Linux输入子系统

为何需要input子系统

Linux系统支持的许多设备，都是输入性的设备，如按键、触摸屏、键盘、鼠标。本质上都是一个个的字符设备驱动，Linux系统为这些设备统一管理实现了input子系统，方便驱动和应用的开发。

input子系统软件架构

linux输入子系统主要分三层：driver层，core层， event hander层。
Driver层根据core层提供的接口，向上报告发生的按键动作。然后core根据驱动的类型，分派这个报告给对应的event hander进行处理。
event hander层把数据变化反应到设备模型的文件中（事件缓冲区）。并通知在这些设备模型文件上等待的进程。

input子系统工作原理

注册匹配过程

device注册：

int input_register_device(struct input_dev *dev){    ...    //加到input_dev_list    list_add_tail(&dev->node, &input_dev_list);    //从input_handler_list匹配    list_for_each_entry(handler, &input_handler_list, node)        input_attach_handler(dev, handler);    ...}

handle注册：

int input_register_handler(struct input_handler *handler){    struct input_dev *dev;    int error;    error = mutex_lock_interruptible(&input_mutex);    if (error)        return error;    INIT_LIST_HEAD(&handler->h_list);    //加入input_handler_list    list_add_tail(&handler->node, &input_handler_list);    //依次对input_dev_list的dev做匹配    list_for_each_entry(dev, &input_dev_list, node)        input_attach_handler(dev, handler);    input_wakeup_procfs_readers();    mutex_unlock(&input_mutex);    return 0;}

input_attach_handler就是根据id匹配的过程。

读取过程

static ssize_t evdev_read(struct file *file, char __user *buffer,
size_t count, loff_t *ppos)
{
struct evdev_client *client = file->private_data;
struct evdev *evdev = client->evdev;
struct input_event event;
size_t read = 0;
int error;

if (count != 0 && count < input_event_size())    return -EINVAL;for (;;) {    if (!evdev->exist)        return -ENODEV;    if (client->packet_head == client->tail &&        (file->f_flags & O_NONBLOCK))        return -EAGAIN;    /*     * count == 0 is special - no IO is done but we check     * for error conditions (see above).     */    if (count == 0)        break;    while (read + input_event_size() <= count &&           evdev_fetch_next_event(client, &event)) {        if (input_event_to_user(buffer + read, &event))            return -EFAULT;        read += input_event_size();    }    if (read)        break;    //睡眠等待数据    if (!(file->f_flags & O_NONBLOCK)) {        error = wait_event_interruptible(evdev->wait,                client->packet_head != client->tail ||                !evdev->exist);        if (error)            return error;    }}return read;

}

事件上报

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_sync(struct input_dev *dev){    input_event(dev, EV_SYN, SYN_REPORT, 0);}

其实都是调用到input_event，最后调用handler->event

static void evdev_events(struct input_handle *handle,             const struct input_value *vals, unsigned int count){    struct evdev *evdev = handle->private;    struct evdev_client *client;    ktime_t time_mono, time_real;    time_mono = ktime_get();    time_real = ktime_sub(time_mono, ktime_get_monotonic_offset());    rcu_read_lock();    client = rcu_dereference(evdev->grab);    if (client)        evdev_pass_values(client, vals, count, time_mono, time_real);    else        list_for_each_entry_rcu(client, &evdev->client_list, node)            evdev_pass_values(client, vals, count,                      time_mono, time_real);    rcu_read_unlock();}static void evdev_pass_values(struct evdev_client *client,            const struct input_value *vals, unsigned int count,            ktime_t mono, ktime_t real){    struct evdev *evdev = client->evdev;    const struct input_value *v;    struct input_event event;    bool wakeup = false;    event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ?                      mono : real);    /* Interrupts are disabled, just acquire the lock. */    spin_lock(&client->buffer_lock);    for (v = vals; v != vals + count; v++) {        event.type = v->type;        event.code = v->code;        event.value = v->value;        __pass_event(client, &event);        if (v->type == EV_SYN && v->code == SYN_REPORT)            wakeup = true;    }    spin_unlock(&client->buffer_lock);    if (wakeup)        wake_up_interruptible(&evdev->wait);//唤醒进程}

如何写input子系统设备驱动

分配一个input_dev结构体

ts->input_dev = input_allocate_device();

设置

ts->input_dev->evbit[0] = BIT_MASK(EV_SYN) | BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS) ;ts->input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);ts->input_dev->absbit[0] = BIT(ABS_X) | BIT(ABS_Y) | BIT(ABS_PRESSURE);input_set_abs_params(ts->input_dev, ABS_X, 0, SCREEN_MAX_X, 0, 0);input_set_abs_params(ts->input_dev, ABS_Y, 0, SCREEN_MAX_Y, 0, 0);input_set_abs_params(ts->input_dev, ABS_PRESSURE, 0, 255, 0, 0);

注册

ret = input_register_device(ts->input_dev);

硬件相关的代码，比如在中断服务程序里上报事件

static irqreturn_t goodix_ts_irq_hanbler(int irq, void *dev_id){    struct goodix_ts_data *ts = (struct goodix_ts_data *)dev_id;    dprintk(DEBUG_INT_INFO,"==========------TS Interrupt-----============\n");    queue_work(goodix_wq, &ts->work);    return IRQ_HANDLED;}static void goodix_ts_work_func(struct work_struct *work){    for (idx= 0; idx < GTP_MAX_KEY_NUM; idx++){        input_report_key(ts->input_dev, touch_key_array[idx], key_value & (0x01<<idx));    }    //input_report_key(ts->input_dev, BTN_TOUCH, (touch_num || key_value));    input_sync(ts->input_dev);}