aboutsummaryrefslogtreecommitdiffstats
path: root/arch/arm/include/asm/mutex.h
diff options
context:
space:
mode:
Diffstat (limited to 'arch/arm/include/asm/mutex.h')
-rw-r--r--arch/arm/include/asm/mutex.h124
1 files changed, 9 insertions, 115 deletions
diff --git a/arch/arm/include/asm/mutex.h b/arch/arm/include/asm/mutex.h
index 93226cf..87c0449 100644
--- a/arch/arm/include/asm/mutex.h
+++ b/arch/arm/include/asm/mutex.h
@@ -7,121 +7,15 @@
*/
#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.
- */
-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.
+ * On pre-ARMv6 hardware this results in a swp-based implementation,
+ * which is the most efficient. For ARMv6+, we have exclusive memory
+ * accessors and use atomic_dec to avoid the extra xchg operations
+ * on the locking slowpaths.
*/
-#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
+#if __LINUX_ARM_ARCH__ < 6
+#include <asm-generic/mutex-xchg.h>
+#else
+#include <asm-generic/mutex-dec.h>
#endif
+#endif /* _ASM_MUTEX_H */