注册中断：对每个pin进行循环遍历for (pin_num = 0; pin_num < min_t(int, ZYNQ_GPIO_NR_GPIOS, (int)chip->ngpio); pin_num++)
gpio_irq = irq_find_mapping(irq_domain, pin_num); 将GPIO号映射为Linux系统中断号。
在Linux中断系统中，一个irq_domain表示一个中断控制器，其内中断由0开始编号（尚存在疑问）
unsigned int irq_find_mapping(struct irq_domain *domain, irq_hw_number_t hwirq)
将一个中断控制器上的某个硬件中断映射为某个Linux系统中断。
/**
* struct irq_domain - Hardware interrupt number translation object
* @link: Element in global irq_domain list.
* @name: Name of interrupt domain
* @ops: pointer to irq_domain methods
* @host_data: private data pointer for use by owner. Not touched by irq_domain
* core code.
*
* Optional elements
* @of_node: Pointer to device tree nodes associated with the irq_domain. Used
* when decoding device tree interrupt specifiers.
* @gc: Pointer to a list of generic chips. There is a helper function for
* setting up one or more generic chips for interrupt controllers
* drivers using the generic chip library which uses this pointer.
*
* Revmap data, used internally by irq_domain
* @revmap_direct_max_irq: The largest hwirq that can be set for controllers that
* support direct mapping
* @revmap_size: Size of the linear map table @linear_revmap[]
* @revmap_tree: Radix map tree for hwirqs that don't fit in the linear map
* @linear_revmap: Linear table of hwirq->virq reverse mappings
*/
struct irq_domain {
struct list_head link;
const char *name;
const struct irq_domain_ops *ops;
void *host_data;
/* Optional data */
struct device_node *of_node;
struct irq_domain_chip_generic *gc;
/* reverse map data. The linear map gets appended to the irq_domain */
irq_hw_number_t hwirq_max;
unsigned int revmap_direct_max_irq;
unsigned int revmap_size;
struct radix_tree_root revmap_tree;
unsigned int linear_revmap[];
};
revmap_direct_max_irq: 小于该值的中断，Linux中断号和硬件中断号相同，直接返回。
revmap_size: 线性反向映射（似乎要求域内IRQ从零开始，有点矛盾），小于该值的hwirq直接利用linear_revmap做查找。
否则用radix tree来查找映射。
irq_set_chip_and_handler(gpio_irq, &zynq_gpio_irqchip, handle_simple_irq);
调用irq_get_desc_lock(irq, &flags, 0);，获取irq对应的irq_desc。并设定irq_desc的chip：desc->irq_data.chip = chip;
调用irq_reserve_irq(irq);，将allocated_irqs中断位图中相应的中断标识为已占用。
调用__irq_set_handler，将irq_desc中的handle_irq设定：desc->handle_irq = handle;
irq_set_chip_data(gpio_irq, (void *)gpio);
这个比较简单，将要用私有的变量关联到irq，desc->irq_data.chip_data = data;
set_irq_flags(gpio_irq, IRQF_VALID);
总体调用：
irq_set_handler_data(irq_num, (void *)gpio);
这里的irq_num是通过irq_num = platform_get_irq(pdev, 0);获取的系统配置文件里面的irq配置。这个函数也简单，实质为：desc->irq_data.handler_data = data;
irq_set_chained_handler(irq_num, zynq_gpio_irqhandler);
这个函数实质为：desc->handle_irq = handle;
最终调用关系为：调用zynq_gpio_irqhandler，然后在该函数中通过调用generic_handle_irq来调用最终的handle_simple_irq。