early_irq_init

int __init early_irq_init(void)
{
	int i, initcnt, node = first_online_node;
	struct irq_desc *desc;

	init_irq_default_affinity();

	/* Let arch update nr_irqs and return the nr of preallocated irqs */
	initcnt = arch_probe_nr_irqs();
	printk(KERN_INFO "NR_IRQS: %d, nr_irqs: %d, preallocated irqs: %d\n",
	       NR_IRQS, nr_irqs, initcnt);

	if (WARN_ON(nr_irqs > MAX_SPARSE_IRQS))
		nr_irqs = MAX_SPARSE_IRQS;

	if (WARN_ON(initcnt > MAX_SPARSE_IRQS))
		initcnt = MAX_SPARSE_IRQS;

	if (initcnt > nr_irqs)
		nr_irqs = initcnt;

	for (i = 0; i < initcnt; i++) {
		desc = alloc_desc(i, node, 0, NULL, NULL);
		irq_insert_desc(i, desc);
	}
	return arch_early_irq_init();
}

#else /* !CONFIG_SPARSE_IRQ */

struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
	[0 ... NR_IRQS-1] = {
		.handle_irq	= handle_bad_irq,
		.depth		= 1,
		.lock		= __RAW_SPIN_LOCK_UNLOCKED(irq_desc->lock),
	}
};

int __init early_irq_init(void)
{
	int count, i, node = first_online_node;
	struct irq_desc *desc;

	init_irq_default_affinity();

	printk(KERN_INFO "NR_IRQS: %d\n", NR_IRQS);

	desc = irq_desc;
	count = ARRAY_SIZE(irq_desc);

	for (i = 0; i < count; i++) {
		desc[i].kstat_irqs = alloc_percpu(unsigned int);
		alloc_masks(&desc[i], node);
		raw_spin_lock_init(&desc[i].lock);
		lockdep_set_class(&desc[i].lock, &irq_desc_lock_class);
		mutex_init(&desc[i].request_mutex);
		init_waitqueue_head(&desc[i].wait_for_threads);
		desc_set_defaults(i, &desc[i], node, NULL, NULL);
		irq_resend_init(desc);
	}
	return arch_early_irq_init();
}

static struct irq_desc *alloc_desc(int irq, int node, unsigned int flags,
				   const struct cpumask *affinity,
				   struct module *owner)
{
	struct irq_desc *desc;

	desc = kzalloc_node(sizeof(*desc), GFP_KERNEL, node);
	if (!desc)
		return NULL;
	/* allocate based on nr_cpu_ids */
	desc->kstat_irqs = alloc_percpu(unsigned int);
	if (!desc->kstat_irqs)
		goto err_desc;

	if (alloc_masks(desc, node))
		goto err_kstat;

	raw_spin_lock_init(&desc->lock);
	lockdep_set_class(&desc->lock, &irq_desc_lock_class);
	mutex_init(&desc->request_mutex);
	init_rcu_head(&desc->rcu);
	init_waitqueue_head(&desc->wait_for_threads);

	desc_set_defaults(irq, desc, node, affinity, owner);
	irqd_set(&desc->irq_data, flags);
	kobject_init(&desc->kobj, &irq_kobj_type);
	irq_resend_init(desc);

	return desc;

err_kstat:
	free_percpu(desc->kstat_irqs);
err_desc:
	kfree(desc);
	return NULL;
}

	desc->irq_data.common = &desc->irq_common_data;
	desc->irq_data.irq = irq;
	desc->irq_data.chip = &no_irq_chip;
	desc->irq_data.chip_data = NULL;
	irq_settings_clr_and_set(desc, ~0, _IRQ_DEFAULT_INIT_FLAGS);
	irqd_set(&desc->irq_data, IRQD_IRQ_DISABLED);
	irqd_set(&desc->irq_data, IRQD_IRQ_MASKED);
	desc->handle_irq = handle_bad_irq;
	desc->depth = 1;