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/*

 * ARM v5 Binary semaphore (mutex) implementation.

 *

 * Copyright (C) 2007-2010 B Labs Ltd.

 * Author: Prem Mallappa <prem.mallappa@b-labs.co.uk>

 */

#include <l4/lib/printk.h>

/* Recap on swp:

 * swp rx, ry, [rz]

 * In one instruction:

 * 1) Stores the value in ry into location pointed by rz.

 * 2) Loads the value in the location of rz into rx.

 * By doing so, in one instruction one can attempt to lock

 * a word, and discover whether it was already locked.

 */

#define MUTEX_UNLOCKED  0

#define MUTEX_LOCKED    1

void __spin_lock(unsigned long *s)

{

        int tmp = 0, tmp2;

        __asm__ __volatile__(

                "1: \n"

                "swp %0, %1, [%2] \n"

                "teq %0, %3 \n"

                "bne 1b \n"

                : "=&r" (tmp2)

                : "r" (tmp), "r"(s), "r"(0)

                : "cc", "memory"

                );

}

void __spin_unlock(unsigned long *s)

{

        int tmp = 1, tmp2;

        __asm__ __volatile__(

                "1: \n"

                "swp %0, %1, [%2] \n"

                "teq %0, %3 \n"

                "bne 1b \n"

                : "=&r" (tmp2)

                : "r" (tmp), "r"(s), "r"(0)

                : "cc", "memory"

                );

}

int __mutex_lock(unsigned long *s)

{

        int tmp = MUTEX_LOCKED, tmp2;

        __asm__ __volatile__(

                "swp %0, %1, [%2] \n"

                : "=&r"(tmp2)

                : "r"(tmp), "r"(s)

                : "cc", "memory"

                );

        if (tmp2 == MUTEX_UNLOCKED)

                return 1;

        return 0;

}

void __mutex_unlock(unsigned long *s)

{

        int tmp, tmp2=MUTEX_UNLOCKED;

        __asm__ __volatile__(

                "swp %0, %1, [%2] \n"

                : "=&r"(tmp)

                : "r"(tmp2), "r"(s)

                : "cc", "memory"

                );

        BUG_ON(tmp != MUTEX_LOCKED);

}