作者：下家山（请尊重原创，转载请注明） http://www.xiajiashan.com 2．2 调用的第二个函数setup_irq

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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