arm linux 下中断流程简要分析注册中断

function might sleep, we want to call it first,

* outside of the atomic block.

* Yes, this might clear the entropy pool if the wrong

* driver is attempted to be loaded, without actually

* installing a new handler, but is this really a problem,

* only the sysadmin is able to do this.

*/

rand_initialize_irq(irq);

}

/*

* The following block of code has to be executed atomically

*/

/*

*下面if代码段主要是查看该中断是否可以共享，如可以，则把中断例程链入中断例程

* list中,至于中断共享的条件有：1触发方式相同，2都允许中断共享*/

spin_lock_irqsave(&desc->lock, flags);

p = &desc->action;

old = *p;

if (old) { /*对于IRQ_WDT，这个if不成立，但它已经设置了handle_irq喔*/

/*

* Cant share interrupts unless both agree to and are

* the same type (level, edge, polarity). So both flag

* fields must have IRQF_SHARED set and the bits which

* set the trigger type must match.

*/

/*判断能否共享中断*/

if (!((old->flags & new->flags) & IRQF_SHARED) ||

((old->flags ^ new->flags) & IRQF_TRIGGER_MASK))

goto mismatch;

#if defined(CONFIG_IRQ_PER_CPU)

/* All handlers must agree on per-cpuness */

if ((old->flags & IRQF_PERCPU) !=

(new->flags & IRQF_PERCPU))

goto mismatch;

#endif

/* add new interrupt at end of irq queue */

/*把中断例程加入list中*/

do {

p = &old->next;

old = *p;

} while (old);

shared = 1;

}

*p = new;/*该行很关键， 它把中断的处理函数添加到该中断描述符的中断例程list里*/

#if defined(CONFIG_IRQ_PER_CPU)

if (new->flags & IRQF_PERCPU)

desc->status |= IRQ_PER_CPU;

#endif

if (!shared) {

/*对于IRQ_WDT来说这步是多余的，初始化的时候已做过*/

irq_chip_set_defaults(desc->chip);

/* Setup the type (level, edge polarity) if configured: */

/*对于IRQ_WDT来说，没有定义触发方式， 即默认触发方式*/

if (new->flags & IRQF_TRIGGER_MASK) {

/*如果要设触发方式，则调用平台特定的函数，因此如果我们的平台要实现该功能则必*须要在irq_chip对象里加入对set_type函数的支持*/

if (desc->chip && desc->chip->set_type)

desc->chip->set_type(irq,

new->flags & IRQF_TRIGGER_MASK);

else

/*

* IRQF_TRIGGER_* but the PIC does not support

* multiple flow-types?

*/

printk(KERN_WARNING "No IRQF_TRIGGER set_type "

"function for IRQ %d (%s)/n", irq,

desc->chip ? desc->chip->name :

"unknown");

} else

/*这函数只是简单的检查是否有handle_irq*/

compat_irq_chip_set_default_handler(desc);

/*去掉中断的相关状态，让它就绪*/

desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |

IRQ_INPROGRESS);

if (!(desc->status & IRQ_NOAUTOEN)) {

/*使能该中断*/

desc->depth = 0;

desc->status &= ~IRQ_DISABLED;

if (desc->chip->startup)

desc->chip->startup(irq); /*平台相关函数*/

else

desc->chip->enable(irq);/*平台相关函数*/

} else

/* Undo nested disables: */

desc->depth = 1;

}

spin_unlock_irqrestore(&desc->lock, flags);

new->irq = irq;

register_irq_proc(irq);/*在/proc/irq/下创建该中断的一个文件*/

new->dir = NULL;

register_handler_proc(irq, new); /*为/proc/irq/下创建的文件设置处理函数*/

return 0;

mismatch:

spin_unlock_irqrestore(&desc->lock, flags);

if (!(new->flags & IRQF_PROBE_SHARED)) {

printk(KERN_ERR "IRQ handler type mismatch for IRQ %d/n", irq);

dump_stack();

}

return -EBUSY;

}

该函数主要是安装了一个中断，并使能它。 我们先看使能函数，它是平台相关的，对于s3c2410的IRQ_WDT来说使用的是默认的使能函数(default_startup(),初始化赋值)，如果我们要使用自己的使能函数，只要在chip对象里添加就行了。

kernel/irq/Chip.c:

static unsigned int default_startup(unsigned int irq)

{

irq_desc[irq].chip->enable(irq);

return 0;

}

对于IRQ_WDT来说调用的irq_desc[irq].chip->enable(irq)仍是默认函数：default_enable（）

kernel/irq/Chip.c:

static void default_enable(unsigned int irq)

{

struct irq_desc *desc = irq_desc + irq;

desc->chip->unmask(irq);/*unmask该中断*/

desc->status &= ~IRQ_MASKED;

}

，对于IRQ_WDT来说这次的调用desc->chip->，对于IRQ_WDT来说这次的调用desc->chip->unmask(irq)，实际上是s3c_irq_unmask,具体可查看前面分析的ch