I2C 驱动核心的数据结构

1 i2c_algorithm 解析
Algorithm 代表了当前I2C adapter 的行为特征，必须能够描述adapter 的所有传输行为。
struct i2c_algorithm

{
    char name[32]; //算法名称
    unsigned int id; //算法ID
    //master_xfer 提供的是i2c_transfer 实现部分。更多的I2C adapter 工作于I2C 总线主机
    模式。
    int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg msgs[],int num);
    // smbus_xfer 提供i2c_smbus_xfer 的实现部分。只有I2C adapter 工作于SMBus 模式，需要提供。也就是说，I2C adapter 必须指定I2C 还是SMBus 其中的一个。
    int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,unsigned short flags, char read_write,u8 command, int size, union i2c_smbus_data * data);
    /* 从机模式，通常adapter 不会做从机*/
    int (*slave_send)(struct i2c_adapter *,char*,int);
    int (*slave_recv)(struct i2c_adapter *,char*,int);
    /* 类似于ioctl，实现一些设定控制功能 */
    int (*algo_control)(struct i2c_adapter *, unsigned int, unsigned long);
    /* I2C adapter 的功能函数，用户自己定义*/
    u32 (*functionality) (struct i2c_adapter *);
};
基于标准I2C bus 的adapter 采用的algorithm 必须提供master_xfer 以描述总线的行为。
2 struct i2c_adapter 解析
struct i2c_adapter

{
   char name[32]; /* 适配器的名字*/
   unsigned int id;/* == is algo->id | hwdep.struct->id, */
   /* for registered values see below */
   struct i2c_algorithm *algo;/* adapter 对应的算法*/
   void *algo_data; /*使用标准算法时，提供算法需要的特殊函数入口*/
   /* --- These may be NULL, but should increase the module use count */
   void (*inc_use)(struct i2c_adapter *);
   void (*dec_use)(struct i2c_adapter *);
   /* --- administration stuff. */
   int (*client_register)(struct i2c_client *);
   int (*client_unregister)(struct i2c_client *);
   void *data; /* private data for the adapter */
   /* some data fields that are used by all types */
   /* these data fields are readonly to the public */
   /* and can be set via the i2c_ioctl call */
   /* data fields that are valid for all devices */
   struct semaphore lock;
   unsigned int flags;/* flags specifying div. data */
   struct i2c_client *clients[I2C_CLIENT_MAX]; //adapter 对应的I2C bus 上的client 列表
   int client_count;
   int timeout; //超时时间
   int retries; //重试次数
   #ifdef CONFIG_PROC_FS
   /* No need to set this when you initialize the adapter */
   int inode;
   #endif /* def CONFIG_PROC_FS */
}
如何给adapter 选择合适的algorithm？内核已经提供了若干标准的algorithm，当我们使用标
准algorithm 时，必须提供algo_data 入口。多数情况，adapter 需要的algorithm 都是自定义
的，这是algo_data 可以为空。
3 i2c_driver 解析
struct i2c_driver

{
   char name[32]; //驱动的名称
   int id; //驱动的ID
   unsigned int flags; /* div., see below */
   /* 寻找当前client 对应的adapter 是否存在。
   若存在，调用 i2c_attach_client 更新adapter 的client
   */
   int (*attach_adapter)(struct i2c_adapter *);
   /* tells the driver that a client is about to be deleted & gives it
   * the chance to remove its private data. Also, if the client struct
   * has been dynamically allocated by the driver in the function above,
   * it must be freed here.
   */
   int (*detach_client)(struct i2c_client *);
   /* 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);
   /* These two are mainly used for bookkeeping & dynamic unloading of
   * kernel modules. inc_use tells the driver that a client is being
   * used by another module & that it should increase its ref. counter.
   * dec_use is the inverse operation.
   * NB: Make sure you have no circular dependencies, or else you get a
   * deadlock when trying to unload the modules.
   * You should use the i2c_{inc,dec}_use_client functions instead of
   * calling this function directly.
   */
   void (*inc_use)(struct i2c_client *client);
   void (*dec_use)(struct i2c_client *client);
};

4 i2c_client 解析
/*
* i2c_client identifies a single device (i.e. chip) that is connected to an
* i2c bus. The behaviour is defined by the routines of the driver. This
* function is mainly used for lookup & other admin. functions.
*/
struct i2c_client

{
   char name[32]; //client 名字
   int id; //client ID
   unsigned int flags; /* div., see below */
   unsigned int addr; /* client 地址: 7bit */
   /* addresses are stored in the */
   /* _LOWER_ 7 bits of this char */
   /* addr: unsigned int to make lm_sensors i2c-isa adapter work
    more cleanly. It does not take any more memory space, due to
   alignment considerations */
   struct i2c_adapter *adapter; /* client 所在I2C bus 对应的adapter */
   struct i2c_driver *driver; /* client 使用的驱动 */
   void *data; /* for the clients */
   int usage_count; /* How many accesses currently */
   /* to the client */
};