2 * arch/sh/include/asm/mutex-llsc.h
4 * SH-4A optimized mutex locking primitives
6 * Please look into asm-generic/mutex-xchg.h for a formal definition.
8 #ifndef __ASM_SH_MUTEX_LLSC_H
9 #define __ASM_SH_MUTEX_LLSC_H
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.
22 __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
26 __asm__ __volatile__ (
31 : "=&z" (__res), "=&r" (__done)
32 : "r" (&(count)->counter)
35 if (unlikely(!__done || __res != 0))
40 __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
44 __asm__ __volatile__ (
49 : "=&z" (__res), "=&r" (__done)
50 : "r" (&(count)->counter)
53 if (unlikely(!__done || __res != 0))
54 __res = fail_fn(count);
60 __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
64 __asm__ __volatile__ (
65 "movli.l @%2, %0 \n\t"
67 "movco.l %0, @%2 \n\t"
69 : "=&z" (__res), "=&r" (__done)
70 : "r" (&(count)->counter)
73 if (unlikely(!__done || __res <= 0))
78 * If the unlock was done on a contended lock, or if the unlock simply fails
79 * then the mutex remains locked.
81 #define __mutex_slowpath_needs_to_unlock() 1
84 * For __mutex_fastpath_trylock we do an atomic decrement and check the
85 * result and put it in the __res variable.
88 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
92 __asm__ __volatile__ (
93 "1: movli.l @%2, %0 \n\t"
103 : "=&z" (__orig), "=&r" (__res)
104 : "r" (&count->counter)
109 #endif /* __ASM_SH_MUTEX_LLSC_H */