在前文 Linux/Android——usb触摸屏驱动 - usbtouchscreen (一) 中记录了如何在kernel中添加input device 类型为touchscreen的驱动，

这在整个输入体系中是最下层的设备驱动部分，往上一层就是linux内核的管理驱动input系统，kernel中的源码位置：/kernel/drivers/input/input.c

                                              撰写不易,转载需注明出处：http://blog.csdn.net/jscese/article/details/42099381

到目前已经完全调通，可以正常使用了，现在记录一下这段时间接触到的Android 输入input 系统，先看一张网上的层次图，蛮不错的：
              

        

上一篇博客里面的 usbtouchscreen 就是对应上图的I2c module的位置，而在kernel中input的核心就是input.c .

input_dev：

 这个结构体表述的是一个输入设备的相关信息，在usbtouchscreen 驱动中的 usbtouch_probe 会初始化input_dev,作为usbtouch设备的一部分.

会对 input_dev  做一系列的初始化，设置参数之类的，具体可参考之前博客

input_dev 结构原型如下，/kernel/include/linux/input.h中定义：

/**
 * 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 array of struct input_mt_slot holding current values
 *	of tracked contacts
 * @mtsize: number of MT slots the device uses
 * @slot: MT slot currently being transmitted
 * @trkid: stores MT tracking ID for the current contact
 * @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.
 * @sync: set to %true when there were no new events since last EV_SYN
 * @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
 */
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_slot *mt;
	int mtsize;
	int slot;
	int trkid;

	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;

	bool sync;

	struct device dev;

	struct list_head	h_list;
	struct list_head	node;
};

我解释可能还会误导，源码上面的注释是最好的解释，都是描述一个input 设备的相关信息.

每一个input设备，都需要初始化一个这样的input_dev结构来描述记录此设备的一些特性，然后通过input_register_device 注册到设备总线上以供后续使用

可以到系统运行目录的/proc/bus/input下 cat devices  查看总线上的已经注册上的input device

input_event：

  设备驱动部分往上传递的就是触发的event事件了，还以usbtouchscreen的为例，回调函数为：

/*****************************************************************************
 * Generic Part
 */
static void usbtouch_process_pkt(struct usbtouch_usb *usbtouch,
                                 unsigned char *pkt, int len)
{
    struct usbtouch_device_info *type = usbtouch->type; 

    if (!type->read_data(usbtouch, pkt))
            return;

    input_report_key(usbtouch->input, BTN_TOUCH, usbtouch->touch); // 上报触摸类型 。touch为按下

    if (swap_xy) {
        input_report_abs(usbtouch->input, ABS_X, usbtouch->y);
        input_report_abs(usbtouch->input, ABS_Y, usbtouch->x);
    } else {
        input_report_abs(usbtouch->input, ABS_X, usbtouch->x);
        input_report_abs(usbtouch->input, ABS_Y, usbtouch->y); // 上报绝对坐标值
    }
    if (type->max_press)
        input_report_abs(usbtouch->input, ABS_PRESSURE, usbtouch->press);
    input_sync(usbtouch->input);   // 同步操作
}

可以看到通过 input_report_* 上报事件到input.c中，这也就是上面层次图中的箭头 9 ，初始在/kernel/include/linux/input.h：

static inline void input_report_key(struct input_dev *dev, unsigned int code, int value)
{
	input_event(dev, EV_KEY, code, !!value);
}

static inline void input_report_rel(struct input_dev *dev, unsigned int code, int value)
{
	input_event(dev, EV_REL, code, value);
}

static inline void input_report_abs(struct input_dev *dev, unsigned int code, int value)
{
	input_event(dev, EV_ABS, code, value);
}

可以看到不同的report 都调用进了input_event，只是传参不同，接下来的事就全交由input.c 来做了！

/**
 * input_event() - report new input event
 * @dev: device that generated the event
 * @type: type of the event
 * @code: event code
 * @value: value of the event
 *
 * This function should be used by drivers implementing various input
 * devices to report input events. See also input_inject_event().
 *
 * NOTE: input_event() may be safely used right after input device was
 * allocated with input_allocate_device(), even before it is registered
 * with input_register_device(), but the event will not reach any of the
 * input handlers. Such early invocation of input_event() may be used
 * to 'seed' initial state of a switch or initial position of absolute
 * axis, etc.
 */
void input_event(struct input_dev *dev,
         unsigned int type, unsigned int code, int value)
{
    unsigned long flags;

    if (is_event_supported(type, dev->evbit, EV_MAX)) {  //判断是否是注册时的event类型，驱动probe时注册input_dev时设置了能响应的event类型

        spin_lock_irqsave(&dev->event_lock, flags); //自旋锁枷锁

       add_input_randomness(type, code, value);
        input_handle_event(dev, type, code, value);  //进一步处理传上来的这个 event
        spin_unlock_irqrestore(&dev->event_lock, flags);//解锁
    }
}

可以看到在这里首先就是过滤了事件类型，这个也是在usbtouchscreen中的probe中初始化过的！

类型有如下几种：

/*
 * Event types
 */

#define EV_SYN			0x00
#define EV_KEY			0x01
#define EV_REL			0x02
#define EV_ABS			0x03
#define EV_MSC			0x04
#define EV_SW			0x05
#define EV_LED			0x11
#define EV_SND			0x12
#define EV_REP			0x14
#define EV_FF			0x15
#define EV_PWR			0x16
#define EV_FF_STATUS		0x17
#define EV_MAX			0x1f
#define EV_CNT			(EV_MAX+1)

input_handle_event：

 由上面的input_event 调入进这个handle处理。这里会根据type进行分类处理：

static void input_handle_event(struct input_dev *dev,
                   unsigned int type, unsigned int code, int value)
{
    int disposition = INPUT_IGNORE_EVENT; //初始为不做处理

    switch (type) {

    case EV_SYN:
        switch (code) {
        case SYN_CONFIG:
            disposition = INPUT_PASS_TO_ALL;
            break;

        case SYN_REPORT:
            if (!dev->sync) {
                dev->sync = true;
                disposition = INPUT_PASS_TO_HANDLERS;
            }
            break;

...

    case EV_KEY:

        if (is_event_supported(code, dev->keybit, KEY_MAX) &&  //按键code是否被keybit支持
            !!test_bit(code, dev->key) != value) {  //key是键盘当前所有键状态，测试code对应键状态，value传来事件的按键状态。此句表示按键状态应有变化

            if (value != 2) {
                __change_bit(code, dev->key);  //改变key的值以改变按键状态。
                if (value)
                    input_start_autorepeat(dev, code);  //如果按键值为按下，则开始重复按键操作。具体会不会重复，input_start_autorepeat还会根据evbit中有没有置位重复事件等判断。
                else
                    input_stop_autorepeat(dev); //如果是松开按键则应停止重复按键相关操作。
            }

            disposition = INPUT_PASS_TO_HANDLERS;
        }
        break;

...

    case EV_ABS:
        if (is_event_supported(code, dev->absbit, ABS_MAX))  //同上面一样看是否支持
            disposition = input_handle_abs_event(dev, code, &value);  //这个函数可以跟进去看，是做为筛选的，第一次是不会返回INPUT_IGNORE_EVENT ，后面如果有跟上次相同的ABS坐标就会被过滤掉，返回IGNORE
//        err("jscese display disposition vlue ==0x%x,code==0x%x, value== 0x%x\n",disposition,code,value);
        break;

...

   }

    if (disposition != INPUT_IGNORE_EVENT && type != EV_SYN)
        dev->sync = false;

    if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)
        dev->event(dev, type, code, value); 

    if (disposition & INPUT_PASS_TO_HANDLERS)
        input_pass_event(dev, type, code, value);  //更深一步调用 ，最终都是 调用到 event(**)方法

}

这里先记录整个输入系统从设备驱动到上层的关系，以及从kernel中的驱动调用到input系统中的传递过程，虽然看到调用了input.c中的一些函数传递，但是对input核心还是没多少概念，

下篇解析记录一下input这个核心模块～