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

   1 /*
   2  * include/asm-xtensa/rwsem.h
   3  *
   4  * This file is subject to the terms and conditions of the GNU General Public
   5  * License.  See the file "COPYING" in the main directory of this archive
   6  * for more details.
   7  *
   8  * Largely copied from include/asm-ppc/rwsem.h
   9  *
  10  * Copyright (C) 2001 - 2005 Tensilica Inc.
  11  */
  12
  13 #ifndef _XTENSA_RWSEM_H
  14 #define _XTENSA_RWSEM_H
  15
  16 #ifndef _LINUX_RWSEM_H
  17 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  18 #endif
  19
  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
  27 /*
  28  * lock for reading
  29  */
  30 static inline void __down_read(struct rw_semaphore *sem)
  31 {
  32         if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
  33                 smp_wmb();
  34         else
  35                 rwsem_down_read_failed(sem);
  36 }
  37
  38 static inline int __down_read_trylock(struct rw_semaphore *sem)
  39 {
  40         int tmp;
  41
  42         while ((tmp = sem->count) >= 0) {
  43                 if (tmp == cmpxchg(&sem->count, tmp,
  44                                    tmp + RWSEM_ACTIVE_READ_BIAS)) {
  45                         smp_wmb();
  46                         return 1;
  47                 }
  48         }
  49         return 0;
  50 }
  51
  52 /*
  53  * lock for writing
  54  */
  55 static inline void __down_write(struct rw_semaphore *sem)
  56 {
  57         int tmp;
  58
  59         tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
  60                                 (atomic_t *)(&sem->count));
  61         if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
  62                 smp_wmb();
  63         else
  64                 rwsem_down_write_failed(sem);
  65 }
  66
  67 static inline int __down_write_trylock(struct rw_semaphore *sem)
  68 {
  69         int tmp;
  70
  71         tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
  72                       RWSEM_ACTIVE_WRITE_BIAS);
  73         smp_wmb();
  74         return tmp == RWSEM_UNLOCKED_VALUE;
  75 }
  76
  77 /*
  78  * unlock after reading
  79  */
  80 static inline void __up_read(struct rw_semaphore *sem)
  81 {
  82         int tmp;
  83
  84         smp_wmb();
  85         tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
  86         if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
  87                 rwsem_wake(sem);
  88 }
  89
  90 /*
  91  * unlock after writing
  92  */
  93 static inline void __up_write(struct rw_semaphore *sem)
  94 {
  95         smp_wmb();
  96         if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
  97                               (atomic_t *)(&sem->count)) < 0)
  98                 rwsem_wake(sem);
  99 }
 100
 101 /*
 102  * implement atomic add functionality
 103  */
 104 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
 105 {
 106         atomic_add(delta, (atomic_t *)(&sem->count));
 107 }
 108
 109 /*
 110  * downgrade write lock to read lock
 111  */
 112 static inline void __downgrade_write(struct rw_semaphore *sem)
 113 {
 114         int tmp;
 115
 116         smp_wmb();
 117         tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 118         if (tmp < 0)
 119                 rwsem_downgrade_wake(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  /* _XTENSA_RWSEM_H */