按键原理图

平时按键电平为高，按下按键后电平为低。

设备树生成工具i.MX Pins Tool v6

        BOARD_InitPinsSnvs: BOARD_InitPinsSnvsGrp {        /*!< Function assigned for the core: Cortex-A7[ca7] */
            fsl,pins = <
                MX6ULL_PAD_SNVS_TAMPER1__GPIO5_IO01        0x000110A0
            >;
        };

在设备树中添加pin controller组

        pinctrl-0 = <&pinctrl_hog_2>;      /* default */
        
         pinctrl_hog_2: hoggrp-2 {
            fsl,pins = <
                MX6ULL_PAD_SNVS_TAMPER9__GPIO5_IO09     0x1b0b0 /* enet1 reset */
                MX6ULL_PAD_SNVS_TAMPER6__GPIO5_IO06     0x1b0b0 /* enet2 reset */
                MX6ULL_PAD_SNVS_TAMPER1__GPIO5_IO01     0x000110A0 /*key 1*/
            >;
        };

在设备树根目录下创建子节点

     myButton{
        compatible = "100ask,Button_drv";
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_hog_2>;
        Button-gpios = <&gpio5 1 GPIO_ACTIVE_LOW>;
        };

编译拷贝设备树

具体操作和上一节一样

程序

Button_drv.c

#include <linux/module.h>
#include <linux/platform_device.h>

#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>
#include <linux/gpio.h>

/* 1. 确定主设备号                                                                 */
static int major = 0;
static struct class *Button_class;
static struct gpio_desc *Button_gpio; // GPIO操作结构体指针
static int err_g = 0;

/* 设备名 设备类 设备节点全局变量 */
static const char *device_name = "100ask_Button";       // 字符设备名
static const char *class_name = "100ask_Button_class";  // 设备类名
static const char *device_node_pattern = "100ask_Button0"; // 设备节点

/* 3. 实现对应的open/read/write等函数，填入file_operations结构体                   */
static ssize_t Button_drv_read(struct file *file, char __user *buf, size_t size, loff_t *offset)
{
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);

    int state;
    state = gpiod_get_value(Button_gpio);
    if (state < 0)
    {
        printk("Failed to get value for Button\n");
        return state;
    }

    state = copy_to_user(buf, &state, 1);
    return 1;
}

/* write(fd, &val, 1); */
static ssize_t Button_drv_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
    // int err;
    // char status;

    // printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    // err = copy_from_user(&status, buf, 1);


    return 0;
}

static int Button_drv_open(struct inode *node, struct file *file)
{

    printk("open file is  ok! \n");

    return 0;
}

static int Button_drv_close(struct inode *node, struct file *file)
{
    printk("close file is ok! \n");
    return 0;
}

/* 定义自己的file_operations结构体                                              */
static struct file_operations Button_drv = {
    .owner = THIS_MODULE,
    .open = Button_drv_open,
    .read = Button_drv_read,
    .write = Button_drv_write,
    .release = Button_drv_close,
};

/* 4. 从platform_device获得GPIO
 *    把file_operations结构体告诉内核：注册驱动程序
 */
static int chip_demo_gpio_probe(struct platform_device *pdev)
{
    // int err;
    err_g = 1;
    printk("err_g:%d\n", err_g);
    /* 4.1 设备树中定义有: led-gpios=<...>;    */
    /*
        该行代码的作用：从设备树中获取与 pdev 关联的设备上的 "led" GPIO 线。
        &pdev->dev: 指向 struct device 结构体的指针，这个结构体描述了一个设备
        gpiod_get():从设备树（Device Tree）中查找并获取一个 GPIO 控制器上的 GPIO 线。
    */
    Button_gpio = gpiod_get(&pdev->dev, "Button", 0); //"led"对应设备树里面的<label>
    if (IS_ERR(Button_gpio))
    {
        dev_err(&pdev->dev, "Failed to get GPIO for Button\n");
        err_g = 2;
        return PTR_ERR(Button_gpio);
    }
    gpiod_direction_input(Button_gpio);

    /* 4.2 注册file_operations     */
    major = register_chrdev(0, device_name, &Button_drv); /* /dev/100ask_led0 */

    Button_class = class_create(THIS_MODULE, class_name);
    if (IS_ERR(Button_class))
    {
        unregister_chrdev(major, device_name); // 卸载驱动
        gpiod_put(Button_gpio);             // 释放GPIO
        err_g = 3;
        return PTR_ERR(Button_class);
    }

    /* /dev/100ask_led */
    device_create(Button_class, NULL, MKDEV(major, 0), NULL, device_node_pattern);

    return 0;
}

static int chip_demo_gpio_remove(struct platform_device *pdev)
{
    device_destroy(Button_class, MKDEV(major, 0));
    class_destroy(Button_class);
    unregister_chrdev(major, device_name);
    gpiod_put(Button_gpio);

    return 0;
}

/* 定义设备树匹配表，用于识别和支持特定的LED驱动器 */
static const struct of_device_id ask100_Buttons[] = {
    /* 匹配字符串 "100ask,leddrv" 用于标识100ASK系列LED驱动器 */
    {.compatible = "100ask,Button_drv"},
    /* 空项作为匹配表的结束标志 */
    {},
};

/* 1. 定义platform_driver */
/* 定义一个平台驱动结构体，用于LED芯片的演示 */
static struct platform_driver chip_demo_gpio_driver = {
    /* 设置探测函数，当设备被探测到时调用 */
    .probe = chip_demo_gpio_probe,
    /* 设置移除函数，当设备被移除时调用 */
    .remove = chip_demo_gpio_remove,
    /* 设置<驱动程序的名称>和<设备树匹配表> */
    .driver = {
        /* 设置驱动程序的名称 */
        .name = "100ask_Button", // 字符设备名
                                 /* 设置设备树匹配表，用于设备的匹配 */
        .of_match_table = ask100_Buttons,
    },
};

/* 2. 在入口函数注册platform_driver */
static int __init Button_init(void)
{
    int err;
    err = platform_driver_register(&chip_demo_gpio_driver);
    printk("err_g:%d init_err:%d\n", err_g, err);
    // printk("__FILE__:%s line:%d  err:%d led_class:%d err_g:%d\n", __FILE__, __LINE__, err, led_class, err_g);

    return err;
}

/* 3. 有入口函数就应该有出口函数：卸载驱动程序时，就会去调用这个出口函数
 *     卸载platform_driver
 */
static void __exit Button_exit(void)
{
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    device_destroy(Button_class, MKDEV(major, 0));
    class_destroy(Button_class);
    unregister_chrdev(major, device_name);
    // gpiod_put(button_gpio);

    platform_driver_unregister(&chip_demo_gpio_driver);
}

/* 7. 其他完善：提供设备信息，自动创建设备节点                                     */

module_init(Button_init);
module_exit(Button_exit);

MODULE_LICENSE("GPL");

Button_test.c

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <poll.h>
#include <signal.h>

#define BUTTON_DEV "/dev/100ask_Button0"


/*
 * ./Button_test /dev/100ask_Button0 
 */
int main(int argc, char **argv)
{
    int fd;
    char val;
    struct pollfd fds[1];
    const int timeout = 10000;


    /* 1. 判断参数 */
    if (argc != 2)
    {
        printf("Usage: %s /dev/<dev> \n", argv[0]);
        return -1;
    }

    /* 2. 打开文件 */
    fd = open(argv[1], O_RDWR | O_NONBLOCK);
    if (fd == -1)
    {
        printf("can not open file %s\n", argv[1]);
        return -1;
    }

    /* 3. 读文件 */
    read(fd, &val, 1);
    printf("get button : %d\n", val);

    fds[0].fd = fd;
    fds[0].events = POLLIN;

    while(1)
    {
        if(poll(fds, 1, -1) == -1)
        {
            printf("poll error\n");
            break;
        }
        if(fds[0].revents & POLLIN)
        {
            
            read(fd, &val, 1);
            printf("get button : %d\n", val);
        }
        usleep(timeout); 
    }


    close(fd);
    return 0;
}

Makefile

# 1. 使用不同的开发板内核时, 一定要修改KERN_DIR
# 2. KERN_DIR中的内核要事先配置、编译, 为了能编译内核, 要先设置下列环境变量:
# 2.1 ARCH,          比如: export ARCH=arm64
# 2.2 CROSS_COMPILE, 比如: export CROSS_COMPILE=aarch64-linux-gnu-
# 2.3 PATH,          比如: export PATH=$PATH:/home/book/100ask_roc-rk3399-pc/ToolChain-6.3.1/gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu/bin 
# 注意: 不同的开发板不同的编译器上述3个环境变量不一定相同,
#       请参考各开发板的高级用户使用手册

KERN_DIR =  /home/book/100ask_imx6ull-sdk/Linux-4.9.88 # 板子所用内核源码的目录

all:
    make -C $(KERN_DIR) M=`pwd` modules 
    $(CROSS_COMPILE)gcc -o Button_test Button_test.c 

clean:
    make -C $(KERN_DIR) M=`pwd` modules clean
    rm -rf modules.order
    rm -f Button_test

# 参考内核源码drivers/char/ipmi/Makefile
# 要想把a.c, b.c编译成ab.ko, 可以这样指定:
# ab-y := a.o b.o
# obj-m += ab.o



obj-m += Button_drv.o

上机验证成功