arch/sparc/include/asm/rwsem.h

   1 /*
   2  * rwsem.h: R/W semaphores implemented using CAS
   3  *
   4  * Written by David S. Miller (davem@redhat.com), 2001.
   5  * Derived from asm-i386/rwsem.h
   6  */
   7 #ifndef _SPARC64_RWSEM_H
   8 #define _SPARC64_RWSEM_H
   9
  10 #ifndef _LINUX_RWSEM_H
  11 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
  12 #endif
  13
  14 #ifdef __KERNEL__
  15
  16 #include <linux/list.h>
  17 #include <linux/spinlock.h>
  18
  19 struct rwsem_waiter;
  20
  21 struct rw_semaphore {
  22         signed long                     count;
  23 #define RWSEM_UNLOCKED_VALUE            0x00000000L
  24 #define RWSEM_ACTIVE_BIAS               0x00000001L
  25 #define RWSEM_ACTIVE_MASK               0xffffffffL
  26 #define RWSEM_WAITING_BIAS              (-RWSEM_ACTIVE_MASK-1)
  27 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  28 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  29         spinlock_t                      wait_lock;
  30         struct list_head                wait_list;
  31 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  32         struct lockdep_map              dep_map;
  33 #endif
  34 };
  35
  36 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  37 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  38 #else
  39 # define __RWSEM_DEP_MAP_INIT(lockname)
  40 #endif
  41
  42 #define __RWSEM_INITIALIZER(name) \
  43 { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
  44   LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }
  45
  46 #define DECLARE_RWSEM(name) \
  47         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  48
  49 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  50 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  51 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  52 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  53
  54 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  55                          struct lock_class_key *key);
  56
  57 #define init_rwsem(sem)                                         \
  58 do {                                                            \
  59         static struct lock_class_key __key;                     \
  60                                                                 \
  61         __init_rwsem((sem), #sem, &__key);                      \
  62 } while (0)
  63
  64 /*
  65  * lock for reading
  66  */
  67 static inline void __down_read(struct rw_semaphore *sem)
  68 {
  69         if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
  70                 rwsem_down_read_failed(sem);
  71 }
  72
  73 static inline int __down_read_trylock(struct rw_semaphore *sem)
  74 {
  75         long tmp;
  76
  77         while ((tmp = sem->count) >= 0L) {
  78                 if (tmp == cmpxchg(&sem->count, tmp,
  79                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  80                         return 1;
  81                 }
  82         }
  83         return 0;
  84 }
  85
  86 /*
  87  * lock for writing
  88  */
  89 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
  90 {
  91         long tmp;
  92
  93         tmp = atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  94                                   (atomic64_t *)(&sem->count));
  95         if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
  96                 rwsem_down_write_failed(sem);
  97 }
  98
  99 static inline void __down_write(struct rw_semaphore *sem)
 100 {
 101         __down_write_nested(sem, 0);
 102 }
 103
 104 static inline int __down_write_trylock(struct rw_semaphore *sem)
 105 {
 106         long tmp;
 107
 108         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 109                       RWSEM_ACTIVE_WRITE_BIAS);
 110         return tmp == RWSEM_UNLOCKED_VALUE;
 111 }
 112
 113 /*
 114  * unlock after reading
 115  */
 116 static inline void __up_read(struct rw_semaphore *sem)
 117 {
 118         long tmp;
 119
 120         tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
 121         if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
 122                 rwsem_wake(sem);
 123 }
 124
 125 /*
 126  * unlock after writing
 127  */
 128 static inline void __up_write(struct rw_semaphore *sem)
 129 {
 130         if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 131                                          (atomic64_t *)(&sem->count)) < 0L))
 132                 rwsem_wake(sem);
 133 }
 134
 135 /*
 136  * implement atomic add functionality
 137  */
 138 static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
 139 {
 140         atomic64_add(delta, (atomic64_t *)(&sem->count));
 141 }
 142
 143 /*
 144  * downgrade write lock to read lock
 145  */
 146 static inline void __downgrade_write(struct rw_semaphore *sem)
 147 {
 148         long tmp;
 149
 150         tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
 151         if (tmp < 0L)
 152                 rwsem_downgrade_wake(sem);
 153 }
 154
 155 /*
 156  * implement exchange and add functionality
 157  */
 158 static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
 159 {
 160         return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
 161 }
 162
 163 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 164 {
 165         return (sem->count != 0);
 166 }
 167
 168 #endif /* __KERNEL__ */
 169
 170 #endif /* _SPARC64_RWSEM_H */