1/*
2 * PowerPC-specific semaphore code.
3 *
4 * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 *
11 * April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
12 * to eliminate the SMP races in the old version between the updates
13 * of `count' and `waking'.  Now we use negative `count' values to
14 * indicate that some process(es) are waiting for the semaphore.
15 */
16
17#include <linux/sched.h>
18#include <linux/init.h>
19#include <linux/module.h>
20
21#include <asm/atomic.h>
22#include <asm/semaphore.h>
23#include <asm/errno.h>
24
25/*
26 * Atomically update sem->count.
27 * This does the equivalent of the following:
28 *
29 *	old_count = sem->count;
30 *	tmp = MAX(old_count, 0) + incr;
31 *	sem->count = tmp;
32 *	return old_count;
33 */
34static inline int __sem_update_count(struct semaphore *sem, int incr)
35{
36	int old_count, tmp;
37
38	__asm__ __volatile__("\n"
39"1:	lwarx	%0,0,%3\n"
40"	srawi	%1,%0,31\n"
41"	andc	%1,%0,%1\n"
42"	add	%1,%1,%4\n"
43	PPC405_ERR77(0,%3)
44"	stwcx.	%1,0,%3\n"
45"	bne	1b"
46	: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
47	: "r" (&sem->count), "r" (incr), "m" (sem->count)
48	: "cc");
49
50	return old_count;
51}
52
53void __up(struct semaphore *sem)
54{
55	/*
56	 * Note that we incremented count in up() before we came here,
57	 * but that was ineffective since the result was <= 0, and
58	 * any negative value of count is equivalent to 0.
59	 * This ends up setting count to 1, unless count is now > 0
60	 * (i.e. because some other cpu has called up() in the meantime),
61	 * in which case we just increment count.
62	 */
63	__sem_update_count(sem, 1);
64	wake_up(&sem->wait);
65}
66EXPORT_SYMBOL(__up);
67
68/*
69 * Note that when we come in to __down or __down_interruptible,
70 * we have already decremented count, but that decrement was
71 * ineffective since the result was < 0, and any negative value
72 * of count is equivalent to 0.
73 * Thus it is only when we decrement count from some value > 0
74 * that we have actually got the semaphore.
75 */
76void __sched __down(struct semaphore *sem)
77{
78	struct task_struct *tsk = current;
79	DECLARE_WAITQUEUE(wait, tsk);
80
81	__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
82	add_wait_queue_exclusive(&sem->wait, &wait);
83
84	/*
85	 * Try to get the semaphore.  If the count is > 0, then we've
86	 * got the semaphore; we decrement count and exit the loop.
87	 * If the count is 0 or negative, we set it to -1, indicating
88	 * that we are asleep, and then sleep.
89	 */
90	while (__sem_update_count(sem, -1) <= 0) {
91		schedule();
92		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
93	}
94	remove_wait_queue(&sem->wait, &wait);
95	__set_task_state(tsk, TASK_RUNNING);
96
97	/*
98	 * If there are any more sleepers, wake one of them up so
99	 * that it can either get the semaphore, or set count to -1
100	 * indicating that there are still processes sleeping.
101	 */
102	wake_up(&sem->wait);
103}
104EXPORT_SYMBOL(__down);
105
106int __sched __down_interruptible(struct semaphore * sem)
107{
108	int retval = 0;
109	struct task_struct *tsk = current;
110	DECLARE_WAITQUEUE(wait, tsk);
111
112	__set_task_state(tsk, TASK_INTERRUPTIBLE);
113	add_wait_queue_exclusive(&sem->wait, &wait);
114
115	while (__sem_update_count(sem, -1) <= 0) {
116		if (signal_pending(current)) {
117			/*
118			 * A signal is pending - give up trying.
119			 * Set sem->count to 0 if it is negative,
120			 * since we are no longer sleeping.
121			 */
122			__sem_update_count(sem, 0);
123			retval = -EINTR;
124			break;
125		}
126		schedule();
127		set_task_state(tsk, TASK_INTERRUPTIBLE);
128	}
129	remove_wait_queue(&sem->wait, &wait);
130	__set_task_state(tsk, TASK_RUNNING);
131
132	wake_up(&sem->wait);
133	return retval;
134}
135EXPORT_SYMBOL(__down_interruptible);
136