arch/powerpc/include/asm/rwsem.h

   1 #ifndef _ASM_POWERPC_RWSEM_H
   2 #define _ASM_POWERPC_RWSEM_H
   3
   4 #ifndef _LINUX_RWSEM_H
   5 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
   6 #endif
   7
   8 #ifdef __KERNEL__
   9
  10 /*
  11  * R/W semaphores for PPC using the stuff in lib/rwsem.c.
  12  * Adapted largely from include/asm-i386/rwsem.h
  13  * by Paul Mackerras <paulus@samba.org>.
  14  */
  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         /* XXX this should be able to be an atomic_t  -- paulus */
  26         signed int              count;
  27 #define RWSEM_UNLOCKED_VALUE            0x00000000
  28 #define RWSEM_ACTIVE_BIAS               0x00000001
  29 #define RWSEM_ACTIVE_MASK               0x0000ffff
  30 #define RWSEM_WAITING_BIAS              (-0x00010000)
  31 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  32 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  33         spinlock_t              wait_lock;
  34         struct list_head        wait_list;
  35 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  36         struct lockdep_map      dep_map;
  37 #endif
  38 };
  39
  40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  41 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  42 #else
  43 # define __RWSEM_DEP_MAP_INIT(lockname)
  44 #endif
  45
  46 #define __RWSEM_INITIALIZER(name) \
  47         { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
  48           LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }
  49
  50 #define DECLARE_RWSEM(name)             \
  51         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  52
  53 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  54 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  55 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  56 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  57
  58 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  59                          struct lock_class_key *key);
  60
  61 #define init_rwsem(sem)                                 \
  62         do {                                            \
  63                 static struct lock_class_key __key;     \
  64                                                         \
  65                 __init_rwsem((sem), #sem, &__key);      \
  66         } while (0)
  67
  68 /*
  69  * lock for reading
  70  */
  71 static inline void __down_read(struct rw_semaphore *sem)
  72 {
  73         if (unlikely(atomic_inc_return((atomic_t *)(&sem->count)) <= 0))
  74                 rwsem_down_read_failed(sem);
  75 }
  76
  77 static inline int __down_read_trylock(struct rw_semaphore *sem)
  78 {
  79         int tmp;
  80
  81         while ((tmp = sem->count) >= 0) {
  82                 if (tmp == cmpxchg(&sem->count, tmp,
  83                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  84                         return 1;
  85                 }
  86         }
  87         return 0;
  88 }
  89
  90 /*
  91  * lock for writing
  92  */
  93 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
  94 {
  95         int tmp;
  96
  97         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  98                                 (atomic_t *)(&sem->count));
  99         if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
 100                 rwsem_down_write_failed(sem);
 101 }
 102
 103 static inline void __down_write(struct rw_semaphore *sem)
 104 {
 105         __down_write_nested(sem, 0);
 106 }
 107
 108 static inline int __down_write_trylock(struct rw_semaphore *sem)
 109 {
 110         int tmp;
 111
 112         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 113                       RWSEM_ACTIVE_WRITE_BIAS);
 114         return tmp == RWSEM_UNLOCKED_VALUE;
 115 }
 116
 117 /*
 118  * unlock after reading
 119  */
 120 static inline void __up_read(struct rw_semaphore *sem)
 121 {
 122         int tmp;
 123
 124         tmp = atomic_dec_return((atomic_t *)(&sem->count));
 125         if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
 126                 rwsem_wake(sem);
 127 }
 128
 129 /*
 130  * unlock after writing
 131  */
 132 static inline void __up_write(struct rw_semaphore *sem)
 133 {
 134         if (unlikely(atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 135                               (atomic_t *)(&sem->count)) < 0))
 136                 rwsem_wake(sem);
 137 }
 138
 139 /*
 140  * implement atomic add functionality
 141  */
 142 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 143 {
 144         atomic_add(delta, (atomic_t *)(&sem->count));
 145 }
 146
 147 /*
 148  * downgrade write lock to read lock
 149  */
 150 static inline void __downgrade_write(struct rw_semaphore *sem)
 151 {
 152         int tmp;
 153
 154         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 155         if (tmp < 0)
 156                 rwsem_downgrade_wake(sem);
 157 }
 158
 159 /*
 160  * implement exchange and add functionality
 161  */
 162 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 163 {
 164         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 165 }
 166
 167 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 168 {
 169         return (sem->count != 0);
 170 }
 171
 172 #endif  /* __KERNEL__ */
 173 #endif  /* _ASM_POWERPC_RWSEM_H */