Linux中断处理流程

风流意气都作罢 提交于 2020-01-26 17:41:11

1. 中断处理流程

  当中断发生时,Linux系统会跳转到asm_do_IRQ()函数(所有中断程序的总入口函数),并且把中断号irq传进来。根据中断号,找到中断号对应的irq_desc结构(irq_desc结构为内核中中断的描述结构,内核中有一个irq_desc结构的数组irq_desc_ptrs[NR_IRQS]),然后调用irq_desc中的handle_irq函数,即中断入口函数。我们编写中断的驱动,即填充并注册irq_desc结构。

 

2. 中断处理数据结构:irq_desc

  Linux内核将所有的中断统一编号,使用一个irq_desc[NR_IRQS]的结构体数组来描述这些中断:每个数组项对应着一个中断源(也可能是一组中断源),记录中断入口函数、中断标记,并提供了中断的底层硬件访问函数(中断清除、屏蔽、使能)。另外通过这个结构体数组项中的action,能够找到用户注册的中断处理函数。

struct irq_desc {
    unsigned int        irq;
    irq_flow_handler_t    handle_irq;
    struct irq_chip        *chip;
    struct msi_desc        *msi_desc;
    void            *handler_data;
    void            *chip_data;
    struct irqaction    *action;    /* IRQ action list */
    unsigned int        status;        /* IRQ status */

    unsigned int        depth;        /* nested irq disables */
    unsigned int        wake_depth;    /* nested wake enables */
    unsigned int        irq_count;    /* For detecting broken IRQs */
    unsigned long        last_unhandled;    /* Aging timer for unhandled count */
    unsigned int        irqs_unhandled;
    spinlock_t        lock;
    const char        *name;
} ____cacheline_internodealigned_in_smp;

(1)handle_irq:中断的入口函数

(2)chip:包含这个中断的清除、屏蔽、使能等底层函数

struct irq_chip {
    const char    *name;
    unsigned int    (*startup)(unsigned int irq);
    void        (*shutdown)(unsigned int irq);
    void        (*enable)(unsigned int irq);
    void        (*disable)(unsigned int irq);

    void        (*ack)(unsigned int irq);
    void        (*mask)(unsigned int irq);
    void        (*mask_ack)(unsigned int irq);
    void        (*unmask)(unsigned int irq);
    void        (*eoi)(unsigned int irq);

    void        (*end)(unsigned int irq);
    void        (*set_affinity)(unsigned int irq,
                    const struct cpumask *dest);
    int        (*retrigger)(unsigned int irq);
    int        (*set_type)(unsigned int irq, unsigned int flow_type);
    int        (*set_wake)(unsigned int irq, unsigned int on);

    /* Currently used only by UML, might disappear one day.*/
#ifdef CONFIG_IRQ_RELEASE_METHOD
    void        (*release)(unsigned int irq, void *dev_id);
#endif
    /*
     * For compatibility, ->typename is copied into ->name.
     * Will disappear.
     */
    const char    *typename;
};

(3)action:记录用户注册的中断处理函数、中断标志等内容

struct irqaction {
    irq_handler_t handler;
    unsigned long flags;
    cpumask_t mask;
    const char *name;
    void *dev_id;
    struct irqaction *next;
    int irq;
    struct proc_dir_entry *dir;
};

 

3. 中断处理流程总结

(1) 发生中断后,CPU执行异常向量vector_irq的代码;

(2)在vector_irq里面,最终会调用中断处理C程序总入口函数asm_do_IRQ();

(3)asm_do_IRQ()根据中断号调用irq_des[NR_IRQS]数组中的对应数组项中的handle_irq();

(4)handle_irq()会使用chip的成员函数来设置硬件,例如清除中断,禁止中断,重新开启中断等;

(5)handle_irq逐个调用用户在action链表中注册的处理函数。

  可见,中断体系结构的初始化,就是构造irq_desc[NR_IRQS]这个数据结构;用户注册中断就是构造action链表;用户卸载中断就是从action链表中去除对应的项。

 

4. Linux操作系统中断初始化

(1)init_IRQ()函数用来初始化中断体系结构,代码位于arch/arm/kernel/irq.c

void __init init_IRQ(void)
{
    int irq;

    for (irq = 0; irq < NR_IRQS; irq++)
        irq_desc[irq].status |= IRQ_NOREQUEST | IRQ_NOPROBE;

#ifdef CONFIG_SMP
    bad_irq_desc.affinity = CPU_MASK_ALL;
    bad_irq_desc.cpu = smp_processor_id();
#endif
    init_arch_irq();
}

(2)init_arch_irq()函数,就是用来初始化irq_desc[NR_IRQS]的,与硬件平台紧密相关。init_arch_irq其实是一个函数指针,我们移植Linux内核时,以S3C2440平台为例,把init_arch_irq指向函数s3c24xx_init_irq()。
(3)s3c24xx_init_irq()函数在arch/arm/plat-s3c24xx/irq.c中定义,它为所有的中断设置了芯片相关的数据结构irq_desc[irq].chip,设置了处理函数入口irq_desc[irq].handle_irq。

(4)以外部中断EINT0为例:

for (irqno = IRQ_EINT0; irqno <= IRQ_EINT3; irqno++) {
    irqdbf("registering irq %d (ext int)\n", irqno);
    set_irq_chip(irqno, &s3c_irq_eint0t4);
    set_irq_handler(irqno, handle_edge_irq);
    set_irq_flags(irqno, IRQF_VALID);
}

① set_irq_chip()的作用就是"irq_desc[irqno].chip = &s3c_irq_eint0t4",s3c_irq_eint0t4为系统提供了一套操作EINT0~EINT4的中断底层函数集,内容如下

static struct irq_chip s3c_irq_eint0t4 = {
    .name        = "s3c-ext0",
    .ack        = s3c_irq_ack,
    .mask        = s3c_irq_mask,
    .unmask        = s3c_irq_unmask,
    .set_wake    = s3c_irq_wake,
    .set_type    = s3c_irqext_type,
};

② set_irq_handler()函数的作用就是“irq_desc[irqno].handle_irq = handle_edge_irq”。发生中断后,asm_do_IRQ()函数会调用中断入口函数handle_edge_irq(),而handle_edge_irq()函数会调用用户注册的处理函数(即irq_desc[irqno].action)。

 

5. 用户注册中断时带来的中断初始化

(1)用户(驱动程序)通过request_irq()函数向内核注册中断处理函数,request_irq()函数根据中断号找到数组irq_desc[irqno]对应的数组项,然后在它的action链表中添加一个action表项。该函数定义于:kernel/irq/manage.c,内容如下

int request_irq(unsigned int irq, irq_handler_t handler,
        unsigned long irqflags, const char *devname, void *dev_id)
{
    struct irqaction *action;
    struct irq_desc *desc;
    int retval;

    /*
     * handle_IRQ_event() always ignores IRQF_DISABLED except for
     * the _first_ irqaction (sigh).  That can cause oopsing, but
     * the behavior is classified as "will not fix" so we need to
     * start nudging drivers away from using that idiom.
     */
    if ((irqflags & (IRQF_SHARED|IRQF_DISABLED))
            == (IRQF_SHARED|IRQF_DISABLED))
        pr_warning("IRQ %d/%s: IRQF_DISABLED is not "
                "guaranteed on shared IRQs\n",
                irq, devname);

#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).
     */
    if ((irqflags & IRQF_SHARED) && !dev_id)
        return -EINVAL;

    desc = irq_to_desc(irq);
    if (!desc)
        return -EINVAL;

    if (desc->status & IRQ_NOREQUEST)
        return -EINVAL;
    if (!handler)
        return -EINVAL;

    action = kmalloc(sizeof(struct irqaction), GFP_ATOMIC);
    if (!action)
        return -ENOMEM;

    action->handler = handler;
    action->flags = irqflags;
    cpus_clear(action->mask);
    action->name = devname;
    action->next = NULL;
    action->dev_id = dev_id;

    retval = __setup_irq(irq, desc, action);
    if (retval)
        kfree(action);

#ifdef CONFIG_DEBUG_SHIRQ
    if (irqflags & IRQF_SHARED) {
        /*
         * It's a shared IRQ -- the driver ought to be prepared for it
         * to happen immediately, so let's make sure....
         * We disable the irq to make sure that a 'real' IRQ doesn't
         * run in parallel with our fake.
         */
        unsigned long flags;

        disable_irq(irq);
        local_irq_save(flags);

        handler(irq, dev_id);

        local_irq_restore(flags);
        enable_irq(irq);
    }
#endif
    return retval;
}

 

(2)  request_irq()函数首先使用4个参数构造一个irqaction结构,然后调用__setup_irq函数将它链入链表中,简要代码如下:

static int __setup_irq(unsigned int irq, struct irqaction *new)
{
    /* 判断是否没有注册过,如果已经注册了就判断是否是可共享的中断 */
    p = &desc->action;
    old = *p;
    if (old) {
        if (!((old->flags & new->flags) & IRQF_SHARED) ||
            ((old->flags ^ new->flags) & IRQF_TRIGGER_MASK)) {
            old_name = old->name;
            goto mismatch;
        }

        /* add new interrupt at end of irq queue */
        do {
            p = &old->next;
            old = *p;
        } while (old);
        shared = 1;
    }

    /* 链入新表项 */
    *p = new;
    
    /* 如果在链入之前不是空链,那么之前的共享中断已经设置了中断触发方式,没有必要重复设置 */
    /* 如果链入之前是空链,那么就需要设置中断触发方式 */
    if (!shared) {
        irq_chip_set_defaults(desc->chip);

        /* Setup the type (level, edge polarity) if configured: */
        if (new->flags & IRQF_TRIGGER_MASK) {
            if (desc->chip && desc->chip->set_type)
                desc->chip->set_type(irq,
                        new->flags & IRQF_TRIGGER_MASK);
            else
                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);

        desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
                  IRQ_INPROGRESS);

        if (!(desc->status & IRQ_NOAUTOEN)) {
            desc->depth = 0;
            desc->status &= ~IRQ_DISABLED;
            /* 启动中断 */
            if (desc->chip->startup)
                desc->chip->startup(irq);
            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;

    new->irq = irq;
    register_irq_proc(irq);
    new->dir = NULL;
    register_handler_proc(irq, new);
}


(3) __setup_irq()函数主要完成功能如下

① 将新建的irqaciton结构链入irq_desc[irq]结构体的action链表中

  * 如果action链表为空,则直接链入

  * 如果非空,则要判断新建的irqaciton结构和链表中的irqaciton结构所表示的中断类型是否一致:即是都声明为“可共享的”,是否都是用相同的触发方式,如果一致,则将新建的irqaciton结构链入

② 设置中断的触发方式;

③ 启动中断

 

6. 卸载中断

   卸载中断使用函数free_irq()函数,该函数定义在kernel/irq/manage.c中,需要用到的两个参数irq、dev_id。通过参数irq可以定位到action链表,再使用dev_id在链表中找到要卸载的表项(共享中断的情况)。如果它是唯一表项,那么删除中断,还需要调用irq_desc[irq].chip->shutdown()或者irq_desc[irq].chip->disable()来关闭中断

void free_irq(unsigned int irq, void *dev_id)
{
    struct irq_desc *desc = irq_to_desc(irq);
    struct irqaction **p;
    unsigned long flags;

    WARN_ON(in_interrupt());

    if (!desc)
        return;

    spin_lock_irqsave(&desc->lock, flags);
    p = &desc->action;
    for (;;) {
        struct irqaction *action = *p;

        if (action) {
            struct irqaction **pp = p;

            p = &action->next;
            if (action->dev_id != dev_id)
                continue;

            /* Found it - now remove it from the list of entries */
            *pp = action->next;

            /* Currently used only by UML, might disappear one day.*/
#ifdef CONFIG_IRQ_RELEASE_METHOD
            if (desc->chip->release)
                desc->chip->release(irq, dev_id);
#endif

            if (!desc->action) {
                desc->status |= IRQ_DISABLED;
                if (desc->chip->shutdown)
                    desc->chip->shutdown(irq);
                else
                    desc->chip->disable(irq);
            }
            spin_unlock_irqrestore(&desc->lock, flags);
            unregister_handler_proc(irq, action);

            /* Make sure it's not being used on another CPU */
            synchronize_irq(irq);
#ifdef CONFIG_DEBUG_SHIRQ
            /*
             * It's a shared IRQ -- the driver ought to be
             * prepared for it to happen even now it's
             * being freed, so let's make sure....  We do
             * this after actually deregistering it, to
             * make sure that a 'real' IRQ doesn't run in
             * parallel with our fake
             */
            if (action->flags & IRQF_SHARED) {
                local_irq_save(flags);
                action->handler(irq, dev_id);
                local_irq_restore(flags);
            }
#endif
            kfree(action);
            return;
        }
        printk(KERN_ERR "Trying to free already-free IRQ %d\n", irq);
#ifdef CONFIG_DEBUG_SHIRQ
        dump_stack();
#endif
        spin_unlock_irqrestore(&desc->lock, flags);
        return;
    }
}

 

7. Linux中断处理流程分析

 

① 中断总入口函数:asm_do_IRQ() (定义在:arch/arm/kernel/irq.c)

asmlinkage void __exception asm_do_IRQ(unsigned int irq, struct pt_regs *regs)
{
    struct pt_regs *old_regs = set_irq_regs(regs);

    irq_enter();

    /*
     * Some hardware gives randomly wrong interrupts.  Rather
     * than crashing, do something sensible.
     */
    if (irq >= NR_IRQS)
        handle_bad_irq(irq, &bad_irq_desc);
    else
        generic_handle_irq(irq);

    /* AT91 specific workaround */
    irq_finish(irq);

    irq_exit();
    set_irq_regs(old_regs);
}

 

② generic_handle_irq()会调用相应中断号描述结构的handle_irq,等价于irq_desc[irq].handle_irq(irq, desc)

 

③ 普通中断流程(以EINT0为例)

(1)irq_desc[IRQ_EINT0].handle_irq函数指针指向handle_edge_irq()(定义在:kernel/irq/chip.c),用来处理边沿触发的中断,内容如下

void fastcall
handle_edge_irq(unsigned int irq, struct irq_desc *desc)
{
    kstat_cpu(cpu).irqs[irq]++;

    /* Start handling the irq */
    desc->chip->ack(irq);

    /* Mark the IRQ currently in progress.*/
    desc->status |= IRQ_INPROGRESS;

    action_ret = handle_IRQ_event(irq, action);
}

(2)通过函数调用desc->chip->ack(irq)来响应中断,实际上就是清除中断以使得可以接受下一个中断,有了之前数据结构初始化的前提了解,可以知道实际上执行的就是s3c_irq_eint0t4.ack函数
(3)handle_IRQ_event函数逐个执行action链表中用户注册的中断处理函数,它在kernel/irq/handle.c中定义,关键代码如下:

irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
{
    do {
        ret = action->handler(irq, action->dev_id);
        if (ret == IRQ_HANDLED)
            status |= action->flags;
        retval |= ret;
        action = action->next;
    } while (action);
}

(4)用户通过函数request_irq()函数注册中断处理函数时候,传入参数irq和dev_id,在这里这两个参数被用户注册的中断处理函数action->handler()所使用。可见用户可以在注册中断处理函数的时候,指定参数dev_id,然后将来再由注册的中断处理函数使用这个参数。

 

④ 特殊处理流程(以外部中断EINT5为例)

(1)在S3C2440处理器架构中,EINT5中断属于EINT4t7中断集合,是一个子中断。当EINT5中断线发生中断事件,那么将先跳转到EINT4t7中断号对应的中断入口处理函数,也即是irq_desc[EINT4t7].handle_irq(irq,desc),进行具体子中断确定,然后再跳转到真正发生中断的中断入口处理函数执行。

(2)EINT5中断注册函数调用:

request_irq(IRQ_EINT5, eint5_irq, IRQT_BOTHEDGE, "S2", NULL);

  其实我们在没有注册EINT5中断源的时候,系统已经注册了EINT4t7的中断入口处理函数。中断集合EINT4t7的中断入口处理函数,是在arch/arm/plat-s3c24xx/irq.c中的函数s3c24xx_init_irq()来初始化的,内容如下:

set_irq_chained_handler(IRQ_EINT4t7, s3c_irq_demux_extint4t7);

(3)当发生EINT5中断事件,汇编阶段根据INTOFFSET确定中断号为IRQ_EINT4t7,asm_do_IRQ函数通过传入的这个参数,将跳转到irq_desc[EINT4t7].handle_irq(irq,desc)函数执行,也就是函数s3c_irq_demux_extint4t7(irq, desc),该函数的主要内容如下:

static void
s3c_irq_demux_extint4t7(unsigned int irq,
            struct irq_desc *desc)
{
    unsigned long eintpnd = __raw_readl(S3C24XX_EINTPEND);
    unsigned long eintmsk = __raw_readl(S3C24XX_EINTMASK);

    eintpnd &= ~eintmsk;
    eintpnd &= 0xff;    /* only lower irqs */

    /* we may as well handle all the pending IRQs here */

    while (eintpnd) {
        irq = __ffs(eintpnd);
        eintpnd &= ~(1<<irq);

        irq += (IRQ_EINT4 - 4);

        generic_handle_irq(irq);
    }
}

(4)函数s3c_irq_demux_extint4t7()根据寄存器S3C24XX_EINTPEND、S3C24XX_EINTMASK重新计算中断号,这个时候将计算出真正的中断号IRQ_EINT5,然后通过generic_handle_irq(irq)来调用irq_desc[EINT5].handle_irq(irq,desc)。此后的过程与EINT0发生中断后的执行过程类似。

 

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