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Linux驱动学习日记(25) Linux I2C 驱动(二)

发表于 分类于 ，

  这是我们上一次的代码，会有连接不上的情况:

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/*
 * @Author: 胡城玮
 * @FilePath: mpu6050.c
 * @Date: 2026-03-16
 * @Description: 
 * @Version: 0.1
 */

#include "mpu6050.h"
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of_gpio.h>
#include <linux/semaphore.h>
#include <linux/timer.h>
#include <linux/i2c.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <asm/io.h>

#define     MPU6050_CNT     1
#define     MPU6050_NAME    "mpu6050"

struct mpu6050_dev{
    dev_t devid;
    struct cdev cdev;
    struct class *class;
    struct device *device;
    struct device_node *nd;
    int major;
    void *private_data;
    s16 acc[3],gyr[3]; // 加速度、角速度
};

static struct mpu6050_dev mpu6050dev;

static int mpu6050_read_regs(struct mpu6050_dev *dev, uint8_t reg, void *val, int len)
{
    int ret;
    struct i2c_msg msg[2];
    struct i2c_client *client = (struct i2c_client *)dev->private_data;

    msg[0].addr = client->addr;
    msg[0].flags = 0;
    msg[0].buf = &reg;
    msg[0].len = 1;

    msg[1].addr = client->addr;
    msg[1].flags = I2C_M_RD;
    msg[1].buf = val;
    msg[1].len = len;

    ret = i2c_transfer(client->adapter, msg, 2);
    if(ret == 2)
    {
        ret = 0;
    } else {
        printk("i2c rd failed = %d,reg = %06x, len = %d\r\n",ret,reg,len);
        return -EREMOTEIO;
    }
    return ret;
}

static int mpu6050_write_regs(struct mpu6050_dev *dev, u8 reg, u8* buf, int len)
{
    u8 b[256];
    struct i2c_msg msg;
    struct i2c_client *client = (struct i2c_client *)dev->private_data;

    b[0] = reg;
    memcpy(&b[1], buf,len);

    msg.addr = client->addr;
    msg.buf = b;
    msg.flags = 0;
    msg.len = len+1;

    return i2c_transfer(client->adapter, &msg, 1);
}

static u8 mpu6050_read_reg(struct mpu6050_dev *dev, u8 reg)
{
    u8 data = 0;
    
    mpu6050_read_regs(dev, reg, &data, 1);
    return data;
}

static void mpu6050_write_reg(struct mpu6050_dev *dev, u8 reg, u8 data)
{
    u8 buf = 0;
    buf = data;
    mpu6050_write_regs(dev, reg, &buf, 1);
}

static void mpu6050_read_data(struct mpu6050_dev *dev)
{
    u8 buf[6];
    int ret = 0;

    mpu6050_read_regs(dev, MPU6050_GYRO_XOUT_H, buf, 6);
    dev->gyr[0] = (buf[0] << 8)|buf[1];
    dev->gyr[1] = (buf[2] << 8)|buf[3];
    dev->gyr[2] = (buf[4] << 8)|buf[5];

    mpu6050_read_regs(dev, MPU6050_ACCEL_XOUT_H, buf, 6);
    dev->acc[0] = (buf[0] << 8)|buf[1];
    dev->acc[1] = (buf[2] << 8)|buf[3];
    dev->acc[2] = (buf[4] << 8)|buf[5];

    s16 data[6];
    data[0] = dev->acc[0];
    data[1] = dev->acc[1];
    data[2] = dev->acc[2];
    data[3] = dev->gyr[0];
    data[4] = dev->gyr[1];
    data[5] = dev->gyr[2];

    ret = copy_to_user(buf, data, sizeof(data));
}

static int mpu6050_open(struct inode *inode,struct file *filp)
{
    filp->private_data = &mpu6050dev;
    return 0;
}

static int mpu6050_release(struct inode *inode,struct file *filp)
{
    return 0;
}

static ssize_t mpu6050_read (struct file *filp, char __user *buf, size_t cnt, loff_t *off)
{
    struct mpu6050_dev *dev = (struct mpu6050_dev *)filp->private_data;

    mpu6050_read_data(dev);
    return 0;
}

static const struct file_operations mpu6050_fops = {
    .owner = THIS_MODULE,
    .open = mpu6050_open,
    .release = mpu6050_release,
    .read = mpu6050_read,
};

static int mpu6050_probe(struct i2c_client *client, 
                        const struct i2c_device_id *id)
{
    int ret = 0;
    u8 buf;
    printk("matched!\n");
    mpu6050dev.device = device_create(mpu6050dev.class, NULL, mpu6050dev.devid, NULL, MPU6050_NAME);
    if(IS_ERR(mpu6050dev.device))
    {
        return PTR_ERR(mpu6050dev.device);
    }

    mpu6050dev.private_data = client;

    msleep(500);

    mpu6050_write_reg(&mpu6050dev, MPU6050_PWR_MGMT_1, 0x00);      //解除休眠状态
    mpu6050_write_reg(&mpu6050dev, MPU6050_SMPLRT_DIV , 0x07);     //陀螺仪采样率
    mpu6050_write_reg(&mpu6050dev, MPU6050_CONFIG , 0x06);
    mpu6050_write_reg(&mpu6050dev, MPU6050_ACCEL_CONFIG , 0x00);   //配置加速度传感器工作在2G模式
    mpu6050_write_reg(&mpu6050dev, MPU6050_GYRO_CONFIG, 0x18);     //陀螺仪自检及测量范围，典型值：0x18(不自检，2000deg/s)

    msleep(200);
    
    buf = mpu6050_read_reg(&mpu6050dev, MPU6050_WHO_AM_I);

    if (buf != 0x68) {
        ret = -ENODEV;
        goto err_dev;
    }

    printk("MPU6050 Init SUCCESS!\n");
    return 0;

err_dev:
    printk("MPU6050 Init failed!\n");
    device_destroy(mpu6050dev.class, mpu6050dev.devid);
    return ret;
}

static void mpu6050_remove(struct i2c_client *client)
{
    device_destroy(mpu6050dev.class,mpu6050dev.devid);
}

static const struct of_device_id mpu6050_of_match[] = {
    {.compatible = "hcw,mpu6050"},
    {}
};

static struct i2c_driver mpu6050_drv = {
    .probe = mpu6050_probe,
    .remove = mpu6050_remove,
    .driver ={
        .name = "mpu6050_drv",
        .of_match_table = mpu6050_of_match,
        .owner = THIS_MODULE,
    },
};

static int __init mpu6050_init(void)
{
    u8 ret = 0;
    if(mpu6050dev.major)
    {
        mpu6050dev.devid = MKDEV(mpu6050dev.major, 0);
        register_chrdev_region(mpu6050dev.devid, MPU6050_CNT, MPU6050_NAME);
    }
    else
    {
        alloc_chrdev_region(&mpu6050dev.devid,0, MPU6050_CNT,MPU6050_NAME);
        mpu6050dev.major = MAJOR(mpu6050dev.devid);
    }

    cdev_init(&mpu6050dev.cdev, &mpu6050_fops);
    cdev_add(&mpu6050dev.cdev, mpu6050dev.devid, MPU6050_CNT);

    mpu6050dev.class = class_create(THIS_MODULE, MPU6050_NAME);
    if(IS_ERR(mpu6050dev.class))
    {
        return PTR_ERR(mpu6050dev.class);
    }
    ret = i2c_add_driver(&mpu6050_drv);
    if (ret)
        goto destroy_class;

    return 0;

destroy_class:
    class_destroy(mpu6050dev.class);
    cdev_del(&mpu6050dev.cdev);
    unregister_chrdev_region(mpu6050dev.devid, MPU6050_CNT);

    return ret;
}

static void __exit mpu6050_exit(void)
{
    i2c_del_driver(&mpu6050_drv);
    class_destroy(mpu6050dev.class);
    cdev_del(&mpu6050dev.cdev);
    unregister_chrdev_region(mpu6050dev.devid, MPU6050_CNT);
}

module_init(mpu6050_init);
module_exit(mpu6050_exit);
MODULE_AUTHOR("hcw");
MODULE_LICENSE("GPL");

  我们将代码喂给 chatgpt，让他给我们一些修改建议
  1、read() 根本没有把数据正确返回给用户层
  我原来的 copy_to_user 放在了 read_data 函数里，正确的做法应该放在 fops 中的 read 函数里，如下所示

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static ssize_t mpu6050_read (struct file *filp, char __user *buf, size_t cnt, loff_t *off)
{
    int ret = 0;
    struct mpu6050_dev *dev = (struct mpu6050_dev *)filp->private_data;

    mpu6050_read_data(dev);

    s16 data[6];
    data[0] = dev->acc[0];
    data[1] = dev->acc[1];
    data[2] = dev->acc[2];
    data[3] = dev->gyr[0];
    data[4] = dev->gyr[1];
    data[5] = dev->gyr[2];

    ret = copy_to_user(buf, data, sizeof(data));
    return 0;
}

  2、I2C 读写函数要做统一返回值检查
  现在的代码中 mpu6050_read_regs() 对 i2c_transfer() 做了检查，但是 mpu6050_write_regs() 直接把 i2c_transfer() 返回值原样交出去，没有统一转成 0 / 负错误码。mpu6050_read_reg() 和 mpu6050_write_reg() 也基本没处理失败情况。
  我们应该改成这样的风格：
  传输成功返回 0，传输失败返回负错误码，单字节读写函数改成 int mpu6050_read_reg(…, u8 *val)，不要直接返回 u8。

  3、优化 probe 初始化流程
  在 probe 初始化中，我们应该先保存 client、做芯片初始化、读 WHO_AM_I 确认正常，最后在 device_create。

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static int mpu6050_probe(struct i2c_client *client, 
                        const struct i2c_device_id *id)
{
    int ret = 0;
    u8 buf;
    printk("matched!\n");

    mpu6050dev.private_data = client;

    int ret;

    msleep(500);

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_PWR_MGMT_1, 0x00);
    if (ret) {
        printk("write MPU6050_PWR_MGMT_1 failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_SMPLRT_DIV, 0x07);
    if (ret) {
        printk("write MPU6050_SMPLRT_DIV failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_CONFIG, 0x06);
    if (ret) {
        printk("write MPU6050_CONFIG failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_ACCEL_CONFIG, 0x00);
    if (ret) {
        printk("write MPU6050_ACCEL_CONFIG failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_GYRO_CONFIG, 0x18);
    if (ret) {
        printk("write MPU6050_GYRO_CONFIG failed, ret=%d\n", ret);
        return ret;
    }

    msleep(200);
    
    mpu6050_read_reg(&mpu6050dev, MPU6050_WHO_AM_I, &buf);
    if (ret)
        return ret;

    if (buf != 0x68) {
        ret = -ENODEV;
        goto err_dev;
    }

    mpu6050dev.device = device_create(mpu6050dev.class, NULL, mpu6050dev.devid, NULL, MPU6050_NAME);
    if(IS_ERR(mpu6050dev.device))
    {
        return PTR_ERR(mpu6050dev.device);
    }

    printk("MPU6050 Init SUCCESS!\n");
    return 0;

err_dev:
    printk("MPU6050 Init failed!\n");
    return ret;
}

  试着装载新编译好的模块，但是依然出现以下报错

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/home/hcw/learn/24_mpu6050 # insmod mpu6050.ko
[  384.326515] matched!
[  385.077229] MPU6050 Init failed!

   说明设备树节点已经和 of_match_table 匹配成功。那么错误点大概率在这里，我们试着将读到的 ID 值打印出来看看

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ret = mpu6050_read_reg(&mpu6050dev, MPU6050_WHO_AM_I, &buf);
if (ret)
    return ret;

printk("WHO_AM_I = 0x%02x\n", buf);

if (buf != 0x68) {
    ret = -ENODEV;
    goto err_dev;
}

  可以看到器件 ID 读取出来以后是 0x70，居然不是 0x68，说明我手上的芯片不是 MPU6050（但它标注的确实是 6050，坑人）。我们修改判断条件，终于初始化成功！

图 1 初始化成功

  运行测试程序，终于读取到了正确的加速度和角速度。

图 2 读取成功

  最终代码如下：

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/*
 * @Author: 胡城玮
 * @FilePath: mpu6050.c
 * @Date: 2026-03-16
 * @Description: 
 * @Version: 0.1
 */

 #include "mpu6050.h"
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of_gpio.h>
#include <linux/semaphore.h>
#include <linux/timer.h>
#include <linux/i2c.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <asm/io.h>

#define     MPU6050_CNT     1
#define     MPU6050_NAME    "mpu6050"

struct mpu6050_dev{
    dev_t devid;
    struct cdev cdev;
    struct class *class;
    struct device *device;
    struct device_node *nd;
    int major;
    void *private_data;
    s16 acc[3],gyr[3]; // 加速度、角速度
};

static struct mpu6050_dev mpu6050dev;

static int mpu6050_read_regs(struct mpu6050_dev *dev, uint8_t reg, void *val, int len)
{
    int ret;
    struct i2c_msg msg[2];
    struct i2c_client *client = (struct i2c_client *)dev->private_data;

    msg[0].addr = client->addr;
    msg[0].flags = 0;
    msg[0].buf = &reg;
    msg[0].len = 1;

    msg[1].addr = client->addr;
    msg[1].flags = I2C_M_RD;
    msg[1].buf = val;
    msg[1].len = len;

    ret = i2c_transfer(client->adapter, msg, 2);
    if (ret != 2) {
        if (ret >= 0)
            ret = -EIO;
        return ret;
    }

    return 0;
}

static int mpu6050_write_regs(struct mpu6050_dev *dev, u8 reg, u8* buf, int len)
{
    u8 b[256];
    int ret;
    struct i2c_msg msg;
    struct i2c_client *client = (struct i2c_client *)dev->private_data;

    b[0] = reg;
    memcpy(&b[1], buf,len);

    msg.addr = client->addr;
    msg.buf = b;
    msg.flags = 0;
    msg.len = len+1;

    ret = i2c_transfer(client->adapter, &msg, 1);
    if(ret != 1)
    {
        if (ret >= 0)
            ret = -EIO;
        return ret;
    }

    return 0;
}

static u8 mpu6050_read_reg(struct mpu6050_dev *dev, u8 reg, u8 *val)
{
    int ret = 0;
    
    ret = mpu6050_read_regs(dev, reg, val, 1);

    if (ret)
        return ret;
    return ret;
}

static int mpu6050_write_reg(struct mpu6050_dev *dev, u8 reg, u8 data)
{
    u8 buf = 0;
    buf = data;
    return mpu6050_write_regs(dev, reg, &buf, 1);
}

static void mpu6050_read_data(struct mpu6050_dev *dev)
{
    u8 buf[6];
    int ret = 0;

    mpu6050_read_regs(dev, MPU6050_GYRO_XOUT_H, buf, 6);
    dev->gyr[0] = (buf[0] << 8)|buf[1];
    dev->gyr[1] = (buf[2] << 8)|buf[3];
    dev->gyr[2] = (buf[4] << 8)|buf[5];

    mpu6050_read_regs(dev, MPU6050_ACCEL_XOUT_H, buf, 6);
    dev->acc[0] = (buf[0] << 8)|buf[1];
    dev->acc[1] = (buf[2] << 8)|buf[3];
    dev->acc[2] = (buf[4] << 8)|buf[5];


}

static int mpu6050_open(struct inode *inode,struct file *filp)
{
    filp->private_data = &mpu6050dev;
    return 0;
}

static int mpu6050_release(struct inode *inode,struct file *filp)
{
    return 0;
}

static ssize_t mpu6050_read (struct file *filp, char __user *buf, size_t cnt, loff_t *off)
{
    int ret = 0;
    struct mpu6050_dev *dev = (struct mpu6050_dev *)filp->private_data;

    mpu6050_read_data(dev);

    s16 data[6];
    data[0] = dev->gyr[0];
    data[1] = dev->gyr[1];
    data[2] = dev->gyr[2];
    data[3] = dev->acc[0];
    data[4] = dev->acc[1];
    data[5] = dev->acc[2];

    ret = copy_to_user(buf, data, sizeof(data));
    return 0;
}

static const struct file_operations mpu6050_fops = {
    .owner = THIS_MODULE,
    .open = mpu6050_open,
    .release = mpu6050_release,
    .read = mpu6050_read,
};

static int mpu6050_probe(struct i2c_client *client, 
                        const struct i2c_device_id *id)
{
    u8 buf;
    printk("matched!\n");

    mpu6050dev.private_data = client;

    int ret = 0;

    msleep(500);

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_PWR_MGMT_1, 0x00);
    if (ret) {
        printk("write MPU6050_PWR_MGMT_1 failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_SMPLRT_DIV, 0x07);
    if (ret) {
        printk("write MPU6050_SMPLRT_DIV failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_CONFIG, 0x06);
    if (ret) {
        printk("write MPU6050_CONFIG failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_ACCEL_CONFIG, 0x00);
    if (ret) {
        printk("write MPU6050_ACCEL_CONFIG failed, ret=%d\n", ret);
        return ret;
    }

    ret = mpu6050_write_reg(&mpu6050dev, MPU6050_GYRO_CONFIG, 0x18);
    if (ret) {
        printk("write MPU6050_GYRO_CONFIG failed, ret=%d\n", ret);
        return ret;
    }

    msleep(200);
    
    ret = mpu6050_read_reg(&mpu6050dev, MPU6050_WHO_AM_I, &buf);
    if (ret)
        return ret;

    printk("WHO_AM_I = 0x%02x\n", buf);

    if (buf != 0x70) {
        ret = -ENODEV;
        goto err_dev;
    }

    mpu6050dev.device = device_create(mpu6050dev.class, NULL, mpu6050dev.devid, NULL, MPU6050_NAME);
    if(IS_ERR(mpu6050dev.device))
    {
        return PTR_ERR(mpu6050dev.device);
    }

    printk("MPU6050 Init SUCCESS!\n");
    return 0;

err_dev:
    printk("MPU6050 Init failed!\n");
    return ret;
}

static void mpu6050_remove(struct i2c_client *client)
{
    device_destroy(mpu6050dev.class,mpu6050dev.devid);
}

static const struct of_device_id mpu6050_of_match[] = {
    {.compatible = "hcw,mpu6050"},
    {}
};

static struct i2c_driver mpu6050_drv = {
    .probe = mpu6050_probe,
    .remove = mpu6050_remove,
    .driver ={
        .name = "mpu6050_drv",
        .of_match_table = mpu6050_of_match,
        .owner = THIS_MODULE,
    },
};

static int __init mpu6050_init(void)
{
    u8 ret = 0;
    if(mpu6050dev.major)
    {
        mpu6050dev.devid = MKDEV(mpu6050dev.major, 0);
        register_chrdev_region(mpu6050dev.devid, MPU6050_CNT, MPU6050_NAME);
    }
    else
    {
        alloc_chrdev_region(&mpu6050dev.devid,0, MPU6050_CNT,MPU6050_NAME);
        mpu6050dev.major = MAJOR(mpu6050dev.devid);
    }

    cdev_init(&mpu6050dev.cdev, &mpu6050_fops);
    cdev_add(&mpu6050dev.cdev, mpu6050dev.devid, MPU6050_CNT);

    mpu6050dev.class = class_create(THIS_MODULE, MPU6050_NAME);
    if(IS_ERR(mpu6050dev.class))
    {
        return PTR_ERR(mpu6050dev.class);
    }
    ret = i2c_add_driver(&mpu6050_drv);
    if (ret)
        goto destroy_class;

    return 0;

destroy_class:
    class_destroy(mpu6050dev.class);
    cdev_del(&mpu6050dev.cdev);
    unregister_chrdev_region(mpu6050dev.devid, MPU6050_CNT);

    return ret;
}

static void __exit mpu6050_exit(void)
{
    i2c_del_driver(&mpu6050_drv);
    class_destroy(mpu6050dev.class);
    cdev_del(&mpu6050dev.cdev);
    unregister_chrdev_region(mpu6050dev.devid, MPU6050_CNT);
}

module_init(mpu6050_init);
module_exit(mpu6050_exit);
MODULE_AUTHOR("hcw");
MODULE_LICENSE("GPL");