include/asm-i386/semaphore.h

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 1 #ifndef _I386_SEMAPHORE_H
 2 #define _I386_SEMAPHORE_H
 3
 4 #include <linux/linkage.h>
 5
 6 /*
 7  * SMP- and interrupt-safe semaphores..
 8  *
 9  * (C) Copyright 1996 Linus Torvalds
 10  *
 11  * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
 12  * the original code and to make semaphore waits
 13  * interruptible so that processes waiting on
 14  * semaphores can be killed.
 15  *
 16  * If you would like to see an analysis of this implementation, please
 17  * ftp to gcom.com and download the file
 18  * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
 19  *
 20  */
 21
 22 #include <asm/system.h>
 23 #include <asm/atomic.h>
 24 #include <asm/spinlock.h>
 25
 26 struct semaphore {
 27  atomic_t count;
 28 int waking;
 29 struct wait_queue * wait;
 30 };
 31
 32 #define MUTEX ((struct semaphore) { ATOMIC_INIT(1), 0, NULL })
 33 #define MUTEX_LOCKED ((struct semaphore) { ATOMIC_INIT(0), 0, NULL })
 34
 35 asmlinkage void__down_failed(void/* special register calling convention */);
 36 asmlinkage int__down_failed_interruptible(void/* params in registers */);
 37 asmlinkage void__up_wakeup(void/* special register calling convention */);
 38
 39 externvoid__down(struct semaphore * sem);
 40 externvoid__up(struct semaphore * sem);
 41
 42 extern spinlock_t semaphore_wake_lock;
 43
 44 #define sema_init(sem, val) atomic_set(&((sem)->count), (val))
 45
 46 /*
 47  * These two _must_ execute atomically wrt each other.
 48  *
 49  * This is trivially done with load_locked/store_cond,
 50  * but on the x86 we need an external synchronizer.
 51  * Currently this is just the global interrupt lock,
 52  * bah. Go for a smaller spinlock some day.
 53  *
 54  * (On the other hand this shouldn't be in any critical
 55  * path, so..)
 56  */
 57 staticinlinevoidwake_one_more(struct semaphore * sem)
 58 {
 59 unsigned long flags;
 60
 61 spin_lock_irqsave(&semaphore_wake_lock, flags);
 62  sem->waking++;
 63 spin_unlock_irqrestore(&semaphore_wake_lock, flags);
 64 }
 65
 66 staticinlineintwaking_non_zero(struct semaphore *sem)
 67 {
 68 unsigned long flags;
 69 int ret =0;
 70
 71 spin_lock_irqsave(&semaphore_wake_lock, flags);
 72 if(sem->waking >0) {
 73  sem->waking--;
 74  ret =1;
 75 }
 76 spin_unlock_irqrestore(&semaphore_wake_lock, flags);
 77 return ret;
 78 }
 79
 80 /*
 81  * This is ugly, but we want the default case to fall through.
 82  * "down_failed" is a special asm handler that calls the C
 83  * routine that actually waits. See arch/i386/lib/semaphore.S
 84  */
 85 extern inlinevoiddown(struct semaphore * sem)
 86 {
 87  __asm__ __volatile__(
 88 "# atomic down operation\n\t"
 89 #ifdef __SMP__
 90 "lock ; "
 91 #endif
 92 "decl 0(%0)\n\t"
 93 "js 2f\n"
 94 "1:\n"
 95 ".section .text.lock,\"ax\"\n"
 96 "2:\tpushl $1b\n\t"
 97 "jmp __down_failed\n"
 98 ".previous"
 99 :/* no outputs */
 100 :"c"(sem)
 101 :"memory");
 102 }
 103
 104 extern inlineintdown_interruptible(struct semaphore * sem)
 105 {
 106 int result;
 107
 108  __asm__ __volatile__(
 109 "# atomic interruptible down operation\n\t"
 110 #ifdef __SMP__
 111 "lock ; "
 112 #endif
 113 "decl 0(%1)\n\t"
 114 "js 2f\n\t"
 115 "xorl %0,%0\n"
 116 "1:\n"
 117 ".section .text.lock,\"ax\"\n"
 118 "2:\tpushl $1b\n\t"
 119 "jmp __down_failed_interruptible\n"
 120 ".previous"
 121 :"=a"(result)
 122 :"c"(sem)
 123 :"memory");
 124 return result;
 125 }
 126
 127
 128 /*
 129  * Note! This is subtle. We jump to wake people up only if
 130  * the semaphore was negative (== somebody was waiting on it).
 131  * The default case (no contention) will result in NO
 132  * jumps for both down() and up().
 133  */
 134 extern inlinevoidup(struct semaphore * sem)
 135 {
 136  __asm__ __volatile__(
 137 "# atomic up operation\n\t"
 138 #ifdef __SMP__
 139 "lock ; "
 140 #endif
 141 "incl 0(%0)\n\t"
 142 "jle 2f\n"
 143 "1:\n"
 144 ".section .text.lock,\"ax\"\n"
 145 "2:\tpushl $1b\n\t"
 146 "jmp __up_wakeup\n"
 147 ".previous"
 148 :/* no outputs */
 149 :"c"(sem)
 150 :"memory");
 151 }
 152
 153 #endif