i.MX6ULL驱动开发 | 20 – Linux input 子系统

一、input子系统概述

1. 什么是input子系统

input子系统是管理输入的子系统,和pinctrl、gpio子系统一样,都是Linux内核针对某一类设备创建的框架。

2. in系统运维是干嘛的pulinux重启命令t子系统的作用

输入设备都是典型的字符设备,比如按键、鼠标、键盘、触摸屏等。

这些设备的工作机理是底层在按键、触摸等动作发生时产生一个中断,或者通过软件定时器去查询时间,然后CPU通过SPI、I2C等总线读取键值、坐标等数据,并将它们放linux是什么操作系统入一个缓冲区,由驱动模块管理这些缓冲区,通过驱动的read接口就可色的笔顺以让用户读取键值、坐标等数据。

显然 ,在这些输入设备英文工作中,只有中断、读取键值/坐标这些操作是与硬件相关的,而输入事件的管理则对输入设备是通用的,因此,Linux内核设计了input子系统,由核心层处理公共的工作。

有了inp输入设备和输出设备的区别ut子系统后,驱动编写时就不需要考虑应用层的事情,只需要按照input子系统的要linux常用命令求,上报输入事件即可

3. input子系统的框架

input子系统分为input驱动层、input核心层、input事件处理层。

  • input驱动层:输入设备的具体驱动程序,sed比如按键驱动,向内核层报告输入事件
  • input核心层:对下提供设备注册和操作接口,对上通知input事件层对输入事件进行处理
  • input事件层:和用户空间进行交互

二、input子系统使用方法

1. 输入设备

input子系输入设备的作用统的核心层会向Linux内核注册一个字符设备,主设备号为INPUT_MAJOR,

#define INPUT_MAJOR   13

因此,input子系统所有设备主设备号都为13,在使用input子系统时不需要再注册字符设备,只注册一个输入设备即可。

1.1. input_dev结构体

Linux内核用 input_dev 结构体描述一个输入设备,定义在文件 ​​include/linux/input.h​​ 文件中,如下:

/**
* 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;
};