buttons.c驱动程序解读

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <asm/irq.h>
#include <linux/interrupt.h>            //中断有关的头文件，request_irq()函数定义在此
#include <asm/uaccess.h>
#include <mach/regs-gpio.h>
#include <mach/hardware.h>
#include <linux/platform_device.h>
#include <linux/cdev.h>
#include <linux/miscdevice.h>

#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
    }
    
    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