arm linux 下中断流程简要分析注册中断

这部分我们以3sc2410下的watchdog的中断为例来讲解中断的注册及调用过程。

drivers/char/watchdog/s3c2410_wdt.c:

static int s3c2410wdt_probe(struct platform_device *pdev)

{

……

/*注册中断*/

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

……

}

在s3c2410wdt_probe函数中为watchdog注册了一个中断，中断号为IRQ_WDT，

#define IRQ_WDTS3C2410_IRQ(9)

中断处理函数是s3c2410wdt_irq。

我们来看request_irq是如何实现的：

kernel/irq/Manage.c:

/

*request_irq - allocate aninterruptline

*@irq: Interrupt line to allocate

*@handler: Function to be calledwhen 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).

*/

/*允许共享的中断必须要有一个独一无二的dev_id,看上面函数的解释

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

return -EINVAL;

if (irq >= NR_IRQS) /*中断号是否合法*/

return -EINVAL;

/*这个标记对s3c2410来说在s3c24xx_init_irq里通过调用set_irq_flags()被去掉了*/

if (irq_desc[irq].status & IRQ_NOREQUEST)

return -EINVAL;

if (!handler)/*中断例程*/

return -EINVAL;

/*分配一个irqaction对象，来保存这个中断信息*/

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

if (!action)

return -ENOMEM;

/*保存中断例程等信息*/

action->handler = handler;

action->flags = irqflags;

cpus_clear(action->mask);/*清除相应位*/

action->name = devname;

action->next = NULL;

action->dev_id = dev_id;

select_smp_affinity(irq);

retval = setup_irq(irq, action);/*申请中断*/

if (retval)

kfree(action);

return retval;

}

该函数的功能及参数含义在函数头有详细的说明，这里就不多介绍了，值得注意的是我们在申请中断之前，必须要去掉该中断的IRQ_NOREQUEST标记(系统初始化的时候赋了这个标记)， 具体方法是调用set_irq_flags()函数。

接着看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; /*获取保存该中断的中断描述符地址*/

struct irqaction *old, p;

unsigned long flags;

int shared = 0;

if (irq >= NR_IRQS)

return -EINVAL;

/*对于s3c2410的中断在s3c24xx_init_irq里已经初始化过了*/

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->unmask(irq)，实际上是s3c_irq_unmask,具体可查看前面分析的chip对象。

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);

}

对着s3c2410的data sheet一看就知道了， 就是打开相应中断。

至此中断处理函数安装好了，中断也打开了，系统就可以正确的响应中断了。

Ok，到此为止IRQ_WDT的中断注册过程已完成，此时的中断描述符如下所示：