ARM: 7495/1: mutex: use generic atomic_dec-based implementation for ARMv6+

[firefly-linux-kernel-4.4.55.git] / arch / arm / include / asm / mutex.h

diff --git a/arch/arm/include/asm/mutex.h b/arch/arm/include/asm/mutex.h
index 93226cf23ae0a838e192be1d675ee886be9dd52e..87c044910fe0a2274cc7198cdcbe00ca76d05795 100644 (file)
--- 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 */