)) < 0)
  98                rwsem_wake(sem);
  99}
 100
 101/*
 102 * implement atomic add functionality
 103 */
 104static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 105{
 106        atomic_add(delta, (atomic_t *)(&sem->count));
 107}
 108
 109/*
 110 * downgrade write lock to read lock
 111 */
 112static inline void __downgrade_write(struct rw_semaphore *sem)
 113{
 114        int tmp;
 115
 116        smp_wmb();
 117        tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 118        if (tmp < 0)
 119                rwsem_downgrade_wake(sem);
 120}
 121
 122/*
 123 * implement exchange and add functionality
 124 */
 125static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 126{
 127        smp_mb();
 128        return atomic_add_return(delta, (atomic_t *)(&sem->count));
 129}
 130
 131#endif  /* _XTENSA_RWSEM_H */
 132