arch/ia64/include/asm/rwsem.h

   1 /*
   2  * R/W semaphores for ia64
   3  *
   4  * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
   5  * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
   6  * Copyright (C) 2005 Christoph Lameter <cl@linux.com>
   7  *
   8  * Based on asm-i386/rwsem.h and other architecture implementation.
   9  *
  10  * The MSW of the count is the negated number of active writers and
  11  * waiting lockers, and the LSW is the total number of active locks.
  12  *
  13  * The lock count is initialized to 0 (no active and no waiting lockers).
  14  *
  15  * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
  16  * the case of an uncontended lock. Readers increment by 1 and see a positive
  17  * value when uncontended, negative if there are writers (and maybe) readers
  18  * waiting (in which case it goes to sleep).
  19  */
  20
  21 #ifndef _ASM_IA64_RWSEM_H
  22 #define _ASM_IA64_RWSEM_H
  23
  24 #ifndef _LINUX_RWSEM_H
  25 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  26 #endif
  27
  28 #include <asm/intrinsics.h>
  29
  30 #define RWSEM_UNLOCKED_VALUE            __IA64_UL_CONST(0x0000000000000000)
  31 #define RWSEM_ACTIVE_BIAS               (1L)
  32 #define RWSEM_ACTIVE_MASK               (0xffffffffL)
  33 #define RWSEM_WAITING_BIAS              (-0x100000000L)
  34 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  35 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  36
  37 /*
  38  * lock for reading
  39  */
  40 static inline int
  41 ___down_read (struct rw_semaphore *sem)
  42 {
  43         long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
  44
  45         return (result < 0);
  46 }
  47
  48 static inline void
  49 __down_read (struct rw_semaphore *sem)
  50 {
  51         if (___down_read(sem))
  52                 rwsem_down_read_failed(sem);
  53 }
  54
  55 static inline int
  56 __down_read_killable (struct rw_semaphore *sem)
  57 {
  58         if (___down_read(sem))
  59                 if (IS_ERR(rwsem_down_read_failed_killable(sem)))
  60                         return -EINTR;
  61
  62         return 0;
  63 }
  64
  65 /*
  66  * lock for writing
  67  */
  68 static inline long
  69 ___down_write (struct rw_semaphore *sem)
  70 {
  71         long old, new;
  72
  73         do {
  74                 old = atomic_long_read(&sem->count);
  75                 new = old + RWSEM_ACTIVE_WRITE_BIAS;
  76         } while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
  77
  78         return old;
  79 }
  80
  81 static inline void
  82 __down_write (struct rw_semaphore *sem)
  83 {
  84         if (___down_write(sem))
  85                 rwsem_down_write_failed(sem);
  86 }
  87
  88 static inline int
  89 __down_write_killable (struct rw_semaphore *sem)
  90 {
  91         if (___down_write(sem)) {
  92                 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
  93                         return -EINTR;
  94         }
  95
  96         return 0;
  97 }
  98
  99 /*
 100  * unlock after reading
 101  */
 102 static inline void
 103 __up_read (struct rw_semaphore *sem)
 104 {
 105         long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
 106
 107         if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
 108                 rwsem_wake(sem);
 109 }
 110
 111 /*
 112  * unlock after writing
 113  */
 114 static inline void
 115 __up_write (struct rw_semaphore *sem)
 116 {
 117         long old, new;
 118
 119         do {
 120                 old = atomic_long_read(&sem->count);
 121                 new = old - RWSEM_ACTIVE_WRITE_BIAS;
 122         } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
 123
 124         if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
 125                 rwsem_wake(sem);
 126 }
 127
 128 /*
 129  * trylock for reading -- returns 1 if successful, 0 if contention
 130  */
 131 static inline int
 132 __down_read_trylock (struct rw_semaphore *sem)
 133 {
 134         long tmp;
 135         while ((tmp = atomic_long_read(&sem->count)) >= 0) {
 136                 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
 137                         return 1;
 138                 }
 139         }
 140         return 0;
 141 }
 142
 143 /*
 144  * trylock for writing -- returns 1 if successful, 0 if contention
 145  */
 146 static inline int
 147 __down_write_trylock (struct rw_semaphore *sem)
 148 {
 149         long tmp = atomic_long_cmpxchg_acquire(&sem->count,
 150                         RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
 151         return tmp == RWSEM_UNLOCKED_VALUE;
 152 }
 153
 154 /*
 155  * downgrade write lock to read lock
 156  */
 157 static inline void
 158 __downgrade_write (struct rw_semaphore *sem)
 159 {
 160         long old, new;
 161
 162         do {
 163                 old = atomic_long_read(&sem->count);
 164                 new = old - RWSEM_WAITING_BIAS;
 165         } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
 166
 167         if (old < 0)
 168                 rwsem_downgrade_wake(sem);
 169 }
 170
 171 #endif /* _ASM_IA64_RWSEM_H */