按键驱动程序（异步通知）

    此驱动程序之前的按键驱动程序（中断方式）上加以优化。用到异步通知。对于内核来讲，既然用户想得到的是按键后的状态，那么自然不必时时都要ｒｅａｄ状态。当它检测到中断发生变主动通知用户，用户再来读。这样，用户空间、内核就可以着手干点其它的事情，而不必忙等按键按下或释放。那么就先从应用程序上面看。

怎么设置相关联到“异步通知”呢？
flag = fcntl(fd, F_GETFL);
fcntl(fd, F_SETFL, flag|FASYNC);
这样的两句就可以将文件描述符fd与异步通知关联，到时候将会接到相关通知。
怎么知道通知道本程序呢？
fcntl(fd, F_SETOWN, getpid());
将其与进程号关联，这样内核就知道要将通知发往本进程。
得到通知后该怎么做呢？
sighandler_t signal(int signum, sighandler_t handler);
后面的handler是接到信号后的处理函数，而对于一般的IO操作，signum通常为SIGIO，这点在内核驱动中要保持一致。handler的定义为
typedef void (*sighandler_t)(int); 在这个函数体内就可以去read数据了。

驱动程序上面又是如何实现的呢？
需要在file_operations结构体里设置.fasync = xxx_fasync,并定义xxx_fasync函数.
static int xxx_fasync(int fd, struct file *filp, int on)
当fcntl(fd, F_SETFL, flag|FASYNC);设置异步通知标志后，就会调用驱动里的xxx_fasync函数，我们需要在驱动程序里先定义一个fasync_struct结构体指针，然后通过xxx_fasync函数再调用int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)去初始化这个结构体。以便在中断服务程序里发送信号。当产生按键中断时，再不是像poll机制那样唤醒等待队列，而是用kill_fasync(struct fasync_struct **fp, int sig, int band)发送信号。应用程序收到信号后会调用自定义的handler做相关处理（本程序是read内核的按键状态）。

详细的驱动程序为：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <linux/cdev.h>
#include <linux/interrupt.h>
#include <linux/device.h>
#include <linux/sched.h>
#include <linux/gpio.h>
#include <linux/poll.h>

#define FIFTHDEV MKDEV(250, 0)
struct cdev fifthdrv_cdev;

static struct class *fifthdrv_class;

struct button {
    int irq;
    char *name;
    int pin;
    int val;
};
//static volatile int pressed = 0;
static unsigned char key_val;

struct fasync_struct *button_async;

//DECLARE_WAIT_QUEUE_HEAD(button_wqh);

/* 六个按键的相关定义整合到结构体 */
static struct button buttons[6] = {
        {IRQ_EINT8,   "K1", S3C2410_GPG(0),  0x1},
        {IRQ_EINT11, "K2", S3C2410_GPG(3),  0x2},
        {IRQ_EINT13, "K3", S3C2410_GPG(5),  0x3},
        {IRQ_EINT14, "K4", S3C2410_GPG(6),  0x4},
        {IRQ_EINT15, "K5", S3C2410_GPG(7),  0x5},
        {IRQ_EINT19, "K6", S3C2410_GPG(11),0x6},
};

/* 中断处理函数 */
static irqreturn_t fifthdrv_intr(int irq, void *data)
{
    struct button *buttonp;
    int val;

    buttonp = (struct button*)data;

    val = s3c2410_gpio_getpin(buttonp->pin);


    if (!val) {/* 按下按键*/
        key_val = buttonp->val;
    } else {  /* 释放按键*/
        key_val = buttonp->val | 0x10;  //将第4位置1，做标记
    }

    //pressed = 1;    //此处改变按下标志，以使队列不继续睡眠
    //wake_up_interruptible(&button_wqh);
    kill_fasync(&button_async, SIGIO, POLL_IN);

    return IRQ_RETVAL(IRQ_HANDLED);
}

static int fifthdrv_open(struct inode * inode, struct file * file)
{
    int i=6;
    while(i--){
        request_irq(buttons[i].irq, &fifthdrv_intr, IRQ_TYPE_EDGE_BOTH,
                    buttons[i].name, &buttons[i]);
    }
    return 0;

}

static ssize_t fifthdrv_read(struct file *file, char __user *user, size_t size,loff_t*o)
{
    int sz = sizeof(key_val) ;

    if (sz != size) {
        return -EINVAL;
    }

    /* 使用异步通知，此处不必休眠 */
    //wait_event_interruptible(button_wqh, pressed);

    copy_to_user(user, &key_val, sz);

    /* 重新清除按下标志 */
    //pressed = 0;

    return sz;
}

static int fifthdrv_close(struct inode *inode, struct file *file)
{
    int i=6;

    while(i--) {
        free_irq(buttons[i].irq, &buttons[i]);
    }
    return 0;
}

/*
static unsigned int fifthdrv_poll(struct file *file, poll_table *wait)
{
    unsigned int res=0;

    poll_wait(file, &button_wqh, wait);

    if (pressed) {
        res |= POLLIN | POLLRDNORM;
    }
    return res;
}
*/
static int fifthdrv_fasync(int fd, struct file *filp, int on)
{
    return fasync_helper(fd, filp, on, &button_async);
}


static struct file_operations fifthdrv_ops = {
    .owner = THIS_MODULE,
    .open   = fifthdrv_open,
    .read    = fifthdrv_read,
    //.poll     = fifthdrv_poll,
    .release = fifthdrv_close,
    .fasync = fifthdrv_fasync,
};
static int fifthdrv_init(void)
{
    int ret;
    int devt = FIFTHDEV;

    ret = register_chrdev_region(devt, 1, "fifthdrv");
    if (ret) {
        printk(KERN_ERR "Unable to register minors for fifthdrv\n");
        goto fail;
    }
    fifthdrv_class = class_create(THIS_MODULE, "fifthdrv_class");
    if (IS_ERR(fifthdrv_class)) {
        printk(KERN_ERR "can't register device class\n");
        return PTR_ERR(fifthdrv_class);
    }
    device_create(fifthdrv_class, NULL, devt, NULL, "buttons");
    cdev_init(&fifthdrv_cdev, &fifthdrv_ops);
    ret = cdev_add(&fifthdrv_cdev, devt, 1);
    if (ret < 0)
        goto fail_cdev;
    return 0;

fail_cdev:
    class_unregister(fifthdrv_class);
    device_destroy(fifthdrv_class, devt);
    cdev_del(&fifthdrv_cdev);
fail:
    unregister_chrdev_region(devt, 1);

    return 0;
}

static void fifthdrv_exit(void)
{
    class_unregister(fifthdrv_class);
    device_destroy(fifthdrv_class, FIFTHDEV);
    cdev_del(&fifthdrv_cdev);
    unregister_chrdev_region(FIFTHDEV, 1);
}

module_init(fifthdrv_init);
module_exit(fifthdrv_exit);
MODULE_LICENSE("GPL");

应用程序为：

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

int fd;

void signal_f(int signum)
{
    unsigned char val;
    static unsigned int cnt = 1;
    read(fd, &val, sizeof(val));
    printf("cnt:%d, val:0x%x\n", cnt++, val);
}

int main(int argc, char *argv[])
{
    int flag;

    fd = open("/dev/buttons", O_RDWR);
    if (fd < 0)
    {
        printf("can't open!\n");
    }
    signal(SIGIO, signal_f);
    fcntl(fd, F_SETOWN, getpid());
    flag = fcntl(fd, F_GETFL);
    fcntl(fd, F_SETFL, flag|FASYNC);
    while (1)
    {
        sleep(1000);
    }
    return 0;
}

运行状态：

文章说明：

此博文只为总结分享学习经验，许多内容不能也并未详细描述，如每个函数的参数、返回值，何为内核空间、用户空间，怎么操作寄存器, Makefile的编写，编译应用程序等等，这些知识点都在相关资料中能得到更专业、详细的解答。