面试被问到IIC，总结。

Linux3.5内核中，IIC。

 i2c_add_driver
     i2c_register_driver
         a. at24cxx_driver放入i2c_bus_type的drv链表
            并且从dev链表里取出能匹配的i2c_client并调用probe
         driver_register

         b. 对于每一个适配器，调用__process_new_driver
            对于每一个适配器，调用它的函数确定address_list里的设备是否存在
            如果存在，再调用detect进一步确定、设置，然后i2c_new_device
         /* Walk the adapters that are already present */
         i2c_for_each_dev(driver, __process_new_driver);
             __process_new_driver
                 i2c_do_add_adapter
                     /* Detect supported devices on that bus, and instantiate them */
                     i2c_detect(adap, driver);
                         for (i = ; address_list[i] != I2C_CLIENT_END; i += ) {
                             err = i2c_detect_address(temp_client, driver);
                                         /* 判断这个设备是否存在：简单的发出S信号确定有ACK */
                                         if (!i2c_default_probe(adapter, addr))
                                             return ;

                                         memset(&info, , sizeof(struct i2c_board_info));
                                         info.addr = addr;    

                                         // 设置info.type
                                         err = driver->detect(temp_client, &info);

                                         i2c_new_device

使用读写IIC器件的函数接口：

/**
*I2c_Master_发送-在主传输模式下发出单个I2c消息
*@客户端：从设备的句柄
*@buf：将写入从系统的数据
*@计数：要写入的字节数，必须小于64K，因为msg.len是u16
*返回负的errno，或者返回写入的字节数。
*/

/**
 * i2c_master_send - issue a single I2C message in master transmit mode
 * @client: Handle to slave device
 * @buf: Data that will be written to the slave
 * @count: How many bytes to write, must be less than 64k since msg.len is u16
 *
 * Returns negative errno, or else the number of bytes written.
 */
int i2c_master_send(const struct i2c_client *client, const char *buf, int count)
{
    int ret;
    struct i2c_adapter *adap = client->adapter;
    struct i2c_msg msg;

    msg.addr = client->addr;
    msg.flags = client->flags & I2C_M_TEN;
    msg.len = count;
    msg.buf = (char *)buf;

    ret = i2c_transfer(adap, &msg, );

    /*
     * If everything went ok (i.e. 1 msg transmitted), return #bytes
     * transmitted, else error code.
     */
    return (ret == ) ? count : ret;
}

/**
*I2c_Master_Recv-在主接收模式下发出单个I2c消息
*@客户端：从设备的句柄
*@buf：从从属服务器读取数据的存储位置
*@计数：要读取的字节数，必须小于64K，因为msg.len是u16
*返回负的errno，否则返回读取的字节数。
*/

/**
 * i2c_master_recv - issue a single I2C message in master receive mode
 * @client: Handle to slave device
 * @buf: Where to store data read from slave
 * @count: How many bytes to read, must be less than 64k since msg.len is u16
 *
 * Returns negative errno, or else the number of bytes read.
 */
int i2c_master_recv(const struct i2c_client *client, char *buf, int count)
{
    struct i2c_adapter *adap = client->adapter;
    struct i2c_msg msg;
    int ret;

    msg.addr = client->addr;
    msg.flags = client->flags & I2C_M_TEN;
    msg.flags |= I2C_M_RD;
    msg.len = count;
    msg.buf = buf;

    ret = i2c_transfer(adap, &msg, );

    /*
     * If everything went ok (i.e. 1 msg received), return #bytes received,
     * else error code.
     */
    return (ret == ) ? count : ret;
}

自己写的时候：

/**
*结构I2c_Board_信息-设备创建模板
*@类型：芯片类型，初始化i2c_client.name
*@标志：初始化i2c_client.flags
*@地址：存储在I2c_client.addr中
*@平台数据：存储在i2c_client.dev.platform_data
*@archdata：复制到i2c_client.dev.archdata
*@节点：指向OpenFirmware设备节点的指针
*@IRQ：存储在i2c_client.irq中
*
*I2c实际上不支持硬件探测，尽管控制器和
*设备可能能够使用I2c总线快速判断是否存在
*位于给定地址的设备。司机通常需要更多的信息
*如芯片类型、配置、相关IRQ等。
*i2c_board_info用于构建列出i2c设备的信息表。
*那是存在的。此信息用于增长驱动程序模型树。
*对于主板，这是使用i2c_register_board_info（）静态完成的。
*总线号标识尚未提供的适配器。对于附加板，
*I2c_new_device（）使用已知的适配器动态执行此操作。
*/
/**
 * struct i2c_board_info - template for device creation
 * @type: chip type, to initialize i2c_client.name
 * @flags: to initialize i2c_client.flags
 * @addr: stored in i2c_client.addr
 * @platform_data: stored in i2c_client.dev.platform_data
 * @archdata: copied into i2c_client.dev.archdata
 * @of_node: pointer to OpenFirmware device node
 * @irq: stored in i2c_client.irq
 *
 * I2C doesn't actually support hardware probing, although controllers and
 * devices may be able to use I2C_SMBUS_QUICK to tell whether or not there's
 * a device at a given address.  Drivers commonly need more information than
 * that, such as chip type, configuration, associated IRQ, and so on.
 *
 * i2c_board_info is used to build tables of information listing I2C devices
 * that are present.  This information is used to grow the driver model tree.
 * For mainboards this is done statically using i2c_register_board_info();
 * bus numbers identify adapters that aren't yet available.  For add-on boards,
 * i2c_new_device() does this dynamically with the adapter already known.
 */
struct i2c_board_info {
        char            type[I2C_NAME_SIZE];
        unsigned short  flags;
        unsigned short  addr;
        void            *platform_data;
        struct dev_archdata     *archdata;
        struct device_node *of_node;
        int             irq;
};

写好  i2c_register_board_info smdk4x12_i2c_devs = {  }；

i2c_register_board_info(i2c_register_board_info）；　　　　//注册硬件信息。

platform_add_devices（smdk4x12_devices）   //smdk4x12_devices是放的所有platform_device结构体数组。