面试被问到IIC，总结。
Linux3.5内核中，IIC。
1 i2c_add_driver 2 i2c_register_driver 3 a. at24cxx_driver放入i2c_bus_type的drv链表 4 并且从dev链表里取出能匹配的i2c_client并调用probe 5 driver_register 6 7 8 b. 对于每一个适配器，调用__process_new_driver 9 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 10 如果存在，再调用detect进一步确定、设置，然后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 /* 判断这个设备是否存在：简单的发出S信号确定有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 // 设置info.type 27 err = driver->detect(temp_client, &info); 28 29 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, 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, 1); /* * If everything went ok (i.e. 1 msg received), return #bytes received, * else error code. */ return (ret == 1) ? 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。
