linux中断（4）：中断处理流程之handle_level_irq

 
文中提到 __irq_set_handler作为中断注册的第一个层次，通过这个函数为desc->handle_irq 安排一个处理函数。
通常安排的处理函数有handle_edge_irq，handle_level_irq等
假如安排的处理函数是   handle_level_irq，我们看一下处理流程

/**
 * handle_level_irq - Level type irq handler
 * @irq: the interrupt number
 * @desc: the interrupt description structure for this irq
 *
 * Level type interrupts are active as long as the hardware line has
 * the active level. This may require to mask the interrupt and unmask
 * it after the associated handler has acknowledged the device, so the
 * interrupt line is back to inactive.
 */
void
handle_level_irq(unsigned int irq, struct irq_desc *desc)
{
 raw_spin_lock(&desc->lock);
 mask_ack_irq(desc); /*  屏蔽掉当前中断  */

 if (unlikely(irqd_irq_inprogress(&desc->irq_data)))   /*  发现同一个中断isr程序正在执行，退出 */
  if (!irq_check_poll(desc))
   goto out_unlock;

 desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);
 kstat_incr_irqs_this_cpu(irq, desc);

 /*
  * If its disabled or no action available
  * keep it masked and get out of here
  */
 if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data)))
  goto out_unlock;

 handle_irq_event(desc); /* 这里调用 handle_irq_event，handle_irq_event->handle_irq_event_percpu->  action->handler */

 cond_unmask_irq(desc);

out_unlock:
 raw_spin_unlock(&desc->lock);
}