按键实验（不带input子系统）

1.设备树代码

2.驱动代码

#include <linux/types.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/ide.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/errno.h> 
#include <linux/gpio.h>
#include <linux/of_gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <asm/mach/map.h>

#define KEY_CNT         1
#define KEY_NAME        "key"
#define KEY0VALUE       0xF0        /* 定义按键值 */
#define INVAKEY         0x00        /* 无效按键值 */

/* key设备结构体 */
struct key_dev{
    dev_t           devid;          /* 设备号 */
    struct cdev     cdev;           /* 字符设备 */
    struct class    *class;         /* 类 */
    struct device   *device;        /* 设备 */
    int             major;          /* 注设备号 */
    int             minor;          /* 次设备号 */
    struct device_node *nd;         /* 设备节点 */
    int             key_gpio;       /* 设备树里面的编号 */
    atomic_t        keyValue;       /* 按键的值，用来读取 */
};

struct key_dev key; /* 定义LED结构体 */

static int keyio_init(void)
{
    int ret;
    /* 1. 获取设备节点 */
    key.nd = of_find_node_by_path("/key");
    if( key.nd == NULL){
        ret = -EINVAL;
        printk("key node can not found!\r\n");
        return ret;
    }

    /* 2. 获取设备所对应的gpio */
    /* 注意第三个参数，因为只有一个索引，所以是0 */
    key.key_gpio = of_get_named_gpio(key.nd, "key-gpios", 0);
    if( key.key_gpio < 0) {
        printk("Can't find key gpio \r\n");
        ret = -EINVAL;
        return ret;
    }
    printk("Led gpio num = %d. \r\n", key.key_gpio);
    
    /* 3. 获取到IO之后，申请IO */
    /* 作用是申请之后，就能知道该IO是否被其他函数占用 */
    /* 如果申请失败，说明被战用啦 */
    /* 解决方法：1.搜索所需管脚 2.在搜索复用管脚，例如 &gpio1 3 */
    ret = gpio_request(key.key_gpio, "key0");
    if(ret) {
        printk("Failed to request the led gpio! \r\n");
        ret = -EINVAL;
        return ret;
    }

    /* 4. 使用IO */
    ret = gpio_direction_input(key.key_gpio); /* 设置输出，默认高电平不点亮 */
    if(ret < 0){
        printk("Failed to set input or output! \r\n");
        gpio_free(key.key_gpio);
        return ret;
    }

    printk("key init! \r\n");
    return 0;
}

static int key_open(struct inode *inode, struct file *filp)
{
    int ret;

    filp->private_data = &key;
    
    ret = keyio_init();
    if(ret < 0){
        return ret;
    }
    return 0;
}

static int key_release(struct inode *inode, struct file *filp)
{
    //struct key_dev *dev = (struct key_dev *)filp->private_data;
    return 0;
}

static ssize_t key_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{  
    return 0;
}

static ssize_t key_read(struct file *filp, char __user *buf,
size_t cnt, loff_t *offt)
{
    /* 获取私有数据 */
    struct key_dev *dev = (struct key_dev *)filp->private_data;
    int ret = 0;
    unsigned char value;

    if (gpio_get_value(dev->key_gpio) == 0) { /* key0 按下 */
        while(!gpio_get_value(dev->key_gpio)); /* 等待按键释放 */
        atomic_set(&dev->keyValue, KEY0VALUE);
    } else { /* 无效的按键值 */
        atomic_set(&dev->keyValue, INVAKEY);
    }

    value = atomic_read(&dev->keyValue); /* 保存按键值 */
    ret = copy_to_user(buf, &value, sizeof(value));
    return ret;
}

/* 字符设备操作集 */
static const struct file_operations key_fops = {
    .owner = THIS_MODULE,
    .write = key_write,
    .open = key_open,
    .read = key_read,
    .release = key_release,
};

/* 模块入口函数 */
static int __init myKey_init(void)
{
    /* 定义一些所需变量 */
    int ret = 0;
    /* 初始化原子变量 */
    atomic_set(&key.keyValue, INVAKEY);

    /* 1. 注册字符设备驱动 */
    key.major = 0;
    if(key.major) {
        key.devid = MKDEV(key.major, 0);
        ret = register_chrdev_region(key.devid, KEY_CNT, KEY_NAME);  
    } else {
        alloc_chrdev_region(&key.devid, 0, KEY_CNT, KEY_NAME);
        key.major = MAJOR(key.devid);
        key.minor = MINOR(key.devid);
    }
    if(ret < 0){
        goto fail_devid;
    }
    printk("Make devid success! \r\n");
    printk("major = %d, minor = %d \r\n", key.major, key.minor);

    /* 2. 初始化cdev */
    key.cdev.owner = THIS_MODULE;
    cdev_init(&key.cdev, &key_fops);
    ret = cdev_add(&key.cdev, key.devid, KEY_CNT);
    if (ret < 0){
        goto fail_cdev;
    } else {
        printk("Cdev add sucess! \r\n");
    }

    /* 3. 自动创建设备节点 */
    key.class = class_create(THIS_MODULE, KEY_NAME);
    if(IS_ERR(key.class)) {
        ret = PTR_ERR(key.class);
        goto fail_class;
    } else {
        printk("Class create sucess! \r\n");
    }

    key.device = device_create(key.class, NULL, key.devid, NULL, KEY_NAME);
    if(IS_ERR(key.device)) {
        ret = PTR_ERR(key.device);
        goto fail_device;
    } else {
        printk("Device create sucess! \r\n");
    }

    return 0;

/* 错误处理 */
fail_device:
    class_destroy(key.class);
fail_class:
    cdev_del(&key.cdev);
fail_cdev:
    unregister_chrdev_region(key.devid, KEY_CNT);
fail_devid:
    return ret;
}

/* 模块出口函数 */
static void __exit myKey_exit(void)
{
    /* 1. 释放设备号 */
    cdev_del(&key.cdev);
    /* 2. 注销设备号 */
    unregister_chrdev_region(key.devid, KEY_CNT);
    /* 3. 摧毁设备 */
    device_destroy(key.class, key.devid);
    /* 4.摧毁类 */
    class_destroy(key.class);

    printk("key exit! \r\n");
}

/* 模块入口和出口注册 */
module_init(myKey_init);
module_exit(myKey_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Shao Zheming");

3.应用代码

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

#define KEY0VALUE       0xF0        /* 定义按键值 */
#define INVAKEY         0x00        /* 无效按键值 */

int main(int argc, char *argv[])
{
    if(argc != 2)
    {
        printf("Error Usage!\r\n");
        return -1;
    }
    
    char *filename;
    int fd, retValue;
    unsigned char keyValue;

    filename = argv[1];
    fd = open(filename, O_RDWR);
    if(fd < 0)
    {
        printf("file %s open failed! \r\n", filename);
        return -1;
    }

    /* 循环读取按键值数据！ */
    while(1) {
        read(fd, &keyValue, sizeof(keyValue));
        if (keyValue == KEY0VALUE) { /* KEY0 */
            printf("KEY0 Press, value = %#X\r\n", keyValue);/* 按下 */
        }
    }

    retValue = close(fd);
    if(retValue < 0){
        printf("file %s close failed!\r\n", argv[1]);
    }
    return 0;
}