這部分我們以3sc2410下的watchdog的中斷為例來講解中斷的注冊及調(diào)用過程。

drivers/char/watchdog/s3c2410_wdt.c:

static int s3c2410wdt_probe(struct platform_device *pdev)

{

……

/*注冊中斷*/

ret = request_irq(res->start, s3c2410wdt_irq, 0, pdev->name, pdev);

……

}

在s3c2410wdt_probe函數(shù)中為watchdog注冊了一個(gè)中斷，中斷號為IRQ_WDT，

#define IRQ_WDTS3C2410_IRQ(9)

中斷處理函數(shù)是s3c2410wdt_irq。

我們來看request_irq是如何實(shí)現(xiàn)的：

kernel/irq/Manage.c:

/

*request_irq - allocate an interrupt line

*@irq: Interrupt line to allocate

*@handler: Function to be called when the IRQ occurs

*@irqflags: Interrupt type flags

*@devname: An ascii name for the claiming device

*@dev_id: A cookie passed back to the handler function

*

*This call allocates interrupt resources and enables the

*interrupt line and IRQ handling. From the point this

*call is made your handler function may be invoked. Since

*your handler function must clear any interrupt the board

*raises, you must take care both to initialise your hardware

*and to set up the interrupt handler in the right order.

*

*Dev_id must be globally unique. Normally the address of the

*device data structure is used as the cookie. Since the handler

*receives this value it makes sense to use it.

*

*If your interrupt is shared you must pass a non NULL dev_id

*as this is required when freeing the interrupt.

*

*Flags:

*

*IRQF_SHAREDInterrupt is shared

*IRQF_DISABLEDDisable local interrupts while processing

*IRQF_SAMPLE_RANDOMThe interrupt can be used for entropy

*

*/

int request_irq(unsigned int irq,

irqreturn_t (*handler)(int, void *, struct pt_regs *),

unsigned long irqflags, const char *devname, void *dev_id)

{

struct irqaction *action;

int retval;

#ifdef CONFIG_LOCKDEP

/*

* Lockdep wants atomic interrupt handlers:

*/

irqflags |= SA_INTERRUPT;

#endif

/*

* Sanity-check: shared interrupts must pass in a real dev-ID,

* otherwise well have trouble later trying to figure out

* which interrupt is which (messes up the interrupt freeing

* logic etc).

*/

/*允許共享的中斷必須要有一個(gè)獨(dú)一無二的dev_id,看上面函數(shù)的解釋

if ((irqflags & IRQF_SHARED) && !dev_id)

return -EINVAL;

if (irq >= NR_IRQS) /*中斷號是否合法*/

return -EINVAL;

/*這個(gè)標(biāo)記對s3c2410來說在s3c24xx_init_irq里通過調(diào)用set_irq_flags()被去掉了*/

if (irq_desc[irq].status & IRQ_NOREQUEST)

return -EINVAL;

if (!handler)/*中斷例程*/

return -EINVAL;

/*分配一個(gè)irqaction對象，來保存這個(gè)中斷信息*/

action = kmalloc(sizeof(struct irqaction), GFP_ATOMIC);

if (!action)

return -ENOMEM;

/*保存中斷例程等信息*/

action->handler = handler;

action->flags = irqflags;

cpus_clear(action->mask);/*清除相應(yīng)位*/

action->name = devname;

action->next = NULL;

action->dev_id = dev_id;

select_smp_affinity(irq);

retval = setup_irq(irq, action);/*申請中斷*/

if (retval)

kfree(action);

return retval;

}

該函數(shù)的功能及參數(shù)含義在函數(shù)頭有詳細(xì)的說明，這里就不多介紹了，值得注意的是我們在申請中斷之前，必須要去掉該中斷的IRQ_NOREQUEST標(biāo)記(系統(tǒng)初始化的時(shí)候賦了這個(gè)標(biāo)記)， 具體方法是調(diào)用set_irq_flags()函數(shù)。

接著看setup_irq

kernel/irq/Manage.c:

/*

* 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; /*獲取保存該中斷的中斷描述符地址*/

struct irqaction *old, p;

unsigned long flags;

int shared = 0;

if (irq >= NR_IRQS)

return -EINVAL;

/*對于s3c2410的中斷在s3c24xx_init_irq里已經(jīng)初始化過了*/

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);

}

/*

* The following block of code has to be executed atomically

*/

/*

*下面if代碼段主要是查看該中斷是否可以共享，如可以，則把中斷例程鏈入中斷例程

* list中,至于中斷共享的條件有：1觸發(fā)方式相同，2都允許中斷共享*/

spin_lock_irqsave(&desc->lock, flags);

p = &desc->action;

old = *p;

if (old) { /*對于IRQ_WDT，這個(gè)if不成立，但它已經(jīng)設(shè)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.

*/

/*判斷能否共享中斷*/

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 */

/*把中斷例程加入list中*/

do {

p = &old->next;

old = *p;

} while (old);

shared = 1;

}

*p = new;/*該行很關(guān)鍵， 它把中斷的處理函數(shù)添加到該中斷描述符的中斷例程list里*/

#if defined(CONFIG_IRQ_PER_CPU)

if (new->flags & IRQF_PERCPU)

desc->status |= IRQ_PER_CPU;

#endif

if (!shared) {

/*對于IRQ_WDT來說這步是多余的，初始化的時(shí)候已做過*/

irq_chip_set_defaults(desc->chip);

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

/*對于IRQ_WDT來說，沒有定義觸發(fā)方式， 即默認(rèn)觸發(fā)方式*/

if (new->flags & IRQF_TRIGGER_MASK) {

/*如果要設(shè)觸發(fā)方式，則調(diào)用平臺(tái)特定的函數(shù)，因此如果我們的平臺(tái)要實(shí)現(xiàn)該功能則必*須要在irq_chip對象里加入對set_type函數(shù)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

/*這函數(shù)只是簡單的檢查是否有handle_irq*/

compat_irq_chip_set_default_handler(desc);

/*去掉中斷的相關(guān)狀態(tài)，讓它就緒*/

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

IRQ_INPROGRESS);

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

/*使能該中斷*/

desc->depth = 0;

desc->status &= ~IRQ_DISABLED;

if (desc->chip->startup)

desc->chip->startup(irq); /*平臺(tái)相關(guān)函數(shù)*/

else

desc->chip->enable(irq);/*平臺(tái)相關(guān)函數(shù)*/

} else

/* Undo nested disables: */

desc->depth = 1;

}

spin_unlock_irqrestore(&desc->lock, flags);

new->irq = irq;

register_irq_proc(irq);/*在/proc/irq/下創(chuàng)建該中斷的一個(gè)文件*/

new->dir = NULL;

register_handler_proc(irq, new); /*為/proc/irq/下創(chuàng)建的文件設(shè)置處理函數(shù)*/

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;

}

該函數(shù)主要是安裝了一個(gè)中斷，并使能它。 我們先看使能函數(shù)，它是平臺(tái)相關(guān)的，對于s3c2410的IRQ_WDT來說使用的是默認(rèn)的使能函數(shù)(default_startup(),初始化賦值)，如果我們要使用自己的使能函數(shù)，只要在chip對象里添加就行了。

kernel/irq/Chip.c:

static unsigned int default_startup(unsigned int irq)

{

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

return 0;

}

對于IRQ_WDT來說調(diào)用的irq_desc[irq].chip->enable(irq)仍是默認(rèn)函數(shù)：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該中斷*/

desc->status &= ~IRQ_MASKED;

}

，對于IRQ_WDT來說這次的調(diào)用desc->chip->unmask(irq)，實(shí)際上是s3c_irq_unmask,具體可查看前面分析的chip對象。

arch/arm/mach-s3c2410/Irq.c:

static void

s3c_irq_unmask(unsigned int irqno)

{

unsigned long mask;

if (irqno != IRQ_TIMER4 && irqno != IRQ_EINT8t23)

irqdbf2("s3c_irq_unmask %d/n", irqno);

irqno -= IRQ_EINT0;

mask = __raw_readl(S3C2410_INTMSK);

mask &= ~(1UL << irqno);

__raw_writel(mask, S3C2410_INTMSK);

}

對著s3c2410的data sheet一看就知道了， 就是打開相應(yīng)中斷。

至此中斷處理函數(shù)安裝好了，中斷也打開了，系統(tǒng)就可以正確的響應(yīng)中斷了。

Ok，到此為止IRQ_WDT的中斷注冊過程已完成，此時(shí)的中斷描述符如下所示：