面試被問到IIC，總結。

時間 2019-12-01

原文原文鏈接

Linux3.5內核中，IIC。node

 1 i2c_add_driver
 2     i2c_register_driver
 3         a. at24cxx_driver放入i2c_bus_type的drv鏈表
 4            而且從dev鏈表裏取出能匹配的i2c_client並調用probe
 5         driver_register
 6             
 7         
 8         b. 對於每個適配器，調用__process_new_driver
 9            對於每個適配器，調用它的函數肯定address_list裏的設備是否存在
10            若是存在，再調用detect進一步肯定、設置，而後i2c_new_device
11         /* Walk the adapters that are already present */
12         i2c_for_each_dev(driver, __process_new_driver);
13             __process_new_driver
14                 i2c_do_add_adapter
15                     /* Detect supported devices on that bus, and instantiate them */
16                     i2c_detect(adap, driver);
17                         for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {
18                             err = i2c_detect_address(temp_client, driver);
19                                         /* 判斷這個設備是否存在：簡單的發出S信號肯定有ACK */
20                                         if (!i2c_default_probe(adapter, addr))
21                                             return 0;
22                                         
23                                         memset(&info, 0, sizeof(struct i2c_board_info));
24                                         info.addr = addr;    
25                                         
26                                         // 設置info.type
27                                         err = driver->detect(temp_client, &info);
28                     
29                                         i2c_new_device

使用讀寫IIC器件的函數接口：數組

/**
*I2c_Master_發送-在主傳輸模式下發出單個I2c消息
*@客戶端：從設備的句柄
*@buf：將寫入從系統的數據
*@計數：要寫入的字節數，必須小於64K，由於msg.len是u16
*返回負的errno，或者返回寫入的字節數。
*/

/**
 * 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, 1);

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

/**
*I2c_Master_Recv-在主接收模式下發出單個I2c消息
*@客戶端：從設備的句柄
*@buf：從從屬服務器讀取數據的存儲位置
*@計數：要讀取的字節數，必須小於64K，由於msg.len是u16
*返回負的errno，不然返回讀取的字節數。
*/

/**
 * 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, 1);

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

本身寫的時候：服務器

/**
*結構I2c_Board_信息-設備建立模板
*@類型：芯片類型，初始化i2c_client.name
*@標誌：初始化i2c_client.flags
*@地址：存儲在I2c_client.addr中
*@平臺數據：存儲在i2c_client.dev.platform_data
*@archdata：複製到i2c_client.dev.archdata
*@節點：指向OpenFirmware設備節點的指針
*@IRQ：存儲在i2c_client.irq中
*
*I2c實際上不支持硬件探測，儘管控制器和
*設備可能可以使用I2c總線快速判斷是否存在
*位於給定地址的設備。司機一般須要更多的信息
*如芯片類型、配置、相關IRQ等。
*i2c_board_info用於構建列出i2c設備的信息表。
*那是存在的。此信息用於增加驅動程序模型樹。
*對於主板，這是使用i2c_register_board_info（）靜態完成的。
*總線號標識還沒有提供的適配器。對於附加板，
*I2c_new_device（）使用已知的適配器動態執行此操做。
*/
/**
 * 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;
};