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-/*
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- * ARM semaphore implementation, taken from
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- *
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- * i386 semaphore implementation.
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- *
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- * (C) Copyright 1999 Linus Torvalds
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- *
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- * Modified for ARM by Russell King
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- *
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- * This program is free software; you can redistribute it and/or modify
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- * it under the terms of the GNU General Public License version 2 as
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- * published by the Free Software Foundation.
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- */
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-#include <linux/module.h>
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-#include <linux/sched.h>
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-#include <linux/errno.h>
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-#include <linux/init.h>
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-
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-#include <asm/semaphore.h>
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-
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-/*
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- * Semaphores are implemented using a two-way counter:
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- * The "count" variable is decremented for each process
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- * that tries to acquire the semaphore, while the "sleeping"
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- * variable is a count of such acquires.
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- *
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- * Notably, the inline "up()" and "down()" functions can
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- * efficiently test if they need to do any extra work (up
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- * needs to do something only if count was negative before
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- * the increment operation.
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- *
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- * "sleeping" and the contention routine ordering is
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- * protected by the semaphore spinlock.
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- *
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- * Note that these functions are only called when there is
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- * contention on the lock, and as such all this is the
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- * "non-critical" part of the whole semaphore business. The
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- * critical part is the inline stuff in <asm/semaphore.h>
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- * where we want to avoid any extra jumps and calls.
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- */
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-
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-/*
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- * Logic:
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- * - only on a boundary condition do we need to care. When we go
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- * from a negative count to a non-negative, we wake people up.
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- * - when we go from a non-negative count to a negative do we
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- * (a) synchronize with the "sleeper" count and (b) make sure
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- * that we're on the wakeup list before we synchronize so that
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- * we cannot lose wakeup events.
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- */
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-
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-void __up(struct semaphore *sem)
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-{
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- wake_up(&sem->wait);
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-}
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-
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-static DEFINE_SPINLOCK(semaphore_lock);
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-
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-void __sched __down(struct semaphore * sem)
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-{
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- struct task_struct *tsk = current;
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- DECLARE_WAITQUEUE(wait, tsk);
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- tsk->state = TASK_UNINTERRUPTIBLE;
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- add_wait_queue_exclusive(&sem->wait, &wait);
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-
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- spin_lock_irq(&semaphore_lock);
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- sem->sleepers++;
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- for (;;) {
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- int sleepers = sem->sleepers;
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-
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- /*
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- * Add "everybody else" into it. They aren't
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- * playing, because we own the spinlock.
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- */
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- if (!atomic_add_negative(sleepers - 1, &sem->count)) {
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- sem->sleepers = 0;
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- break;
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- }
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- sem->sleepers = 1; /* us - see -1 above */
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- spin_unlock_irq(&semaphore_lock);
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-
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- schedule();
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- tsk->state = TASK_UNINTERRUPTIBLE;
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- spin_lock_irq(&semaphore_lock);
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- }
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- spin_unlock_irq(&semaphore_lock);
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- remove_wait_queue(&sem->wait, &wait);
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- tsk->state = TASK_RUNNING;
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- wake_up(&sem->wait);
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-}
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-
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-int __sched __down_interruptible(struct semaphore * sem)
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-{
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- int retval = 0;
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- struct task_struct *tsk = current;
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- DECLARE_WAITQUEUE(wait, tsk);
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- tsk->state = TASK_INTERRUPTIBLE;
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- add_wait_queue_exclusive(&sem->wait, &wait);
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-
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- spin_lock_irq(&semaphore_lock);
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- sem->sleepers ++;
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- for (;;) {
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- int sleepers = sem->sleepers;
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-
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- /*
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- * With signals pending, this turns into
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- * the trylock failure case - we won't be
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- * sleeping, and we* can't get the lock as
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- * it has contention. Just correct the count
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- * and exit.
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- */
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- if (signal_pending(current)) {
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- retval = -EINTR;
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- sem->sleepers = 0;
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- atomic_add(sleepers, &sem->count);
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- break;
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- }
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-
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- /*
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- * Add "everybody else" into it. They aren't
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- * playing, because we own the spinlock. The
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- * "-1" is because we're still hoping to get
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- * the lock.
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- */
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- if (!atomic_add_negative(sleepers - 1, &sem->count)) {
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- sem->sleepers = 0;
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- break;
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- }
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- sem->sleepers = 1; /* us - see -1 above */
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- spin_unlock_irq(&semaphore_lock);
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-
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- schedule();
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- tsk->state = TASK_INTERRUPTIBLE;
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- spin_lock_irq(&semaphore_lock);
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- }
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- spin_unlock_irq(&semaphore_lock);
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- tsk->state = TASK_RUNNING;
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- remove_wait_queue(&sem->wait, &wait);
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- wake_up(&sem->wait);
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- return retval;
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-}
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-
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-/*
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- * Trylock failed - make sure we correct for
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- * having decremented the count.
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- *
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- * We could have done the trylock with a
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- * single "cmpxchg" without failure cases,
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- * but then it wouldn't work on a 386.
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- */
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-int __down_trylock(struct semaphore * sem)
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-{
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- int sleepers;
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- unsigned long flags;
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-
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- spin_lock_irqsave(&semaphore_lock, flags);
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- sleepers = sem->sleepers + 1;
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- sem->sleepers = 0;
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-
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- /*
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- * Add "everybody else" and us into it. They aren't
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- * playing, because we own the spinlock.
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- */
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- if (!atomic_add_negative(sleepers, &sem->count))
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- wake_up(&sem->wait);
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-
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- spin_unlock_irqrestore(&semaphore_lock, flags);
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- return 1;
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-}
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-
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-/*
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- * The semaphore operations have a special calling sequence that
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- * allow us to do a simpler in-line version of them. These routines
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- * need to convert that sequence back into the C sequence when
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- * there is contention on the semaphore.
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- *
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- * ip contains the semaphore pointer on entry. Save the C-clobbered
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- * registers (r0 to r3 and lr), but not ip, as we use it as a return
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- * value in some cases..
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- * To remain AAPCS compliant (64-bit stack align) we save r4 as well.
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- */
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-asm(" .section .sched.text,\"ax\",%progbits \n\
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- .align 5 \n\
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- .globl __down_failed \n\
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-__down_failed: \n\
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- stmfd sp!, {r0 - r4, lr} \n\
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- mov r0, ip \n\
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- bl __down \n\
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- ldmfd sp!, {r0 - r4, pc} \n\
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- \n\
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- .align 5 \n\
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- .globl __down_interruptible_failed \n\
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-__down_interruptible_failed: \n\
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- stmfd sp!, {r0 - r4, lr} \n\
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- mov r0, ip \n\
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- bl __down_interruptible \n\
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- mov ip, r0 \n\
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- ldmfd sp!, {r0 - r4, pc} \n\
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- \n\
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- .align 5 \n\
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- .globl __down_trylock_failed \n\
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-__down_trylock_failed: \n\
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- stmfd sp!, {r0 - r4, lr} \n\
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- mov r0, ip \n\
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- bl __down_trylock \n\
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- mov ip, r0 \n\
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- ldmfd sp!, {r0 - r4, pc} \n\
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- \n\
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- .align 5 \n\
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- .globl __up_wakeup \n\
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-__up_wakeup: \n\
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- stmfd sp!, {r0 - r4, lr} \n\
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- mov r0, ip \n\
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- bl __up \n\
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- ldmfd sp!, {r0 - r4, pc} \n\
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- ");
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-
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-EXPORT_SYMBOL(__down_failed);
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-EXPORT_SYMBOL(__down_interruptible_failed);
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-EXPORT_SYMBOL(__down_trylock_failed);
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-EXPORT_SYMBOL(__up_wakeup);
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