+++ /dev/null
-/*
- * ARM semaphore implementation, taken from
- *
- * i386 semaphore implementation.
- *
- * (C) Copyright 1999 Linus Torvalds
- * (C) Copyright 2003 Ian Molton (ARM26 mods)
- *
- * Modified for ARM by Russell King
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-#include <linux/module.h>
-#include <linux/sched.h>
-#include <linux/errno.h>
-#include <linux/init.h>
-
-#include <asm/semaphore.h>
-
-/*
- * Semaphores are implemented using a two-way counter:
- * The "count" variable is decremented for each process
- * that tries to acquire the semaphore, while the "sleeping"
- * variable is a count of such acquires.
- *
- * Notably, the inline "up()" and "down()" functions can
- * efficiently test if they need to do any extra work (up
- * needs to do something only if count was negative before
- * the increment operation.
- *
- * "sleeping" and the contention routine ordering is
- * protected by the semaphore spinlock.
- *
- * Note that these functions are only called when there is
- * contention on the lock, and as such all this is the
- * "non-critical" part of the whole semaphore business. The
- * critical part is the inline stuff in <asm/semaphore.h>
- * where we want to avoid any extra jumps and calls.
- */
-
-/*
- * Logic:
- * - only on a boundary condition do we need to care. When we go
- * from a negative count to a non-negative, we wake people up.
- * - when we go from a non-negative count to a negative do we
- * (a) synchronize with the "sleeper" count and (b) make sure
- * that we're on the wakeup list before we synchronize so that
- * we cannot lose wakeup events.
- */
-
-void __up(struct semaphore *sem)
-{
- wake_up(&sem->wait);
-}
-
-static DEFINE_SPINLOCK(semaphore_lock);
-
-void __sched __down(struct semaphore * sem)
-{
- struct task_struct *tsk = current;
- DECLARE_WAITQUEUE(wait, tsk);
- tsk->state = TASK_UNINTERRUPTIBLE;
- add_wait_queue_exclusive(&sem->wait, &wait);
-
- spin_lock_irq(&semaphore_lock);
- sem->sleepers++;
- for (;;) {
- int sleepers = sem->sleepers;
-
- /*
- * Add "everybody else" into it. They aren't
- * playing, because we own the spinlock.
- */
- if (!atomic_add_negative(sleepers - 1, &sem->count)) {
- sem->sleepers = 0;
- break;
- }
- sem->sleepers = 1; /* us - see -1 above */
- spin_unlock_irq(&semaphore_lock);
-
- schedule();
- tsk->state = TASK_UNINTERRUPTIBLE;
- spin_lock_irq(&semaphore_lock);
- }
- spin_unlock_irq(&semaphore_lock);
- remove_wait_queue(&sem->wait, &wait);
- tsk->state = TASK_RUNNING;
- wake_up(&sem->wait);
-}
-
-int __sched __down_interruptible(struct semaphore * sem)
-{
- int retval = 0;
- struct task_struct *tsk = current;
- DECLARE_WAITQUEUE(wait, tsk);
- tsk->state = TASK_INTERRUPTIBLE;
- add_wait_queue_exclusive(&sem->wait, &wait);
-
- spin_lock_irq(&semaphore_lock);
- sem->sleepers ++;
- for (;;) {
- int sleepers = sem->sleepers;
-
- /*
- * With signals pending, this turns into
- * the trylock failure case - we won't be
- * sleeping, and we* can't get the lock as
- * it has contention. Just correct the count
- * and exit.
- */
- if (signal_pending(current)) {
- retval = -EINTR;
- sem->sleepers = 0;
- atomic_add(sleepers, &sem->count);
- break;
- }
-
- /*
- * Add "everybody else" into it. They aren't
- * playing, because we own the spinlock. The
- * "-1" is because we're still hoping to get
- * the lock.
- */
- if (!atomic_add_negative(sleepers - 1, &sem->count)) {
- sem->sleepers = 0;
- break;
- }
- sem->sleepers = 1; /* us - see -1 above */
- spin_unlock_irq(&semaphore_lock);
-
- schedule();
- tsk->state = TASK_INTERRUPTIBLE;
- spin_lock_irq(&semaphore_lock);
- }
- spin_unlock_irq(&semaphore_lock);
- tsk->state = TASK_RUNNING;
- remove_wait_queue(&sem->wait, &wait);
- wake_up(&sem->wait);
- return retval;
-}
-
-/*
- * Trylock failed - make sure we correct for
- * having decremented the count.
- *
- * We could have done the trylock with a
- * single "cmpxchg" without failure cases,
- * but then it wouldn't work on a 386.
- */
-int __down_trylock(struct semaphore * sem)
-{
- int sleepers;
- unsigned long flags;
-
- spin_lock_irqsave(&semaphore_lock, flags);
- sleepers = sem->sleepers + 1;
- sem->sleepers = 0;
-
- /*
- * Add "everybody else" and us into it. They aren't
- * playing, because we own the spinlock.
- */
- if (!atomic_add_negative(sleepers, &sem->count))
- wake_up(&sem->wait);
-
- spin_unlock_irqrestore(&semaphore_lock, flags);
- return 1;
-}
-
-/*
- * The semaphore operations have a special calling sequence that
- * allow us to do a simpler in-line version of them. These routines
- * need to convert that sequence back into the C sequence when
- * there is contention on the semaphore.
- *
- * ip contains the semaphore pointer on entry. Save the C-clobbered
- * registers (r0 to r3 and lr), but not ip, as we use it as a return
- * value in some cases..
- */
-asm(" .section .sched.text , #alloc, #execinstr \n\
- .align 5 \n\
- .globl __down_failed \n\
-__down_failed: \n\
- stmfd sp!, {r0 - r3, lr} \n\
- mov r0, ip \n\
- bl __down \n\
- ldmfd sp!, {r0 - r3, pc}^ \n\
- \n\
- .align 5 \n\
- .globl __down_interruptible_failed \n\
-__down_interruptible_failed: \n\
- stmfd sp!, {r0 - r3, lr} \n\
- mov r0, ip \n\
- bl __down_interruptible \n\
- mov ip, r0 \n\
- ldmfd sp!, {r0 - r3, pc}^ \n\
- \n\
- .align 5 \n\
- .globl __down_trylock_failed \n\
-__down_trylock_failed: \n\
- stmfd sp!, {r0 - r3, lr} \n\
- mov r0, ip \n\
- bl __down_trylock \n\
- mov ip, r0 \n\
- ldmfd sp!, {r0 - r3, pc}^ \n\
- \n\
- .align 5 \n\
- .globl __up_wakeup \n\
-__up_wakeup: \n\
- stmfd sp!, {r0 - r3, lr} \n\
- mov r0, ip \n\
- bl __up \n\
- ldmfd sp!, {r0 - r3, pc}^ \n\
- ");
-
-EXPORT_SYMBOL(__down_failed);
-EXPORT_SYMBOL(__down_interruptible_failed);
-EXPORT_SYMBOL(__down_trylock_failed);
-EXPORT_SYMBOL(__up_wakeup);
-
git.openpandora.org / pandora-kernel.git / blobdiff