I2C Data Structure

我們要搞懂一個 Linux 子系統，必須研究它的數據結構，搞懂每個結構體存儲了什么東西，才能梳理清楚該子系統的架構。

I2C 子系統有幾個主要的結構體：

I2C 控制器:i2c_adapter、i2c_algorithm、mtk_i2c

I2C 設備驅動：i2c_client、i2c_driver

I2C 傳輸：i2c_msg

i2c_adapter：i2c-core 層描述一個 I2C 控制器，假如一個芯片有 8 路 I2C bus，則有 8 個 i2c_adapter。請詳細看博主對 code 的注釋說明。

struct i2c_adapter {
 struct module *owner;
 unsigned int class; /* 該 I2C bus 支持哪些類型的從設備 */
 const struct i2c_algorithm *algo; /* the algorithm to access the bus */
 void *algo_data;

 /* data fields that are valid for all devices */
 const struct i2c_lock_operations *lock_ops;
 struct rt_mutex bus_lock;
 struct rt_mutex mux_lock;

 int timeout;/* 超過該時間無法重發 */
 int retries;/* I2C發送失敗重試次數 */
 struct device dev;  /* the adapter device */
 unsigned long locked_flags; /* owned by the I2C core */
#define I2C_ALF_IS_SUSPENDED  0
#define I2C_ALF_SUSPEND_REPORTED 1

 int nr;/*I2C bus id*/
 char name[48];
 struct completion dev_released;

 struct mutex userspace_clients_lock;
 struct list_head userspace_clients;

 struct i2c_bus_recovery_info *bus_recovery_info;
 const struct i2c_adapter_quirks *quirks;

 struct irq_domain *host_notify_domain;
 struct regulator *bus_regulator;
};

i2c_algorithm：I2C 傳輸函數合集，其中 master_xfer 是真正的傳輸函數 ，芯片原廠寫 I2C 控制器驅動時必須實現。functionality 函數會返回該 I2C 控制器支持什么通信協議，也需要實現，其他的函數即便 Linux 規定了，芯片原廠也可以不實現，因為不常用。

struct i2c_algorithm {
 int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,int num);
 int (*master_xfer_atomic)(struct i2c_adapter *adap,struct i2c_msg *msgs, int num);
 int (*smbus_xfer)(struct i2c_adapter *adap, u16 addr,unsigned short flags, char read_write,u8 command, int size, union i2c_smbus_data *data);
 int (*smbus_xfer_atomic)(struct i2c_adapter *adap, u16 addr,unsigned short flags, char read_write,u8 command, int size, union i2c_smbus_data *data);

 /* To determine what the adapter supports */
 u32 (*functionality)(struct i2c_adapter *adap);

#if IS_ENABLED(CONFIG_I2C_SLAVE)
 int (*reg_slave)(struct i2c_client *client);
 int (*unreg_slave)(struct i2c_client *client);
#endif
};

MTK 只實現了其中兩個

i2c_client：描述設備信息

struct i2c_client {
 unsigned short flags;/* I2C 傳輸標志位如下*/
#define I2C_CLIENT_PEC  0x04 /* Use Packet Error Checking */
#define I2C_CLIENT_TEN  0x10 /* we have a ten bit chip address */
/* Must equal I2C_M_TEN below */
#define I2C_CLIENT_SLAVE 0x20 /* we are the slave */
#define I2C_CLIENT_HOST_NOTIFY 0x40 /* We want to use I2C host notify */
#define I2C_CLIENT_WAKE  0x80 /* for board_info; true iff can wake */
#define I2C_CLIENT_SCCB  0x9000 /* Use Omnivision SCCB protocol */
     /* Must match I2C_M_STOP|IGNORE_NAK */

 unsigned short addr;  /* chip address - NOTE: 7bit */
     /* addresses are stored in the */
     /* _LOWER_ 7 bits  */
 char name[I2C_NAME_SIZE];
 struct i2c_adapter *adapter;/* 所處的那一路 I2C bus */
 struct device dev;  /* the device structure  */
 int init_irq;   /* irq set at initialization */
 int irq;   /* irq issued by device  */
 struct list_head detected;
#if IS_ENABLED(CONFIG_I2C_SLAVE)
 i2c_slave_cb_t slave_cb; /* callback for slave mode */
#endif
 void *devres_group_id;  /* ID of probe devres group */
};

i2c_driver：普通驅動工程師寫驅動時，必須實現其中的 probe 函數和 remove 函數，其余的函數一般用不到。

struct i2c_driver {
 unsigned int class;

 /* Standard driver model interfaces */
 int (*probe)(struct i2c_client *client, const struct i2c_device_id *id);
 int (*remove)(struct i2c_client *client);

 int (*probe_new)(struct i2c_client *client);
 void (*shutdown)(struct i2c_client *client);
 void (*alert)(struct i2c_client *client, enum i2c_alert_protocol protocol,unsigned int data);
 int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);

 struct device_driver driver;
 const struct i2c_device_id *id_table;

 int (*detect)(struct i2c_client *client, struct i2c_board_info *info);
 const unsigned short *address_list;
 struct list_head clients;
};

mtk_i2c：MTK 平臺用該結構體表示 I2C 控制器，定義在/kernel-5.10/drivers/i2c/busses/i2c-mt65xx.c

struct mtk_i2c {
 struct i2c_adapter adap; /* i2c host adapter */
 struct device *dev;
 struct completion msg_complete;

 /* set in i2c probe */
 void __iomem *base;  /* i2c base addr */
 void __iomem *pdmabase;  /* dma base address*/
 struct clk *clk_main;  /* main clock for i2c bus */
 struct clk *clk_dma;  /* DMA clock for i2c via DMA */
 struct clk *clk_pmic;  /* PMIC clock for i2c from PMIC */
 bool have_pmic;   /* can use i2c pins from PMIC */
 bool use_push_pull;  /* IO config push-pull mode */

 u16 irq_stat;   /* interrupt status */
 unsigned int clk_src_div;
 unsigned int speed_hz;  /* The speed in transfer */
 enum mtk_trans_op op;
 u16 timing_reg;
 u16 high_speed_reg;
 unsigned char auto_restart;
 bool ignore_restart_irq;
 const struct mtk_i2c_compatible *dev_comp;
};

i2c_msg：I2C 讀寫時，必須填充 i2c_msg。

標志位：寫為 0 ，讀為 I2C_M_RD，其他的 flag 大家可以參考。

I2C 單筆傳輸最大 64KB，len 的長度博主在注釋中有說明。