/**
 *    disable_irq_nosync - disable an irq without waiting
 *    @irq: Interrupt to disable
 *
 *    Disable the selected interrupt line. Disables and Enables are
 *    nested.
 *    Unlike disable_irq(), this function does not ensure existing
 *    instances of the IRQ handler have completed before returning.

/**
 * disable_irq - disable an irq and wait for completion
 * @irq: Interrupt to disable
 *
 * Disable the selected interrupt line. Enables and Disables are
 * nested.
 * This function waits for any pending IRQ handlers for this interrupt
 * to complete before returning. If you use this function while
 * holding a resource the IRQ handler may need you will deadlock.
 *
 * This function may be called - with care - from IRQ context.
 */

/**
 * synchronize_irq - wait for pending IRQ handlers (on other CPUs)
 * @irq: interrupt number to wait for
 *
 * This function waits for any pending IRQ handlers for this interrupt
 * to complete before returning. If you use this function while
 * holding a resource the IRQ handler may need you will deadlock.
 *
 * This function may be called - with care - from IRQ context.
 */
void synchronize_irq(unsigned int irq)
{
 struct irq_desc *desc = irq_to_desc(irq);
 unsigned int status;
 if (!desc)
  return;
 do {
  unsigned long flags;
  /*
   * Wait until we're out of the critical section. This might
   * give the wrong answer due to the lack of memory barriers.
   */
  while (desc->status & IRQ_INPROGRESS)
   cpu_relax();
  /* Ok, that indicated we're done: double-check carefully. */
  spin_lock_irqsave(&desc->lock, flags);
  status = desc->status;
  spin_unlock_irqrestore(&desc->lock, flags);
  /* Oops, that failed? */
 } while (status & IRQ_INPROGRESS);
 /*
  * We made sure that no hardirq handler is running. Now verify
  * that no threaded handlers are active.
  */
 wait_event(desc->wait_for_threads, !atomic_read(&desc->threads_active));
}