arch/sh/include/asm/mutex-llsc.h

   1 /*
   2  * arch/sh/include/asm/mutex-llsc.h
   3  *
   4  * SH-4A optimized mutex locking primitives
   5  *
   6  * Please look into asm-generic/mutex-xchg.h for a formal definition.
   7  */
   8 #ifndef __ASM_SH_MUTEX_LLSC_H
   9 #define __ASM_SH_MUTEX_LLSC_H
  10
  11 /*
  12  * Attempting to lock a mutex on SH4A is done like in ARMv6+ architecure.
  13  * with a bastardized atomic decrement (it is not a reliable atomic decrement
  14  * but it satisfies the defined semantics for our purpose, while being
  15  * smaller and faster than a real atomic decrement or atomic swap.
  16  * The idea is to attempt  decrementing the lock value only once. If once
  17  * decremented it isn't zero, or if its store-back fails due to a dispute
  18  * on the exclusive store, we simply bail out immediately through the slow
  19  * path where the lock will be reattempted until it succeeds.
  20  */
  21 static inline void
  22 __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
  23 {
  24         int __done, __res;
  25
  26         __asm__ __volatile__ (
  27                 "movli.l        @%2, %0 \n"
  28                 "add            #-1, %0 \n"
  29                 "movco.l        %0, @%2 \n"
  30                 "movt           %1      \n"
  31                 : "=&z" (__res), "=&r" (__done)
  32                 : "r" (&(count)->counter)
  33                 : "t");
  34
  35         if (unlikely(!__done || __res != 0))
  36                 fail_fn(count);
  37 }
  38
  39 static inline int
  40 __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
  41 {
  42         int __done, __res;
  43
  44         __asm__ __volatile__ (
  45                 "movli.l        @%2, %0 \n"
  46                 "add            #-1, %0 \n"
  47                 "movco.l        %0, @%2 \n"
  48                 "movt           %1      \n"
  49                 : "=&z" (__res), "=&r" (__done)
  50                 : "r" (&(count)->counter)
  51                 : "t");
  52
  53         if (unlikely(!__done || __res != 0))
  54                 __res = fail_fn(count);
  55
  56         return __res;
  57 }
  58
  59 static inline void
  60 __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
  61 {
  62         int __done, __res;
  63
  64         __asm__ __volatile__ (
  65                 "movli.l        @%2, %0 \n\t"
  66                 "add            #1, %0  \n\t"
  67                 "movco.l        %0, @%2 \n\t"
  68                 "movt           %1      \n\t"
  69                 : "=&z" (__res), "=&r" (__done)
  70                 : "r" (&(count)->counter)
  71                 : "t");
  72
  73         if (unlikely(!__done || __res <= 0))
  74                 fail_fn(count);
  75 }
  76
  77 /*
  78  * If the unlock was done on a contended lock, or if the unlock simply fails
  79  * then the mutex remains locked.
  80  */
  81 #define __mutex_slowpath_needs_to_unlock()      1
  82
  83 /*
  84  * For __mutex_fastpath_trylock we do an atomic decrement and check the
  85  * result and put it in the __res variable.
  86  */
  87 static inline int
  88 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
  89 {
  90         int __res, __orig;
  91
  92         __asm__ __volatile__ (
  93                 "1: movli.l     @%2, %0         \n\t"
  94                 "dt             %0              \n\t"
  95                 "movco.l        %0,@%2          \n\t"
  96                 "bf             1b              \n\t"
  97                 "cmp/eq         #0,%0           \n\t"
  98                 "bt             2f              \n\t"
  99                 "mov            #0, %1          \n\t"
 100                 "bf             3f              \n\t"
 101                 "2: mov         #1, %1          \n\t"
 102                 "3:                             "
 103                 : "=&z" (__orig), "=&r" (__res)
 104                 : "r" (&count->counter)
 105                 : "t");
 106
 107         return __res;
 108 }
 109 #endif /* __ASM_SH_MUTEX_LLSC_H */