arch/sh/include/asm/rwsem.h

   1 /*
   2  * include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
   3  * in lib/rwsem.c.
   4  */
   5
   6 #ifndef _ASM_SH_RWSEM_H
   7 #define _ASM_SH_RWSEM_H
   8
   9 #ifndef _LINUX_RWSEM_H
  10 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
  11 #endif
  12
  13 #ifdef __KERNEL__
  14 #include <linux/list.h>
  15 #include <linux/spinlock.h>
  16 #include <asm/atomic.h>
  17 #include <asm/system.h>
  18
  19 /*
  20  * the semaphore definition
  21  */
  22 struct rw_semaphore {
  23         long            count;
  24 #define RWSEM_UNLOCKED_VALUE            0x00000000
  25 #define RWSEM_ACTIVE_BIAS               0x00000001
  26 #define RWSEM_ACTIVE_MASK               0x0000ffff
  27 #define RWSEM_WAITING_BIAS              (-0x00010000)
  28 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  29 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  30         spinlock_t              wait_lock;
  31         struct list_head        wait_list;
  32 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  33         struct lockdep_map      dep_map;
  34 #endif
  35 };
  36
  37 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  38 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  39 #else
  40 # define __RWSEM_DEP_MAP_INIT(lockname)
  41 #endif
  42
  43 #define __RWSEM_INITIALIZER(name) \
  44         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
  45           LIST_HEAD_INIT((name).wait_list) \
  46           __RWSEM_DEP_MAP_INIT(name) }
  47
  48 #define DECLARE_RWSEM(name)             \
  49         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  50
  51 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  52 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  53 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  54 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  55
  56 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  57                          struct lock_class_key *key);
  58
  59 #define init_rwsem(sem)                         \
  60 do {                                            \
  61         static struct lock_class_key __key;     \
  62                                                 \
  63         __init_rwsem((sem), #sem, &__key);      \
  64 } while (0)
  65
  66 static inline void init_rwsem(struct rw_semaphore *sem)
  67 {
  68         sem->count = RWSEM_UNLOCKED_VALUE;
  69         spin_lock_init(&sem->wait_lock);
  70         INIT_LIST_HEAD(&sem->wait_list);
  71 }
  72
  73 /*
  74  * lock for reading
  75  */
  76 static inline void __down_read(struct rw_semaphore *sem)
  77 {
  78         if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
  79                 smp_wmb();
  80         else
  81                 rwsem_down_read_failed(sem);
  82 }
  83
  84 static inline int __down_read_trylock(struct rw_semaphore *sem)
  85 {
  86         int tmp;
  87
  88         while ((tmp = sem->count) >= 0) {
  89                 if (tmp == cmpxchg(&sem->count, tmp,
  90                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  91                         smp_wmb();
  92                         return 1;
  93                 }
  94         }
  95         return 0;
  96 }
  97
  98 /*
  99  * lock for writing
 100  */
 101 static inline void __down_write(struct rw_semaphore *sem)
 102 {
 103         int tmp;
 104
 105         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 106                                 (atomic_t *)(&sem->count));
 107         if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
 108                 smp_wmb();
 109         else
 110                 rwsem_down_write_failed(sem);
 111 }
 112
 113 static inline int __down_write_trylock(struct rw_semaphore *sem)
 114 {
 115         int tmp;
 116
 117         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 118                       RWSEM_ACTIVE_WRITE_BIAS);
 119         smp_wmb();
 120         return tmp == RWSEM_UNLOCKED_VALUE;
 121 }
 122
 123 /*
 124  * unlock after reading
 125  */
 126 static inline void __up_read(struct rw_semaphore *sem)
 127 {
 128         int tmp;
 129
 130         smp_wmb();
 131         tmp = atomic_dec_return((atomic_t *)(&sem->count));
 132         if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 133                 rwsem_wake(sem);
 134 }
 135
 136 /*
 137  * unlock after writing
 138  */
 139 static inline void __up_write(struct rw_semaphore *sem)
 140 {
 141         smp_wmb();
 142         if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 143                               (atomic_t *)(&sem->count)) < 0)
 144                 rwsem_wake(sem);
 145 }
 146
 147 /*
 148  * implement atomic add functionality
 149  */
 150 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 151 {
 152         atomic_add(delta, (atomic_t *)(&sem->count));
 153 }
 154
 155 /*
 156  * downgrade write lock to read lock
 157  */
 158 static inline void __downgrade_write(struct rw_semaphore *sem)
 159 {
 160         int tmp;
 161
 162         smp_wmb();
 163         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 164         if (tmp < 0)
 165                 rwsem_downgrade_wake(sem);
 166 }
 167
 168 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 169 {
 170         __down_write(sem);
 171 }
 172
 173 /*
 174  * implement exchange and add functionality
 175  */
 176 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 177 {
 178         smp_mb();
 179         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 180 }
 181
 182 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 183 {
 184         return (sem->count != 0);
 185 }
 186
 187 #endif /* __KERNEL__ */
 188 #endif /* _ASM_SH_RWSEM_H */