驱动代码：
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/init.h>
#include <linux/serio.h>
#include <linux/delay.h>
#include <linux/clk.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/uaccess.h>
#include <mach/regs-clock.h>
#include <plat/regs-timer.h>
#include <mach/regs-gpio.h>
#include <linux/cdev.h>
#include <linux/miscdevice.h>
#include <linux/gpio.h>
#include <asm-generic/poll.h>
#include <linux/poll.h>
#include <linux/device.h>//udev
struct class *key_class;
static int key_major = 0;
struct key_desc_t {
int pin; //which gpio pin
int pin_dir;//input or output
int number;
char *name;
};
/*设备结构体*/
static struct key_dev
{
struct cdev cdev;
struct timer_list key_timer;/*内核定时器*/
};
struct key_dev *key_devp;//设备结构体指针
#define MAX_KEYS 5
/* 用来指定按键所用gpio的编号,方向和名字 */
static struct key_desc_t key_desc [] = {
{S5PV210_GPH0(3), S3C_GPIO_INPUT, 0, "KEY1"}, /* K1 */
{S5PV210_GPH0(4), S3C_GPIO_INPUT, 1, "KEY2"}, /* K2 */
{S5PV210_GPH0(5), S3C_GPIO_INPUT, 2, "KEY3"}, /* K3 */
{S5PV210_GPH0(6), S3C_GPIO_INPUT, 3, "KEY4"}, /* K4 */
{S5PV210_GPH0(7), S3C_GPIO_INPUT, 4, "KEY5"}, /* K5 */
};
/* 按键被按下的次数*/
static volatile int key_values [MAX_KEYS] = {0, 0, 0, 0, 0};
/* 等待队列:
* 当没有按键被按下时，如果有进程调用key_read函数，
* 它将休眠
*/
static DECLARE_WAIT_QUEUE_HEAD(key_waitq);
#define KEY_TIMER_DELAY HZ/50 /*20ms*/
/* 事件标志, 有键按下时将它置1，key_read将它清0 */
static volatile int ev_press = 0;
static void key_timer_handle(unsigned long data)
{
struct key_desc_t *key_p = (struct key_desc_t *)data;
int down;
static unsigned char pressed[MAX_KEYS] = {0};
int i;
for(i=0;i<MAX_KEYS;i ++,key_p ++)
{
down = gpio_get_value(key_p->pin);
if(!down) //key pressed
{
pressed[i] ++;
if(pressed[i] > 2) pressed[i] = 3;
}
if((!down) && (2 == pressed[i]))//要等待20ms再检查一下该按键确实是被按下,而不是抖动
{
printk("pressed\n");
key_values[i] = i + 1;
ev_press = 1; /* 表示按键被按下了 */
wake_up_interruptible(&key_waitq); /* 唤醒休眠的进程 */
}
if(down && pressed[i]) //如果该键被释放
{
pressed[i] = 0;
}
}
/*调度定时器再次执行*/
key_devp->key_timer.expires = jiffies + KEY_TIMER_DELAY;
add_timer(&key_devp->key_timer);
}
/* 应用程序对设备文件/dev/key执行open(...)时，
* 就会调用key_open函数
*/
static int key_open(struct inode *inode, struct file *file)
{
return 0;
}
/* 应用程序对设备文件/dev/key执行close(...)时，
* 就会调用key_close函数
*/
static int key_close(struct inode *inode, struct file *file)
{
int i=0;
for(i=0;i<MAX_KEYS;i++)
gpio_free(key_desc[i].pin);
return 0;
}
/* 应用程序对设备文件/dev/key执行read(...)时，
* 就会调用key_read函数
*/
static int key_read(struct file *filp, char __user *buff,
size_t count, loff_t *offp)
{
unsigned long err;
if (!ev_press) {
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
else
/* 如果ev_press等于0，休眠 */
wait_event_interruptible(key_waitq, ev_press);
}
/* 执行到这里时，ev_press等于1，将它清0 */
ev_press = 0;
/* 将按键状态复制给用户，并清0 */
err = copy_to_user(buff, (const void *)key_values, min(sizeof(key_values), count));
memset((void *)key_values, 0, sizeof(key_values));
return err ? -EFAULT : min(sizeof(key_values), count);
}
/**************************************************
* 当用户程序调用select函数时，本函数被调用
* 如果有按键数据，则select函数会立刻返回
* 如果没有按键数据，本函数使用poll_wait等待
**************************************************/
static unsigned int key_poll(struct file *file,
struct poll_table_struct *wait)
{
unsigned int mask = 0;
poll_wait(file, &key_waitq, wait);
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
/* 这个结构是字符设备驱动程序的核心
* 当应用程序操作设备文件时所调用的open、read、write等函数，
* 最终会调用这个结构中的对应函数
*/
static struct file_operations key_fops = {
.owner = THIS_MODULE, /* 这是一个宏，指向编译模块时自动创建的__this_module变量 */
.open = key_open,
.release = key_close,
.read = key_read,
.poll = key_poll,
};
void set_gpio_mode_for_key(struct key_desc_t * key)
{
int i;
for(i = 0; i < MAX_KEYS; i ++,key ++)
{
//s3c_gpio_pullup(key->pin, 1);
s3c_gpio_cfgpin(key->pin, key->pin_dir);
}
}
/*
* Set up the cdev structure for a device.
*/
static void key_setup_cdev(struct key_dev *dev, int minor)
{
printk("in the key_setup_cdev!!\n");
int err, devno = MKDEV(key_major, minor);
cdev_init(&dev->cdev, &key_fops);
//dev->cdev.owner = THIS_MODULE;
//dev->cdev.ops = &key_fops;
printk("cdev_init success!!\n");
err = cdev_add (&dev->cdev, devno, 1);
/* Fail gracefully if need be */
if (err)
printk (KERN_NOTICE "Error %d adding key%d", err, minor);
printk("key_setup_cdev success!!\n");
}
/*
* We export one key device. There's no need for us to maintain any
* special housekeeping info, so we just deal with raw cdev.
*/
//static struct cdev key_cdev;
/*
* 执行“insmod *.ko”命令时就会调用这个函数
*/
static int __init button_init(void)
{
int result;
dev_t dev = MKDEV(key_major, 0);
char dev_name[]="key";
/*申请gpio*/
int ret;
int i=0;
for(i=0;i<MAX_KEYS;i++)
{
ret=gpio_request(key_desc[i].pin,"KEY");
if(ret)
{
printk("fail to request gpio %d !!\n",key_desc[i].pin);
return 0;
}
}
printk("request gpio success!!\n");
/* Figure out our device number. */
if (key_major)
result = register_chrdev_region(dev, 1, dev_name);
else {
result = alloc_chrdev_region(&dev, 0, 1, dev_name);
key_major = MAJOR(dev);
}
if (result < 0) {
printk(KERN_WARNING "key: unable to get major %d\n", key_major);
return result;
}
if (key_major == 0)
key_major = result;
printk("alloc_chrdev_region success !!\n");
/* 动态申请设备结构体的内存*/
key_devp = kmalloc(sizeof(struct key_dev), GFP_KERNEL);//kmalloc()内核空间；malloc()用户空间。返回起始地址
if (!key_devp) /*申请失败*/
{
result = - ENOMEM;
printk("key_devp kmalloc failed!!\n");
}
memset(key_devp, 0, sizeof(struct key_dev));//把此内存空间清零
/* Now set up cdev. */
key_setup_cdev(key_devp, 0);
printk("key device installed, with major %d\n", key_major);
printk("The device name is: /dev/%s\n", dev_name);
/*set gpio mode*/
//set_gpio_mode_for_key(key_desc);
/*init kernel timer*/
init_timer(&key_devp->key_timer);
key_devp->key_timer.function = &key_timer_handle;
key_devp->key_timer.data = (unsigned long)key_desc;
key_devp->key_timer.expires = jiffies + KEY_TIMER_DELAY;
add_timer(&key_devp->key_timer);
/*用udev机制自动添加设备结点*/
key_class=class_create(THIS_MODULE,"key_class");
device_create(key_class,NULL,key_devp->cdev.dev,NULL,dev_name);
return 0;
}
/*
* 执行rmmod key_drv.ko”命令时就会调用这个函数
*/
static void __exit button_cleanup(void)
{
cdev_del(&key_devp->cdev);
unregister_chrdev_region(MKDEV(key_major, 0), 1);
del_timer_sync(&key_devp->key_timer);
printk("key device uninstalled\n");
}
/* 这两行指定驱动程序的初始化函数和卸载函数 */
module_init(button_init);
module_exit(button_cleanup);
/* 描述驱动程序的一些信息，不是必须的 */
MODULE_AUTHOR("mhb@SEU"); // 驱动程序的作者
MODULE_DESCRIPTION("KEY Driver"); // 一些描述信息
MODULE_LICENSE("GPL"); // 遵循的协议
测试代码：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <errno.h>
int main(void)
{
int i;
int key_fd;
int key_value[5];
/*打开键盘设备文件*/
key_fd = open("/dev/key", 0);
if (key_fd < 0) {
perror("open device key");
exit(1);
}
for (;;) {
fd_set rds;
int ret;
FD_ZERO(&rds);
FD_SET(key_fd, &rds);
/*使用系统调用select检查是否能够从/dev/key设备读取数据*/
ret = select(key_fd + 1, &rds, NULL, NULL, NULL);
/*读取出错则退出程序*/
if (ret < 0) {
perror("select");
exit(1);
}
if (ret == 0) {
printf("Timeout.\n");
}
/*能够读取到数据*/
else if (FD_ISSET(key_fd, &rds)) {
/*开始读取键盘驱动发出的数据，注意key_value和键盘驱动中定义为一致的类型*/
int ret = read(key_fd, key_value, sizeof key_value);
if (ret != sizeof key_value) {
if (errno != EAGAIN)
perror("read key\n");
continue;
} else {
/*打印键值*/
for (i = 0; i < 5; i++)
printf("K%d %s, key value = 0x%02x\n", \
i+1, (key_value[i] & 0x80) ? "released": \
key_value[i] ? "pressed down" : "", key_value[i]);
}
}
}
/*关闭设备文件句柄*/
close(key_fd);
return 0;
}
来源：https://www.cnblogs.com/hello2mhb/p/3299803.html