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/*
* arch/sh/include/asm/mutex-llsc.h
*
* SH-4A optimized mutex locking primitives
*
* Please look into asm-generic/mutex-xchg.h for a formal definition.
*/
#ifndef __ASM_SH_MUTEX_LLSC_H
#define __ASM_SH_MUTEX_LLSC_H
/*
* Attempting to lock a mutex on SH4A is done like in ARMv6+ architecure.
* with a bastardized atomic decrement (it is not a reliable atomic decrement
* but it satisfies the defined semantics for our purpose, while being
* smaller and faster than a real atomic decrement or atomic swap.
* The idea is to attempt decrementing the lock value only once. If once
* decremented it isn't zero, or if its store-back fails due to a dispute
* on the exclusive store, we simply bail out immediately through the slow
* path where the lock will be reattempted until it succeeds.
*/
static inline void
__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
int __done, __res;
__asm__ __volatile__ (
"movli.l @%2, %0 \n"
"add #-1, %0 \n"
"movco.l %0, @%2 \n"
"movt %1 \n"
: "=&z" (__res), "=&r" (__done)
: "r" (&(count)->counter)
: "t");
if (unlikely(!__done || __res != 0))
fail_fn(count);
}
static inline int
__mutex_fastpath_lock_retval(atomic_t *count)
{
int __done, __res;
__asm__ __volatile__ (
"movli.l @%2, %0 \n"
"add #-1, %0 \n"
"movco.l %0, @%2 \n"
"movt %1 \n"
: "=&z" (__res), "=&r" (__done)
: "r" (&(count)->counter)
: "t");
if (unlikely(!__done || __res != 0))
__res = -1;
return __res;
}
static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
int __done, __res;
__asm__ __volatile__ (
"movli.l @%2, %0 \n\t"
"add #1, %0 \n\t"
"movco.l %0, @%2 \n\t"
"movt %1 \n\t"
: "=&z" (__res), "=&r" (__done)
: "r" (&(count)->counter)
: "t");
if (unlikely(!__done || __res <= 0))
fail_fn(count);
}
/*
* If the unlock was done on a contended lock, or if the unlock simply fails
* then the mutex remains locked.
*/
#define __mutex_slowpath_needs_to_unlock() 1
/*
* For __mutex_fastpath_trylock we do an atomic decrement and check the
* result and put it in the __res variable.
*/
static inline int
__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
{
int __res, __orig;
__asm__ __volatile__ (
"1: movli.l @%2, %0 \n\t"
"dt %0 \n\t"
"movco.l %0,@%2 \n\t"
"bf 1b \n\t"
"cmp/eq #0,%0 \n\t"
"bt 2f \n\t"
"mov #0, %1 \n\t"
"bf 3f \n\t"
"2: mov #1, %1 \n\t"
"3: "
: "=&z" (__orig), "=&r" (__res)
: "r" (&count->counter)
: "t");
return __res;
}
#endif /* __ASM_SH_MUTEX_LLSC_H */
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