mini2440_buttons.c驱动程序解读-电子工程世界

#include <linux/module.h>
#include
#include
#include
#include
#include
#include
#include
#include             //中断有关的头文件，request_irq()函数定义在此
#include
#include gpio.h>
#include
#include
#include
#include

#define DEVICE_NAME     'buttons'

struct button_irq_desc {                //定义按键中断结构体
    int irq;
    int pin;
    int pin_setting;
    int number;
    char *name;
};

#if !defined (CONFIG_QQ2440_BUTTONS)
static struct button_irq_desc button_irqs [] = {
    {IRQ_EINT8 , S3C2410_GPG0 , S3C2410_GPG0_EINT8 , 0, 'KEY0'},
    {IRQ_EINT11, S3C2410_GPG3 , S3C2410_GPG3_EINT11 , 1, 'KEY1'},
    {IRQ_EINT13, S3C2410_GPG5 , S3C2410_GPG5_EINT13 , 2, 'KEY2'},
    {IRQ_EINT14, S3C2410_GPG6 , S3C2410_GPG6_EINT14 , 3, 'KEY3'},
    {IRQ_EINT15, S3C2410_GPG7 , S3C2410_GPG7_EINT15 , 4, 'KEY4'},
    {IRQ_EINT19, S3C2410_GPG11, S3C2410_GPG11_EINT19, 5, 'KEY5'},
};
#else /* means QQ */
static struct button_irq_desc button_irqs [] = {
    {IRQ_EINT19, S3C2410_GPG11, S3C2410_GPG11_EINT19, 0, 'KEY0'},
    {IRQ_EINT11, S3C2410_GPG3, S3C2410_GPG3_EINT11, 1, 'KEY1'},
    {IRQ_EINT2, S3C2410_GPF2, S3C2410_GPF2_EINT2,   2, 'KEY2'},
    {IRQ_EINT0, S3C2410_GPF0, S3C2410_GPF0_EINT0,   3, 'KEY3'},
    {       -1,            -1,                 -1,    4, 'KEY4'},
    {       -1,            -1,                 -1,    5, 'KEY5'},
};
#endif
static volatile char key_values [] = {'0', '0', '0', '0', '0', '0'};

static DECLARE_WAIT_QUEUE_HEAD(button_waitq); //声明一个名为button_waitq的等待队列头

static volatile int ev_press = 0; /*中断事件标志,中断服务程序将它置1，tq2440_buttons_read将它清0 */

static irqreturn_t buttons_interrupt(int irq, void *dev_id)   //按键中断服务程序
{
    struct button_irq_desc *button_irqs = (struct button_irq_desc *)dev_id;
    int down;

    // udelay(0);
    down = !s3c2410_gpio_getpin(button_irqs->pin); //得到该pin的状态0/1

    if (down != (key_values[button_irqs->number] & 1)) { // Changed

   key_values[button_irqs->number] = '0' + down;

        ev_press = 1;
        wake_up_interruptible(&button_waitq);   //唤醒休眠的进程www.linuxidc.com
    }

    return IRQ_RETVAL(IRQ_HANDLED);
}

/*应用程序执行open('/dev/buttons',...)系统调用时，s3c24xx_buttons_open函数将
*被调用，它用来注册6个按键的中断处理程序*/
static int s3c24xx_buttons_open(struct inode *inode, struct file *file)
{
    int i;
    int err = 0;

    for (i = 0; i < sizeof(button_irqs)/sizeof(button_irqs[0]); i++) {
   if (button_irqs[i].irq < 0) {
       continue;

}

//注册中断服务程序 irq中断号 buttons_interrupt中断服务程序 IRQ_TYPE_EDGE_BOTH中断触发方式 name 中断名字

        err = request_irq(button_irqs[i].irq, buttons_interrupt, IRQ_TYPE_EDGE_BOTH,
                          button_irqs[i].name, (void *)&button_irqs[i]);
        if (err)
            break;
    }

    if (err) {             //如果发生错误，free掉所有的中断服务程序
        i--;
        for (; i >= 0; i--) {
        if (button_irqs[i].irq < 0) {
       continue;
        }
        disable_irq(button_irqs[i].irq);
            free_irq(button_irqs[i].irq, (void *)&button_irqs[i]);
        }
        return -EBUSY;
    }

    ev_press = 1;//标志中断发生了

    return 0;
}

/*应用程序对设备文件/dev/buttons执行close(...)时，
*就会调用s3c24xx_buttons_close函数*/
static int s3c24xx_buttons_close(struct inode *inode, struct file *file)
{
    int i;

    for (i = 0; i < sizeof(button_irqs)/sizeof(button_irqs[0]); i++) {         //设备关闭实际上就是free掉中断服务程序
   if (button_irqs[i].irq < 0) {
        continue;
   }
   free_irq(button_irqs[i].irq, (void *)&button_irqs[i]);
    }

    return 0;
}

/*应用程序对设备文件/dev/buttons执行read(...)时，
*就会调用s3c24xx_buttons_read函数
*/
static int s3c24xx_buttons_read(struct file *filp, char __user *buff, size_t count, loff_t *offp)
{
    unsigned long err;

    if (!ev_press) {
   if (filp->f_flags & O_NONBLOCK)
        return -EAGAIN;

else

/* __wait_event_interruptible()首先定义并初始化一个wait_queue_t变量__wait，

                                                                 * 其中数据为当前进程current，并把__wait入队。
                                                                 * 在无限循环中，__wait_event_interruptible()将本进程置为可中断的挂起状态，
                                                                 *反复检查condition是否成立，如果成立则退出，如果不成立则继续休眠；
                                                                 *条件满足后，即把本进程运行状态置为运行态，并将__wait从等待队列中清除掉，

*从而进程能够调度运行。如果进程当前有异步信号(POSIX的)，则返回-ERESTARTSYS。

        wait_event_interruptible(button_waitq, ev_press);
    }

    ev_press = 0;

    err = copy_to_user(buff, (const void *)key_values, min(sizeof(key_values), count));

    return err ? -EFAULT : min(sizeof(key_values), count);
}
/*应用程序对设备文件/dev/buttons执行select(...)时，
*就会调用s3c24xx_buttons_poll函数，作用：判断设备的可读写状态
*/
static unsigned int s3c24xx_buttons_poll( struct file *file, struct poll_table_struct *wait)
{
    unsigned int mask = 0;
    poll_wait(file, &button_waitq, wait);
    if (ev_press)
        mask |= POLLIN | POLLRDNORM;
    return mask;
}

/*这个结构是字符驱动设备程序的核心www.linuxidc.com
*当应用程序操作设备文件时所调用的open,read,write等函数
*最终会调用这个结构中的对应函数
*/
static struct file_operations dev_fops = {     //定义dev_fops结构
    .owner   =   THIS_MODULE,                  /*这是一个宏，指向编译模块时自动创建的__this_module变量*/
    .open    =   s3c24xx_buttons_open,
    .release =   s3c24xx_buttons_close,
    .read    =   s3c24xx_buttons_read,
    .poll    =   s3c24xx_buttons_poll,
};

static struct miscdevice misc = {        //定义名为misc的混杂设备
   .minor = MISC_DYNAMIC_MINOR,
   .name = DEVICE_NAME,
   .fops = &dev_fops,
};

static int __init dev_init(void)
{
   int ret;

   ret = misc_register(&misc);      //注册misc混杂设备

   printk (DEVICE_NAME'tinitializedn');

   return ret;
}

static void __exit dev_exit(void)
{
   misc_deregister(&misc);          //注销misc混杂设备
}

module_init(dev_init);
module_exit(dev_exit);
MODULE_LICENSE('GPL');
MODULE_AUTHOR('FriendlyARM Inc.');