kernel/arch/sh/include/asm/rwsem.h

   1 /*
   2  * include/asm-sh/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 #ifndef _LINUX_RWSEM_H
  10 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
  11 #endif
  12
  13 #ifdef __KERNEL__
  14
  15 #define RWSEM_UNLOCKED_VALUE            0x00000000
  16 #define RWSEM_ACTIVE_BIAS               0x00000001
  17 #define RWSEM_ACTIVE_MASK               0x0000ffff
  18 #define RWSEM_WAITING_BIAS              (-0x00010000)
  19 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  20 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  21
  22 /*
  23  * lock for reading
  24  */
  25 static inline void __down_read(struct rw_semaphore *sem)
  26 {
  27         if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
  28                 smp_wmb();
  29         else
  30                 rwsem_down_read_failed(sem);
  31 }
  32
  33 static inline int __down_read_trylock(struct rw_semaphore *sem)
  34 {
  35         int tmp;
  36
  37         while ((tmp = sem->count) >= 0) {
  38                 if (tmp == cmpxchg(&sem->count, tmp,
  39                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  40                         smp_wmb();
  41                         return 1;
  42                 }
  43         }
  44         return 0;
  45 }
  46
  47 /*
  48  * lock for writing
  49  */
  50 static inline void __down_write(struct rw_semaphore *sem)
  51 {
  52         int tmp;
  53
  54         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  55                                 (atomic_t *)(&sem->count));
  56         if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
  57                 smp_wmb();
  58         else
  59                 rwsem_down_write_failed(sem);
  60 }
  61
  62 static inline int __down_write_trylock(struct rw_semaphore *sem)
  63 {
  64         int tmp;
  65
  66         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
  67                       RWSEM_ACTIVE_WRITE_BIAS);
  68         smp_wmb();
  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         int tmp;
  78
  79         smp_wmb();
  80         tmp = atomic_dec_return((atomic_t *)(&sem->count));
  81         if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
  82                 rwsem_wake(sem);
  83 }
  84
  85 /*
  86  * unlock after writing
  87  */
  88 static inline void __up_write(struct rw_semaphore *sem)
  89 {
  90         smp_wmb();
  91         if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
  92                               (atomic_t *)(&sem->count)) < 0)
  93                 rwsem_wake(sem);
  94 }
  95
  96 /*
  97  * implement atomic add functionality
  98  */
  99 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 100 {
 101         atomic_add(delta, (atomic_t *)(&sem->count));
 102 }
 103
 104 /*
 105  * downgrade write lock to read lock
 106  */
 107 static inline void __downgrade_write(struct rw_semaphore *sem)
 108 {
 109         int tmp;
 110
 111         smp_wmb();
 112         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 113         if (tmp < 0)
 114                 rwsem_downgrade_wake(sem);
 115 }
 116
 117 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 118 {
 119         __down_write(sem);
 120 }
 121
 122 /*
 123  * implement exchange and add functionality
 124  */
 125 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 126 {
 127         smp_mb();
 128         return atomic_add_return(delta, (atomic_t *)(&sem->count));
 129 }
 130
 131 #endif /* __KERNEL__ */
 132 #endif /* _ASM_SH_RWSEM_H */