# 检测当前系统有几组i2c总线
i2cdetect -l
# 查看i2c-0接口上的设备
i2cdetect -y -a 0 # Force scanning of non-regular addresses
i2cdetect -y -r 0
# 读取指定设备的全部寄存器的值
i2cdump -f -y 0 0x68
# 读取指定i2c设备的某个寄存器的值，如下读取i2c-0地址为0x68器件中的0x01寄存器
i2cget -f -y 0 0x68 0x01
# 写入指定i2c设备的某个寄存器的值，如下写入i2c-0地址为0x68器件中的0x01寄存器值为0x6f
i2cset -f -y 0 0x68 0x01 0x6f
# 写入i2c-0地址为0x50的eeprom，从偏移为0x64地址读8个byte。
i2ctransfer -f -y 0 w1@0x50 0x64 r8

struct i2c_adapter {
	struct module *owner;
	unsigned int class;		  /* classes to allow probing for */
	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;			/* in jiffies */
	int retries;
	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;
	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 i2c_algorithm {
	int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,
			   int num);
  	// 功能跟master_xfer一样，在atomic context环境下使用
	int (*master_xfer_atomic)(struct i2c_adapter *adap,
				   struct i2c_msg *msgs, int num);
    // 实现SMBus传输，如果不提供这个函数，SMBus传输会使用master_xfer来模拟
	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)
  	// reg_slave就是把一个i2c_client注册到I2C Adapter，就是让这个I2C Adapter模拟该i2c_client
	int (*reg_slave)(struct i2c_client *client);
	int (*unreg_slave)(struct i2c_client *client);
#endif
};

struct i2c_msg {
	__u16 addr;	/* slave address*/
	__u16 flags;
#define I2C_M_RD		0x0001	/* read data, from slave to master */
					/* I2C_M_RD is guaranteed to be 0x0001! */
#define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
#define I2C_M_DMA_SAFE		0x0200	/* the buffer of this message is DMA safe */
					/* makes only sense in kernelspace */
					/* userspace buffers are copied anyway */
#define I2C_M_RECV_LEN		0x0400	/* length will be first received byte */
#define I2C_M_NO_RD_ACK		0x0800	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK	0x1000	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR	0x2000	/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NOSTART		0x4000	/* if I2C_FUNC_NOSTART */
#define I2C_M_STOP		0x8000	/* if I2C_FUNC_PROTOCOL_MANGLING */
	__u16 len;		/* msg length				*/
	__u8 *buf;		/* pointer to msg data			*/
};

&i2c1 {
        clock-frequency = <100000>;
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_i2c1>;
        status = "okay";
        …
        pmic: pf0100@08 {
                compatible = "fsl,pfuze100";
                …
        };

&hdmi {
       ddc-i2c-bus = <&i2c2>;
        status = "okay";
};

adap = of_parse_phandle(dev->of_node, "ddc-i2c-bus", 0);
if (adap) {
        panel->adap = of_find_i2c_adapter_by_node(adap); //获取i2c adapter指针
        of_node_put(adap);
}

struct i2c_client {
	unsigned short flags;		/* flags，指示该I2C slave device一些特性 */
#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;		/* 该设备的7-bit的slave地址。	*/
					/* addresses are stored in the	*/
					/* _LOWER_ 7 bits		*/
	char name[I2C_NAME_SIZE];
	struct i2c_adapter *adapter;	/* 该设备所在的I2C controller	*/
	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
};

xxx:xxx@08 {
        reg = <0x08>;                               /* 对应struct i2c_client中的‘addr’*/
        interrupts = <16 8>;                       /* 对应struct i2c_client中的‘irq’*/
        wakeup-source;                             /* 对应flags中的I2C_CLIENT_WAKE */
};

dw_i2c_plat_probe()
  	struct dw_i2c_dev *dev;
  	dw_i2c_plat_request_regs(dev);
		dev->base = devm_platform_ioremap_resource(pdev, 0);
	i2c_parse_fw_timings(&pdev->dev, t, false);
	i2c_dw_configure();
          i2c_dw_configure_slave();
          i2c_dw_configure_master(); // 设置一些dev->func dev->master_cfg等属性后续使用
     i2c_dw_probe()
          i2c_dw_probe_slave();
		 i2c_dw_probe_master();

i2c_dw_probe_master(struct dw_i2c_dev *dev)
  	dev->init = i2c_dw_init_master;
	dev->disable = i2c_dw_disable;
	dev->disable_int = i2c_dw_disable_int;
	i2c_dw_init_regmap();
    i2c_dw_set_timings_master(); //设置standard/fast h/lcnt
		i2c_dw_set_sda_hold(); // 设置sda_hold,不过rts直接在dev->init中设置为20
    i2c_dw_set_fifo_size(); //设置tx/rx_fifo_depth
	dev->init(); // 写之前设置好配置的寄存器
		__i2c_dw_disable(); // disable adapter
			__i2c_dw_disable_nowait();
		i2c_dw_configure_fifo_master();	//写tx/rx_fifo寄存器,根据dev->master_cfg写con寄存器
	i2c_dw_disable_int(); // 先把中断mask全部置1，禁止中断
	devm_request_irq();
	i2c_dw_init_recovery_info();
	i2c_add_numbered_adapter();