1/*
  2 * arch/sh/include/asm/mutex-llsc.h
  3 *
  4 * SH-4A optimized mutex locking primitives
  5 *
  6 * Please look into asm-generic/mutex-xchg.h for a formal definition.
  7 */
  8#ifndef __ASM_SH_MUTEX_LLSC_H
  9#define __ASM_SH_MUTEX_LLSC_H
 10
 11/*
 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.
 20 */
 21static inline void
 22__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
 23{
 24	int __done, __res;
 25
 26	__asm__ __volatile__ (
 27		"movli.l	@%2, %0	\n"
 28		"add		#-1, %0	\n"
 29		"movco.l	%0, @%2	\n"
 30		"movt		%1	\n"
 31		: "=&z" (__res), "=&r" (__done)
 32		: "r" (&(count)->counter)
 33		: "t");
 34
 35	if (unlikely(!__done || __res != 0))
 36		fail_fn(count);
 37}
 38
 39static inline int
 40__mutex_fastpath_lock_retval(atomic_t *count)
 41{
 42	int __done, __res;
 43
 44	__asm__ __volatile__ (
 45		"movli.l	@%2, %0	\n"
 46		"add		#-1, %0	\n"
 47		"movco.l	%0, @%2	\n"
 48		"movt		%1	\n"
 49		: "=&z" (__res), "=&r" (__done)
 50		: "r" (&(count)->counter)
 51		: "t");
 52
 53	if (unlikely(!__done || __res != 0))
 54		__res = -1;
 55
 56	return __res;
 57}
 58
 59static inline void
 60__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
 61{
 62	int __done, __res;
 63
 64	__asm__ __volatile__ (
 65		"movli.l	@%2, %0	\n\t"
 66		"add		#1, %0	\n\t"
 67		"movco.l	%0, @%2 \n\t"
 68		"movt		%1	\n\t"
 69		: "=&z" (__res), "=&r" (__done)
 70		: "r" (&(count)->counter)
 71		: "t");
 72
 73	if (unlikely(!__done || __res <= 0))
 74		fail_fn(count);
 75}
 76
 77/*
 78 * If the unlock was done on a contended lock, or if the unlock simply fails
 79 * then the mutex remains locked.
 80 */
 81#define __mutex_slowpath_needs_to_unlock()	1
 82
 83/*
 84 * For __mutex_fastpath_trylock we do an atomic decrement and check the
 85 * result and put it in the __res variable.
 86 */
 87static inline int
 88__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
 89{
 90	int __res, __orig;
 91
 92	__asm__ __volatile__ (
 93		"1: movli.l	@%2, %0		\n\t"
 94		"dt		%0		\n\t"
 95		"movco.l	%0,@%2		\n\t"
 96		"bf		1b		\n\t"
 97		"cmp/eq		#0,%0		\n\t"
 98		"bt		2f		\n\t"
 99		"mov		#0, %1		\n\t"
100		"bf		3f		\n\t"
101		"2: mov		#1, %1		\n\t"
102		"3:				"
103		: "=&z" (__orig), "=&r" (__res)
104		: "r" (&count->counter)
105		: "t");
106
107	return __res;
108}
109#endif /* __ASM_SH_MUTEX_LLSC_H */