提示：基于之前I2C 基础知识了解：设备树配置、配置GPIO、I2C驱动框架的了解，这里在此基础上进行I2C 通信。

前言

在之前I2C基础上进行I2C 通信，打通通信知识点。

一、参考资料

之前基础笔记：
驱动-I2C-客户端代码编写-编写设备树

Linux驱动-i2c 驱动框架编写

Linux驱动-IIC完善FT5X06设备节点和驱动

关联内容：
Linux驱动开发—内核I2C驱动详解

IIC驱动

二、知识点分析

搞清楚需求-IIC驱动程序

如上，我们最终目的是什么，就是在之前IIC 驱动框架的基础上进行IIC通讯，让IIC工作起来。
那么如何验证，在之前程序基础上进行了IIC 读写操作并调用读写来验证IIC 。

IIC 用到的api

这里仅从IIC 通讯案例中涉及到的api 来进行讲解。

i2c_master_send / i2c_master_recv

路径：kernel/include/linux/i2c.h

具体源码如下：

/** * i2c_master_send - issue a single I2C message in master transmit mode * @client: Handle to slave device * @buf: Data that will be written to the slave * @count: How many bytes to write, must be less than 64k since msg.len is u16 * * Returns negative errno, or else the number of bytes written. */staticinlineinti2c_master_send(conststruct i2c_client*client,constchar*buf,intcount){returni2c_transfer_buffer_flags(client,(char*)buf,count,0);};/** * i2c_master_recv - issue a single I2C message in master receive mode * @client: Handle to slave device * @buf: Where to store data read from slave * @count: How many bytes to read, must be less than 64k since msg.len is u16 * * Returns negative errno, or else the number of bytes read. */staticinlineinti2c_master_recv(conststruct i2c_client*client,char*buf,intcount){returni2c_transfer_buffer_flags(client,buf,count,I2C_M_RD);};

其实就是单收发报文，然后都调用了i2c_transfer_buffer_flags

i2c_transfer

如上分析i2c_master_send / i2c_master_recv都是指向i2c_transfer_buffer_flags，那么我们看看i2c_transfer_buffer_flags方法函数源码，如下：

路径：kernel/drivers/i2c/i2c-core-base.c

/** * i2c_transfer_buffer_flags - issue a single I2C message transferring data * to/from a buffer * @client: Handle to slave device * @buf: Where the data is stored * @count: How many bytes to transfer, must be less than 64k since msg.len is u16 * @flags: The flags to be used for the message, e.g. I2C_M_RD for reads * * Returns negative errno, or else the number of bytes transferred. */inti2c_transfer_buffer_flags(conststruct i2c_client*client,char*buf,intcount,u16 flags){intret;struct i2c_msg msg={.addr=client->addr,.flags=flags|(client->flags&I2C_M_TEN),.len=count,.buf=buf,};ret=i2c_transfer(client->adapter,&msg,1);/* * If everything went ok (i.e. 1 msg transferred), return #bytes * transferred, else error code. */return(ret==1)?count:ret;}EXPORT_SYMBOL(i2c_transfer_buffer_flags);

继续看i2c_transfer源码，如下

/** * i2c_transfer - execute a single or combined I2C message * @adap: Handle to I2C bus * @msgs: One or more messages to execute before STOP is issued to * terminate the operation; each message begins with a START. * @num: Number of messages to be executed. * * Returns negative errno, else the number of messages executed. * * Note that there is no requirement that each message be sent to * the same slave address, although that is the most common model. */inti2c_transfer(struct i2c_adapter*adap,struct i2c_msg*msgs,intnum){intret;/* 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){#ifdefDEBUGfor(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)?"+":"");}#endifif(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);returnret;}else{dev_dbg(&adap->dev,"I2C level transfers not supported\n");return-EOPNOTSUPP;}}EXPORT_SYMBOL(i2c_transfer);

三大函数核心区别对照

综合上面源码，看注释就可以明白区别，这里直接对照表如下：

所以 大多数场景我们用的是i2c_transfer方法，只是需要自己去拼接i2c_msg结构体。

struct i2c_msg msg={.addr=client->addr,.flags=flags|(client->flags&I2C_M_TEN),.len=count,.buf=buf,};

结构体-i2c_msg-i2c_client

路径：include/uapi/linux/i2c.h，i2c_msg这个是永远传输i2c 数据，读写中会用到，可以理解为通信介质。

struct i2c_msg{__u16 addr;/* slave address */__u16 flags;#defineI2C_M_RD0x0001/* read data, from slave to master *//* I2C_M_RD is guaranteed to be 0x0001! */#defineI2C_M_TEN0x0010/* this is a ten bit chip address */#defineI2C_M_DMA_SAFE0x0200/* the buffer of this message is DMA safe *//* makes only sense in kernelspace *//* userspace buffers are copied anyway */#defineI2C_M_RECV_LEN0x0400/* length will be first received byte */#defineI2C_M_NO_RD_ACK0x0800/* if I2C_FUNC_PROTOCOL_MANGLING */#defineI2C_M_IGNORE_NAK0x1000/* if I2C_FUNC_PROTOCOL_MANGLING */#defineI2C_M_REV_DIR_ADDR0x2000/* if I2C_FUNC_PROTOCOL_MANGLING */#defineI2C_M_NOSTART0x4000/* if I2C_FUNC_NOSTART */#defineI2C_M_STOP0x8000/* if I2C_FUNC_PROTOCOL_MANGLING */__u16 len;/* msg length */__u8*buf;/* pointer to msg data */};

具体核心参数说明如下：

struct i2c_msg{__u16 addr;// I2C从设备7位地址__u16 flags;// 传输控制标志位（多个宏按位或组合）__u16 len;// 当前这条消息要传输的字节数量__u8*buf;// 数据缓冲区指针，存放收发的字节数据};

i2c_client结构体定义如下：

struct i2c_client{unsignedshortflags;/* div., see below */unsignedshortaddr;/* chip address - NOTE: 7bit *//* addresses are stored in the *//* _LOWER_ 7 bits */charname[I2C_NAME_SIZE];struct i2c_adapter*adapter;/* the adapter we sit on */struct device dev;/* the device structure */intinit_irq;/* irq set at initialization */intirq;/* irq issued by device */struct list_head detected;#ifIS_ENABLED(CONFIG_I2C_SLAVE)i2c_slave_cb_t slave_cb;/* callback for slave mode */#endif};

IIC 读操作

//i2c 读函数intft5x06_read_reg(u8 reg_addr){u8 data;//i2c 通讯，以最小8位为最小单位// i2c_transfer标准读写流程：先写寄存器地址，再读数据struct i2c_msg msgs[2]={[0]={.addr=ft5x06_client->addr,// I2C从机地址0x38.flags=0,// 标志0 = I2C写操作.len=sizeof(reg_addr),// 长度1字节（寄存器地址）.buf=&reg_addr,// 缓冲区：要读取的寄存器号},[1]={.addr=ft5x06_client->addr,.flags=I2C_M_RD,// I2C_M_RD = 读操作标志.len=sizeof(data),// 读取1字节返回值.buf=&data,// 读到的数据存入data},};// i2c_transfer：发起一组I2C消息，返回成功执行的msg数量// ARRAY_SIZE(msgs)=2，必须两条消息都执行成功才算读取正常if(i2c_transfer(ft5x06_client->adapter,msgs,ARRAY_SIZE(msgs))!=ARRAY_SIZE(msgs)){return-EIO;// 读写失败，返回IO错误码}returndata;// 返回寄存器读到的值}

那么构造从机地址 addr从哪里来？ 在 方法int ft5x06_probe(struct i2c_client *client, const struct i2c_device_id *id)也就是 probe 函数中的i2c_client指针变量中去取

所以在程序中定义全局变量：struct i2c_client *ft5x06_client;，然后赋值

intft5x06_probe(struct i2c_client*client,conststruct i2c_device_id*id){.....ft5x06_client=client;.....

IIC 写操作

写操作其实跟简单，对比读操作来说：

voidft5x06_write_reg(u8 reg_addr,u8 data,u16 len){u8 buff[256];// 本地缓冲区，最大255字节数据+1字节寄存器地址struct i2c_msg msgs[]={[0]={.addr=ft5x06_client->addr,.flags=0,// 纯写操作.len=len+1,// 总长度 = 寄存器地址1字节 + 有效数据长度.buf=buff,},};buff[0]=reg_addr;// 缓冲区首字节：寄存器地址memcpy(&buff[1],&data,len);// 后续空间拷贝待写入数据// 发起I2C写传输if(i2c_transfer(ft5x06_client->adapter,msgs,ARRAY_SIZE(msgs))!=ARRAY_SIZE(msgs)){return;// 写入失败直接退出，无错误返回、无打印}}

IIC 调用

接下来就开始调用了，如下：

intft5x06_probe(struct i2c_client*client,conststruct i2c_device_id*id){intret=0;intvalue=0;ft5x06_client=client;....................ft5x06_write_reg(0x80,0x4b,1);value=ft5x06_read_reg(0x80);printk("reg 0x80 is %#x\n",value);return0;}

有人会问，未删除传递寄存器地址0x80，哪里来的？？？ 那当然是数据手册里面找的，不是瞎写的。

三、驱动源码实现-实现IIC读写

#include<linux/init.h>#include<linux/module.h>#include<linux/i2c.h>#include<linux/of_device.h>#include<linux/gpio/consumer.h>#include<linux/delay.h>#include<linux/interrupt.h>struct gpio_desc*reset_gpio;struct gpio_desc*irq_gpio;struct i2c_client*ft5x06_client;//i2c 读函数intft5x06_read_reg(u8 reg_addr){u8 data;//i2c 通讯，以最小8位为最小单位// i2c_transfer标准读写流程：先写寄存器地址，再读数据struct i2c_msg msgs[2]={[0]={.addr=ft5x06_client->addr,// I2C从机地址0x38.flags=0,// 标志0 = I2C写操作.len=sizeof(reg_addr),// 长度1字节（寄存器地址）.buf=&reg_addr,// 缓冲区：要读取的寄存器号},[1]={.addr=ft5x06_client->addr,.flags=I2C_M_RD,// I2C_M_RD = 读操作标志.len=sizeof(data),// 读取1字节返回值.buf=&data,// 读到的数据存入data},};// i2c_transfer：发起一组I2C消息，返回成功执行的msg数量// ARRAY_SIZE(msgs)=2，必须两条消息都执行成功才算读取正常if(i2c_transfer(ft5x06_client->adapter,msgs,ARRAY_SIZE(msgs))!=ARRAY_SIZE(msgs)){return-EIO;// 读写失败，返回IO错误码}returndata;// 返回寄存器读到的值}// // 为什么一个是u8 类型，一个是u16类型：因为u8是用来i2c通讯的，u16是用來賦值給i2c_msg 的voidft5x06_write_reg(u8 reg_addr,u8 data,u16 len){u8 buff[256];// 本地缓冲区，最大255字节数据+1字节寄存器地址：就是要struct i2c_msg msgs[]={[0]={.addr=ft5x06_client->addr,.flags=0,// 纯写操作.len=len+1,// 总长度 = 寄存器地址1字节 + 有效数据长度.buf=buff,},};buff[0]=reg_addr;// 缓冲区首字节：寄存器地址memcpy(&buff[1],&data,len);// 后续空间拷贝待写入数据// 发起I2C写传输if(i2c_transfer(ft5x06_client->adapter,msgs,ARRAY_SIZE(msgs))!=ARRAY_SIZE(msgs)){return;// 写入失败直接退出，无错误返回、无打印}}irqreturn_tft5x06_handler(intirq,void*args){printk("==========ft5x06_handler==========\n");returnIRQ_RETVAL(IRQ_HANDLED);}intft5x06_probe(struct i2c_client*client,conststruct i2c_device_id*id){intret=0;intvalue=0;ft5x06_client=client;printk(KERN_INFO"###### This is ft5x06 probe ######\n");// 获取复位GPIO描述符reset_gpio=gpiod_get_optional(&client->dev,"reset",0);// 第二个参数是属性（reset-gpios）前缀resetif(reset_gpio==NULL){printk("gpiod_get_optional reset_gpio error\n");return-1;}// 获取中断GPIO描述符irq_gpio=gpiod_get_optional(&client->dev,"interrupts",0);// 第二个参数是属性（interrupts-gpio）前缀interruptsif(irq_gpio==NULL){printk("gpiod_get_optional irq_gpio error\n");return-1;}gpiod_direction_output(reset_gpio,0);ssleep(5);gpiod_direction_output(reset_gpio,1);ret=request_irq(client->irq,ft5x06_handler,IRQF_TRIGGER_FALLING|IRQF_ONESHOT,"ft5x06_irq",NULL);if(ret<0){printk("request_irq request error\n");return-1;}ft5x06_write_reg(0x80,0x4b,1);value=ft5x06_read_reg(0x80);printk("reg 0x80 is %#x\n",value);return0;}intft5x06_remove(struct i2c_client*client){printk(KERN_INFO"###### This is ft5x06_remove ######\n");return0;}staticconststruct of_device_id ft5x06_id[]={{.compatible="my-ft5x06"},{/* Sentinel */},};// 关键补充MODULE_DEVICE_TABLE(of,ft5x06_id);staticstruct i2c_driver ft5x06_driver={.driver={.owner=THIS_MODULE,.name="my-ft5x06",.of_match_table=ft5x06_id,},.probe=ft5x06_probe,.remove=ft5x06_remove,};staticint__initft5x06_driver_init(void){intret;ret=i2c_add_driver(&ft5x06_driver);if(ret<0){printk(KERN_ERR"i2c_add_driver failed ret=%d\n",ret);returnret;}printk(KERN_INFO"###### ft5x06 driver register success ######\n");return0;}staticvoid__exitft5x06_driver_exit(void){i2c_del_driver(&ft5x06_driver);printk(KERN_INFO"###### ft5x06 driver unregister ######\n");}module_init(ft5x06_driver_init);module_exit(ft5x06_driver_exit);MODULE_LICENSE("GPL");

四、驱动验证

编译后，make 编译.ko 文件，然后加载驱动验证，结果如下：

总结

• 这里其实就是一个简单的IIC通讯，还没有涉及到实际的功能，就是验证IIC通不通，读写寄存器
• 这里重点还是理解思路、对于读写操作和api 操作要熟悉。