include/asm-sh/rwsem.h

   1 /*
   2  * include/asm-ppc/rwsem.h: R/W semaphores for SH using the stuff
   3  * in lib/rwsem.c.
   4  */
   5
   6 #ifndef _ASM_SH_RWSEM_H
   7 #define _ASM_SH_RWSEM_H
   8
   9 #ifdef __KERNEL__
  10 #include <linux/list.h>
  11 #include <linux/spinlock.h>
  12 #include <asm/atomic.h>
  13 #include <asm/system.h>
  14
  15 /*
  16  * the semaphore definition
  17  */
  18 struct rw_semaphore {
  19         long            count;
  20 #define RWSEM_UNLOCKED_VALUE            0x00000000
  21 #define RWSEM_ACTIVE_BIAS               0x00000001
  22 #define RWSEM_ACTIVE_MASK               0x0000ffff
  23 #define RWSEM_WAITING_BIAS              (-0x00010000)
  24 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  25 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  26         spinlock_t              wait_lock;
  27         struct list_head        wait_list;
  28 #if RWSEM_DEBUG
  29         int                     debug;
  30 #endif
  31 };
  32
  33 /*
  34  * initialisation
  35  */
  36 #if RWSEM_DEBUG
  37 #define __RWSEM_DEBUG_INIT      , 0
  38 #else
  39 #define __RWSEM_DEBUG_INIT      /* */
  40 #endif
  41
  42 #define __RWSEM_INITIALIZER(name) \
  43         { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
  44           LIST_HEAD_INIT((name).wait_list) \
  45           __RWSEM_DEBUG_INIT }
  46
  47 #define DECLARE_RWSEM(name)             \
  48         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  49
  50 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  51 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  52 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
  53 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  54
  55 static inline void init_rwsem(struct rw_semaphore *sem)
  56 {
  57         sem->count = RWSEM_UNLOCKED_VALUE;
  58         spin_lock_init(&sem->wait_lock);
  59         INIT_LIST_HEAD(&sem->wait_list);
  60 #if RWSEM_DEBUG
  61         sem->debug = 0;
  62 #endif
  63 }
  64
  65 /*
  66  * lock for reading
  67  */
  68 static inline void __down_read(struct rw_semaphore *sem)
  69 {
  70         if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
  71                 smp_wmb();
  72         else
  73                 rwsem_down_read_failed(sem);
  74 }
  75
  76 static inline int __down_read_trylock(struct rw_semaphore *sem)
  77 {
  78         int tmp;
  79
  80         while ((tmp = sem->count) >= 0) {
  81                 if (tmp == cmpxchg(&sem->count, tmp,
  82                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  83                         smp_wmb();
  84                         return 1;
  85                 }
  86         }
  87         return 0;
  88 }
  89
  90 /*
  91  * lock for writing
  92  */
  93 static inline void __down_write(struct rw_semaphore *sem)
  94 {
  95         int tmp;
  96
  97         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  98                                 (atomic_t *)(&sem->count));
  99         if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
 100                 smp_wmb();
 101         else
 102                 rwsem_down_write_failed(sem);
 103 }
 104
 105 static inline int __down_write_trylock(struct rw_semaphore *sem)
 106 {
 107         int tmp;
 108
 109         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 110                       RWSEM_ACTIVE_WRITE_BIAS);
 111         smp_wmb();
 112         return tmp == RWSEM_UNLOCKED_VALUE;
 113 }
 114
 115 /*
 116  * unlock after reading
 117  */
 118 static inline void __up_read(struct rw_semaphore *sem)
 119 {
 120         int tmp;
 121
 122         smp_wmb();
 123         tmp = atomic_dec_return((atomic_t *)(&sem->count));
 124         if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 125                 rwsem_wake(sem);
 126 }
 127
 128 /*
 129  * unlock after writing
 130  */
 131 static inline void __up_write(struct rw_semaphore *sem)
 132 {
 133         smp_wmb();
 134         if (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         smp_wmb();
 155         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 156         if (tmp < 0)
 157                 rwsem_downgrade_wake(sem);
 158 }
 159
 160 /*
 161  * implement exchange and add functionality
 162  */
 163 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 164 {
 165         smp_mb();
 166         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 167 }
 168
 169 #endif /* __KERNEL__ */
 170 #endif /* _ASM_SH_RWSEM_H */