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   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 #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         signed long             count;
  26 #define RWSEM_UNLOCKED_VALUE            0x00000000
  27 #define RWSEM_ACTIVE_BIAS               0x00000001
  28 #define RWSEM_ACTIVE_MASK               0x0000ffff
  29 #define RWSEM_WAITING_BIAS              (-0x00010000)
  30 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  31 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  32         spinlock_t              wait_lock;
  33         struct list_head        wait_list;
  34 #if RWSEM_DEBUG
  35         int                     debug;
  36 #endif
  37 };
  38
  39 /*
  40  * initialisation
  41  */
  42 #if RWSEM_DEBUG
  43 #define __RWSEM_DEBUG_INIT      , 0
  44 #else
  45 #define __RWSEM_DEBUG_INIT      /* */
  46 #endif
  47
  48 #define __RWSEM_INITIALIZER(name) \
  49         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
  50           LIST_HEAD_INIT((name).wait_list) \
  51           __RWSEM_DEBUG_INIT }
  52
  53 #define DECLARE_RWSEM(name)             \
  54         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  55
  56 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  57 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  58 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  59 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  60
  61 static inline void init_rwsem(struct rw_semaphore *sem)
  62 {
  63         sem->count = RWSEM_UNLOCKED_VALUE;
  64         spin_lock_init(&sem->wait_lock);
  65         INIT_LIST_HEAD(&sem->wait_list);
  66 #if RWSEM_DEBUG
  67         sem->debug = 0;
  68 #endif
  69 }
  70
  71 /*
  72  * lock for reading
  73  */
  74 static inline void __down_read(struct rw_semaphore *sem)
  75 {
  76         if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
  77                 smp_wmb();
  78         else
  79                 rwsem_down_read_failed(sem);
  80 }
  81
  82 static inline int __down_read_trylock(struct rw_semaphore *sem)
  83 {
  84         int tmp;
  85
  86         while ((tmp = sem->count) >= 0) {
  87                 if (tmp == cmpxchg(&sem->count, tmp,
  88                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  89                         smp_wmb();
  90                         return 1;
  91                 }
  92         }
  93         return 0;
  94 }
  95
  96 /*
  97  * lock for writing
  98  */
  99 static inline void __down_write(struct rw_semaphore *sem)
 100 {
 101         int tmp;
 102
 103         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 104                                 (atomic_t *)(&sem->count));
 105         if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
 106                 smp_wmb();
 107         else
 108                 rwsem_down_write_failed(sem);
 109 }
 110
 111 static inline int __down_write_trylock(struct rw_semaphore *sem)
 112 {
 113         int tmp;
 114
 115         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 116                       RWSEM_ACTIVE_WRITE_BIAS);
 117         smp_wmb();
 118         return tmp == RWSEM_UNLOCKED_VALUE;
 119 }
 120
 121 /*
 122  * unlock after reading
 123  */
 124 static inline void __up_read(struct rw_semaphore *sem)
 125 {
 126         int tmp;
 127
 128         smp_wmb();
 129         tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
 130         if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 131                 rwsem_wake(sem);
 132 }
 133
 134 /*
 135  * unlock after writing
 136  */
 137 static inline void __up_write(struct rw_semaphore *sem)
 138 {
 139         smp_wmb();
 140         if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 141                               (atomic_t *)(&sem->count)) < 0)
 142                 rwsem_wake(sem);
 143 }
 144
 145 /*
 146  * implement atomic add functionality
 147  */
 148 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 149 {
 150         atomic_add(delta, (atomic_t *)(&sem->count));
 151 }
 152
 153 /*
 154  * downgrade write lock to read lock
 155  */
 156 static inline void __downgrade_write(struct rw_semaphore *sem)
 157 {
 158         int tmp;
 159
 160         smp_wmb();
 161         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 162         if (tmp < 0)
 163                 rwsem_downgrade_wake(sem);
 164 }
 165
 166 /*
 167  * implement exchange and add functionality
 168  */
 169 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 170 {
 171         smp_mb();
 172         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 173 }
 174
 175 #endif  /* _XTENSA_RWSEM_XADD_H */