include/asm-powerpc/rwsem.h

   1 #ifndef _ASM_POWERPC_RWSEM_H
   2 #define _ASM_POWERPC_RWSEM_H
   3
   4 #ifdef __KERNEL__
   5
   6 /*
   7  * include/asm-powerpc/rwsem.h: R/W semaphores for PPC using the stuff
   8  * in lib/rwsem.c.  Adapted largely from include/asm-i386/rwsem.h
   9  * by Paul Mackerras <paulus@samba.org>.
  10  */
  11
  12 #include <linux/list.h>
  13 #include <linux/spinlock.h>
  14 #include <asm/atomic.h>
  15 #include <asm/system.h>
  16
  17 /*
  18  * the semaphore definition
  19  */
  20 struct rw_semaphore {
  21         /* XXX this should be able to be an atomic_t  -- paulus */
  22         signed int              count;
  23 #define RWSEM_UNLOCKED_VALUE            0x00000000
  24 #define RWSEM_ACTIVE_BIAS               0x00000001
  25 #define RWSEM_ACTIVE_MASK               0x0000ffff
  26 #define RWSEM_WAITING_BIAS              (-0x00010000)
  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 };
  32
  33 #define __RWSEM_INITIALIZER(name) \
  34         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
  35           LIST_HEAD_INIT((name).wait_list) }
  36
  37 #define DECLARE_RWSEM(name)             \
  38         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  39
  40 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  41 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  42 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  43 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  44
  45 static inline void init_rwsem(struct rw_semaphore *sem)
  46 {
  47         sem->count = RWSEM_UNLOCKED_VALUE;
  48         spin_lock_init(&sem->wait_lock);
  49         INIT_LIST_HEAD(&sem->wait_list);
  50 }
  51
  52 /*
  53  * lock for reading
  54  */
  55 static inline void __down_read(struct rw_semaphore *sem)
  56 {
  57         if (unlikely(atomic_inc_return((atomic_t *)(&sem->count)) <= 0))
  58                 rwsem_down_read_failed(sem);
  59 }
  60
  61 static inline int __down_read_trylock(struct rw_semaphore *sem)
  62 {
  63         int tmp;
  64
  65         while ((tmp = sem->count) >= 0) {
  66                 if (tmp == cmpxchg(&sem->count, tmp,
  67                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  68                         return 1;
  69                 }
  70         }
  71         return 0;
  72 }
  73
  74 /*
  75  * lock for writing
  76  */
  77 static inline void __down_write(struct rw_semaphore *sem)
  78 {
  79         int tmp;
  80
  81         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  82                                 (atomic_t *)(&sem->count));
  83         if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
  84                 rwsem_down_write_failed(sem);
  85 }
  86
  87 static inline int __down_write_trylock(struct rw_semaphore *sem)
  88 {
  89         int tmp;
  90
  91         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
  92                       RWSEM_ACTIVE_WRITE_BIAS);
  93         return tmp == RWSEM_UNLOCKED_VALUE;
  94 }
  95
  96 /*
  97  * unlock after reading
  98  */
  99 static inline void __up_read(struct rw_semaphore *sem)
 100 {
 101         int tmp;
 102
 103         tmp = atomic_dec_return((atomic_t *)(&sem->count));
 104         if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
 105                 rwsem_wake(sem);
 106 }
 107
 108 /*
 109  * unlock after writing
 110  */
 111 static inline void __up_write(struct rw_semaphore *sem)
 112 {
 113         if (unlikely(atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 114                               (atomic_t *)(&sem->count)) < 0))
 115                 rwsem_wake(sem);
 116 }
 117
 118 /*
 119  * implement atomic add functionality
 120  */
 121 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 122 {
 123         atomic_add(delta, (atomic_t *)(&sem->count));
 124 }
 125
 126 /*
 127  * downgrade write lock to read lock
 128  */
 129 static inline void __downgrade_write(struct rw_semaphore *sem)
 130 {
 131         int tmp;
 132
 133         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 134         if (tmp < 0)
 135                 rwsem_downgrade_wake(sem);
 136 }
 137
 138 /*
 139  * implement exchange and add functionality
 140  */
 141 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 142 {
 143         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 144 }
 145
 146 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 147 {
 148         return (sem->count != 0);
 149 }
 150
 151 #endif  /* __KERNEL__ */
 152 #endif  /* _ASM_POWERPC_RWSEM_H */