mfd_add_devices(struct device *dev, 0, struct mfd_cell* cells, cell_num, NULL, 0, NULL);

struct mfd_cell {
	const char		*name;	//设备名字，会在注册platform设备时使用该名字
	int			id;			//同名设备需要使用id进行区分

	/* refcounting for multiple drivers to use a single cell */
	atomic_t		*usage_count;
	int			(*enable)(struct platform_device *dev);
	int			(*disable)(struct platform_device *dev);

	int			(*suspend)(struct platform_device *dev);
	int			(*resume)(struct platform_device *dev);

	/* platform data passed to the sub devices drivers */
	void			*platform_data;		//设备私有数据
	size_t			pdata_size;			//platform_data的大小

	/* device properties passed to the sub devices drivers */
	struct property_entry *properties;	// 如果需要为新注册的设备添加一个properties的话，可以使用该域

	/*
	 * Device Tree compatible string
	 * See: Documentation/devicetree/usage-model.txt Chapter 2.2 for details
	 */
	const char		*of_compatible;		// compatible属性，会在添加cell设备时通过该域寻找设备树生成的设备节点

	/* Matches ACPI */
	const struct mfd_cell_acpi_match	*acpi_match;	// acpi不管

	/*
	 * These resources can be specified relative to the parent device.
	 * For accessing hardware you should use resources from the platform dev
	 */
	int			num_resources;				// 资源数
	const struct resource	*resources;		// 设备资源，如果想为platform_device设置resource的话可以使用该域。设备树中的resource一般都是寄存器地址信息。

	/* don't check for resource conflicts */
	bool			ignore_resource_conflicts;

	/*
	 * Disable runtime PM callbacks for this subdevice - see
	 * pm_runtime_no_callbacks().
	 */
	bool			pm_runtime_no_callbacks;

	/* A list of regulator supplies that should be mapped to the MFD
	 * device rather than the child device when requested
	 */
	const char * const	*parent_supplies;
	int			num_parent_supplies;
};

static struct resource pmic_pek_resources[] = {

	// 13,连到controller(中断控制器PMIC)上的硬件中断号。
	// 这两个是同一按键然后分配了不同的中断，按键按下和松开各分配了一个中断
	// struct resource时用来描述platform总线设备的设备资源的结构体.
	{ 
		.start = 13,					// PMIC第13号中断, 按键下降沿中断
		.end = 13,	
		.name = "PEK_DBF",
		.flags = IORESOURCE_IRQ,
		.desc = IORES_DESC_NONE,
	},
	{ 
		.start = 14,	// PMIC第14号中断, 按键上升沿中断
		.end = 14,	
		.name = "PEK_DBR",
		.flags = IORESOURCE_IRQ,
		.desc = IORES_DESC_NONE,
	}

};

//内核有相关宏定义来定义中断资源
DEFINE_RES_IRQ_NAMED(statrt, name)
    
#define DEFINE_RES_IRQ_NAMED(_irq, _name)				\
	DEFINE_RES_NAMED((_irq), 1, (_name), IORESOURCE_IRQ)
    
#define DEFINE_RES_NAMED(_start, _size, _name, _flags)			\
	{								\
		.start = (_start),					\
		.end = (_start) + (_size) - 1,				\
		.name = (_name),					\
		.flags = (_flags),					\
		.desc = IORES_DESC_NONE,				\
	}
    
...
static struct mfd_cell mfd_i2cdev_cells[] = {
	{
		.name = "axpxxx-pek",	// 最终该name会被设置为为该cell注册的platform_device的name
		.num_resources = ARRAY_SIZE(pmic_pek_resources),	// 资源数
		.resources = pmic_pek_resources,					// 设备资源
		.of_compatible = "x-powers,axp305-pek",				// 在注册设备时会通过cell的该域和设备树节点的compatible匹配，来寻找设备树生成的设备树节点of_node，然后添加到注册的platform_device->dev.of_node
	},
	{
		// 这个cell啥都没有,但是仍然有.name。
		// 因为platform bus的匹配方式有一种匹配方式就是直接匹配platform_device->name和driver->name
		// 所以这也要求，driver注册的时候一定要初始化.name域，而且一定是"axp2101-regulator"，否则就没别的匹配方法给这个cell用了
		// 而这个cell没有of_compatible,说明这个cell可能没有对应的设备树节点,可能不是一个物理设备.
		.name = "axp305-regulator",
	},
	{
		.of_compatible = "xpower-vregulator,dcdc1",
		.name = "reg-virt-consumer",
		.id = 1, // 这个id会在platform_device_alloc(name, id)的时候传入，作为platform_dev->id，区分同名设备
		.platform_data = 根据driver的需求,自己定义,// 会被添加到注册的platform_dev->dev.platform_data,该platform_dev对应的driver需要用到时可以取出来
		.pdata_size = sizeof(AXP305_DCDC1_NAME),
	},
	{
		.of_compatible = "xpower-vregulator,dcdc2",
		.name = "reg-virt-consumer",
		.id = 2,
		.platform_data = ....,
		.pdata_size = sizeof(AXP305_DCDC2_NAME),
	},
	...
	...
};