linux驅動之poll

poll機制是指驅動中，如果事件(如中斷)沒有發生，在一段時間內事件還沒有發生，那麼就超時返回，如果在這段時間有時間發生，那麼就直接相應事件，等事件相應後返回。

驅動代碼

#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 <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/poll.h>


static struct class *poll_class;
static struct class_device	*poll_class_dev;

//volatile unsigned long *gpfcon;
//volatile unsigned long *gpfdat;

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

/* 中斷事件標誌, 中斷服務程序將它置1，forth_drv_read將它清0 */
static volatile int ev_press = 0;


struct pin_desc{
	unsigned int pin;
	unsigned int key_val;
};


/* 鍵值: 按下時, 0x01, 0x02, 0x03, 0x04 */
/* 鍵值: 鬆開時, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;

/*
 * K1,K2,K3,K4對應GPG0，GPG3，GPG5，GPG6
 */

struct pin_desc pins_desc[4] = {
	{S3C2410_GPG0, 0x01},
	{S3C2410_GPG3, 0x02},
	{S3C2410_GPG5, 0x03},
	{S3C2410_GPG6, 0x04},
};


/*
  * 確定按鍵值
  */
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
	struct pin_desc * pindesc = (struct pin_desc *)dev_id;
	unsigned int pinval;
	
	pinval = s3c2410_gpio_getpin(pindesc->pin);

	if (pinval)
	{
		/* 鬆開 */
		key_val = 0x80 | pindesc->key_val;
	}
	else
	{
		/* 按下 */
		key_val = pindesc->key_val;
	}

    ev_press = 1;                  /* 表示中斷髮生了 */
    wake_up_interruptible(&button_waitq);   /* 喚醒休眠的進程 */

	
	return IRQ_RETVAL(IRQ_HANDLED);
}

static int forth_drv_open(struct inode *inode, struct file *file)
{
	/* GPG0，GPG3，GPG5，GPG6爲中斷引腳: EINT8,EINT11,EINT13,EINT14 */
	request_irq(IRQ_EINT8,  buttons_irq, IRQT_BOTHEDGE, "K1", &pins_desc[0]);
	request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "K2", &pins_desc[1]);
	request_irq(IRQ_EINT13, buttons_irq, IRQT_BOTHEDGE, "K3", &pins_desc[2]);
	request_irq(IRQ_EINT14, buttons_irq, IRQT_BOTHEDGE, "K4", &pins_desc[3]);	

	return 0;
}

ssize_t forth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
	if (size != 1)
		return -EINVAL;

	/* 如果沒有按鍵動作, 休眠 */
	wait_event_interruptible(button_waitq, ev_press);

	/* 如果有按鍵動作, 返回鍵值 */
	copy_to_user(buf, &key_val, 1);
	ev_press = 0;
	
	return 1;
}


int forth_drv_close(struct inode *inode, struct file *file)
{
	free_irq(IRQ_EINT8,  &pins_desc[0]);
	free_irq(IRQ_EINT11, &pins_desc[1]);
	free_irq(IRQ_EINT13, &pins_desc[2]);
	free_irq(IRQ_EINT14, &pins_desc[3]);
	return 0;
}

static unsigned forth_drv_poll(struct file *file, poll_table *wait)
{
	unsigned int mask = 0;
	poll_wait(file, &button_waitq, wait); // 不會立即休眠

	if (ev_press)
		mask |= POLLIN | POLLRDNORM;

	return mask;
}



static struct file_operations sencod_drv_fops = {
    .owner   =  THIS_MODULE,    /* 這是一個宏，推向編譯模塊時自動創建的__this_module變量 */
    .open    =  forth_drv_open,     
	.read	 =	forth_drv_read,	   
	.release =  forth_drv_close,
	.poll    =  forth_drv_poll,
};


int major;
static int forth_drv_init(void)
{
	major = register_chrdev(0, "forth_drv", &sencod_drv_fops);

	poll_class = class_create(THIS_MODULE, "forth_drv");

	poll_class_dev = class_device_create(poll_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */

//	gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
//	gpfdat = gpfcon + 1;

	return 0;
}

static void forth_drv_exit(void)
{
	unregister_chrdev(major, "forth_drv");
	class_device_unregister(poll_class_dev);
	class_destroy(poll_class);
//	iounmap(gpfcon);
	return 0;
}


module_init(forth_drv_init);

module_exit(forth_drv_exit);

MODULE_LICENSE("GPL");

app測試函數

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

int main(int argc, char **argv)
{
	int fd;
	unsigned char key_val;
	int ret;

	struct pollfd fds[1];
	
	fd = open("/dev/buttons", O_RDWR);
	if (fd < 0)
	{
		printf("can't open!\n");
	}

	fds[0].fd     = fd;
	fds[0].events = POLLIN;
	while (1)
	{
		ret = poll(fds, 1, 5000);
		if (ret == 0)
		{
			printf("time out\n");
		}
		else
		{
			read(fd, &key_val, 1);
			printf("key_val = 0x%x\n", key_val);
		}
	}
	
	return 0;
}