1. 概述

        如果 pinctrl子系统将一个 PIN 复用为 GPIO 的话，那么接下来要用到 gpio 子系统了。gpio 子系统顾名思义，就是用于初始化 GPIO 并且提供相应的 API 函数，比如设置 GPIO为输入输出，设置读取 GPIO 的值等。

        gpio 子系统的主要目的就是方便驱动开发者使用 gpio，驱动开发者在设备树中添加 gpio 相关信息，然后就可以在驱动程序中使用 gpio 子系统提供的 API函数来操作 GPIO，Linux 内核向驱动开发者屏蔽掉了 GPIO 的设置过程，极大的方便了驱动开发者使用 GPIO

Linux的GPIO子系统驱动框架由三个主要部分组成：① GPIO控制器驱动程序、②gpio lib驱动程序 ③GPIO字符设备驱动程序： 

2. gpio 子系统相关结构体

2.1 struct gpio_chip

/**
 * struct gpio_chip - abstract a GPIO controller
 * @label: for diagnostics
 * @dev: optional device providing the GPIOs
 * @owner: helps prevent removal of modules exporting active GPIOs
 * @list: links gpio_chips together for traversal
 * @request: optional hook for chip-specific activation, such as
 *	enabling module power and clock; may sleep
 * @free: optional hook for chip-specific deactivation, such as
 *	disabling module power and clock; may sleep
 * @get_direction: returns direction for signal "offset", 0=out, 1=in,
 *	(same as GPIOF_DIR_XXX), or negative error
 * @direction_input: configures signal "offset" as input, or returns error
 * @direction_output: configures signal "offset" as output, or returns error
 * @get: returns value for signal "offset"; for output signals this
 *	returns either the value actually sensed, or zero
 * @set: assigns output value for signal "offset"
 * @set_multiple: assigns output values for multiple signals defined by "mask"
 * @set_debounce: optional hook for setting debounce time for specified gpio in
 *      interrupt triggered gpio chips
 * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;
 *	implementation may not sleep
 * @dbg_show: optional routine to show contents in debugfs; default code
 *	will be used when this is omitted, but custom code can show extra
 *	state (such as pullup/pulldown configuration).
 * @base: identifies the first GPIO number handled by this chip; or, if
 *	negative during registration, requests dynamic ID allocation.
 * @ngpio: the number of GPIOs handled by this controller; the last GPIO
 *	handled is (base + ngpio - 1).
 * @desc: array of ngpio descriptors. Private.
 * @names: if set, must be an array of strings to use as alternative
 *      names for the GPIOs in this chip. Any entry in the array
 *      may be NULL if there is no alias for the GPIO, however the
 *      array must be @ngpio entries long.  A name can include a single printk
 *      format specifier for an unsigned int.  It is substituted by the actual
 *      number of the gpio.
 * @can_sleep: flag must be set iff get()/set() methods sleep, as they
 *	must while accessing GPIO expander chips over I2C or SPI. This
 *	implies that if the chip supports IRQs, these IRQs need to be threaded
 *	as the chip access may sleep when e.g. reading out the IRQ status
 *	registers.
 * @exported: flags if the gpiochip is exported for use from sysfs. Private.
 * @irq_not_threaded: flag must be set if @can_sleep is set but the
 *	IRQs don't need to be threaded
 *
 * A gpio_chip can help platforms abstract various sources of GPIOs so
 * they can all be accessed through a common programing interface.
 * Example sources would be SOC controllers, FPGAs, multifunction
 * chips, dedicated GPIO expanders, and so on.
 *
 * Each chip controls a number of signals, identified in method calls
 * by "offset" values in the range 0..(@ngpio - 1).  When those signals
 * are referenced through calls like gpio_get_value(gpio), the offset
 * is calculated by subtracting @base from the gpio number.
 */
struct gpio_chip {
	const char		*label;
	struct device		*dev;
	struct module		*owner;
	struct list_head        list;

    //请求一个 GPIO引脚
	int			(*request)(struct gpio_chip *chip,
						unsigned offset);
    //释放一个GPIO引脚
	void			(*free)(struct gpio_chip *chip,
						unsigned offset);
    //获取方向
	int			(*get_direction)(struct gpio_chip *chip,
						unsigned offset);
    //输入模式
	int			(*direction_input)(struct gpio_chip *chip,
						unsigned offset);
    //输出模式，并且set gpio val
	int			(*direction_output)(struct gpio_chip *chip,
						unsigned offset, int value);
    //读取 GPIO 引脚的值
	int			(*get)(struct gpio_chip *chip,
						unsigned offset);
    //设置gpio 引脚值
	void			(*set)(struct gpio_chip *chip,
						unsigned offset, int value);
    //设置多个gpio 引脚值
	void			(*set_multiple)(struct gpio_chip *chip,
						unsigned long *mask,
						unsigned long *bits);
    //设置 GPIO 引脚的去抖动时间
	int			(*set_debounce)(struct gpio_chip *chip,
						unsigned offset,
						unsigned debounce);

	int			(*to_irq)(struct gpio_chip *chip,
						unsigned offset);

	void			(*dbg_show)(struct seq_file *s,
						struct gpio_chip *chip);
	int			base;     //chip的基地址
	u16			ngpio;    //GPIO 引脚数量
	struct gpio_desc	*desc;    //gpio描述结构体数组，里面保存了此控制器可以控制的引脚描述
	const char		*const *names;
	bool			can_sleep;
	bool			irq_not_threaded;
	bool			exported;

#ifdef CONFIG_GPIOLIB_IRQCHIP
	/*
	 * With CONFIG_GPIOLIB_IRQCHIP we get an irqchip inside the gpiolib
	 * to handle IRQs for most practical cases.
	 */
	struct irq_chip		*irqchip;
	struct irq_domain	*irqdomain;
	unsigned int		irq_base;
	irq_flow_handler_t	irq_handler;
	unsigned int		irq_default_type;
#endif

#if defined(CONFIG_OF_GPIO)
	/*
	 * If CONFIG_OF is enabled, then all GPIO controllers described in the
	 * device tree automatically may have an OF translation
	 */
	struct device_node *of_node;
	int of_gpio_n_cells;
	int (*of_xlate)(struct gpio_chip *gc,
			const struct of_phandle_args *gpiospec, u32 *flags);
#endif
#ifdef CONFIG_PINCTRL
	/*
	 * If CONFIG_PINCTRL is enabled, then gpio controllers can optionally
	 * describe the actual pin range which they serve in an SoC. This
	 * information would be used by pinctrl subsystem to configure
	 * corresponding pins for gpio usage.
	 */
	struct list_head pin_ranges;
#endif
};

 2.2 struct gpio_desc

struct gpio_desc {
	struct gpio_chip	*chip;    //属于哪个gpio_chip
	unsigned long		flags;    
/* flag symbols are bit numbers */
#define FLAG_REQUESTED	0
#define FLAG_IS_OUT	1
#define FLAG_EXPORT	2	/* protected by sysfs_lock */
#define FLAG_SYSFS	3	/* exported via /sys/class/gpio/control */
#define FLAG_TRIG_FALL	4	/* trigger on falling edge */
#define FLAG_TRIG_RISE	5	/* trigger on rising edge */
#define FLAG_ACTIVE_LOW	6	/* value has active low */
#define FLAG_OPEN_DRAIN	7	/* Gpio is open drain type */
#define FLAG_OPEN_SOURCE 8	/* Gpio is open source type */
#define FLAG_USED_AS_IRQ 9	/* GPIO is connected to an IRQ */
#define FLAG_SYSFS_DIR	10	/* show sysfs direction attribute */
#define FLAG_IS_HOGGED	11	/* GPIO is hogged */

#define ID_SHIFT	16	/* add new flags before this one */

#define GPIO_FLAGS_MASK		((1 << ID_SHIFT) - 1)
#define GPIO_TRIGGER_MASK	(BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE))

	const char		*label;   
};

3. IMX6ULL gpio-controller构造过程

 4. gpiochip_add

 

5. gpio api与gpio子系统的调用关系