arm-linux注册中断

二 注册中断
这部分我们仍以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)
{
        struct resource *res;
        int started = 0;
        int ret;
        int size;

        DBG("%s: probe=%p\n", __FUNCTION__, pdev);

        /* get the memory region for the watchdog timer */

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (res == NULL) {
                printk(KERN_INFO PFX "failed to get memory region resouce\n");
                return -ENOENT;
        }

        size = (res->end-res->start)+1;
        wdt_mem = request_mem_region(res->start, size, pdev->name);
        if (wdt_mem == NULL) {
                printk(KERN_INFO PFX "failed to get memory region\n");
                ret = -ENOENT;
                goto err_req;
        }

        wdt_base = ioremap(res->start, size);
        if (wdt_base == 0) {
                printk(KERN_INFO PFX "failed to ioremap() region\n");
                ret = -EINVAL;
                goto err_req;
        }

        DBG("probe: mapped wdt_base=%p\n", wdt_base);

        res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
        if (res == NULL) {
                printk(KERN_INFO PFX "failed to get irq resource\n");
                ret = -ENOENT;
                goto err_map;
        }

        ret = request_irq(res->start, s3c2410wdt_irq, 0, pdev->name, pdev);
        if (ret != 0) {
                printk(KERN_INFO PFX "failed to install irq (%d)\n", ret);
                goto err_map;
        }

        wdt_clock = clk_get(&pdev->dev, "watchdog");
        if (IS_ERR(wdt_clock)) {
                printk(KERN_INFO PFX "failed to find watchdog clock source\n");
                ret = PTR_ERR(wdt_clock);
                goto err_irq;
        }

        clk_enable(wdt_clock);

        /* see if we can actually set the requested timer margin, and if
         * not, try the default value */

        if (s3c2410wdt_set_heartbeat(tmr_margin)) {
                started = s3c2410wdt_set_heartbeat(CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME);

                if (started == 0) {
                        printk(KERN_INFO PFX "tmr_margin value out of range, default %d used\n",
                               CONFIG_S3C2410_WATCHDOG_DEFAULT_TIME);
                } else {
                        printk(KERN_INFO PFX "default timer value is out of range, cannot start\n");
                }
        }

        ret = misc_register(&s3c2410wdt_miscdev);
        if (ret) {
                printk (KERN_ERR PFX "cannot register miscdev on minor=%d (%d)\n",
                        WATCHDOG_MINOR, ret);
                goto err_clk;
        }

        if (tmr_atboot && started == 0) {
                printk(KERN_INFO PFX "Starting Watchdog Timer\n");
                s3c2410wdt_start();
        } else if (!tmr_atboot) {
                /* if we're not enabling the watchdog, then ensure it is
                 * disabled if it has been left running from the bootloader
                 * or other source */

                s3c2410wdt_stop();
        }

        return 0;

 err_clk:
        clk_disable(wdt_clock);
        clk_put(wdt_clock);

 err_irq:
        free_irq(wdt_irq->start, pdev);

 err_map:
        iounmap(wdt_base);

 err_req:
        release_resource(wdt_mem);
        kfree(wdt_mem);

        return ret;
}

在s3c2410wdt_probe函数中为watchdog注册了一个中断，中断号为IRQ_WDT，
#define IRQ_WDT S3C2410_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 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_SHARED     Interrupt is shared
 *  IRQF_DISABLED   Disable local interrupts while processing
 *  IRQF_SAMPLE_RANDOM The 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 |= IRQF_DISABLED;
#endif
    /*
     * Sanity-check: shared interrupts must pass in a real dev-ID,
     * otherwise we'll 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);/*安装中断*/
    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*/
        /*
         * 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.
         */
        /*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;  
}

呵呵，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：