struct irq_desc {
	struct irq_common_data	irq_common_data;
	struct irq_data		irq_data;
	unsigned int __percpu	*kstat_irqs;
	irq_flow_handler_t	handle_irq;
	struct irqaction	*action;	/* IRQ action list */   // 里面存放了用戶注冊(cè)的中斷服務(wù)代碼
	unsigned int		status_use_accessors;
	unsigned int		core_internal_state__do_not_mess_with_it;
	unsigned int		depth;		/* nested irq disables */
	unsigned int		wake_depth;	/* nested wake enables */
	unsigned int		tot_count;
	unsigned int		irq_count;	/* For detecting broken IRQs */
	unsigned long		last_unhandled;	/* Aging timer for unhandled count */
	unsigned int		irqs_unhandled;
	atomic_t		threads_handled;
	int			threads_handled_last;
	raw_spinlock_t		lock;
	struct cpumask		*percpu_enabled;
	const struct cpumask	*percpu_affinity;
#ifdef CONFIG_SMP
	const struct cpumask	*affinity_hint;
	struct irq_affinity_notify *affinity_notify;
#ifdef CONFIG_GENERIC_PENDING_IRQ
	cpumask_var_t		pending_mask;
#endif
#endif
	unsigned long		threads_oneshot;
	atomic_t		threads_active;
	wait_queue_head_t       wait_for_threads;
#ifdef CONFIG_PM_SLEEP
	unsigned int		nr_actions;
	unsigned int		no_suspend_depth;
	unsigned int		cond_suspend_depth;
	unsigned int		force_resume_depth;
#endif
#ifdef CONFIG_PROC_FS
	struct proc_dir_entry	*dir;
#endif
#ifdef CONFIG_GENERIC_IRQ_DEBUGFS
	struct dentry		*debugfs_file;
	const char		*dev_name;
#endif
#ifdef CONFIG_SPARSE_IRQ
	struct rcu_head		rcu;
	struct kobject		kobj;
#endif
	struct mutex		request_mutex;
	int			parent_irq;
	struct module		*owner;
	const char		*name;
} ____cacheline_internodealigned_in_smp;

struct irqaction {
	irq_handler_t		handler;  // 用戶注冊(cè)的中斷服務(wù)代碼， 中斷發(fā)生時(shí)就會(huì)運(yùn)行這個(gè)中斷處理函數(shù)
	void			*dev_id;
	void __percpu		*percpu_dev_id;
	struct irqaction	*next;
	irq_handler_t		thread_fn;
	struct task_struct	*thread;
	struct irqaction	*secondary;
	unsigned int		irq;    //hw中斷號(hào),
	unsigned int		flags;  //中斷標(biāo)志,注冊(cè)時(shí)設(shè)置,比如上升沿中斷，下降沿中斷等
	unsigned long		thread_flags;
	unsigned long		thread_mask;
	const char		*name;  //中斷名稱,產(chǎn)生中斷的硬件的名字
	struct proc_dir_entry	*dir;  // proc/irq/
} ____cacheline_internodealigned_in_smp;

struct irq_data {
	u32			mask;
	unsigned int		irq;
	unsigned long		hwirq;
	struct irq_common_data	*common;
	struct irq_chip		*chip;　　　 // 芯片端的中斷處理函數(shù)
	struct irq_domain	*domain;    // 代表一個(gè)interrupt controller 設(shè)備樹(shù)中的INTC
#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
	struct irq_data		*parent_data;
#endif
	void			*chip_data;
};

	.macro	irq_handler
#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
	ldr	r1, =handle_arch_irq
	mov	r0, sp
	badr	lr, 9997f
	ldr	pc, [r1]
#else
	arch_irq_handler_default
#endif

#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
#ifndef CONFIG_IRQCHIP_XILINX_INTC_MODULE_SUPPORT_EXPERIMENTAL
int __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
#else
int set_handle_irq(void (*handle_irq)(struct pt_regs *))
#endif
{
	if (handle_arch_irq)
		return -EBUSY;

	handle_arch_irq = handle_irq;
	return 0;
}
#endif

static int __init intc_of_init(struct device_node *node,
			     struct device_node *parent)
{
	int ret;

	omap_nr_pending = 3;
	omap_nr_irqs = 96;

	if (WARN_ON(!node))
		return -ENODEV;

	if (of_device_is_compatible(node, "ti,dm814-intc") ||
	    of_device_is_compatible(node, "ti,dm816-intc") ||
	    of_device_is_compatible(node, "ti,am33xx-intc")) {
		omap_nr_irqs = 128;
		omap_nr_pending = 4;
	}

	ret = omap_init_irq(-1, of_node_get(node));
	if (ret < 0)
		return ret;

	set_handle_irq(omap_intc_handle_irq);   // 設(shè)置硬中斷服務(wù)函數(shù)入口

	return 0;
}

static asmlinkage void __exception_irq_entry
omap_intc_handle_irq(struct pt_regs *regs)
{
	extern unsigned long irq_err_count;
	u32 irqnr;

	irqnr = intc_readl(INTC_SIR);  // 獲取硬件中斷號(hào)

	/*
	 * A spurious IRQ can result if interrupt that triggered the
	 * sorting is no longer active during the sorting (10 INTC
	 * functional clock cycles after interrupt assertion). Or a
	 * change in interrupt mask affected the result during sorting
	 * time. There is no special handling required except ignoring
	 * the SIR register value just read and retrying.
	 * See section 6.2.5 of AM335x TRM Literature Number: SPRUH73K
	 *
	 * Many a times, a spurious interrupt situation has been fixed
	 * by adding a flush for the posted write acking the IRQ in
	 * the device driver. Typically, this is going be the device
	 * driver whose interrupt was handled just before the spurious
	 * IRQ occurred. Pay attention to those device drivers if you
	 * run into hitting the spurious IRQ condition below.
	 */
	if (unlikely((irqnr & SPURIOUSIRQ_MASK) == SPURIOUSIRQ_MASK)) {
		pr_err_once("%s: spurious irq!\n", __func__);
		irq_err_count++;
		omap_ack_irq(NULL);
		return;
	}

	irqnr &= ACTIVEIRQ_MASK;
	handle_domain_irq(domain, irqnr, regs); // 根據(jù)硬件中斷號(hào)，在domain鏈表中查找映射好的IRQ number， 實(shí)現(xiàn)原理是怎樣的？
}

int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
			bool lookup, struct pt_regs *regs)
{
	struct pt_regs *old_regs = set_irq_regs(regs);
	unsigned int irq = hwirq;
	int ret = 0;

	irq_enter();

#ifdef CONFIG_IRQ_DOMAIN
	if (lookup)
		irq = irq_find_mapping(domain, hwirq);  // 根據(jù)硬中斷號(hào)，在映射表中找到對(duì)應(yīng)的 IRQ number
#endif

	/*
	 * Some hardware gives randomly wrong interrupts.  Rather
	 * than crashing, do something sensible.
	 */
	if (unlikely(!irq || irq >= nr_irqs)) {
		ack_bad_irq(irq);
		ret = -EINVAL;
	} else {
		generic_handle_irq(irq);  // 根據(jù)IRQ number，查找中斷服務(wù)，并執(zhí)行
	}

	irq_exit();　　// 退出硬件中斷服務(wù)，然后 invoke_softirq()，再 __do_softirq()，喚醒softirq隊(duì)列，進(jìn)入下半部開(kāi)始執(zhí)行
	set_irq_regs(old_regs);
	return ret;
}

int generic_handle_irq(unsigned int irq)
{
	struct irq_desc *desc = irq_to_desc(irq); // 根據(jù)IRQ number 找到 中斷描述符
	struct irq_data *data;

	if (!desc)
		return -EINVAL;

	data = irq_desc_get_irq_data(desc);
	if (WARN_ON_ONCE(!in_irq() && handle_enforce_irqctx(data)))
		return -EPERM;

	generic_handle_irq_desc(desc); // 根據(jù)中斷描述符，找到對(duì)應(yīng)的 handler
	return 0;
}

static int omap_gpio_irq_type(struct irq_data *d, unsigned type)
{
	struct gpio_bank *bank = omap_irq_data_get_bank(d);
	int retval;
	unsigned long flags;
	unsigned offset = d->hwirq;

	if (type & ~IRQ_TYPE_SENSE_MASK)
		return -EINVAL;

	if (!bank->regs->leveldetect0 &&
		(type & (IRQ_TYPE_LEVEL_LOW|IRQ_TYPE_LEVEL_HIGH)))
		return -EINVAL;

	raw_spin_lock_irqsave(&bank->lock, flags);
	retval = omap_set_gpio_triggering(bank, offset, type);
	if (retval) {
		raw_spin_unlock_irqrestore(&bank->lock, flags);
		goto error;
	}
	omap_gpio_init_irq(bank, offset);
	if (!omap_gpio_is_input(bank, offset)) {
		raw_spin_unlock_irqrestore(&bank->lock, flags);
		retval = -EINVAL;
		goto error;
	}
	raw_spin_unlock_irqrestore(&bank->lock, flags);

	if (type & (IRQ_TYPE_LEVEL_LOW | IRQ_TYPE_LEVEL_HIGH))
		irq_set_handler_locked(d, handle_level_irq);    // 電平觸發(fā)中斷
	else if (type & (IRQ_TYPE_EDGE_FALLING | IRQ_TYPE_EDGE_RISING))
		/*
		 * Edge IRQs are already cleared/acked in irq_handler and
		 * not need to be masked, as result handle_edge_irq()
		 * logic is excessed here and may cause lose of interrupts.
		 * So just use handle_simple_irq.
		 */
		irq_set_handler_locked(d, handle_simple_irq);   // 邊沿觸發(fā)中斷

	return 0;

error:
	return retval;
}    

void handle_simple_irq(struct irq_desc *desc)
{
	raw_spin_lock(&desc->lock);

	if (!irq_may_run(desc))
		goto out_unlock;

	desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);

	if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
		desc->istate |= IRQS_PENDING;
		goto out_unlock;
	}

	kstat_incr_irqs_this_cpu(desc);  // 設(shè)置處理標(biāo)記，避免多次重復(fù)進(jìn)入中斷處理
	handle_irq_event(desc);    // 中斷服務(wù)相關(guān)

out_unlock:
	raw_spin_unlock(&desc->lock);
}

{
	irqreturn_t ret;

	desc->istate &= ~IRQS_PENDING;
	irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);
	raw_spin_unlock(&desc->lock);

	ret = handle_irq_event_percpu(desc);  // 進(jìn)入中斷服務(wù)

	raw_spin_lock(&desc->lock);
	irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
	return ret;
}


irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
{
	irqreturn_t retval;
	unsigned int flags = 0;

	retval = __handle_irq_event_percpu(desc, &flags);   // 進(jìn)入中斷服務(wù)

	add_interrupt_randomness(desc->irq_data.irq);

	if (!noirqdebug)
		note_interrupt(desc, retval);
	return retval;
}

irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc, unsigned int *flags)
{
	irqreturn_t retval = IRQ_NONE;
	unsigned int irq = desc->irq_data.irq;
	struct irqaction *action;

	record_irq_time(desc);

	for_each_action_of_desc(desc, action) {   // 輪詢?cè)撝袛嗝枋龇锩娴乃?action
		irqreturn_t res;

		/*
		 * If this IRQ would be threaded under force_irqthreads, mark it so.
		 */
		if (irq_settings_can_thread(desc) &&
		    !(action->flags & (IRQF_NO_THREAD | IRQF_PERCPU | IRQF_ONESHOT)))
			lockdep_hardirq_threaded();

		trace_irq_handler_entry(irq, action);
		res = action->handler(irq, action->dev_id);　　// 調(diào)用用戶注冊(cè)的中斷服務(wù)
		trace_irq_handler_exit(irq, action, res);

		if (WARN_ONCE(!irqs_disabled(),"irq %u handler %pS enabled interrupts\n",
			      irq, action->handler))
			local_irq_disable();

		switch (res) {
		case IRQ_WAKE_THREAD:
			/*
			 * Catch drivers which return WAKE_THREAD but
			 * did not set up a thread function
			 */
			if (unlikely(!action->thread_fn)) {
				warn_no_thread(irq, action);
				break;
			}

			__irq_wake_thread(desc, action);

			fallthrough;	/* to add to randomness */
		case IRQ_HANDLED:
			*flags |= action->flags;
			break;

		default:
			break;
		}

		retval |= res;
	}

	return retval;
}