spinlock.h

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#ifndef ARCH_SMP_SPINLOCK_H
#define ARCH_SMP_SPINLOCK_H

/*
 * Your basic SMP spinlocks, allowing only a single CPU anywhere
 */

typedef struct {
        volatile unsigned int lock;
} spinlock_t;


#define SPIN_LOCK_UNLOCKED (spinlock_t) { 1 }

/*
 * Simple spin lock operations.  There are two variants, one clears IRQ's
 * on the local processor, one does not.
 *
 * We make no fairness assumptions. They have a cost.
 */
#define barrier() __asm__ __volatile__("": : :"memory")
#define spin_is_locked(x)       (*(volatile char *)(&(x)->lock) <= 0)
#define spin_unlock_wait(x)     do { barrier(); } while(spin_is_locked(x))

#define spin_lock_string \
        "\n1:\t" \
        "lock ; decb %0\n\t" \
        "js 2f\n" \
        ".section .text.lock,\"ax\"\n" \
        "2:\t" \
        "cmpb $0,%0\n\t" \
        "rep;nop\n\t" \
        "jle 2b\n\t" \
        "jmp 1b\n" \
        ".previous"

/*
 * This works. Despite all the confusion.
 */
#define spin_unlock_string \
        "movb $1,%0"

static inline __attribute__((always_inline)) void spin_lock(spinlock_t *lock)
{
        __asm__ __volatile__(
                spin_lock_string
                :"=m" (lock->lock) : : "memory");
}

static inline __attribute__((always_inline)) void spin_unlock(spinlock_t *lock)
{
        __asm__ __volatile__(
                spin_unlock_string
                :"=m" (lock->lock) : : "memory");
}

/* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
static inline __attribute__((always_inline)) void cpu_relax(void)
{
        __asm__ __volatile__("rep;nop": : :"memory");
}

#endif /* ARCH_SMP_SPINLOCK_H */

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