嵌入式[基础] Linux下IIC设备驱动描述

IIC特点

IIC总线架构分析

设备驱动层组件 linux*/drivers/i2c/i2c-dev.c

设备核心层组件 linux*/drivers/i2c/i2c-core.c

设备总线驱动层组件 linux*/drivers/i2c/busses/i2c-xxx.c 不同芯片实现不同

这三个文件的目的是为了相互配合实现操作相应的外围设备

IIC核心层分析

核心层文件 i2c-core-base.c

postcore_initcall(i2c_init); i2c注册函数

i2c_init函数分析

/* 注册i2c设备，最终形成一个i2c的驱动链表 */
static int __init i2c_init(void)
{
    // 注册一根i2c物理总线
    retval = bus_register(&i2c_bus_type); ----|
                                              |
    struct bus_type i2c_bus_type = { dev_groups = i2c_groups;

	/* Keep track of adapters which will be added or removed later */
	res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);
	if (res)
		goto out_unreg_class;

	/* Bind to already existing adapters right away */
	/* 绑定适配器，绑定具体操作的哪一台设备，搜索I2C总线的设备链表，
           每搜索到一个设备，都会调用i2cdev_attach_adapter */
        i2c_for_each_dev(NULL, i2c_dev_attach_adapter);

	return 0;

out_unreg_class:
	class_destroy(i2c_dev_class);
out_unreg_chrdev:
	unregister_chrdev_region(MKDEV(I2C_MAJOR, 0), I2C_MINORS);
out:
	pr_err("Driver Initialisation failedn");
	return res;
}

static int i2cdev_attach_adapter(struct device *dev)
{
	struct i2c_adapter *adap;
	struct i2c_dev *i2c_dev;
        
        /* 判断是否是适配器，如果不是则返回 */
	if (dev->type != &i2c_adapter_type)
		return NOTIFY_DONE;
                
	i2c_dev = get_free_i2c_dev(adap);
        /* 初始化一个i2c设备链表节点 */
        device_initialize(&i2c_dev->dev);
        /* 设置i2c设备名称 /dev/i2c-0 dev/i2c-1... */
	i2c_dev->dev.devt = MKDEV(I2C_MAJOR, adap->nr);
	i2c_dev->dev.class = i2c_dev_class;
	i2c_dev->dev.parent = &adap->dev;
	i2c_dev->dev.release = i2cdev_dev_release;
}

iic开发涉及到的设备层的重要函数

int i2c_master_send(const struct i2c_client *client,
				  const char *buf, int count) 发送函数 字节发送
int i2c_master_recv(const struct i2c_client *client,
				  char *buf, int count) 接收函数 字节接收
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num); 传输一个i2c数据包
int i2c_register_board_info(int busnum, struct i2c_board_info const *info,
			unsigned n); 注册i2c板级信息，如i2c的oled屏幕名称

int i2c_add_adapter(struct i2c_adapter *adap); 注册/控制器
void i2c_del_adapter(struct i2c_adapter *adap); 注销/控制器
int i2c_add_numbered_adapter(struct i2c_adapter *adap);

注册/注销i2c驱动
int i2c_register_driver(struct module *owner, struct i2c_driver *driver);
void i2c_del_driver(struct i2c_driver *driver);

注册/注销i2c设备