【Linux 驱动】IMX6ULL input驱动

1. input子系统介绍

input 子系统分为 input 驱动层、input 核心层、input 事件处理层，最终给用户空间提供可访问的设备节点。

驱动层：输入设备的具体驱动程序，比如按键驱动程序，向内核层报告输入内容
核心层：承上启下，为驱动层提供输入设备注册和操作接口。通知事件层对输入事件进行处理。
事件层：主要和用户空间进行交互。

2. 重要结构体

2.1 struct input_dev

/**
 * struct input_dev - represents an input device
 * @name: name of the device
 * @phys: physical path to the device in the system hierarchy
 * @uniq: unique identification code for the device (if device has it)
 * @id: id of the device (struct input_id)
 * @propbit: bitmap of device properties and quirks
 * @evbit: bitmap of types of events supported by the device (EV_KEY,
 *	EV_REL, etc.)
 * @keybit: bitmap of keys/buttons this device has
 * @relbit: bitmap of relative axes for the device
 * @absbit: bitmap of absolute axes for the device
 * @mscbit: bitmap of miscellaneous events supported by the device
 * @ledbit: bitmap of leds present on the device
 * @sndbit: bitmap of sound effects supported by the device
 * @ffbit: bitmap of force feedback effects supported by the device
 * @swbit: bitmap of switches present on the device
 * @hint_events_per_packet: average number of events generated by the
 *	device in a packet (between EV_SYN/SYN_REPORT events). Used by
 *	event handlers to estimate size of the buffer needed to hold
 *	events.
 * @keycodemax: size of keycode table
 * @keycodesize: size of elements in keycode table
 * @keycode: map of scancodes to keycodes for this device
 * @getkeycode: optional legacy method to retrieve current keymap.
 * @setkeycode: optional method to alter current keymap, used to implement
 *	sparse keymaps. If not supplied default mechanism will be used.
 *	The method is being called while holding event_lock and thus must
 *	not sleep
 * @ff: force feedback structure associated with the device if device
 *	supports force feedback effects
 * @repeat_key: stores key code of the last key pressed; used to implement
 *	software autorepeat
 * @timer: timer for software autorepeat
 * @rep: current values for autorepeat parameters (delay, rate)
 * @mt: pointer to multitouch state
 * @absinfo: array of &struct input_absinfo elements holding information
 *	about absolute axes (current value, min, max, flat, fuzz,
 *	resolution)
 * @key: reflects current state of device's keys/buttons
 * @led: reflects current state of device's LEDs
 * @snd: reflects current state of sound effects
 * @sw: reflects current state of device's switches
 * @open: this method is called when the very first user calls
 *	input_open_device(). The driver must prepare the device
 *	to start generating events (start polling thread,
 *	request an IRQ, submit URB, etc.)
 * @close: this method is called when the very last user calls
 *	input_close_device().
 * @flush: purges the device. Most commonly used to get rid of force
 *	feedback effects loaded into the device when disconnecting
 *	from it
 * @event: event handler for events sent _to_ the device, like EV_LED
 *	or EV_SND. The device is expected to carry out the requested
 *	action (turn on a LED, play sound, etc.) The call is protected
 *	by @event_lock and must not sleep
 * @grab: input handle that currently has the device grabbed (via
 *	EVIOCGRAB ioctl). When a handle grabs a device it becomes sole
 *	recipient for all input events coming from the device
 * @event_lock: this spinlock is is taken when input core receives
 *	and processes a new event for the device (in input_event()).
 *	Code that accesses and/or modifies parameters of a device
 *	(such as keymap or absmin, absmax, absfuzz, etc.) after device
 *	has been registered with input core must take this lock.
 * @mutex: serializes calls to open(), close() and flush() methods
 * @users: stores number of users (input handlers) that opened this
 *	device. It is used by input_open_device() and input_close_device()
 *	to make sure that dev->open() is only called when the first
 *	user opens device and dev->close() is called when the very
 *	last user closes the device
 * @going_away: marks devices that are in a middle of unregistering and
 *	causes input_open_device*() fail with -ENODEV.
 * @dev: driver model's view of this device
 * @h_list: list of input handles associated with the device. When
 *	accessing the list dev->mutex must be held
 * @node: used to place the device onto input_dev_list
 * @num_vals: number of values queued in the current frame
 * @max_vals: maximum number of values queued in a frame
 * @vals: array of values queued in the current frame
 * @devres_managed: indicates that devices is managed with devres framework
 *	and needs not be explicitly unregistered or freed.
 */
struct input_dev {
	const char *name;
	const char *phys;
	const char *uniq;
	struct input_id id;

	unsigned long propbit[BITS_TO_LONGS(INPUT_PROP_CNT)];

	unsigned long evbit[BITS_TO_LONGS(EV_CNT)];
	unsigned long keybit[BITS_TO_LONGS(KEY_CNT)];
	unsigned long relbit[BITS_TO_LONGS(REL_CNT)];
	unsigned long absbit[BITS_TO_LONGS(ABS_CNT)];
	unsigned long mscbit[BITS_TO_LONGS(MSC_CNT)];
	unsigned long ledbit[BITS_TO_LONGS(LED_CNT)];
	unsigned long sndbit[BITS_TO_LONGS(SND_CNT)];
	unsigned long ffbit[BITS_TO_LONGS(FF_CNT)];
	unsigned long swbit[BITS_TO_LONGS(SW_CNT)];

	unsigned int hint_events_per_packet;

	unsigned int keycodemax;
	unsigned int keycodesize;
	void *keycode;

	int (*setkeycode)(struct input_dev *dev,
			  const struct input_keymap_entry *ke,
			  unsigned int *old_keycode);
	int (*getkeycode)(struct input_dev *dev,
			  struct input_keymap_entry *ke);

	struct ff_device *ff;

	unsigned int repeat_key;
	struct timer_list timer;

	int rep[REP_CNT];

	struct input_mt *mt;

	struct input_absinfo *absinfo;

	unsigned long key[BITS_TO_LONGS(KEY_CNT)];
	unsigned long led[BITS_TO_LONGS(LED_CNT)];
	unsigned long snd[BITS_TO_LONGS(SND_CNT)];
	unsigned long sw[BITS_TO_LONGS(SW_CNT)];

	int (*open)(struct input_dev *dev);
	void (*close)(struct input_dev *dev);
	int (*flush)(struct input_dev *dev, struct file *file);
	int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);

	struct input_handle __rcu *grab;

	spinlock_t event_lock;
	struct mutex mutex;

	unsigned int users;
	bool going_away;

	struct device dev;

	struct list_head	h_list;
	struct list_head	node;

	unsigned int num_vals;
	unsigned int max_vals;
	struct input_value *vals;

	bool devres_managed;
};

evbit 表示输入事件类型，比如同步事件、按键事件等

#define EV_SYN 0x00 /* 同步事件 */
#define EV_KEY 0x01 /* 按键事件 */
#define EV_REL 0x02 /* 相对坐标事件 */
#define EV_ABS 0x03 /* 绝对坐标事件 */
#define EV_MSC 0x04 /* 杂项(其他)事件 */
#define EV_SW 0x05 /* 开关事件 */
#define EV_LED 0x11 /* LED */
#define EV_SND 0x12 /* sound(声音) */
#define EV_REP 0x14 /* 重复事件 */
#define EV_FF 0x15 /* 压力事件 */
#define EV_PWR 0x16 /* 电源事件 */
#define EV_FF_STATUS 0x17 /* 压力状态事件 */

keybit、relbit 等等都是存放不同事件对应的值，比如keybit支持KEY_1、KEY_2等

#define KEY_RESERVED 0
#define KEY_ESC 1
#define KEY_1 2
#define KEY_2 3
#define KEY_3 4
#define KEY_4 5
#define KEY_5 6
#define KEY_6 7
#define KEY_7 8
#define KEY_8 9
#define KEY_9 10
#define KEY_0 11
......
#define BTN_TRIGGER_HAPPY39 0x2e6
#define BTN_TRIGGER_HAPPY40 0x2e7

2.2 struct input_handler

/**
 * struct input_handler - implements one of interfaces for input devices
 * @private: driver-specific data
 * @event: event handler. This method is being called by input core with
 *	interrupts disabled and dev->event_lock spinlock held and so
 *	it may not sleep
 * @events: event sequence handler. This method is being called by
 *	input core with interrupts disabled and dev->event_lock
 *	spinlock held and so it may not sleep
 * @filter: similar to @event; separates normal event handlers from
 *	"filters".
 * @match: called after comparing device's id with handler's id_table
 *	to perform fine-grained matching between device and handler
 * @connect: called when attaching a handler to an input device
 * @disconnect: disconnects a handler from input device
 * @start: starts handler for given handle. This function is called by
 *	input core right after connect() method and also when a process
 *	that "grabbed" a device releases it
 * @legacy_minors: set to %true by drivers using legacy minor ranges
 * @minor: beginning of range of 32 legacy minors for devices this driver
 *	can provide
 * @name: name of the handler, to be shown in /proc/bus/input/handlers
 * @id_table: pointer to a table of input_device_ids this driver can
 *	handle
 * @h_list: list of input handles associated with the handler
 * @node: for placing the driver onto input_handler_list
 *
 * Input handlers attach to input devices and create input handles. There
 * are likely several handlers attached to any given input device at the
 * same time. All of them will get their copy of input event generated by
 * the device.
 *
 * The very same structure is used to implement input filters. Input core
 * allows filters to run first and will not pass event to regular handlers
 * if any of the filters indicate that the event should be filtered (by
 * returning %true from their filter() method).
 *
 * Note that input core serializes calls to connect() and disconnect()
 * methods.
 */
struct input_handler {

	void *private;

	void (*event)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
	void (*events)(struct input_handle *handle,
		       const struct input_value *vals, unsigned int count);
	bool (*filter)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
	bool (*match)(struct input_handler *handler, struct input_dev *dev);
	int (*connect)(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id);
	void (*disconnect)(struct input_handle *handle);
	void (*start)(struct input_handle *handle);

	bool legacy_minors;
	int minor;
	const char *name;

	const struct input_device_id *id_table;

	struct list_head	h_list;
	struct list_head	node;
};

2.3 设备获取、上报数据：struct input_event

/*
 * The event structure itself
 */

struct input_event {
	struct timeval time;
	__u16 type;
	__u16 code;
	__s32 value;
};

struct timeval {
	__kernel_time_t		tv_sec;		/* seconds */
	__kernel_suseconds_t	tv_usec;	/* microseconds */
};

time：事件发生时间
type：事件类型，EV_KEY、EV_ABS等
code：事件码，KEY_1、KEY_2等
value：值，比如 EV_KEY 事件中 value 就是按键值，表示按键有没有被按下，如果为 1 的话说明按键按下，如果为 0 的话说明按键没有被按下或者按键松开了

3. input 内部实现

和platform总线驱动相似，左右两边依次比较，如果匹配，则调用input_handler结构体的connect函数

3.1 input 驱动编写流程

static int __init input_init(void)
{
	int err;

	err = class_register(&input_class);
	if (err) {
		pr_err("unable to register input_dev class\n");
		return err;
	}

	err = input_proc_init();
	if (err)
		goto fail1;

	err = register_chrdev_region(MKDEV(INPUT_MAJOR, 0),
				     INPUT_MAX_CHAR_DEVICES, "input");
	if (err) {
		pr_err("unable to register char major %d", INPUT_MAJOR);
		goto fail2;
	}

	return 0;

 fail2:	input_proc_exit();
 fail1:	class_unregister(&input_class);
	return err;
}

static void __exit input_exit(void)
{
	input_proc_exit();
	unregister_chrdev_region(MKDEV(INPUT_MAJOR, 0),
				 INPUT_MAX_CHAR_DEVICES);
	class_unregister(&input_class);
}

subsys_initcall(input_init);
module_exit(input_exit);