Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

/*

 * MIPS-specific semaphore code.

 *

 * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>

 * Copyright (C) 2004 Ralf Baechle <ralf@linux-mips.org>

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version

 * 2 of the License, or (at your option) any later version.

 *

 * April 2001 - Reworked by Paul Mackerras <paulus@samba.org>

 * to eliminate the SMP races in the old version between the updates

 * of `count' and `waking'.  Now we use negative `count' values to

 * indicate that some process(es) are waiting for the semaphore.

 */

#include <linux/module.h>

#include <linux/sched.h>

#include <linux/init.h>

#include <asm/atomic.h>

#include <asm/cpu-features.h>

#include <asm/errno.h>

#include <asm/semaphore.h>

#include <asm/war.h>

/*

 * Atomically update sem->count.

 * This does the equivalent of the following:

 *

 *      old_count = sem->count;

 *      tmp = MAX(old_count, 0) + incr;

 *      sem->count = tmp;

 *      return old_count;

 *

 * On machines without lld/scd we need a spinlock to make the manipulation of

 * sem->count and sem->waking atomic.  Scalability isn't an issue because

 * this lock is used on UP only so it's just an empty variable.

 */

static inline int __sem_update_count(struct semaphore *sem, int incr)

{

        int old_count, tmp;

        if (cpu_has_llsc && R10000_LLSC_WAR) {

                __asm__ __volatile__(

                "       .set    mips3                                   \n"

                "1:     ll      %0, %2          # __sem_update_count    \n"

                "       sra     %1, %0, 31                              \n"

                "       not     %1                                      \n"

                "       and     %1, %0, %1                              \n"

                "       addu    %1, %1, %3                              \n"

                "       sc      %1, %2                                  \n"

                "       beqzl   %1, 1b                                  \n"

                "       .set    mips0                                   \n"

                : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)

                : "r" (incr), "m" (sem->count));

        } else if (cpu_has_llsc) {

                __asm__ __volatile__(

                "       .set    mips3                                   \n"

                "1:     ll      %0, %2          # __sem_update_count    \n"

                "       sra     %1, %0, 31                              \n"

                "       not     %1                                      \n"

                "       and     %1, %0, %1                              \n"

                "       addu    %1, %1, %3                              \n"

                "       sc      %1, %2                                  \n"

                "       beqz    %1, 1b                                  \n"

                "       .set    mips0                                   \n"

                : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)

                : "r" (incr), "m" (sem->count));

        } else {

                static DEFINE_SPINLOCK(semaphore_lock);

                unsigned long flags;

                spin_lock_irqsave(&semaphore_lock, flags);

                old_count = atomic_read(&sem->count);

                tmp = max_t(int, old_count, 0) + incr;

                atomic_set(&sem->count, tmp);

                spin_unlock_irqrestore(&semaphore_lock, flags);

        }

        return old_count;

}

void __up(struct semaphore *sem)

{

        /*

         * Note that we incremented count in up() before we came here,

         * but that was ineffective since the result was <= 0, and

         * any negative value of count is equivalent to 0.

         * This ends up setting count to 1, unless count is now > 0

         * (i.e. because some other cpu has called up() in the meantime),

         * in which case we just increment count.

         */

        __sem_update_count(sem, 1);

        wake_up(&sem->wait);

}

EXPORT_SYMBOL(__up);

/*

 * Note that when we come in to __down or __down_interruptible,

 * we have already decremented count, but that decrement was

 * ineffective since the result was < 0, and any negative value

 * of count is equivalent to 0.

 * Thus it is only when we decrement count from some value > 0

 * that we have actually got the semaphore.

 */

void __sched __down(struct semaphore *sem)

{

        struct task_struct *tsk = current;

        DECLARE_WAITQUEUE(wait, tsk);

        __set_task_state(tsk, TASK_UNINTERRUPTIBLE);

        add_wait_queue_exclusive(&sem->wait, &wait);

        /*

         * Try to get the semaphore.  If the count is > 0, then we've

         * got the semaphore; we decrement count and exit the loop.

         * If the count is 0 or negative, we set it to -1, indicating

         * that we are asleep, and then sleep.

         */

        while (__sem_update_count(sem, -1) <= 0) {

                schedule();

                set_task_state(tsk, TASK_UNINTERRUPTIBLE);

        }

        remove_wait_queue(&sem->wait, &wait);

        __set_task_state(tsk, TASK_RUNNING);

        /*

         * If there are any more sleepers, wake one of them up so

         * that it can either get the semaphore, or set count to -1

         * indicating that there are still processes sleeping.

         */

        wake_up(&sem->wait);

}

EXPORT_SYMBOL(__down);

int __sched __down_interruptible(struct semaphore * sem)

{

        int retval = 0;

        struct task_struct *tsk = current;

        DECLARE_WAITQUEUE(wait, tsk);

        __set_task_state(tsk, TASK_INTERRUPTIBLE);

        add_wait_queue_exclusive(&sem->wait, &wait);

        while (__sem_update_count(sem, -1) <= 0) {

                if (signal_pending(current)) {

                        /*

                         * A signal is pending - give up trying.

                         * Set sem->count to 0 if it is negative,

                         * since we are no longer sleeping.

                         */

                        __sem_update_count(sem, 0);

                        retval = -EINTR;

                        break;

                }

                schedule();

                set_task_state(tsk, TASK_INTERRUPTIBLE);

        }

        remove_wait_queue(&sem->wait, &wait);

        __set_task_state(tsk, TASK_RUNNING);

        wake_up(&sem->wait);

        return retval;

}

EXPORT_SYMBOL(__down_interruptible);