异步通知

一、异步通知

1、应用场景

当应用程序不想休眠时，可以使用异步通知的方式；当驱动程序有数据时主动通知应用程序，应用程序收到信号后执行信息处理函数。

2、执行流程（基于读取按键值的情景）

大致思想：驱动程序会发送信号给应用程序，应用程序收到信号会执行指定函数；

应用程序使用的关键函数：

• sighandler_t signal(int signum, sighandler_t handler)
• int fcntl(int fd, int cmd, … /* arg */ )

驱动程序使用的关键函数：

• int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
• void kill_fasync(struct fasync_struct **fp, int sig, int band)

2.1、应用程序具体做什么？

以下涉及的函数并不是函数原型，而是从实际程序里复制出来的；以下步骤序号和上图序号无关联；
①、应用程序需要使用 signal(SIGIO, func) 函数绑定信号与函数，这样收到驱动程序发送的信号后func()函数会自动执行，读按键操作就在func()函数里完成；
②、那驱动程序到底发送信号给谁是由 fcntl(fd, F_SETOWN, getpid()) 函数决定，这个函数是把应用程序的pid告诉驱动程序；
③、随后使用 flags = fcntl(fd, F_GETFL) 来获取标志位；再通过 fcntl(fd, F_SETFL, flags | FASYNC) 启动fasync功能，启用fasync功能实际上就会调用驱动层的drv_fasync()函数，下面介绍drv_fasync()；

2.2、驱动程序具体做什么？

以下涉及的函数并不是函数原型，而是从实际程序里复制出来的；以下步骤序号和上图序号无关联；
①、驱动程序里需要实现drv_fasync()函数，而该函数里只需要调用 fasync_helper(fd, file, on, &button_fasync) 函数，button_fasync是一个fasync_struct类型的结构体，里面会存放应用程序的pid，后续发送信号时也会用到button_fasync；
②、信号的发送在按键中断程序里，调用 kill_fasync(&button_fasync, SIGIO, POLL_IN) 发送信号；

三、程序

1、驱动程序

#include <linux/module.h>

#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/gpio/consumer.h>
#include <linux/platform_device.h>
#include <linux/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/slab.h>


struct gpio_key{
	int gpio;
	struct gpio_desc *gpiod;
	int flag;
	int irq;
};

static struct gpio_key *gpio_keys_f1c100s;

static int major = 0;
static struct class *key_class;
static int g_key = 0;

struct fasync_struct *button_fasync;

static DECLARE_WAIT_QUEUE_HEAD(gpio_key_wait);

static ssize_t key_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
	int err;
	
	wait_event_interruptible(gpio_key_wait, g_key);
	err = copy_to_user(buf, &g_key, 4);
	g_key = 0;
	
	return 4;
}

static int key_drv_fasync(int fd, struct file *file, int on)
{
	if (fasync_helper(fd, file, on, &button_fasync) >= 0)
		return 0;
	else
		return -EIO;
}

static struct file_operations key_drv = {
	.owner	 = THIS_MODULE,
	.read    = key_drv_read,
	.fasync  = key_drv_fasync,
};

static irqreturn_t gpio_key_isr(int irq, void *dev_id)
{
	struct gpio_key *gpio_key = dev_id;
	int val;
	val = gpiod_get_value(gpio_key->gpiod);
	
	printk("key %d %d\n", gpio_key->gpio, val);
	g_key = (gpio_key->gpio << 8) | val;
	wake_up_interruptible(&gpio_key_wait);
	kill_fasync(&button_fasync, SIGIO, POLL_IN);	//发送信号
	
	return IRQ_HANDLED;
}

static int f1c100s_key_probe(struct platform_device *pdev)
{	
	struct device_node *node = pdev->dev.of_node;
	int err;
	int i;
	int count;
	enum of_gpio_flags flag;

	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	
	count = of_gpio_count(node);	//获取GPIO数量
	if(!count)
	{
		printk("%s %s line %d, there isn't any gpio available\n", __FILE__, __FUNCTION__, __LINE__);
		return -1;
	}
	
	gpio_keys_f1c100s = kzalloc(sizeof(struct gpio_key) * count, GFP_KERNEL);
	if(gpio_keys_f1c100s == NULL)
	{
		printk("%s %s line %d, kzalloc fail\n", __FILE__, __FUNCTION__, __LINE__);
		return -1;
	}
	
	for(i = 0; i < count; i++)
	{

		gpio_keys_f1c100s[i].gpio = of_get_gpio_flags(node, i, &flag);
		if (gpio_keys_f1c100s[i].gpio < 0)
		{
			printk("%s %s line %d, of_get_gpio_flags fail\n", __FILE__, __FUNCTION__, __LINE__);
			return -1;
		}
		
		gpio_keys_f1c100s[i].gpiod = gpio_to_desc(gpio_keys_f1c100s[i].gpio);
		gpio_keys_f1c100s[i].flag = flag & OF_GPIO_ACTIVE_LOW;
		gpio_keys_f1c100s[i].irq  = gpio_to_irq(gpio_keys_f1c100s[i].gpio);		//获取中断号
	}
	
	for(i = 0; i < count; i++)
	{

		err = request_irq(gpio_keys_f1c100s[i].irq, gpio_key_isr, IRQF_TRIGGER_RISING, "f1c100s_gpio_key", &gpio_keys_f1c100s[i]);	//申请中断
	}
	
	major = register_chrdev(0, "f1c100s_key", &key_drv);

	key_class = class_create(THIS_MODULE, "f1c100s_key_class");
	if (IS_ERR(key_class)) {
		unregister_chrdev(major, "f1c100s_key");
		printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
		return PTR_ERR(key_class);
	}
	
	device_create(key_class, NULL, MKDEV(major, 0), NULL, "keys-key");
	
    return 0;
}

static int f1c100s_key_remove(struct platform_device *pdev)
{
	struct device_node *node = pdev->dev.of_node;
	int count;
	int i;
	
	device_destroy(key_class, MKDEV(major, 0));
	class_destroy(key_class);
	unregister_chrdev(major, "f1c100s_key");
	
	count = of_gpio_count(node);
	for (i = 0; i < count; i++)
	{
		free_irq(gpio_keys_f1c100s[i].irq, &gpio_keys_f1c100s[i]);
	}
	kfree(gpio_keys_f1c100s);
   
    return 0;
}

static const struct of_device_id f1c100s_key_table[] = {
    { .compatible = "f1c100s,keysdrv" },
    { },
};

static struct platform_driver f1c100s_key_driver = {
    .probe      = f1c100s_key_probe,
    .remove     = f1c100s_key_remove,
    .driver     = {
        .name   = "f1c100s_keys",
        .of_match_table = f1c100s_key_table,
    },
};

static int __init f1c100s_key_init(void)
{
	int err;
	
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	err = platform_driver_register(&f1c100s_key_driver);

	return err;
}

static void __exit f1c100s_key_exit(void)
{
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	platform_driver_unregister(&f1c100s_key_driver);
}

module_init(f1c100s_key_init);
module_exit(f1c100s_key_exit);

MODULE_LICENSE("GPL");

2、测试应用程序

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

static int fd;
static void sig_func(int sig)
{
	int bit = 1;
	int val;
	
	read(fd, &val, 4);

	bit &= val;
	val >>= 8;
	
	printf("get %d button : %d\n", val, bit);

	bit = 1;
}

/*
 * ./button_test /dev/keys-key
 *
 */
int main(int argc, char **argv)
{	
	int	flags;
	
	/* 1. 判断参数 */
	if (argc != 2) 
	{
		printf("Usage: %s <dev>\n", argv[0]);
		return -1;
	}

	signal(SIGIO, sig_func);				//绑定信号与函数
	
	/* 2. 打开文件 */
	fd = open(argv[1], O_RDWR);
	if (fd == -1)
	{
		printf("can not open file %s\n", argv[1]);
		return -1;
	}

	fcntl(fd, F_SETOWN, getpid());			//传入应用程序pid
	flags = fcntl(fd, F_GETFL);				//获取flags
	fcntl(fd, F_SETFL, flags | FASYNC);		//启动fasync功能，驱动程序的key_drv_fasync()会被调用
	
	/* 3. 写文件 */
	while(1)
	{
		printf("asyn button test\n");
		sleep(2);
	}
	close(fd);
	
	return 0;
}

三、总结

1、以上专业术语或名词解释有个人理解，感谢指点纠错！
2、视频学习B站韦东山：【第5篇】嵌入式Linux驱动开发基础知识 - 异步通知