韦东山驱动视频笔记——3.字符设备驱动程序之poll机制

linux内核版本：linux-2.6.30.4

目的：我们在中断方式的按键应用程序中，如果没有按键按下，read就会永远在那等待，所以如果在这个程序里还想做其他事就不可能了。因此我们这次改进它，让它在等待5秒钟，如果5秒钟内没有按键按下就返回，可以在read后面做其他事，只需要在驱动程序里加入poll机制就可以完成目的。

 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/delay.h>
 #include <asm/uaccess.h>
 #include <asm/irq.h>
 #include <asm/io.h>
 #include <linux/device.h>
 #include <linux/irq.h>
 #include <linux/interrupt.h>
 #include <mach/regs-gpio.h>
 #include <linux/poll.h>  
 
 static struct class *fourth_drv_class;
 static struct class_device  *fourth_drv_class_dev;  
 
 static volatile unsigned long *gpfcon;
 static volatile unsigned long *gpfdat;
 static int major;  
 
 struct pin_desc
 {
     unsigned int pin;
     unsigned int key_val;
 };  
 
 static unsigned char key_val;  
 
 static struct pin_desc pins_desc[] =
 {
     {S3C2410_GPF1, 0x01},
     {S3C2410_GPF4, 0x02},
     {S3C2410_GPF2, 0x03},
     {S3C2410_GPF0, 0x04},
 };  
 
 static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
 static volatile int ev_press = ;  
 
 static irqreturn_t buttons_irq(int irq, void *dev_id)
 {
     struct pin_desc *pin = (struct pin_desc *)dev_id;
     unsigned int pinval;
     pinval = s3c2410_gpio_getpin(pin->pin);  
 
     if (pinval)
     {
         //松开
         key_val = 0x80 | pin->key_val;
     }
     else
     {
         //按下
         key_val = pin->key_val;
     }  
 
     wake_up_interruptible(&button_waitq);
     ev_press = ;  
 
     return IRQ_HANDLED;
 }  
 
 static int fourth_drv_open(struct inode *inode, struct file *file)
 {
     request_irq(IRQ_EINT1, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S1", &pins_desc[]);
     request_irq(IRQ_EINT4, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S2", &pins_desc[]);
     request_irq(IRQ_EINT2, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S3", &pins_desc[]);
     request_irq(IRQ_EINT0, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S4", &pins_desc[]);
     return ;
 }  
 
 static ssize_t fourth_drv_read(struct file *file, char __user *buf,
             size_t count, loff_t *ppos)
 {
     if (count != )
         return -EINVAL;
     /*如果没有按键动作，休眠*/
     wait_event_interruptible(button_waitq, ev_press);  
 
     /*如果有按键动作发生，返回键值*/
     copy_to_user(buf, &key_val, );
     ev_press = ;
     return ;
 }  
 
 static int fourth_drv_release(struct inode *inode, struct file *file)
 {
     free_irq(IRQ_EINT1, &pins_desc[]);
     free_irq(IRQ_EINT4, &pins_desc[]);
     free_irq(IRQ_EINT2, &pins_desc[]);
     free_irq(IRQ_EINT0, &pins_desc[]);
     return ;
 }  
 
 static unsigned int fourth_drv_poll(struct file *file, poll_table *wait)  
 
 {
     unsigned int mask = ;  
 
     /*这并不会休眠，只是把当前进程挂到队列里*/
     poll_wait(file, &button_waitq, wait);  
 
     if (ev_press)
     {
         mask |= (POLLIN | POLLRDNORM);
     }
     return mask;
 }  
 
 static struct file_operations fourth_fops = {
     .owner = THIS_MODULE,
     .open = fourth_drv_open,
     .read = fourth_drv_read,
     .poll = fourth_drv_poll,
     .release  = fourth_drv_release,
 };  
 
 int fourth_init()
 {
     int ret;
     major = register_chrdev(, "fourth_drv", &fourth_fops);
     fourth_drv_class = class_create(THIS_MODULE, "fourth_drv");
     device_create(fourth_drv_class, NULL, MKDEV(major, ), NULL, "buttons");  
 
     gpfcon = (volatile unsigned long *)ioremap(0x56000050, );
     gpfdat = gpfcon + ;  
 
     return ;
 }
 static void fourth_exit()
 {
     unregister_chrdev(major, "fourth_drv");
     device_destroy(fourth_drv_class, MKDEV(major, ));
     class_destroy(fourth_drv_class);
     iounmap(gpfcon);
 }  
 
 module_init(fourth_init);
 module_exit(fourth_exit);  
 
 MODULE_LICENSE("GPL");  

测试程序：

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <poll.h>  
 
 /* fourthdrvtest
   */
 int main(int argc, char **argv)
 {
     int fd;
     unsigned char key_val;
     int ret;
     struct pollfd fds[];  
 
     fd = open("/dev/buttons", O_RDWR);
     if (fd < )
     {
         printf("can't open!\n");
     }  
 
     fds[].fd = fd;
     fds[].events = POLLIN;
     while ()
     {
         ret = poll(fds, , );
         if (ret == )
         {
             printf("time out!\n");
         }
         else
         {
             read(fd, &key_val, );
             printf("key_val === 0x%x\n", key_val);
         }
     }  
 
     return ;
 }  

运行效果：