LXR linux/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 */
  24struct 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
  53extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  54extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  55extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  56extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  57
  58extern 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 */
  71static 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
  77static 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 */
  93static 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
 103static inline void __down_write(struct rw_semaphore *sem)
 104{
 105        __down_write_nested(sem, 0);
 106}
 107
 108static 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 */
 120static 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 */
 132static 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 */
 142static 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 */
 150static 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 */
 162static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 163{
 164        return atomic_add_return(delta, (atomic_t *)(&sem->count));
 165}
 166
 167static 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 */
 174