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Linux驱动学习实战(5) 写出流水灯

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设计思路

  将流水灯的三个灯作为一组，写入设备树中。在驱动程序中开启一个每 0.5s 触发的中断，在中断里每次移动一位，让 GPIO 实现流水灯效果。

硬件分析

  我们将二极管的正极接在 IO 口上，负极接在 GND，因此当 IO 口使用推挽输出模式输出高电平时，二极管将被点亮。正极分别接在板子上的 12、14、16。查阅原理图可以得知，其分别对应 GPIO01_IO04/8/6。

编写代码

  打开 imx6ull-hcw-emmc.dtsi 文件，在 iomuxc 节点下添加 pinctrl_flowingled，并写入如下内容：

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pinctrl_flowingled: flowingledgrp{
    fsl,pins = <
        MX6UL_PAD_GPIO1_IO04__GPIO1_IO04    0x10B0
        MX6UL_PAD_GPIO1_IO08__GPIO1_IO08    0x10B0
        MX6UL_PAD_GPIO1_IO06__GPIO1_IO06    0x10B0
    >;
};

  在根节点下添加 flowingled 设备，写入如下内容，写好后检查是否由 pin 被占用：

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flowingled{
    #address-cells = <1>;
    #size-cells = <1>;
    compatible = "hcw-flowingled";
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_flowingled>;
    flowingled-gpios = <&gpio1 4 GPIO_ACTIVE_HIGH>,
                        <&gpio1 8 GPIO_ACTIVE_HIGH>,
                        <&gpio1 6 GPIO_ACTIVE_HIGH>;
    
    status = "okay";
};

  新建文件夹，新建 C 文件，接下来我们一步一步写出完整的驱动代码！

  我们先将大体框架搭建完毕，写入以下代码

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/*
 * @Author: 胡城玮
 * @FilePath: flowingled.c
 * @Date: 2026-03-11
 * @Description: 
 * @Version: 0.1
 */
#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/irq.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <linux/fs.h>
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/platform_device.h>
#include <linux/irq.h>

#define     FLOWINGLED_CNT      1
#define     FLOWINGLED_NAME     "hcw-flowingled"
#define     FLOWINGLED_ON       1
#define     FLOWINGLED_OFF      0

struct flowingled_dev{
    dev_t           devid;
    struct cdev     cdev;
    struct class    *class;
    struct device   *device;
    int             major;
    struct device_node  *node;

    int             gpio[3];
    int             led_num;

    struct timer_list   timer;
    unsigned int        period_ms;  // 控制闪烁周期
    unsigned int        cur_led;    // 当前灯号   
    unsigned int        dir;        // 闪烁方向
    unsigned int        running;    // 是否运行
};

struct flowingled_dev flowingled;

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

static ssize_t flowingled_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt)
{
    int retvalue;
    unsigned char databuf[2];
    unsigned char led_running_flag;

    retvalue = copy_from_user(databuf,buf,cnt);
    if(retvalue < 0)
    {
        printk("kernel write failed\r\n");
        return -EFAULT;
    }

    led_running_flag = databuf[0];

    return 0;
}

static struct file_operations flowingled_fops = {
    .owner = THIS_MODULE,
    .open = flowingled_open,
    .write = flowingled_write
};

static int flowingled_probe(struct platform_device *dev)
{
    printk("driver and device matched");

    if(flowingled.major){
        flowingled.devid = MKDEV(flowingled.major, 0);
        register_chrdev_region(flowingled.devid, FLOWINGLED_CNT, FLOWINGLED_NAME);
    }
    else
    {
        alloc_chrdev_region(&flowingled.devid, 0, FLOWINGLED_CNT, FLOWINGLED_NAME);
        flowingled.major = MAJOR(flowingled.devid);
    }

    cdev_init(&flowingled.cdev, &flowingled_fops);
    cdev_add(&flowingled.cdev, flowingled.devid,FLOWINGLED_CNT);

    flowingled.class = class_create(THIS_MODULE, FLOWINGLED_NAME);
    if(IS_ERR(flowingled.class))
    {
        return PTR_ERR(flowingled.class);
    }

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

    flowingled.node = of_find_node_by_path("/flowingled");
    if(flowingled.node == NULL)
    {
        printk("flowingled does not found\r\n");
        return -EINVAL;
    }

    for (int i = 0; i < 3; i++)
    {
        char buf[8];
        flowingled.gpio[i] = of_get_named_gpio(flowingled.node, "flowingled-gpios", i);
        if (flowingled.gpio[i] < 0) {
            printk("can't get flowingled-gpios[%d]\n", i);
            return flowingled.gpio[i];
        }
        sprintf(buf ,"LED%d", i);
        gpio_request(flowingled.gpio[i],buf);
        gpio_direction_output(flowingled.gpio[i],0);
    }
    return 0;
}

static int flowingled_remove(struct platform_device *dev)
{
    for(int i = 0;i < FLOWINGLED_CNT; i++)
    {
        gpio_set_value(flowingled.gpio[i],0);
    }

    cdev_del(&flowingled.cdev);

    unregister_chrdev_region(flowingled.devid, FLOWINGLED_CNT);
    device_destroy(flowingled.class, flowingled.devid);
    class_destroy(flowingled.class);
    return 0;
}

static const struct of_device_id flowing_of_match[] = {
    {.compatible = "hcw-flowingled"},
    {}
};

static struct platform_driver flowingled_drv = {
    .driver = {
        .name = "imx6u-flowingled",
        .of_match_table = flowing_of_match,
    },
    .probe = flowingled_probe,
    .remove = flowingled_remove
};

static int __init flowingled_init(void)
{
    return platform_driver_register(&flowingled_drv);
}

static void __exit flowingled_exit(void)
{
    platform_driver_unregister(&flowingled_drv);
}

module_init(flowingled_init);
module_exit(flowingled_exit);

MODULE_AUTHOR("hcw");
MODULE_LICENSE("GPL");

  编译，并将 ko 文件装载到根文件系统中，试图装载，但出现以下报错：

图 1 IO被占用

  阅读报错信息，可以看到原本我们要用的 GPIO01_IO08 被占用。回到原理图，观察，也许我们可以临时关闭 USB_OTG1 来实现 3 个 IO 口的流水灯功能，修改设备树，重新编译、装载。没有报错了！（实际上博主在这一步消耗了大量时间，最终使用了1、2、4 三个 IO 口），终于无报错设备驱动匹配成功！

图 2 GPIO原理图

  接下来我们进一步写更详细的驱动代码，我想的是当用户输入 1 时，流水灯开启，当用户输入 0 时，流水灯关闭。主要就是开启一个固定时间的定时中断，在中断里调整 GPIO 的高低电平。首先写下回调函数：

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static void timer_callbacl(struct timer_list *t)
{
    mod_timer(&flowingled.timer, jiffies + msecs_to_jiffies(500));
}

  接着，在 probe 函数中写下初始化，并在 remove 函数中删除定时器。

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static int flowingled_probe(struct platform_device *dev)
{
    ·····

    timer_setup(&flowingled.timer, timer_callbacl, 0);

    mod_timer(&flowingled.timer, jiffies + msecs_to_jiffies(500));

    return 0;
}

static int flowingled_remove(struct platform_device *dev)
{
    for(int i = 0;i < FLOWINGLED_CNT; i++)
    {
        gpio_set_value(flowingled.gpio[i],0);
    }

    del_timer_sync(&flowingled.timer);

    ······
}

  接下来我们来完成流水灯的具体功能。最终代码如下：

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/*
 * @Author: 胡城玮
 * @FilePath: flowingled.c
 * @Date: 2026-03-11
 * @Description: 
 * @Version: 0.1
 */
#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/irq.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <linux/fs.h>
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/platform_device.h>
#include <linux/irq.h>

#define     FLOWINGLED_CNT      1
#define     FLOWINGLED_NAME     "hcw-flowingled"
#define     FLOWINGLED_ON       1
#define     FLOWINGLED_OFF      0

struct flowingled_dev{
    dev_t           devid;
    struct cdev     cdev;
    struct class    *class;
    struct device   *device;
    int             major;
    struct device_node  *node;

    int             gpio[3];
    int             led_num;

    struct timer_list   timer;
    unsigned int        period_ms;  // 控制闪烁周期
    unsigned int        cur_led;    // 当前灯号   
    unsigned int        dir;        // 闪烁方向
    unsigned int        running;    // 是否运行
};

struct flowingled_dev flowingled;

static void timer_callbacl(struct timer_list *t)
{
    if(flowingled.running)
    {
        flowingled.cur_led ++;
        if(flowingled.cur_led > 2)
            flowingled.cur_led = 0;
        else if(flowingled.cur_led < 0)
            flowingled.cur_led = 2;

        for(int i = 0;i < 3;i++)
        {
            if(i == flowingled.cur_led)
            {
                gpio_set_value(flowingled.gpio[i],1);
                continue;
            }
            gpio_set_value(flowingled.gpio[i],0);
        }
    }
    mod_timer(&flowingled.timer, jiffies + msecs_to_jiffies(500));
}

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

static ssize_t flowingled_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt)
{
    int retvalue;
    unsigned char databuf[2];
    unsigned char led_running_flag;

    struct flowingled_dev *dev = (struct flowingled_dev *)filp->private_data;

    retvalue = copy_from_user(databuf,buf,cnt);
    if(retvalue < 0)
    {
        printk("kernel write failed\r\n");
        return -EFAULT;
    }

    led_running_flag = databuf[0];

    if(led_running_flag == FLOWINGLED_ON)
    {
        dev->running = 1;
    }
    else if(led_running_flag == FLOWINGLED_OFF)
    {
        dev->running = 0;
    }

    return 0;
}

static struct file_operations flowingled_fops = {
    .owner = THIS_MODULE,
    .open = flowingled_open,
    .write = flowingled_write
};

static int flowingled_probe(struct platform_device *dev)
{
    printk("driver and device matched");

    if(flowingled.major){
        flowingled.devid = MKDEV(flowingled.major, 0);
        register_chrdev_region(flowingled.devid, FLOWINGLED_CNT, FLOWINGLED_NAME);
    }
    else
    {
        alloc_chrdev_region(&flowingled.devid, 0, FLOWINGLED_CNT, FLOWINGLED_NAME);
        flowingled.major = MAJOR(flowingled.devid);
    }

    cdev_init(&flowingled.cdev, &flowingled_fops);
    cdev_add(&flowingled.cdev, flowingled.devid,FLOWINGLED_CNT);

    flowingled.class = class_create(THIS_MODULE, FLOWINGLED_NAME);
    if(IS_ERR(flowingled.class))
    {
        return PTR_ERR(flowingled.class);
    }

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

    flowingled.node = of_find_node_by_path("/flowingled");
    if(flowingled.node == NULL)
    {
        printk("flowingled does not found\r\n");
        return -EINVAL;
    }

    for (int i = 0; i < 3; i++)
    {
        char buf[8];
        flowingled.gpio[i] = of_get_named_gpio(flowingled.node, "flowingled-gpios", i);
        if (flowingled.gpio[i] < 0) {
            printk("can't get flowingled-gpios[%d]\n", i);
            return flowingled.gpio[i];
        }
        sprintf(buf ,"LED%d", i);
        gpio_request(flowingled.gpio[i],buf);
        gpio_direction_output(flowingled.gpio[i],0);
    }

    timer_setup(&flowingled.timer, timer_callbacl, 0);

    mod_timer(&flowingled.timer, jiffies + msecs_to_jiffies(500));

    flowingled.running = 0;
    flowingled.cur_led = 0;

    return 0;
}

static int flowingled_remove(struct platform_device *dev)
{
    for(int i = 0;i < 3; i++)
    {
        gpio_set_value(flowingled.gpio[i],0);
    }

    del_timer_sync(&flowingled.timer);

    cdev_del(&flowingled.cdev);

    unregister_chrdev_region(flowingled.devid, FLOWINGLED_CNT);
    device_destroy(flowingled.class, flowingled.devid);
    class_destroy(flowingled.class);
    return 0;
}

static const struct of_device_id flowing_of_match[] = {
    {.compatible = "hcw-flowingled"},
    {}
};

static struct platform_driver flowingled_drv = {
    .driver = {
        .name = "imx6u-flowingled",
        .of_match_table = flowing_of_match,
    },
    .probe = flowingled_probe,
    .remove = flowingled_remove
};

static int __init flowingled_init(void)
{
    return platform_driver_register(&flowingled_drv);
}

static void __exit flowingled_exit(void)
{
    
    platform_driver_unregister(&flowingled_drv);
}

module_init(flowingled_init);
module_exit(flowingled_exit);

MODULE_AUTHOR("hcw");
MODULE_LICENSE("GPL");

  装载 ko 文件，运行测试程序向设备写入 1，成功点亮流水灯！