I2C子系统-应用视角

I2C子系统层次

LINUX-I2C关键结构体与函数

i2c.h

1. i2c控制器 - i2c_adapter

主要的成员包括

• nr - 表示是哪个i2c控制器（i2c总线）

• const struct i2c_algorithm *algo - i2c的算法，含有传输函数，用来收发I2C数据

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 */

	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 i2c_algorithm {
	/* If an adapter algorithm can't do I2C-level access, set master_xfer
	   to NULL. If an adapter algorithm can do SMBus access, set
	   smbus_xfer. If set to NULL, the SMBus protocol is simulated
	   using common I2C messages */
	/* master_xfer should return the number of messages successfully
	   processed, or a negative value on error */
	int (*master_xfer)(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);

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

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

2. i2c设备 - i2c_client

主要成员：

• addr - i2c的设备地址
• struct i2c_adapter *adapter - 指向i2c控制器的指针，表示连接在哪个I2C Controller上

LINUX 4.9.88

struct i2c_client {
	unsigned short flags;		/* div., see below		*/
	unsigned short addr;		/* chip address - NOTE: 7bit	*/
					/* addresses are stored in the	*/
					/* _LOWER_ 7 bits		*/
	char name[I2C_NAME_SIZE];
	struct i2c_adapter *adapter;	/* the adapter we sit on	*/
	struct device dev;		/* the device structure		*/
	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
};

LINUX 6.9

struct i2c_client {
	unsigned short flags;		/* div., see below		*/
#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 c;		/* chip address - NOTE: 7bit	*/
					/* addresses are stored in the	*/
					/* _LOWER_ 7 bits		*/
	char name[I2C_NAME_SIZE];
	struct i2c_adapter *adapter;	/* the adapter we sit on	*/
	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	*/
};

3. i2c消息 - i2c_msg

在上面的i2c_algorithm结构体中可以看到要传输的数据被称为：i2c_msg

• flags用来表示传输方向：bit 0等于I2C_M_RD表示读，bit 0等于0表示写。其余bit可以使用下面定义的宏来设置一些特殊配置。

struct i2c_msg {
	__u16 addr;	//设备地址
	__u16 flags;	//读写标志
#define I2C_M_RD		0x0001	/* guaranteed to be 0x0001! */
#define I2C_M_TEN		0x0010	/* use only if I2C_FUNC_10BIT_ADDR */
#define I2C_M_DMA_SAFE		0x0200	/* use only in kernel space */
#define I2C_M_RECV_LEN		0x0400	/* use only if I2C_FUNC_SMBUS_READ_BLOCK_DATA */
#define I2C_M_NO_RD_ACK		0x0800	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK	0x1000	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR	0x2000	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NOSTART		0x4000	/* use only if I2C_FUNC_NOSTART */
#define I2C_M_STOP		0x8000	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
	__u16 len;	//消息长度
	__u8 *buf;	//消息
};

示例：设备地址为0x50的EEPROM，要读取它里面存储地址为0x10的一个字节，应该构造几个i2c_msg？

• 要构造2个i2c_msg

• 第一个i2c_msg表示写操作，把要访问的存储地址0x10发给设备

• 第二个i2c_msg表示读操作

• 代码如下

u8 data_addr = 0x10;
i8 data;
struct i2c_msg msgs[2];

msgs[0].addr   = 0x50;
msgs[0].flags  = 0;
msgs[0].len    = 1;
msgs[0].buf    = &data_addr;

msgs[1].addr   = 0x50;
msgs[1].flags  = I2C_M_RD;
msgs[1].len    = 1;
msgs[1].buf    = &data;

4. i2c传输数据概括

• APP通过I2C Controller与I2C Device传输数据

• APP通过i2c_adapter与i2c_client传输i2c_msg

• 内核函数i2c_transfer

  • i2c_msg里含有addr，所以这个函数里不需要i2c_client

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

5. i2c读写函数

i2c-core-base.c(LINUX 6)

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

	/* REVISIT the fault reporting model here is weak:
	 *
	 *  - When we get an error after receiving N bytes from a slave,
	 *    there is no way to report "N".
	 *
	 *  - When we get a NAK after transmitting N bytes to a slave,
	 *    there is no way to report "N" ... or to let the master
	 *    continue executing the rest of this combined message, if
	 *    that's the appropriate response.
	 *
	 *  - When for example "num" is two and we successfully complete
	 *    the first message but get an error part way through the
	 *    second, it's unclear whether that should be reported as
	 *    one (discarding status on the second message) or errno
	 *    (discarding status on the first one).
	 */
	ret = __i2c_lock_bus_helper(adap);
	if (ret)
		return ret;

	ret = __i2c_transfer(adap, msgs, num);
	i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);

	return ret;
}
EXPORT_SYMBOL(i2c_transfer);

i2c-core.c(LINUX 4.9)

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

	/* REVISIT the fault reporting model here is weak:
	 *
	 *  - When we get an error after receiving N bytes from a slave,
	 *    there is no way to report "N".
	 *
	 *  - When we get a NAK after transmitting N bytes to a slave,
	 *    there is no way to report "N" ... or to let the master
	 *    continue executing the rest of this combined message, if
	 *    that's the appropriate response.
	 *
	 *  - When for example "num" is two and we successfully complete
	 *    the first message but get an error part way through the
	 *    second, it's unclear whether that should be reported as
	 *    one (discarding status on the second message) or errno
	 *    (discarding status on the first one).
	 */

	if (adap->algo->master_xfer) {
#ifdef DEBUG
		for (ret = 0; ret < num; ret++) {
			dev_dbg(&adap->dev,
				"master_xfer[%d] %c, addr=0x%02x, len=%d%s\n",
				ret, (msgs[ret].flags & I2C_M_RD) ? 'R' : 'W',
				msgs[ret].addr, msgs[ret].len,
				(msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
		}
#endif

		if (in_atomic() || irqs_disabled()) {
			ret = i2c_trylock_bus(adap, I2C_LOCK_SEGMENT);
			if (!ret)
				/* I2C activity is ongoing. */
				return -EAGAIN;
		} else {
			i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
		}

		ret = __i2c_transfer(adap, msgs, num);
		i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);

		return ret;
	} else {
		dev_dbg(&adap->dev, "I2C level transfers not supported\n");
		return -EOPNOTSUPP;
	}
}
EXPORT_SYMBOL(i2c_transfer);

APP使用i2ctools访问EEPROM

一句话概括：APP通过I2C Controller与I2C Device传输数据

在APP里，有这三个问题：

(1) 怎么指定I2C控制器？

• i2c-dev.c提供为每个I2C控制器(I2C Bus、I2C Adapter)都生成一个设备节点：/dev/i2c-0、/dev/i2c-1等待
• open某个/dev/i2c-X节点，就是去访问该I2C控制器下的设备

(2) 怎么指定I2C设备？

• 通过ioctl指定I2C设备的地址
• ioctl(file, I2C_SLAVE, address)
  • 如果该设备已经有了对应的设备驱动程序，则返回失败
• ioctl(file, I2C_SLAVE_FORCE, address)
  • 如果该设备已经有了对应的设备驱动程序
  • 但是还是想通过i2c-dev驱动来访问它
  • 则使用这个ioctl来指定I2C设备地址

(3) 怎么传输数据？

• 两种方式
  • 一般的I2C方式：ioctl(file, I2C_RDWR, &rdwr)
  • SMBus方式：ioctl(file, I2C_SMBUS, &args)

编写程序：

• file = open_i2c_dev(i2c总线编号, 返回的文件名, 文件名大小, 0 - 不打印信息)
• set_slave_addr(file, dev_addr, 1 - 强制) - 设置从机设备地址（AT24C02的设备地址是0x50）
• 写：i2c_smbus_write_byte_data(file, command - 寄存器地址，value) - 按字节写入
• 读：i2c_smbus_read_i2c_block_data(file, mem_addr, sizeof(data), data) - I2C连续读

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "i2cbusses.h"

/**
 * Usage:
 * ./at24c02  w "100ask.taobao.com"
 * ./at24c02  r
 */
int main(int argc, char const *argv[])
{
    unsigned char dev_addr = 0x50;
    unsigned char mem_addr = 0;
    unsigned char data[32];

    int file, ret;
    char filename[20];
    unsigned char *pstr;

    struct timespec req;

    if (argc != 3 && argc != 4)
    {
        printf("Usage:\n");
        printf("\t%s   [write data]\n", argv[0]);

        return -1;
    }
    // 打开i2c设备
    file = open_i2c_dev(argv[1][0] - '0', filename, sizeof(filename), 0);
    if (file < 0)
    {
        printf("Unable to open %s\n", filename);
        return -1;
    }
    // 设置i2c设备地址
    if (set_slave_addr(file, dev_addr, 1))
    {
        printf("Error: Could not set address to 0x%02x\n", dev_addr);
        return -1;
    }

    // 读or写
    if (strcmp(argv[2], "w") == 0)
    {
        req.tv_sec = 0;
        req.tv_nsec = 20000000; // 20ms
        // write
        pstr = (char *)argv[3];
        while (*pstr)
        {
            // 写入mem_addr和*pstr指向要写入的数据
            ret = i2c_smbus_write_byte_data(file, mem_addr++, *pstr++);
            if (ret != 0)
            {
                printf("Error: i2c_smbus_write_byte_data failed\n");
                return -1;
            }

            // wait TWR 20ms
            nanosleep(&req, NULL);
        }
        ret = i2c_smbus_write_byte_data(file, mem_addr, 0); // end char
        if (ret != 0)
        {
            printf("Error: i2c_smbus_write_byte_data failed\n");
            return -1;
        }
    }
    else if (strcmp(argv[2], "r") == 0)
    {
        ret = i2c_smbus_read_i2c_block_data(file, mem_addr, sizeof(data), data);
        if (ret < 0)
        {
            printf("Error: i2c_smbus_read_i2c_block_data failed\n");
            return -1;
        }
        data[31] = '\0';
        printf("get data: %s\n", data);
    }

    // 关闭i2c设备
    close(file);
    return 0;
}

led\n");
return -1;
}
}
else if (strcmp(argv[2], “r”) == 0)
{
ret = i2c_smbus_read_i2c_block_data(file, mem_addr, sizeof(data), data);
if (ret < 0)
{
printf(“Error: i2c_smbus_read_i2c_block_data failed\n”);
return -1;
}
data[31] = ‘\0’;
printf(“get data: %s\n”, data);
}

// 关闭i2c设备
close(file);
return 0;

}