Linux设备驱动之五----带poll机制的驱动程序

驱动程序的代码如下：

#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 *forthdrv_class;static struct class_device*forthdrv_class_dev;volatile unsigned long *gpfcon;volatile unsigned long *gpfdat;volatile unsigned long *gpgcon;volatile unsigned long *gpgdat;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;struct pin_desc pins_desc[4] = {{S3C2410_GPF0, 0x01},{S3C2410_GPF2, 0x02},{S3C2410_GPG3, 0x03},{S3C2410_GPG11, 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;//通过调用系统提供的一个函数来读取按键值，当然你也完全可以自己手动实现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;                  /* 弄一个中断标志位，表示此刻中断发生了，以便下边使用 */return IRQ_RETVAL(IRQ_HANDLED);}static int forth_drv_open(struct inode *inode, struct file *file){/* 配置相应引脚为中断引脚 */request_irq(IRQ_EINT0,  buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);request_irq(IRQ_EINT2,  buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &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_EINT0, &pins_desc[0]);free_irq(IRQ_EINT2, &pins_desc[1]);free_irq(IRQ_EINT11, &pins_desc[2]);free_irq(IRQ_EINT19, &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); // 把当前进程添加到wait参数指定的等待列表中；这个函数并不会引起阻塞；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);forthdrv_class = class_create(THIS_MODULE, "forth_drv");forthdrv_class_dev = class_device_create(forthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);gpfdat = gpfcon + 1;gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);gpgdat = gpgcon + 1;return 0;}static void forth_drv_exit(void){unregister_chrdev(major, "forth_drv");class_device_unregister(forthdrv_class_dev);class_destroy(forthdrv_class);iounmap(gpfcon);iounmap(gpgcon);return 0;}module_init(forth_drv_init);module_exit(forth_drv_exit);MODULE_LICENSE("GPL");

注：

1>

驱动程序的poll函数应该返回设备资源的可获取状态，即POLLIN,POLLOUT,POLLPRI,POLLERR,POLLNVAL等宏的位

“或”结果，每个宏的含义都表明设备的一种状态，如POLLIN(定义0x01)意味着设备可以无阻塞地读，POLLOUT(定义为0x04)

意味着设备可以无阻塞地写；

2>

阻塞与非阻塞访问时I/O操作的两种不同模式，前者在I/O操作暂时不可进行时会让进程睡眠，后者则不然；

在设备驱动中阻塞I/O一般基于等待队列来实现，等待队列可用于同步驱动中时间发生的先后顺序。使用

非阻塞I/O的应用程序也可借助轮询函数来查询设备是否能立即被访问，用户空间调用select()和poll()接口，

设备驱动提供poll()函数。设备驱动的poll()本身不会阻塞，但是poll()和select()系统调用则会阻塞地等待

文件描述符集合中的至少一个可访问或超时。至于poll()和select()系统调用是如何知道文件描述符集合

是否可访问，这一点还有待深究；

测试程序的代码如下：

#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>#include <poll.h>/* forthdrvtest   */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;}

注：关于应用程序中的poll函数的使用，具体可man page