Linux驱动学习笔记（4）

poll机制，就是一种查询机制--给定一段时间，如果在这段时间内有按键按下，则立刻返回键值；如果在这段时间里没有按键按下，则处于休眠状态，如果这段时间到了就会返回。

1. poll > sys_poll > do_sys_poll > poll_initwait，poll_initwait函数注册一下回调函数__pollwait，它就是我们的驱动程序执行poll_wait时，真正被调用的函数。

 

2. 接下来执行file->f_op->poll，即我们驱动程序里自己实现的poll函数

   它会调用poll_wait把自己挂入某个队列，这个队列也是我们的驱动自己定义的；

   它还判断一下设备是否就绪。

 

3. 如果设备未就绪，do_sys_poll里会让进程休眠一定时间

 

4. 进程被唤醒的条件有2：一是上面说的“一定时间”到了，二是被驱动程序唤醒。驱动程序发现条件就绪时，就把“某个队列”上挂着的进程唤醒，这个队列，就是前面通过poll_wait把本进程挂过去的队列。

 

5. 如果驱动程序没有去唤醒进程，那么chedule_timeout(__timeou)超时后，会重复2、3动作，直到应用程序的poll调用传入的时间到达。

#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;

    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)
{
    /* 配置GPF0,2为输入引脚 */
    /* 配置GPG3,11为输入引脚 */
    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_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); // 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);

    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");

poll的用法可以在linux终端下通过命令man poll来查询。
测试程序：

#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)             // 等待5s如果没有按键按下返回值为0，则打印超时并退出
        {
            printf("time out\n");
        }
        else
        {
            read(fd, &key_val, 1);  // 在5s内有按键按下立即返回按键值。
            printf("key_val = 0x%x\n", key_val);
        }
    }

    return 0;
}