初探linux中断系统（2）

中断系统初始化的过程

用来初始化中断系统的函数位于arch/x86/kernel/irqinit.c，定义如下

void __init init_IRQ(void)
{
    int i;

    /*
     * On cpu 0, Assign IRQ0_VECTOR..IRQ15_VECTOR's to IRQ 0..15.
     * If these IRQ's are handled by legacy interrupt-controllers like PIC,
     * then this configuration will likely be static after the boot. If
     * these IRQ's are handled by more mordern controllers like IO-APIC,
     * then this vector space can be freed and re-used dynamically as the
     * irq's migrate etc.
     */
    for (i = 0; i < legacy_pic->nr_legacy_irqs; i++)
        per_cpu(vector_irq, 0)[IRQ0_VECTOR + i] = i;

    x86_init.irqs.intr_init();
}

函数写的很简单，留下的疑问是x86_init是做什么的？

在arch/x86/include/asm/x86_init.h中可以找到，x86_init是一个x86_init_ops类型的结构体，其中irqs是一个x86_init_irqs类型的结构体。

struct x86_init_irqs {
    void (*pre_vector_init)(void);
    void (*intr_init)(void);
    void (*trap_init)(void);
};

在arch/x86/kernel/x86_init.c中找到x86_init的初始默认赋值：

struct x86_init_ops x86_init __initdata = {

    ...

    .irqs = {
        .pre_vector_init    = init_ISA_irqs,
        .intr_init        = native_init_IRQ,
        .trap_init        = x86_init_noop,
    },

    ...
};

对于这几个函数，我们又要回到开头的irqinit.c中来寻找了。先看之前调用的intr_init，也就是native_init_IRQ:

void __init native_init_IRQ(void)
{
    int i;

    /* Execute any quirks before the call gates are initialised: */
    x86_init.irqs.pre_vector_init();

    apic_intr_init();

    /*
     * Cover the whole vector space, no vector can escape
     * us. (some of these will be overridden and become
     * 'special' SMP interrupts)
     */
    for (i = FIRST_EXTERNAL_VECTOR; i < NR_VECTORS; i++) {
        /* IA32_SYSCALL_VECTOR could be used in trap_init already. */
        if (!test_bit(i, used_vectors))
            set_intr_gate(i, interrupt[i-FIRST_EXTERNAL_VECTOR]);
    }

    if (!acpi_ioapic)
        setup_irq(2, &irq2);

#ifdef CONFIG_X86_32
    /*
     * External FPU? Set up irq13 if so, for
     * original braindamaged IBM FERR coupling.
     */
    if (boot_cpu_data.hard_math && !cpu_has_fpu)
        setup_irq(FPU_IRQ, &fpu_irq);

    irq_ctx_init(smp_processor_id());
#endif
}

其中pre_vector_init对应着init_ISA_irqs，主要完成了irq_desc的初始化分配。

void __init init_ISA_irqs(void)
{
    int i;

#if defined(CONFIG_X86_64) || defined(CONFIG_X86_LOCAL_APIC)
    init_bsp_APIC();
#endif
    legacy_pic->init(0);

    /*
     * 16 old-style INTA-cycle interrupts:
     */
    for (i = 0; i < legacy_pic->nr_legacy_irqs; i++) {
        struct irq_desc *desc = irq_to_desc(i);

        desc->status = IRQ_DISABLED;
        desc->action = NULL;
        desc->depth = 1;

        set_irq_chip_and_handler_name(i, &i8259A_chip,
                          handle_level_irq, "XT");
    }
}

完成数据结构的初始化后就是对硬件资源的分配了，不做深究。

在完成初始化后，每当用户request一个新的中断操作后，成功注册将更新系统维护的链表，具体可见前篇。