字符设备驱动程序——按键中断之互斥阻塞操作

一、互斥操作
在编程中，引入了对象互斥锁的概念，来保证共享数据操作的完整性。每个对象都对应于一个可称为" 互斥锁" 的标记，这个标记用来保证在任一时刻，只能有一个线程访问该对象。

实现方式

1. 原子操作
   原子操作指的是在执行过程中不会被别的代码路径所中断的操作。
   常用原子操作函数举例：
   atomic_t v = ATOMIC_INIT(0); //定义原子变量v并初始化为0
   atomic_read(atomic_t *v); //返回原子变量的值
   void atomic_inc(atomic_t *v); //原子变量增加1
   void atomic_dec(atomic_t *v); //原子变量减少1
   int atomic_dec_and_test(atomic_t *v); //自减操作后测试其是否为0，为0则返回true，否则返回false。

2. 信号量
   信号量（semaphore）是用于保护临界区的一种常用方法，只有得到信号量的进程才能执行临界区代码。
   当获取不到信号量时，进程进入休眠等待状态。

   2.1、定义信号量
   struct semaphore sem;
   初始化信号量
   void sema_init (struct semaphore *sem, int val);
   void init_MUTEX(struct semaphore *sem);//初始化为0

   static DECLARE_MUTEX(button_lock); //定义互斥锁

   2.2、获得信号量
   void down(struct semaphore * sem);//获取信号量失败进入睡眠状态时
   int down_interruptible(struct semaphore * sem); //在进入睡眠状态时的进程能被信号打断，获取失败返回非0值
   int down_trylock(struct semaphore * sem);//若无法获得则直接返回1而不睡眠

   2.3、释放信号量
   void up(struct semaphore * sem);

驱动程序

#include <linux/module.h>
#include <linux/sched.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 <linux/device.h>
#include <mach/gpio.h>
#include <linux/interrupt.h>
#include <linux/poll.h>

static struct class *newdrv_class;

volatile unsigned long *gpfcon = NULL;
volatile unsigned long *gpfdat = NULL;
volatile unsigned long *gpgdat = NULL;
volatile unsigned long *gpgcon = NULL;

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

static unsigned char key;

static struct fasync_struct *newdrv_async;

/* 原子操作：在执行过程中不会被别的代码路径所中断的操作
 * 驱动程序在一个时刻，只能由一个应用程序打开*/
//atomic_t v = ATOMIC_INIT(1);     //定义原子变量v并初始化为1

static DECLARE_MUTEX(button_lock);     //定义信号量/互斥锁


struct pin_desc{
	unsigned int pin;//引脚
	unsigned int key_val;//键值,按下01 02 03 04；松开81 82 83 84
};

struct pin_desc pins_desc[4]={
	{S3C2410_GPF(0), 0x01},
	{S3C2410_GPF(2), 0x02},
	{S3C2410_GPG(3), 0x03},
	{S3C2410_GPG(11), 0x04},
};
	
static int 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);//读引脚
	if(pinval)//1 松开
	{
		key=0x80|pindesc->key_val;
	}
	else//按下
		key=pindesc->key_val;

	  kill_fasync(&newdrv_async,SIGIO,POLL_IN);//发送信号，给newdrv_async
	  
	return IRQ_RETVAL(IRQ_HANDLED);//接收到了中断信号,并处理，返回1
}


static int new_drv_open(struct inode *inode, struct file *file)
{
	/*if(!atomic_dec_and_test(&v))//自减操作后测试其是否为0，为0则返回true，跳出，否则返回false。
	{
		atomic_inc(&v);//原子变量增加1
		return -EBUSY;
	}*/
	down(&button_lock);//第一次获得信号量，若没有释放再次进入，陷入休眠
	
	/* 中断引脚			中断函数		触发方式（双边沿）									名称	   传入dev?id */
	request_irq(IRQ_EINT0,  buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S2", &pins_desc[0]);
	request_irq(IRQ_EINT2,  buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S3", &pins_desc[1]);
	request_irq(IRQ_EINT11, buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S4", &pins_desc[2]);
	request_irq(IRQ_EINT19, buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S5", &pins_desc[3]);
	return 0;
}
}

static ssize_t new_drv_read(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
	if(count!=1)
		return -EINVAL;

	copy_to_user(buf, &key, 1);
	
	return 1;
}

static int new_drv_close(struct inode *inode, struct file *file)
{
	//atomic_inc(&v);//释放原子操作
	up(&button_lock);//释放信号量，释放后才能再次被打开进入open
	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 int new_drv_fasync (int fd, struct file *filp, int on)
{
	return fasync_helper (fd, filp, on, &newdrv_async);//初始化newdrv_async
}

static struct file_operations new_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   =new_drv_open,     
	.read   =new_drv_read,
	.release=new_drv_close,
	.fasync   =new_drv_fasync,
};

int major;
static int new_drv_init(void)
{
	major = register_chrdev(0, "newdrv", &new_drv_fops); // 注册, 自动分配并返回主设备号
		/*在/sys/class/下创建类目录*/
	newdrv_class = class_create(THIS_MODULE, "newdrv");
		/*根据类目录，在驱动模块初始化函数中实现设备节点的自动创建*/
	device_create(newdrv_class, NULL, MKDEV(major, 0), NULL, "newdrv"); 

	gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
	gpfdat = gpfcon + 1;
	gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);
	gpgdat = gpgcon + 1;

	return 0;
}

static void new_drv_exit(void)
{
	unregister_chrdev(major, "newdrv"); // 卸载，删除
	device_destroy(newdrv_class,MKDEV(major, 0));
	class_destroy(newdrv_class);
	iounmap(gpfcon);
	iounmap(gpgcon);
}

module_init(new_drv_init);//入口函数
module_exit(new_drv_exit);//出口函数

MODULE_LICENSE("GPL");

二、阻塞操作
是指在执行设备操作时若不能获得资源则挂起进程，直到满足可操作的条件后再进行操作。
被挂起的进程进入休眠状态，被从调度器的运行队列移走，直到等待的条件被满足。

非阻塞操作
进程在不能进行设备操作时并不挂起，它或者放弃，或者不停地查询，直至可以进行操作为止。

fd = open("…", O_RDWR | O_NONBLOCK);

驱动程序

#include <linux/module.h>
#include <linux/sched.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 <linux/device.h>
#include <mach/gpio.h>
#include <linux/interrupt.h>
#include <linux/poll.h>

static struct class *sixthdrv_class;

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，sixth_drv_read将它清0 */
static volatile int ev_press = 0;

static struct fasync_struct *button_async;

struct pin_desc{
	unsigned int pin;
	unsigned int key_val;
};

static unsigned char key_val;

struct pin_desc pins_desc[4] = {
	{S3C2410_GPF(0), 0x01},
	{S3C2410_GPF(2), 0x02},
	{S3C2410_GPG(3), 0x03},
	{S3C2410_GPG(11), 0x04},
};

struct semaphore button_lock;/*定义信号量*/

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 sixth_drv_open(struct inode *inode, struct file *file)
{	
		/*以非阻塞方式打开，*/
	if (file->f_flags & O_NONBLOCK)
	{
		/*获取信号量，若无法获取信号量则返回*/
		if (down_trylock(&button_lock))
			return -EBUSY;
	}
	else
	{
		/* 获取信号量 */
		down(&button_lock);
	}

	/* 配置GPF0,2为输入引脚      配置GPG3,11为输入引脚 */
	request_irq(IRQ_EINT0,  buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S2", &pins_desc[0]);
	request_irq(IRQ_EINT2,  buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S3", &pins_desc[1]);
	request_irq(IRQ_EINT11, buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S4", &pins_desc[2]);
	request_irq(IRQ_EINT19, buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S5", &pins_desc[3]);	

	return 0;
}

ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
	if (size != 1)
		return -EINVAL;
/*以非阻塞方式打开，若没有按键按下，返回错误*/
	if (file->f_flags& O_NONBLOCK)
	{
		if (!ev_press)
			return -EAGAIN;
	}
	else
	{
		/* 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 sixth_drv_close(struct inode *inode, struct file *file)
{
	//atomic_inc(&canopen);
	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]);
	up(&button_lock);
	return 0;
}

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    =  sixth_drv_open,     
	.read	 =	sixth_drv_read,	   
	.release =  sixth_drv_close,
};

int major;
static int sixth_drv_init(void)
{
	major = register_chrdev(0, "sixth_drv", &sencod_drv_fops);

	sixthdrv_class = class_create(THIS_MODULE, "sixth_drv");

	sixthdrv_class_dev = device_create(sixthdrv_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;

	sema_init(&button_lock, 1);

	return 0;
}

static void sixth_drv_exit(void)
{
	unregister_chrdev(major, "sixth_drv");
	device_destroy(sixthdrv_class, MKDEV(major, 0));
	class_destroy(sixthdrv_class);
	iounmap(gpfcon);
	iounmap(gpgcon);
	return 0;
}

module_init(sixth_drv_init);
module_exit(sixth_drv_exit);

MODULE_LICENSE("GPL");

应用程序

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <poll.h>
#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

int fd;

int main(int argc, char **argv)
{
	unsigned char key_val;
	int ret;
	/*以非阻塞方式打开*/
	fd = open("/dev/buttons", O_RDWR | O_NONBLOCK);
	if (fd < 0)
	{
		printf("can't open!\n");
		return -1;
	}

	while (1)
	{
		ret = read(fd, &key_val, 1);
		printf("key_val: 0x%x, ret = %d\n", key_val, ret);
		sleep(5);
	}
	
	return 0;