# 通用驱动i2c-dev分析

参考资料：

* Linux驱动程序: `drivers/i2c/i2c-dev.c`
* I2C-Tools-4.2: `https://mirrors.edge.kernel.org/pub/software/utils/i2c-tools/`
* AT24cxx.pdf

通用的i2c-dev驱动走的还是字符设备驱动那一套，怎么编写字符设备驱动程序？

* 创建file_operations结构体吗，在里面填充drv_open/drv_read/drv_ioctl等函数
* 入口函数调用`register_chrdev(major, &fops, name)`注册file_operations结构体
* 创建类class_create
* 在类型创建设备节点 device_create



## i2c-dev.c注册过程分析

### i2c-dev驱动的注册过程

![image-20210226164128588](media/047_i2c-dev_register.png)



### file_operations函数分析

`i2c-dev.c`的核心：

```c
static const struct file_operations i2cdev_fops = {
	.owner		= THIS_MODULE,
	.llseek		= no_llseek,
	.read		= i2cdev_read,
	.write		= i2cdev_write,
	.unlocked_ioctl	= i2cdev_ioctl,
	.compat_ioctl	= compat_i2cdev_ioctl,
	.open		= i2cdev_open,
	.release	= i2cdev_release,
};
```

主要的系统调用：`open, ioctl`：
![image-20210226165250492](media/048_i2c-dev_interface.png)

#### i2cdev_open

![image-20210226170350844](media/049_i2cdev_open.png)



#### i2cdev_ioctl: 设置器件地址 I2C_SLAVE/I2C_SLAVE_FORCE

![image-20210226172800990](media/050_ioctl_I2C_SLAVE_FORCE.png)



#### i2cdev_ioctl: 传输数据i2c的形式 I2C_RDWR

![image-20210226173625871](media/051_ioctl_I2C_RDWR.png)

#### i2cdev_ioctl: 传输数据smbus的形式I2C_SMBUS

![](media/052_ioctl_I2C_SMBUS.png)



#### 总结

![](media/053_app_to_i2c_driver.png)