了解了i2c总线的主要结构成员及适配器、设备驱动的注册后，现在我们从上而下的来研究一下i2c总线的使用(仍然以i2c-dev.c为例)：

1、这是面向用户的虚拟字符设备所提供的所有i2c总线操作接口函数：
static const struct file_operations i2cdev_fops = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .read           = i2cdev_read,
        .write          = i2cdev_write,
        .ioctl          = i2cdev_ioctl,
        .open           = i2cdev_open,
        .release        = i2cdev_release,
};

1)drivers/i2c/i2c-dev.c
static int i2cdev_open(struct inode *inode, struct file *file)
{
        unsigned int minor = iminor(inode);
        struct i2c_client *client;
        struct i2c_adapter *adap;
        struct i2c_dev *i2c_dev;

        i2c_dev = i2c_dev_get_by_minor(minor);    //通过设备文件的从设备号查找对应的i2c_dev
        if (!i2c_dev)
                return -ENODEV;

        adap = i2c_get_adapter(i2c_dev->adap->nr);    //查找对于的adap
        if (!adap)
                return -ENODEV;

        client = kzalloc(sizeof(*client), GFP_KERNEL);    //i2c从设备描述结构体
        if (!client) {
                i2c_put_adapter(adap);
                return -ENOMEM;
        }
        snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);
        client->driver = &i2cdev_driver;

        /* registered with adapter, passed as client to user */
        client->adapter = adap;
        file->private_data = client;

        return 0;
}

注：
    i2cdev_open的主要作用是构建并初始化用于描述i2c从设备的结构体struct i2c_client。

2)drivers/i2c/i2c-dev.c
i2cdev_read
    -> i2c_master_recv
        -> i2c_transfer
            -> adap->algo->master_xfer(s3c24xx_i2c_xfer)

3)drivers/i2c/i2c-dev.c
i2cdev_write
    -> i2c_master_send
        -> i2c_transfer
            -> adap->algo->master_xfer(s3c24xx_i2c_xfer)



7)drivers/i2c/busses/i2c-s3c2410.c
s3c24xx_i2c_xfer
    -> s3c24xx_i2c_doxfer(wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5)) <----|
        -> s3c24xx_i2c_irq |
            -> i2s_s3c_irq_nextbyte |
                 -> s3c24xx_i2c_stop |
                    -> s3c24xx_i2c_master_complete(wake_up(&i2c->wait))------------------|