linux驱动之poll

poll机制是指驱动中，如果事件(如中断)没有发生，在一段时间内事件还没有发生，那么就超时返回，如果在这段时间有时间发生，那么就直接相应事件，等事件相应后返回。

驱动代码

#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);/* 中断事件标志, 中断服务程序将它置1，forth_drv_read将它清0 */static volatile int ev_press = 0;struct pin_desc{unsigned int pin;unsigned int key_val;};/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 *//* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */static unsigned char key_val;/* * K1,K2,K3,K4对应GPG0，GPG3，GPG5，GPG6 */struct pin_desc pins_desc[4] = {{S3C2410_GPG0, 0x01},{S3C2410_GPG3, 0x02},{S3C2410_GPG5, 0x03},{S3C2410_GPG6, 0x04},};/*  * 确定按键值  */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){/* 松开 */key_val = 0x80 | pindesc->key_val;}else{/* 按下 */key_val = pindesc->key_val;}    ev_press = 1;                  /* 表示中断发生了 */    wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */return IRQ_RETVAL(IRQ_HANDLED);}static int forth_drv_open(struct inode *inode, struct file *file){/* GPG0，GPG3，GPG5，GPG6为中断引脚: 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;/* 如果没有按键动作, 休眠 */wait_event_interruptible(button_waitq, ev_press);/* 如果有按键动作, 返回键值 */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); // 不会立即休眠if (ev_press)mask |= POLLIN | POLLRDNORM;return mask;}static struct file_operations sencod_drv_fops = {    .owner   =  THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */    .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测试函数

#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;}