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setup_irq的函数原形为
int setup_irq(unsigned int irq, struct irqaction *new)
{}(见kernel/irq/manage.c)
这个函数做的事情就多了：
下面逐句解释：
/*
* Internal function to register an irqaction - typically used to
* allocate special interrupts that are part of the architecture.
*/
int setup_irq(unsigned int irq, struct irqaction *new)
{
struct irq_desc *desc = irq_desc + irq;/* irq_desc是一个结构体数组，是一个全局变量，定义在include/linux/irq.h中，其初始化在后面会讲到*/
struct irqaction *old, **p;
const char *old_name = NULL;
unsigned long flags;
int shared = 0;
if (irq >= NR_IRQS) /* 定义在/include/asm/irq.h 初始值为128*/
return -EINVAL;
if (desc->chip == &no_irq_chip)
return -ENOSYS;
/*
* Some drivers like serial.c use request_irq() heavily,
* so we have to be careful not to interfere with a
* running system.
*/
if (new->flags & IRQF_SAMPLE_RANDOM) {
/*
* This 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); /*当你在注册驱动时加入了IRQF_SAMPLE_RANDOM标志，则调用此函数，这个函数是内核引入的一个通过中断产生随机数的机制，毛德操写的《Linux内核源代码情景分析上册》P209解释的很清楚*/
}
/*
* The following block of code has to be executed atomically
*/
spin_lock_irqsave(&desc->lock, flags);/*对于中断请求队列的操作是一个原子性操作，不允许其他操作打扰，故加锁，使CPU进入临界区*/
p = &desc->action;
old = *p;
if (old) {/*一般*p应为空（初始化时为空，后面会讲到），因为是第一次注册这个中断（我们大部分情况中断是不去共享的，也就是一个中断不会注册两次）,故这里就不熬述了*/
/*
* Can't 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.
*/
if (!((old->flags & new->flags) & IRQF_SHARED) ||
((old->flags ^ new->flags) & IRQF_TRIGGER_MASK)) {
old_name = old->name;
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 */
do {
p = &old->next;
old = *p;
} while (old);
shared = 1;
}
*p = new; /*把新的irq放到队列里*/
#if defined(CONFIG_IRQ_PER_CPU)
if (new->flags & IRQF_PERCPU)
desc->status |= IRQ_PER_CPU;
#endif
/* Exclude IRQ from balancing */
if (new->flags & IRQF_NOBALANCING)
desc->status |= IRQ_NO_BALANCING;
if (!shared) {
irq_chip_set_defaults(desc->chip);/*函数原型见/kernel/irq/chip.c，主要设置几个重要的函数指针，后面专门做解释*/
/* Setup the type (level, edge polarity) if configured: */
if (new->flags & IRQF_TRIGGER_MASK) {/*注册新irq时如果标志位带触发条件，则执行，我们平常注册一个中断时只会带SA_INTERRUPT和SA_SHIRQ标志，触发条件有专门的函数实现*/
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
compat_irq_chip_set_default_handler(desc);/*检查 新irq对应desc结构体的handle_irq*/
desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
IRQ_INPROGRESS);/*确信这三个位不会置位，其定义见/include/linux/irq.h */
/*在kernel启动初始化irq_desc 结构体时对desc->status 的设置值为IRQ_NOPROBE | IRQ_NOAUTOEN，故下面的if语句为真 */
if (!(desc->status & IRQ_NOAUTOEN)) {
desc->depth = 0;
desc->status &= ~IRQ_DISABLED;/*当然要清这位*/
if (desc->chip->startup)/* 在上面已调用irq_chip_set_defaults(desc->chip);，其中就注册了desc->chip->startup 函数指针，见/kernel/irq/chip.c*/
desc->chip->startup(irq);/*会调用desc->chip->unmask ,而desc->chip->unmask最终会调用到s3c_irq_unmask,见/arch/arm/plat-s3c24xx/irq-pl192.c ,后面会专门讲*/
else
desc->chip->enable(irq);
} else
/* Undo nested disables: */
desc->depth = 1;
}
/* Reset broken irq detection when installing new handler */
desc->irq_count = 0;
desc->irqs_unhandled = 0;
spin_unlock_irqrestore(&desc->lock, flags);
new->irq = irq;
register_irq_proc(irq);
new->dir = NULL;
register_handler_proc(irq, new);
/* register_irq_proc(irq); register_handler_proc(irq, new);这两句主要是做在文件系统中建立一个与此irq对应的文件相关的事情*/
return 0;
mismatch:
#ifdef CONFIG_DEBUG_SHIRQ
if (!(new->flags & IRQF_PROBE_SHARED)) {
printk(KERN_ERR "IRQ handler type mismatch for IRQ %d\n", irq);
if (old_name)
printk(KERN_ERR "current handler: %s\n", old_name);
dump_stack();
}
#endif
spin_unlock_irqrestore(&desc->lock, flags);
return -EBUSY;
}
2009-2-13 下家山 写于上海.漕河泾
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