summaryrefslogtreecommitdiffstats
path: root/include/asm-i386/semaphore.h
blob: a68b23fc638e54e0185b7c80f778bde4e9a3e40d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
#ifndef _I386_SEMAPHORE_H
#define _I386_SEMAPHORE_H

#include <linux/linkage.h>

/*
 * SMP- and interrupt-safe semaphores..
 *
 * (C) Copyright 1996 Linus Torvalds
 *
 * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
 *                     the original code and to make semaphore waits
 *                     interruptible so that processes waiting on
 *                     semaphores can be killed.
 *
 * If you would like to see an analysis of this implementation, please
 * ftp to gcom.com and download the file
 * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
 *
 */

#include <asm/system.h>
#include <asm/atomic.h>
#include <asm/spinlock.h>

struct semaphore {
	atomic_t count;
	int waking;
	struct wait_queue * wait;
};

#define MUTEX ((struct semaphore) { ATOMIC_INIT(1), 0, NULL })
#define MUTEX_LOCKED ((struct semaphore) { ATOMIC_INIT(0), 0, NULL })

asmlinkage void __down_failed(void /* special register calling convention */);
asmlinkage int  __down_failed_interruptible(void  /* params in registers */);
asmlinkage void __up_wakeup(void /* special register calling convention */);

extern void __down(struct semaphore * sem);
extern void __up(struct semaphore * sem);

extern spinlock_t semaphore_wake_lock;

#define sema_init(sem, val)	atomic_set(&((sem)->count), (val))

/*
 * These two _must_ execute atomically wrt each other.
 *
 * This is trivially done with load_locked/store_cond,
 * but on the x86 we need an external synchronizer.
 * Currently this is just the global interrupt lock,
 * bah. Go for a smaller spinlock some day.
 *
 * (On the other hand this shouldn't be in any critical
 * path, so..)
 */
static inline void wake_one_more(struct semaphore * sem)
{
	unsigned long flags;

	spin_lock_irqsave(&semaphore_wake_lock, flags);
	sem->waking++;
	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
}

static inline int waking_non_zero(struct semaphore *sem)
{
	unsigned long flags;
	int ret = 0;

	spin_lock_irqsave(&semaphore_wake_lock, flags);
	if (sem->waking > 0) {
		sem->waking--;
		ret = 1;
	}
	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
	return ret;
}

/*
 * This is ugly, but we want the default case to fall through.
 * "down_failed" is a special asm handler that calls the C
 * routine that actually waits. See arch/i386/lib/semaphore.S
 */
extern inline void down(struct semaphore * sem)
{
	__asm__ __volatile__(
		"# atomic down operation\n\t"
#ifdef __SMP__
		"lock ; "
#endif
		"decl 0(%0)\n\t"
		"js 2f\n"
		"1:\n"
		".section .text.lock,\"ax\"\n"
		"2:\tpushl $1b\n\t"
		"jmp __down_failed\n"
		".previous"
		:/* no outputs */
		:"c" (sem)
		:"memory");
}

extern inline int down_interruptible(struct semaphore * sem)
{
	int result;

	__asm__ __volatile__(
		"# atomic interruptible down operation\n\t"
#ifdef __SMP__
		"lock ; "
#endif
		"decl 0(%1)\n\t"
		"js 2f\n\t"
		"xorl %0,%0\n"
		"1:\n"
		".section .text.lock,\"ax\"\n"
		"2:\tpushl $1b\n\t"
		"jmp __down_failed_interruptible\n"
		".previous"
		:"=a" (result)
		:"c" (sem)
		:"memory");
	return result;
}


/*
 * Note! This is subtle. We jump to wake people up only if
 * the semaphore was negative (== somebody was waiting on it).
 * The default case (no contention) will result in NO
 * jumps for both down() and up().
 */
extern inline void up(struct semaphore * sem)
{
	__asm__ __volatile__(
		"# atomic up operation\n\t"
#ifdef __SMP__
		"lock ; "
#endif
		"incl 0(%0)\n\t"
		"jle 2f\n"
		"1:\n"
		".section .text.lock,\"ax\"\n"
		"2:\tpushl $1b\n\t"
		"jmp __up_wakeup\n"
		".previous"
		:/* no outputs */
		:"c" (sem)
		:"memory");
}

#endif