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   1 /*
   2  * include/asm-ppc64/rwsem.h: R/W semaphores for PPC using the stuff
   3  * in lib/rwsem.c.  Adapted largely from include/asm-i386/rwsem.h
   4  * by Paul Mackerras <paulus@samba.org>.
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #ifndef _PPC64_RWSEM_H
  13 #define _PPC64_RWSEM_H
  14
  15 #ifdef __KERNEL__
  16 #include <linux/list.h>
  17 #include <linux/spinlock.h>
  18 #include <asm/atomic.h>
  19 #include <asm/system.h>
  20
  21 /*
  22  * the semaphore definition
  23  */
  24 struct rw_semaphore {
  25         /* XXX this should be able to be an atomic_t  -- paulus */
  26         signed int              count;
  27 #define RWSEM_UNLOCKED_VALUE            0x00000000
  28 #define RWSEM_ACTIVE_BIAS               0x00000001
  29 #define RWSEM_ACTIVE_MASK               0x0000ffff
  30 #define RWSEM_WAITING_BIAS              (-0x00010000)
  31 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  32 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  33         spinlock_t              wait_lock;
  34         struct list_head        wait_list;
  35 #if RWSEM_DEBUG
  36         int                     debug;
  37 #endif
  38 };
  39
  40 /*
  41  * initialisation
  42  */
  43 #if RWSEM_DEBUG
  44 #define __RWSEM_DEBUG_INIT      , 0
  45 #else
  46 #define __RWSEM_DEBUG_INIT      /* */
  47 #endif
  48
  49 #define __RWSEM_INITIALIZER(name) \
  50         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
  51           LIST_HEAD_INIT((name).wait_list) \
  52           __RWSEM_DEBUG_INIT }
  53
  54 #define DECLARE_RWSEM(name)             \
  55         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  56
  57 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  58 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  59 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  60 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  61
  62 static inline void init_rwsem(struct rw_semaphore *sem)
  63 {
  64         sem->count = RWSEM_UNLOCKED_VALUE;
  65         spin_lock_init(&sem->wait_lock);
  66         INIT_LIST_HEAD(&sem->wait_list);
  67 #if RWSEM_DEBUG
  68         sem->debug = 0;
  69 #endif
  70 }
  71
  72 /*
  73  * lock for reading
  74  */
  75 static inline void __down_read(struct rw_semaphore *sem)
  76 {
  77         if (unlikely(atomic_inc_return((atomic_t *)(&sem->count)) <= 0))
  78                 rwsem_down_read_failed(sem);
  79 }
  80
  81 static inline int __down_read_trylock(struct rw_semaphore *sem)
  82 {
  83         int tmp;
  84
  85         while ((tmp = sem->count) >= 0) {
  86                 if (tmp == cmpxchg(&sem->count, tmp,
  87                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  88                         return 1;
  89                 }
  90         }
  91         return 0;
  92 }
  93
  94 /*
  95  * lock for writing
  96  */
  97 static inline void __down_write(struct rw_semaphore *sem)
  98 {
  99         int tmp;
 100
 101         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 102                                 (atomic_t *)(&sem->count));
 103         if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
 104                 rwsem_down_write_failed(sem);
 105 }
 106
 107 static inline int __down_write_trylock(struct rw_semaphore *sem)
 108 {
 109         int tmp;
 110
 111         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 112                       RWSEM_ACTIVE_WRITE_BIAS);
 113         return tmp == RWSEM_UNLOCKED_VALUE;
 114 }
 115
 116 /*
 117  * unlock after reading
 118  */
 119 static inline void __up_read(struct rw_semaphore *sem)
 120 {
 121         int tmp;
 122
 123         tmp = atomic_dec_return((atomic_t *)(&sem->count));
 124         if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
 125                 rwsem_wake(sem);
 126 }
 127
 128 /*
 129  * unlock after writing
 130  */
 131 static inline void __up_write(struct rw_semaphore *sem)
 132 {
 133         if (unlikely(atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 134                               (atomic_t *)(&sem->count)) < 0))
 135                 rwsem_wake(sem);
 136 }
 137
 138 /*
 139  * implement atomic add functionality
 140  */
 141 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 142 {
 143         atomic_add(delta, (atomic_t *)(&sem->count));
 144 }
 145
 146 /*
 147  * downgrade write lock to read lock
 148  */
 149 static inline void __downgrade_write(struct rw_semaphore *sem)
 150 {
 151         int tmp;
 152
 153         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 154         if (tmp < 0)
 155                 rwsem_downgrade_wake(sem);
 156 }
 157
 158 /*
 159  * implement exchange and add functionality
 160  */
 161 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 162 {
 163         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 164 }
 165
 166 #endif /* __KERNEL__ */
 167 #endif /* _PPC_RWSEM_XADD_H */