i2c 驱动四：sysfs文件系统

来源：互联网发布：殷保华一线法源码编辑：程序博客网时间：2024/05/29 17:20

有关linux的i2c相关文章有一下几篇，他们互相关联，应该一同看：

- i2c 驱动一：简介

- i2c 驱动二：devfs文件系统

- i2c 驱动三：自己实现设备和驱动分离

- i2c 驱动四：sysfs文件系统

- i2c 驱动五：gpio模拟i2c

1. 用 sysfs 实现 i2c，其实质是将 i2c 和 sysfs 结合起来，那首先来看看什么是 sysfs：

【1】sysfs简介：sysfs 是基于内存的虚拟的文件系统，他的作用于 proc 相似，他的设计是吸取的 proc 中的很多教训，使之导出内核或其他的数据的方式更为统一

【2】此部分，有一个博客写的很好，在这里，暂时不做整理，直接点击跳转

【3】借助于 sysfs ，我们可以把要呈现的参数/数据以文件夹的形式呈现给用户，最直接的好处是你能够用命令行来读(cat)写(echo)参数/数据

【4】对sysfs中的函数，有一篇文章写的很好，直接点击跳转

2. 说的再多，不如一个例子：

由于手头上有个 mpu6050，所以，就以mpu6050为例，采用的传感器的小板子是 GY-521

目录结构：

.
├── dev
│ ├── Makefile
│ └── mpu6050_dev.c
└── dri
├── Makefile
└── mpu6050_dri.c

mpu6050_dev.c

#include <linux/kernel.h>#include <linux/module.h>#include <linux/i2c.h>#include <linux/delay.h>MODULE_LICENSE("GPL");static struct i2c_client *mpu6050_clientp;static struct i2c_board_info mpu6050_i2c_devs = {        .type = "mpu6050",        .addr = 0x68,        /*I2C_BOARD_INFO("mpu6050", 0x50), //这个宏是上边两个变量赋值的替换*/};static int mpu6050_dev_init(void){    struct i2c_adapter *i2c_adap;    //分配一个适配器的指针    printk("mpu6050_dev_init.\n");    i2c_adap = i2c_get_adapter(0);   //0 是 i2c 总线编号    mpu6050_clientp = i2c_new_device(i2c_adap, &mpu6050_i2c_devs); //只能添加一个    if (!mpu6050_clientp)        printk("register i2c error!\n");    i2c_put_adapter(i2c_adap);       //释放 adapter    return 0;}static void mpu6050_dev_exit(void){    printk("mpu6050_dev_exit.\n");    i2c_unregister_device(mpu6050_clientp);}module_init(mpu6050_dev_init);module_exit(mpu6050_dev_exit);

Makefile

ifeq ($(KERNELRELEASE),)#KERNELDIR ?= /lib/modules/$(shell uname -r)/build KERNELDIR ?= ~/wor_lip/linux-3.4.112PWD := $(shell pwd)modules:$(MAKE) -C $(KERNELDIR) M=$(PWD) modulesmodules_install:$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_installclean:rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules* Module*.PHONY: modules modules_install cleanelseobj-m := mpu6050_dev.oendif

mpu6050_dri.c

#include <linux/kernel.h>#include <linux/module.h>#include <linux/i2c.h>#include <linux/delay.h>MODULE_LICENSE("GPL");#define SMPLRT_DIV      0x19#define CONFIG          0x1A#define GYRO_CONFIG     0x1B#define ACCEL_CONFIG    0x1C#define ACCEL_XOUT_H    0x3B#define ACCEL_XOUT_L    0x3C#define ACCEL_YOUT_H    0x3D#define ACCEL_YOUT_L    0x3E#define ACCEL_ZOUT_H    0x3F#define ACCEL_ZOUT_L    0x40#define TEMP_OUT_H      0x41#define TEMP_OUT_L      0x42#define GYRO_XOUT_H     0x43#define GYRO_XOUT_L     0x44#define GYRO_YOUT_H     0x45#define GYRO_YOUT_L     0x46#define GYRO_ZOUT_H     0x47#define GYRO_ZOUT_L     0x48#define PWR_MGMT_1      0x6Bstatic struct kobject *example_kobj;struct i2c_client *glb_client;static int mpu6050_read_byte(struct i2c_client *client, unsigned char reg){    int ret;    char txbuf[1] = { reg  };    char rxbuf[1];    struct i2c_msg msg[] = {        {client->addr, 0, 1, txbuf},        {client->addr, I2C_M_RD, 1, rxbuf}    };    ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg));    if (ret < 0) {        printk("ret = %d\n", ret);        return ret;    }    return rxbuf[0];}static int mpu6050_write_byte(struct i2c_client *client, unsigned char reg, unsigned char val){    char txbuf[2] = {reg, val};    struct i2c_msg msg[] = {        {client->addr, 0, 2, txbuf},    };    i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg));    return 0;}/* 读/sys/kernel/mpu6050_i2c文件下的文件时调用 */static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,        char *buf) /* buf是返回给用户空间的值 */{    unsigned short accel_x = 0, accel_y = 0, accel_z = 0;      unsigned short gyro_x = 0, gyro_y = 0, gyro_z = 0;      unsigned short temp = 0;      mpu6050_write_byte(glb_client, PWR_MGMT_1, 0x00);    mpu6050_write_byte(glb_client, SMPLRT_DIV, 0x07);    mpu6050_write_byte(glb_client, CONFIG, 0x06);    mpu6050_write_byte(glb_client, GYRO_CONFIG, 0x18);    mpu6050_write_byte(glb_client, ACCEL_CONFIG, 0x01);    mdelay(10);    accel_x = mpu6050_read_byte(glb_client, ACCEL_XOUT_L);    accel_x |= mpu6050_read_byte(glb_client, ACCEL_XOUT_H) << 8;    accel_y =  mpu6050_read_byte(glb_client, ACCEL_YOUT_L);    accel_y |= mpu6050_read_byte(glb_client, ACCEL_YOUT_H) << 8;    accel_z = mpu6050_read_byte(glb_client, ACCEL_ZOUT_L);    accel_z |= mpu6050_read_byte(glb_client, ACCEL_ZOUT_H) << 8;    printk("acceleration data: x = %04x, y = %04x, z = %04x\n", accel_x, accel_y, accel_z);    gyro_x = mpu6050_read_byte(glb_client, GYRO_XOUT_L);    gyro_x |= mpu6050_read_byte(glb_client, GYRO_XOUT_H) << 8;    gyro_y = mpu6050_read_byte(glb_client, GYRO_YOUT_L);    gyro_y |= mpu6050_read_byte(glb_client, GYRO_YOUT_H) << 8;    gyro_z = mpu6050_read_byte(glb_client, GYRO_ZOUT_L);    gyro_z |= mpu6050_read_byte(glb_client, GYRO_ZOUT_H) << 8;    printk("gyroscope data: x = %04x, y = %04x, z = %04x\n", gyro_x, gyro_y, gyro_z);     temp = mpu6050_read_byte(glb_client, TEMP_OUT_L);     temp |= mpu6050_read_byte(glb_client, TEMP_OUT_H) << 8;     printk("temperature data: %x\n", temp);    return sprintf(buf, "%x\n", temp);}/* 写/sys/kernel/mpu6050_i2c文件下的文件时调用 */static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,        const char *buf, size_t count){    return 0;}static struct kobj_attribute foo_attribute =__ATTR(mpu6050_accelerationd, 0666, foo_show, foo_store);/* (文件名, 文件权限, 读这个文件时调用的函数, 写文件时调用时的函数) * 在/sys/kernel/mpu6050_i2c/下的文件 */static struct kobj_attribute foo_attribute2 =__ATTR(mpu6050_gyroscope, 0666, foo_show, foo_store);static struct kobj_attribute foo_attribute3 =__ATTR(mpu6050_temperature, 0666, foo_show, foo_store);/* * 创建一个属性组,方便我们一次性的创建和删除 */static struct attribute *attrs[] = {    &foo_attribute.attr,    &foo_attribute2.attr,    &foo_attribute3.attr,    NULL,  /* 需要用NULL来表示属性列表的结束 */};/* * An unnamed attribute group will put all of the attributes directly in * the kobject directory.  If we specify a name, a subdirectory will be * created for the attributes with the directory being the name of the * attribute group. */static struct attribute_group attr_group = {    .attrs = attrs,};static int mpu6050_probe(struct i2c_client *client, const struct i2c_device_id *id){    int retval;    glb_client = client;    /*     * 创建目录 /sys/kernel/mpu6050_i2c     */    example_kobj = kobject_create_and_add("mpu6050_i2c", kernel_kobj); /* (kernel_kobj这个父文件夹下的叫mpu6050_i2c的文件夹) */    if (!example_kobj)        return -ENOMEM;    /* Create the files associated with this kobject */    retval = sysfs_create_group(example_kobj, &attr_group);    if (retval)        kobject_put(example_kobj);    return 0;}static int mpu6050_remove(struct i2c_client *client){    /*struct bin_attribute *binp;*/    /*binp = i2c_get_clientdata(client);*/    /*sysfs_remove_bin_file(&client->dev.kobj, binp);*/    kobject_put(example_kobj);    printk("driver removed.\n");    return 0;}static const struct i2c_device_id mpu6050_id[] = {    { "mpu6050", 0 },}; /*MODULE_DEVICE_TABLE(i2c, mpu6050_id);*/static struct i2c_driver mpu6050_driver = {    .driver = {        .name           = "xx",    //供模块匹配用        .owner          = THIS_MODULE,    },    .probe      = mpu6050_probe,    .remove     = mpu6050_remove,    .id_table   = mpu6050_id,     /* 用于I2C driver的probe函数调用 */};/*i2c_add_driver();*/module_i2c_driver(mpu6050_driver);//简单方式，内核中是个宏，完成了模块的初始化和卸载

【1】当设备和驱动匹配成功后，会在 /sys/kernel/ 下创建一个mpu6050_i2c 目录，里边有3个文件，如下图

【2】读传感器的值

【3】很明显，程序中3个参数以文件夹的方式呈现给了用户，用户可以像操作文件的形式读写相应文件，在本程序中，我偷了个懒，读这3个参数执行了相同的函数，没有实现写的函数

【4】可以想到的是，程序中可以实现不同的读函数，实现单独的参数读取

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