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, int (*fail_fn)(atomic_t *))
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 = fail_fn(count);
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 */
110