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 #define RWSEM_UNLOCKED_VALUE            0x00000000L
  17 #define RWSEM_ACTIVE_BIAS               0x00000001L
  18 #define RWSEM_ACTIVE_MASK               0xffffffffL
  19 #define RWSEM_WAITING_BIAS              (-RWSEM_ACTIVE_MASK-1)
  20 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  21 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  22
  23 /*
  24  * lock for reading
  25  */
  26 static inline void __down_read(struct rw_semaphore *sem)
  27 {
  28         if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
  29                 rwsem_down_read_failed(sem);
  30 }
  31
  32 static inline int __down_read_trylock(struct rw_semaphore *sem)
  33 {
  34         long tmp;
  35
  36         while ((tmp = sem->count) >= 0L) {
  37                 if (tmp == cmpxchg(&sem->count, tmp,
  38                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  39                         return 1;
  40                 }
  41         }
  42         return 0;
  43 }
  44
  45 /*
  46  * lock for writing
  47  */
  48 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
  49 {
  50         long tmp;
  51
  52         tmp = atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  53                                   (atomic64_t *)(&sem->count));
  54         if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
  55                 rwsem_down_write_failed(sem);
  56 }
  57
  58 static inline void __down_write(struct rw_semaphore *sem)
  59 {
  60         __down_write_nested(sem, 0);
  61 }
  62
  63 static inline int __down_write_trylock(struct rw_semaphore *sem)
  64 {
  65         long tmp;
  66
  67         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
  68                       RWSEM_ACTIVE_WRITE_BIAS);
  69         return tmp == RWSEM_UNLOCKED_VALUE;
  70 }
  71
  72 /*
  73  * unlock after reading
  74  */
  75 static inline void __up_read(struct rw_semaphore *sem)
  76 {
  77         long tmp;
  78
  79         tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
  80         if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
  81                 rwsem_wake(sem);
  82 }
  83
  84 /*
  85  * unlock after writing
  86  */
  87 static inline void __up_write(struct rw_semaphore *sem)
  88 {
  89         if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
  90                                          (atomic64_t *)(&sem->count)) < 0L))
  91                 rwsem_wake(sem);
  92 }
  93
  94 /*
  95  * implement atomic add functionality
  96  */
  97 static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
  98 {
  99         atomic64_add(delta, (atomic64_t *)(&sem->count));
 100 }
 101
 102 /*
 103  * downgrade write lock to read lock
 104  */
 105 static inline void __downgrade_write(struct rw_semaphore *sem)
 106 {
 107         long tmp;
 108
 109         tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
 110         if (tmp < 0L)
 111                 rwsem_downgrade_wake(sem);
 112 }
 113
 114 /*
 115  * implement exchange and add functionality
 116  */
 117 static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
 118 {
 119         return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
 120 }
 121
 122 #endif /* __KERNEL__ */
 123
 124 #endif /* _SPARC64_RWSEM_H */