浅析Input 子系统

在android中，定时alarm功能是很常用的，现在来分析下怎么实现的，这里将采用自下而上的方式讲解。

输入子系统又叫input子系统。其构建非常灵活，只需要调用一些简单的函数，就可以将一个输入设备的功能呈现给应用程序。

Input子系统 主要有下面几个结构：

struct input_dev；         //表示一个输入设备，包含输入设备的一些相关信息(如支持的按键码,s设备的名称，设备支持的事件。)
                  struct input_handler；         //表示对输入事件的具体处理。为输入设备的功能实现了一个接口。输入事件最终传递到handler处理。
        struct input_handle；         用来关联struct input_dev和struct input_handler

输入子系统由驱动层，输入子系统核心层（input core）和事件处理层（event handler） 3部分组成。一个shuru事件，如键盘按键等通过驱动层-> 系统核心层->事件处理层->用户空间的顺序到达用户空间并传给应用程序使用。其中input core由内核源码下driver/input/input.c 及相关头文件实现。核心层对下提供了设备驱动的接口，对上提供了事件处理层的编程接口。输入子系统主要涉及上面三个结构体。

做linux驱动，一般用结构体来描述设备；我们需要做的是申请相应的结构体空间，然后填充相关结构体内成员；之后注册这个结构体；主要就这么三步；

struct input_dev *input_dev;
                input_dev = input_allocate_device();         //申请相应的结构体空间

input_dev ->evbit[0] = 0xb;
                  input_dev ->keybit[0xa] = 0x400;
                  input_set_abs_params(input_dev, ABS_X, 0, 0x3FF, 0, 0);
                  input_set_abs_params(input_dev, ABS_Y, 0, 0x3FF, 0, 0);
                  input_set_abs_params(input_dev, ABS_PRESSURE, 0, 1, 0, 0);
                  input_dev ->name = s3c2410ts_name;
                  input_dev ->id.bustype = BUS_RS232;
                  input_dev ->id.vendor = 0xDEAD;
                  input_dev ->id.product = 0xBEEF;
                input_dev ->id.version = S3C2410TSVERSION;         //填充相关结构体内成员；

input_register_device(input_dev);        // 注册struct input_dev这个结构体

然后跟代码会发现注册input_dev,做了如下步骤；

input_register_device()
                          -->input_attach_handler();
                                  -->input_match_device();
                                  -->handler->connect();

注册这个设备后，它回去找与它匹配的struct handler结构；找到之后调用struct handler的connect()方法；

简单的实例

#include <linux/module.h>
                  #include <linux/kernel.h>
                  #include <linux/init.h>
                  #include <linux/fs.h>
                  #include <linux/cdev.h>
                  #include <linux/irqreturn.h>
                  #include <asm/io.h>
                  #include <asm/irq.h>
                  #include <linux/input.h>
                  struct file_operations hello_fops = {
                          .owner = THIS_MODULE
                  };
                          static struct input_dev *button_dev;    /*输入设备结构体*/
                          static irqreturn_t button_interrupt(int irq, void *dummy)
                          /*中断处理函数*/
                          {
                                  input_report_key(button_dev, BTN_0, inb(BUTTON_PORT) & 1);
                                  /*向输入子系统报告产生按键事件*/
                                  input_sync(button_dev);             /*通知接收者，一个报告发送完毕*/
                                  return IRQ_HANDLED;
                          }
                          static int __init button_init(void) /*加载函数*/
                          {
                                  int error;
                                  int result;
                                  dev = MKDEV (hello_major, hello_minor);
                                  result = register_chrdev_region (dev, number_of_devices, "hello");
                                  if (result<0) {
                                  printk (KERN_WARNING "hello: can't get major number %d\n", hello_major);
                                  return result;
                                  }
                                  /* dynamic allocation */
                                  cdev_init (cdev, &hello_fops);
                                  cdev->owner = THIS_MODULE;
                                  result = cdev_add (cdev, dev, 1);
                                  if (request_irq(BUTTON_IRQ, button_interrupt, 0, "button", NULL))
                                  /*申请中断处理函数*/
                                  {
                                          /*申请失败，则打印出错信息*/
                                          printk(KERN_ERR "button.c: Can't allocate irq %d\n", button_
                                          irq);
                                          return -EBUSY;
                                  }
                                  button_dev = input_allocate_device();   /*分配一个设备结构体*/
                                  if (!button_dev)                        /*判断分配是否成功*/
                                  {
                                          printk(KERN_ERR "button.c: Not enough memory\n");
                                          error = -ENOMEM;
                                          goto err_free_irq;
                                  }
                                  button_dev->evbit[0] = BIT_MASK(EV_KEY);    /*设置按键信息*/
                                  button_dev->keybit[BIT_WORD(BTN_0)] = BIT_MASK(BTN_0);
                                  error = input_register_device(button_dev);  /*注册一个输入设备*/
                                  if (error)
                                  {
                                          printk(KERN_ERR "button.c: Failed to register device\n");
                                          goto err_free_dev;
                                  }
                                  return 0;
                                  err_free_dev:                               /*以下是错误处理*/
                                          input_free_device(button_dev);
                                  err_free_irq:
                                          free_irq(BUTTON_IRQ, button_interrupt);
                                  return error;
                          }
                          static void __exit button_exit(void)            /*卸载函数*/
                          {
                                  input_unregister_device(button_dev);        /*注销按键设备*/
                                  free_irq(BUTTON_IRQ, button_interrupt); /*释放按键占用的中断线*/
                          }
                          module_init(button_init);
                        module_exit(button_exit);