Linux内核I2C子系统驱动(一)

I2C子系统驱动（一）

一、I2C体系结构

Linux的I2C体系结构分为3个组成部分：I2C核心、I2C总线驱动、I2C设备驱动，如下图所示。I2C核心提供总线驱动和设备驱动的注册、注销方法，algorithm；I2C总线驱动对硬件体系结构中适配器的实现，主要包括适配器i2c_adapter、适配器通信算法i2c_algorithm，如果CPU集成了I2C控制器并且linux内核支持这个CPU，那么总线驱动就不用管，比如S3C2440就属于这类情况，在后文中我们将分析它的总线驱动；I2C设备驱动是具体的一个设备(如AT24C02)，挂接在CPU控制的I2C适配器的设备驱动，有了这部分驱动才能使用控制器操作该设备，设备驱动主要包括i2c_driver
和i2c_client数据结构。



在linux-2.6.32.2的include/linux/i2c.h中定义了i2c_adapter、i2c_algorithm、i2c_driver、i2c_client数据结构如下所示，这4个结构体相互之间的关系。

[cpp] view plaincopyprint?struct i2c_adapter {

struct module *owner;

unsigned int id;

unsigned int class; /* classes to allow probing for */

const struct i2c_algorithm *algo; /* the algorithm to access the bus总线通信方法结构体指针 */

void *algo_data; /* algorithm数据 */

/* data fields that are valid for all devices */

u8 level; /* nesting level for lockdep */

struct mutex bus_lock;

int timeout; /* in jiffies */

int retries; /* 重试次数 */

struct device dev; /* the adapter device */

int nr;

char name[48];

struct completion dev_released;

};

struct i2c_algorithm {

int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,

int num); /*i2c传输函数指针*/

int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,

unsigned short flags, char read_write,

u8 command, int size, union i2c_smbus_data *data); /*smbus传输函数指针*/

/* To determine what the adapter supports */

u32 (*functionality) (struct i2c_adapter *); /*返回适配器支持的功能*/

};

struct i2c_driver {

unsigned int class;

int (*attach_adapter)(struct i2c_adapter *); /*依附i2c_adapter函数指针*/

int (*detach_adapter)(struct i2c_adapter *); /*脱离i2c_adapter函数指针*/

/* Standard driver model interfaces */

int (*probe)(struct i2c_client *, const struct i2c_device_id *);

int (*remove)(struct i2c_client *);

/* driver model interfaces that don't relate to enumeration */

void (*shutdown)(struct i2c_client *);

int (*suspend)(struct i2c_client *, pm_message_t mesg);

int (*resume)(struct i2c_client *); /* probe，remove，suspend，resume驱动方法重要成员函数 */

/* a ioctl like command that can be used to perform specific functions

* with the device.

*/

int (*command)(struct i2c_client *client, unsigned int cmd, void *arg); /*类似ioctl*/

struct device_driver driver;

const struct i2c_device_id *id_table; /* 驱动支持多个设备，这里面就要包含这些设备的ID */

/* Device detection callback for automatic device creation */

int (*detect)(struct i2c_client *, int kind, struct i2c_board_info *); /*i2c client脱离函数指针*/

const struct i2c_client_address_data *address_data;

struct list_head clients;

};

struct i2c_client {

unsigned short flags; /* div., see below */

unsigned short addr; /* chip address - NOTE: 7bit 芯片地址 */

/* addresses are stored in the */

/* _LOWER_ 7 bits */

char name[I2C_NAME_SIZE];

struct i2c_adapter *adapter; /* the adapter we sit on 依附的i2c_adapter */

struct i2c_driver *driver; /* and our access routines 依附的i2c_driver */

struct device dev; /* the device structure */

int irq; /* irq issued by device */

struct list_head detected;

};

struct i2c_adapter {

struct module *owner;

unsigned int id;

unsigned int class; /* classes to allow probing for */

const struct i2c_algorithm *algo; /* the algorithm to access the bus总线通信方法结构体指针 */

void *algo_data; /* algorithm数据 */

/* data fields that are valid for all devices */

u8 level; /* nesting level for lockdep */

struct mutex bus_lock;

int timeout; /* in jiffies */

int retries; /* 重试次数 */

struct device dev; /* the adapter device */

int nr;

char name[48];

struct completion dev_released;

};

struct i2c_algorithm {

int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,

int num); /*i2c传输函数指针*/

int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,

unsigned short flags, char read_write,

u8 command, int size, union i2c_smbus_data *data); /*smbus传输函数指针*/

/* To determine what the adapter supports */

u32 (*functionality) (struct i2c_adapter *); /*返回适配器支持的功能*/

};

struct i2c_driver {

unsigned int class;

int (*attach_adapter)(struct i2c_adapter *); /*依附i2c_adapter函数指针*/

int (*detach_adapter)(struct i2c_adapter *); /*脱离i2c_adapter函数指针*/

/* Standard driver model interfaces */

int (*probe)(struct i2c_client *, const struct i2c_device_id *);

int (*remove)(struct i2c_client *);

/* driver model interfaces that don't relate to enumeration */

void (*shutdown)(struct i2c_client *);

int (*suspend)(struct i2c_client *, pm_message_t mesg);

int (*resume)(struct i2c_client *); /* probe，remove，suspend，resume驱动方法重要成员函数 */

/* a ioctl like command that can be used to perform specific functions

* with the device.

*/

int (*command)(struct i2c_client *client, unsigned int cmd, void *arg); /*类似ioctl*/

struct device_driver driver;

const struct i2c_device_id *id_table; /* 驱动支持多个设备，这里面就要包含这些设备的ID */

/* Device detection callback for automatic device creation */

int (*detect)(struct i2c_client *, int kind, struct i2c_board_info *); /*i2c client脱离函数指针*/

const struct i2c_client_address_data *address_data;

struct list_head clients;

};

struct i2c_client {

unsigned short flags; /* div., see below */

unsigned short addr; /* chip address - NOTE: 7bit 芯片地址 */

/* addresses are stored in the */

/* _LOWER_ 7 bits */

char name[I2C_NAME_SIZE];

struct i2c_adapter *adapter; /* the adapter we sit on 依附的i2c_adapter */

struct i2c_driver *driver; /* and our access routines 依附的i2c_driver */

struct device dev; /* the device structure */

int irq; /* irq issued by device */

struct list_head detected;

};1、i2c_adapter 与i2c_algorithm，i2c_adapter 对应于物理上的一个适配器，而i2c_algorithm对应一套通信方法。一个I2C适配器需要i2c_algorithm中提供的通信函数来控制适配器上产生特定的访问周期。缺少i2c_algorithm 的i2c_adapter 什么也做不了，因此i2c_adapter 中包含其使用的i2c_algorithm的指针。i2c_algorithm 中的关键函数master_xfer()用于产生I2C 访问周期需要的信号，以i2c_msg（即I2C消息）为单位。i2c_msg结构体也非常关键。

struct i2c_msg {

__u16 addr; /* slave address */

__u16 flags;

#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */

#define I2C_M_RD 0x0001 /* read data, from slave to master */

#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */

#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */

#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */

#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */

#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */

__u16 len; /* msg length */

__u8 *buf; /* pointer to msg data */

};

2、i2c_driver 与i2c_client，i2c_driver 对应一套驱动方法，是纯粹的用于辅助作用的数据结构，它不对应于任何的物理实体。i2c_client对应于真实的物理设备，每个I2C设备都需要一个i2c_client来描述。i2c_client一般被包含在I2C字符设备的私有信息结构体中。

3、i2c_adpater 与i2c_client，i2c_adpater 与i2c_client 的关系与I2C 硬件体系中适配器和设备的关系一致，即i2c_client 依附于i2c_adpater。

二、I2C核心

I2C核心是总线驱动和设备驱动的纽带，源码位于drivers/i2c/i2c-core.c,它并不依赖于硬件平台的接口函数，I2C核心中一些重要函数如下：

增加/删除i2c_adapter

int i2c_add_adapter(struct i2c_adapter *adapter)

int i2c_del_adapter(struct i2c_adapter *adapter)

增加/删除i2c_driver

int i2c_register_driver(struct module *owner, struct i2c_driver *driver)

int i2c_add_driver(struct i2c_driver *driver) //调用i2c_register_driver

void i2c_del_driver(struct i2c_driver *driver)

增加/删除i2c_client

struct i2c_client *i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)

void i2c_unregister_device(struct i2c_client *client)

注：在2.6.30版本之前使用的是i2c_attach_client()和i2c_detach_client()函数。之后attach被merge到了i2c_new_device中，而detach直接被unresister取代。实际上这两个函数内部都是调用了device_register()和device_unregister()

I2C传输、发送接收

int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)

int i2c_master_send(struct i2c_client *client,const char *buf ,int count)

int i2c_master_recv(struct i2c_client *client, char *buf ,int count)

i2c_transfer()函数用于进行I2C 适配器和I2C 设备之间的一组消息交互，i2c_master_send()函数和i2c_master_recv()函数内部会调用i2c_transfer()函数分别完成一条写消息和一条读消息，i2c_transfer()本身不能喝硬件完成消息交互，它寻找i2c_adapter对应的i2c_algorithm，要实现数据传送就要实现i2c_algorithm的master_xfer()，在总线驱动中就是重点。