i2c總線使用
了解了i2c總線的主要結構成員及適配器、設備驅動的註冊後，現在我們從上而下的來研究一下i2c總線的使用(仍然以i2c-dev.c為例)：

1、這是面向用戶的虛擬字符設備所提供的所有i2c總線操作接口函數：
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); //通過設備文件的從設備號查找對應的i2c_dev
        if (!i2c_dev)
                return -ENODEV;

        adap = i2c_get_adapter(i2c_dev->adap->nr); //查找對於的adap
        if (!adap)
                return -ENODEV;

        client = kzalloc(sizeof(*client), GFP_KERNEL); //i2c從設備描述結構體
        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的主要作用是構建並初始化用於描述i2c從設備的結構體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))------------------|
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