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