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/*
* do_IRQ handles all normal device IRQ's (the special
* SMP cross-CPU interrupts have their own specific
* handlers).
*/
fastcall unsigned int __do_IRQ(unsigned int irq, struct pt_regs *regs)
{
irq_desc_t *desc = irq_desc + irq;
struct irqaction * action;
unsigned int status;
kstat_this_cpu.irqs[irq]++;
if (desc->status & IRQ_PER_CPU) {
irqreturn_t action_ret;
/*
* No locking required for CPU-local interrupts:
*/
desc->handler->ack(irq);
action_ret = handle_IRQ_event(irq, regs, desc->action);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
desc->handler->end(irq);
return 1;
}
spin_lock(&desc->lock);//获得锁
desc->handler->ack(irq);//做中断应答，同时锁irq对应的中断线，此时不应再产生同样类型的中断
/*
* REPLAY is when Linux resends an IRQ that was dropped earlier
* WAITING is used by probe to mark irqs that are being tested
*/
status = desc->status & ~(IRQ_REPLAY | IRQ_WAITING);//开始中断处理前初始化一些状态
status |= IRQ_PENDING; /* we _want_ to handle it */
/*
* If the IRQ is disabled for whatever reason, we cannot
* use the action we have.
*/
action = NULL;
if (likely(!(status & (IRQ_DISABLED | IRQ_INPROGRESS)))) {//判断是否在其他CPU上有相同类型的中断处理程序
//正在执行若有则直接退出
action = desc->action;
status &= ~IRQ_PENDING; /* we commit to handling */
status |= IRQ_INPROGRESS; /* we are handling it */
}
desc->status = status;
/*
* If there is no IRQ handler or it was disabled, exit early.
* Since we set PENDING, if another processor is handling
* a different instance of this same irq, the other processor
* will take care of it.
*/
if (unlikely(!action))
goto out;
/*
* Edge triggered interrupts need to remember
* pending events.
* This applies to any hw interrupts that allow a second
* instance of the same irq to arrive while we are in do_IRQ
* or in the handler. But the code here only handles the _second_
* instance of the irq, not the third or fourth. So it is mostly
* useful for irq hardware that does not mask cleanly in an
* SMP environment.
*/
for (; {
irqreturn_t action_ret;
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, regs, action);//执行真正的中断处理程序
spin_lock(&desc->lock);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
if (likely(!(desc->status & IRQ_PENDING)))//若没有同类型的中断处理程序在执行ISR时被触发则break；
//否则继续循环
//问题就在这里，既然前面已经关了对应irq的中断线，此处为何
//还可能出现同类型的irq被触发，等待处理的情况呢？实际解除
//中断线屏蔽状态的代码在后边注释处
break;
desc->status &= ~IRQ_PENDING;
}
desc->status &= ~IRQ_INPROGRESS;
out:
/*
* The ->end() handler has to deal with interrupts which got
* disabled while the handler was running.
*/
desc->handler->end(irq);//打开被屏蔽的中断线
spin_unlock(&desc->lock);
return 1;
} |
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发表于 2008-04-01 17:52
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