对于不同中断源的默认处理函数(irq_desc结构体中的handle_irq)，内核将之分成了3类。除了PF0-PF47的中断和IRQ_PROG0_INTA、IRQ_PROG1_INTA、IRQ_PROG2_INTA这三个由PF口共享的中断外对于其它的中断源则使用handle_simple_irq进行处理。
handle_simple_irq函数位于kernel/irq/chip.c：
/**
* handle_simple_irq - Simple and software-decoded IRQs.
* @irq: the interrupt number
* @desc: the interrupt description structure for this irq
*
* Simple interrupts are either sent from a demultiplexing interrupt
* handler or come from hardware, where no interrupt hardware control
* is necessary.
*
* Note: The caller is expected to handle the ack, clear, mask and
* unmask issues if necessary.
*/
void fastcall
handle_simple_irq(unsigned int irq, struct irq_desc *desc)
{
struct irqaction *action;
irqreturn_t action_ret;
const unsigned int cpu = smp_processor_id();
spin_lock(&desc->lock);
if (unlikely(desc->status & IRQ_INPROGRESS))
goto out_unlock;
kstat_cpu(cpu).irqs[irq]++;
action = desc->action;
if (unlikely(!action || (desc->status & IRQ_DISABLED))) {
if (desc->chip->mask)
desc->chip->mask(irq);
desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
desc->status |= IRQ_PENDING;
goto out_unlock;
}
desc->status &= ~(IRQ_REPLAY | IRQ_WAITING | IRQ_PENDING);
desc->status |= IRQ_INPROGRESS;
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, action);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
spin_lock(&desc->lock);
desc->status &= ~IRQ_INPROGRESS;
out_unlock:
spin_unlock(&desc->lock);
}
从这个函数的代码可以看出，这个函数的作用就是调用handle_IRQ_event，并更新desc中的状态。在中断初始化完成的时候，除了EVT_TMR之外，其它的中断源的action都为NULL，因此对大部分中断源造成的中断此函数将直接返回。
下面看看handle_IRQ_event的实现：
/**
* handle_IRQ_event - irq action chain handler
* @irq: the interrupt number
* @action: the interrupt action chain for this irq
*
* Handles the action chain of an irq event
*/
irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
{
irqreturn_t ret, retval = IRQ_NONE;
unsigned int status = 0;
handle_dynamic_tick(action);
if (!(action->flags & IRQF_DISABLED))
local_irq_enable_in_hardirq();
do {
ret = action->handler(irq, action->dev_id);
if (ret == IRQ_HANDLED)
status |= action->flags;
retval |= ret;
action = action->next;
} while (action);
local_irq_disable();
return retval;
}
很简单，就是按顺序调用action链表中的处理函数。