diff options
Diffstat (limited to 'arch/arm/include/asm/mutex.h')
-rw-r--r-- | arch/arm/include/asm/mutex.h | 119 |
1 files changed, 4 insertions, 115 deletions
diff --git a/arch/arm/include/asm/mutex.h b/arch/arm/include/asm/mutex.h index 93226cf..b1479fd 100644 --- a/arch/arm/include/asm/mutex.h +++ b/arch/arm/include/asm/mutex.h @@ -7,121 +7,10 @@ */ #ifndef _ASM_MUTEX_H #define _ASM_MUTEX_H - -#if __LINUX_ARM_ARCH__ < 6 -/* On pre-ARMv6 hardware the swp based implementation is the most efficient. */ -# include <asm-generic/mutex-xchg.h> -#else - /* - * Attempting to lock a mutex on ARMv6+ can be done 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. + * On pre-ARMv6 hardware this results in a swp-based implementation, + * which is the most efficient. For ARMv6+, we emit a pair of exclusive + * accesses instead. */ -static inline void -__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) -{ - int __ex_flag, __res; - - __asm__ ( - - "ldrex %0, [%2] \n\t" - "sub %0, %0, #1 \n\t" - "strex %1, %0, [%2] " - - : "=&r" (__res), "=&r" (__ex_flag) - : "r" (&(count)->counter) - : "cc","memory" ); - - __res |= __ex_flag; - if (unlikely(__res != 0)) - fail_fn(count); -} - -static inline int -__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *)) -{ - int __ex_flag, __res; - - __asm__ ( - - "ldrex %0, [%2] \n\t" - "sub %0, %0, #1 \n\t" - "strex %1, %0, [%2] " - - : "=&r" (__res), "=&r" (__ex_flag) - : "r" (&(count)->counter) - : "cc","memory" ); - - __res |= __ex_flag; - if (unlikely(__res != 0)) - __res = fail_fn(count); - return __res; -} - -/* - * Same trick is used for the unlock fast path. However the original value, - * rather than the result, is used to test for success in order to have - * better generated assembly. - */ -static inline void -__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) -{ - int __ex_flag, __res, __orig; - - __asm__ ( - - "ldrex %0, [%3] \n\t" - "add %1, %0, #1 \n\t" - "strex %2, %1, [%3] " - - : "=&r" (__orig), "=&r" (__res), "=&r" (__ex_flag) - : "r" (&(count)->counter) - : "cc","memory" ); - - __orig |= __ex_flag; - if (unlikely(__orig != 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 use another construct which could be - * described as a "single value cmpxchg". - * - * This provides the needed trylock semantics like cmpxchg would, but it is - * lighter and less generic than a true cmpxchg implementation. - */ -static inline int -__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) -{ - int __ex_flag, __res, __orig; - - __asm__ ( - - "1: ldrex %0, [%3] \n\t" - "subs %1, %0, #1 \n\t" - "strexeq %2, %1, [%3] \n\t" - "movlt %0, #0 \n\t" - "cmpeq %2, #0 \n\t" - "bgt 1b " - - : "=&r" (__orig), "=&r" (__res), "=&r" (__ex_flag) - : "r" (&count->counter) - : "cc", "memory" ); - - return __orig; -} - -#endif +#include <asm-generic/mutex-xchg.h> #endif |