DeviceDriver（八）：异步通知

一：异步通知

        异步通知的核心是信号，它不同于阻塞与非阻塞方式，阻塞方式访问会使应用程序处于休眠态，等待驱动设备可以使用，非阻塞方式则会通过应用程序的poll函数来不断的轮询，查看驱动设备文件是否可以使用。这两种方式都需要应用程序主动去查询设备的使用情况。而异步通知则是驱动主动去通知应用程序自己可以被访问，应用程序获取到信号后就可以对驱动设备进行读写操作，类似于硬件上使用的“中断”处理方式。

Linux所支持的信号：这些信号相当于中断号，不同的中断号代表了不同的中断，不同的中断所做的处理不同，因此，驱动程序可以通过向应用程序发送不同的信号来实现不同的功能。

#define SIGHUP 1 /* 终端挂起或控制进程终止 */
#define SIGINT 2 /* 终端中断(Ctrl+C 组合键) */
#define SIGQUIT 3 /* 终端退出(Ctrl+\组合键) */
#define SIGILL 4 /* 非法指令 */
#define SIGTRAP 5 /* debug 使用，有断点指令产生 */
#define SIGABRT 6 /* 由 abort(3)发出的退出指令 */
#define SIGIOT 6 /* IOT 指令 */
#define SIGBUS 7 /* 总线错误 */
#define SIGFPE 8 /* 浮点运算错误 */
#define SIGKILL 9 /* 杀死、终止进程 */
#define SIGUSR1 10 /* 用户自定义信号 1 */
#define SIGSEGV 11 /* 段违例(无效的内存段) */
#define SIGUSR2 12 /* 用户自定义信号 2 */
#define SIGPIPE 13 /* 向非读管道写入数据 */
#define SIGALRM 14 /* 闹钟 */
#define SIGTERM 15 /* 软件终止 */
#define SIGSTKFLT 16 /* 栈异常 */
#define SIGCHLD 17 /* 子进程结束 */
#define SIGCONT 18 /* 进程继续 */
#define SIGSTOP 19 /* 停止进程的执行，只是暂停 */
#define SIGTSTP 20 /* 停止进程的运行(Ctrl+Z 组合键) */
#define SIGTTIN 21 /* 后台进程需要从终端读取数据 */
#define SIGTTOU 22 /* 后台进程需要向终端写数据 */
#define SIGURG 23 /* 有"紧急"数据 */
#define SIGXCPU 24 /* 超过 CPU 资源限制 */
#define SIGXFSZ 25 /* 文件大小超额 */
#define SIGVTALRM 26 /* 虚拟时钟信号 */
#define SIGPROF 27 /* 时钟信号描述 */
#define SIGWINCH 28 /* 窗口大小改变 */
#define SIGIO 29 /* 可以进行输入/输出操作 */
#define SIGPOLL SIGIO
/* #define SIGLOS 29 */
#define SIGPWR 30 /* 断点重启 */
#define SIGSYS 31 /* 非法的系统调用 */
#define SIGUNUSED 31 /* 未使用信号 */

如果在应用程序中使用信号，那么就必须设置信号所使用的信号处理函数，在应用程序中使用signal函数来设置指定信号的处理函数：

signum：要设置处理函数的信号

handler：信号的处理函数

返回值：设置成功的话返回信号的前一个处理函数，设置失败返回SIG_ERR。

sighandler_t signal(int signum, sighandler_t handler)

信号处理函数：

typedef void (*sighandler_t)(int)

二：驱动中的信号处理

1、fasync_struct结构体

struct fasync_struct {
	spinlock_t		fa_lock;
	int			magic;
	int			fa_fd;
	struct fasync_struct	*fa_next; /* singly linked list */
	struct file		*fa_file;
	struct rcu_head		fa_rcu;
};

2、fasync函数

如果要使用异步通知，需要实现file_operations中的fasync函数：

int (*fasync) (int fd, struct file *filp, int on)

fasync函数中一般通过调用fasync_helper函数来初始化前面定义的fasync_strcut结构体指针：

int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)

当应用程序通过函数“fcntl”改变fasync标记的时候，驱动程序file_operations中的fasync函数就会被执行：

（1）应用程序：

重点最后三行代码

fcntl(fd, F_SETOWN, getpid()); //告诉内核
 oflags = fcntl(fd, F_GETFL);   // 获取当前进程状态
fcntl(fd, F_SETFL, oflags | FASYNC);//改变fasync，会调用驱动中的fasync函数指针对应的函数。

void signal_fun(int signum)
{
    unsigned char key_val;
    read(fd, &key_val, 1);
    printf("key_val: 0x%x\n", key_val);
}

int main(int argc, char **argv)
{
    unsigned char key_val;
    int ret;
    int oflags;
    signal(SIGIO, signal_fun);
    
    fd = open("/dev/signal", O_RDWR);
    if (fd < 0)
    {
        printf("can't open!\n");
    }

    fcntl(fd, F_SETOWN, getpid()); //告诉内核
    oflags = fcntl(fd, F_GETFL);   // 获取当前进程状态
    fcntl(fd, F_SETFL, oflags | FASYNC);//改变fasync，会调用驱动中的fasync函数指针对应的函数。

}

（2）驱动程序：

static int signal_drv_fasync(int fd, struct file *filp, int on)
{
    printk("driver: signal_drv_fasync\n");
    return fasync_helper (fd, filp, on, &signal_fasync);
}

static int signal_drv_release(struct inode *inode, struct file *filp)
{
    return signal_drv_fasync(-1, filp, 0); /* 删除异步通知 */
}

static struct file_operations signal_drv_fops = 
{
    .fasync  = signal_drv_fasync,
    .release = signal_drv_release,
};

3、kill_fasync函数

当设备可以访问的时候，驱动程序需要向应用程序发出信号，相当于产生“中断”，kill_fasync函数负责发送指定信号：

fp：要操作的fasync_struct

sig：要发送的信号

band：可读时设置为POLL_IN，可写时设置为POLL_OUT

void kill_fasync(struct fasync_struct **fp, int sig, int band)

static irqreturn_t xxx_irq(int irq, void *dev_id)
{
    struct pin_desc *pindesc = (struct pin_desc *)dev_id;
    unsigned int pinval;

    pinval = xxx_gpio_getpin(pindesc->pin);

    kill_fasync(&signal_fasync, SIGIO, POLL_IN);
    
    return IRQ_RETVAL(IRQ_HANDLED);
}

三：示例

1、应用程序

#include "sys/stat.h"
#include "sys/types.h"
#include "unistd.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"
#include "stdio.h"
#include "poll.h"
#include "sys/time.h"
#include "linux/ioctl.h"
#include "signal.h"

#define LED_ON  1
#define LED_OFF 0

int fd1, fd2;
char keyval, ledval;
char val = 0;

static void key_fasync(int signum)
{
    read(fd1, &keyval, sizeof(keyval));
    if(keyval == LED_ON)
    {
        val = !val;
    }
    if(val == LED_ON)
    {
        ledval = LED_ON;
        write(fd2, &ledval, sizeof(ledval));
    }
    else if(val == LED_OFF)
    {
        ledval = LED_OFF;
        write(fd2, &ledval, sizeof(ledval));
    }
}

int main(int argc, char const *argv[])
{
    int flags = 0;
    if(argc != 3)
    {
        printf("Error Usage : ./app /dev/key /dev/led\n");
    }

    fd1 = open(argv[1], O_RDWR | O_NONBLOCK);
    if(fd1 < 0)
    {
        printf("%s can't open!\n", argv[1]);
        return -1;
    }

    fd2 = open(argv[2], O_RDWR);
    if(fd2 < 0)
    {
        printf("%s can't open!\n", argv[2]);
        return -1;
    }

    signal(SIGIO, key_fasync);
    fcntl(fd1, F_SETOWN, getpid());
    flags = fcntl(fd1, F_GETFD);
    fcntl(fd1, F_SETFL, flags | FASYNC);

    while (1)
    {
        sleep(2);
    }

    close(fd2);
    close(fd1);

    return 0;
}

2、按键驱动，（LED驱动与第七章内容相同）

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <linux/semaphore.h>
#include <linux/timer.h>
#include <linux/of_irq.h>
#include <linux/irq.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <linux/poll.h>
#include <linux/fcntl.h>

#define KEY_NUM     1

struct st_keyirq
{
    int gpio;
    int irqnum;
    unsigned char value;
    char name[10];
    irqreturn_t (*handler)(int, void *);
};

struct st_keydev {
    dev_t devid;
    struct cdev cdev;
    struct class *class;
    struct device *device;
    int major;
    int minor;
    struct device_node *nd;
    struct mutex lock;
    atomic_t keyvalue;
    atomic_t releasekey;
    struct timer_list timer;
    struct st_keyirq irqkeydesc[KEY_NUM];
    unsigned char curkeynum;
    struct fasync_struct *key_fasync;
};
struct st_keydev keydev;
static DECLARE_WAIT_QUEUE_HEAD(key_waitq);


static int key_open(struct inode *inode, struct file *file)
{
    file->private_data = &keydev;

    if(mutex_trylock(&keydev.lock) == 0)
    {
        return -EBUSY;
    }
    return 0;
}

static ssize_t key_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
    struct st_keydev *dev = (struct st_keydev *)file->private_data;
    unsigned char releasekey = 0;
    char val = 0;
    int retvalue = 0;


    releasekey = atomic_read(&dev->releasekey);

    if(releasekey)
    {
        val = 1;
        retvalue = copy_to_user(buf, &val, sizeof(val));
        atomic_set(&dev->releasekey, 0);
    }
    else
    {
        val = 0;
        retvalue = copy_to_user(buf, &val, sizeof(val));
    }
    
    return 0;
}

static int key_fasync(int fd, struct file *filp, int on)
{
    struct st_keydev *dev = (struct st_keydev *)filp->private_data;

    return fasync_helper(fd, filp, on, &dev->key_fasync);
}

static int key_release(struct inode *inode, struct file *file)
{
    struct st_keydev *dev = (struct st_keydev *)file->private_data;

    mutex_unlock(&dev->lock);

    return key_fasync(-1, file, 0);
};


struct file_operations key_fops = {
    .owner      =   THIS_MODULE,
    .open       =   key_open,
    .read       =   key_read,
    .fasync     =   key_fasync,
    .release    =   key_release, 
};

static irqreturn_t key1_handler(int irq, void *keydev)
{
    struct st_keydev *dev = (struct st_keydev *)keydev;

    dev->curkeynum = 0;
    dev->timer.data = (volatile long)keydev;
    mod_timer(&dev->timer, jiffies + msecs_to_jiffies(5));
    return IRQ_RETVAL(IRQ_HANDLED);
}

void timer_function(unsigned long data)
{
    unsigned char value;
    unsigned char num;
    struct st_keyirq *keydesc;
    struct st_keydev *dev = (struct st_keydev *)data;

    num = dev->curkeynum;
    keydesc = &dev->irqkeydesc[num];

    value = gpio_get_value(keydesc->gpio);
    if(value == 0)
    {
        atomic_set(&dev->releasekey, 0);
    }
    else
    {
        atomic_set(&dev->releasekey, 1);
        if(dev->key_fasync)
        {
            kill_fasync(&dev->key_fasync, SIGIO, POLL_IN);
        }
    }
}

static int key1_init(void)
{
    int retval = 0;
    unsigned char i = 0;

    mutex_init(&keydev.lock);

    keydev.nd = of_find_node_by_path("/key");
    if(keydev.nd == NULL)
    {
        printk("Key node not find!\n");
        return -EINVAL;
    }
    else
    {
        printk("key node find!\n");
    }

    for (i = 0; i < KEY_NUM; i++)
    {
        keydev.irqkeydesc[i].gpio = of_get_named_gpio(keydev.nd, "key-gpio", i);
        if(keydev.irqkeydesc[i].gpio < 0)
        {
            printk("Can't get key%d!\n", i);
            return -EINVAL;
        }
    }

    for (i = 0; i < KEY_NUM; i++)
    {
        memset(keydev.irqkeydesc[i].name, 0, sizeof(keydev.irqkeydesc[i].name));
        sprintf(keydev.irqkeydesc[i].name, "KEY%d", i);
        retval = gpio_request(keydev.irqkeydesc[i].gpio, keydev.irqkeydesc[i].name);
        if(retval < 0)
        {
            printk("request failed!\n");
            return -EINVAL;
        }
        retval = gpio_direction_input(keydev.irqkeydesc[i].gpio);
        if(retval < 0)
        {
            printk("set input failed!\n");
            return -EINVAL;
        }
        keydev.irqkeydesc[i].irqnum = irq_of_parse_and_map(keydev.nd, i);

        printk("key%d:gpio=%d, irqnum=%d\n", i, keydev.irqkeydesc[i].gpio, keydev.irqkeydesc[i].irqnum);
    }

    keydev.irqkeydesc[0].handler = key1_handler;
    for (i = 0; i < KEY_NUM; i++)
    {
        /* code */
        retval = request_irq(keydev.irqkeydesc[i].irqnum, keydev.irqkeydesc[i].handler,
                                IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING, keydev.irqkeydesc[i].name, &keydev);
        if(retval < 0)
        {
            printk("irq %d request failed!\n", keydev.irqkeydesc[i].irqnum);
            return -EFAULT;
        }
    }

    if(keydev.major)
    {
        keydev.devid = MKDEV(keydev.major, 0);
        register_chrdev_region(keydev.devid, 1, "key");
    }
    else
    {
        alloc_chrdev_region(&keydev.devid, 0, 1, "key");
        keydev.major = MAJOR(keydev.devid);
        keydev.minor = MINOR(keydev.devid);
    }
    printk("keydev major : %d minor : %d\n", keydev.major, keydev.minor);

    keydev.cdev.owner = THIS_MODULE;
    cdev_init(&keydev.cdev, &key_fops);
    cdev_add(&keydev.cdev, keydev.devid, 1);

    keydev.class = class_create(THIS_MODULE, "key");
    keydev.device = device_create(keydev.class, NULL, keydev.devid, NULL, "key");

    init_timer(&keydev.timer);
    keydev.timer.function = timer_function;

    return 0;
}

static void key1_exit(void)
{
    unsigned char i = 0;

    del_timer_sync(&keydev.timer);
    for (i = 0; i < KEY_NUM; i++)
    {
        /* code */
        free_irq(keydev.irqkeydesc[i].irqnum, &keydev);
    }
    
    device_destroy(keydev.class, keydev.devid);
    class_destroy(keydev.class);

    cdev_del(&keydev.cdev);
    unregister_chrdev_region(keydev.devid, 1);
}

module_init(key1_init);
module_exit(key1_exit);
MODULE_LICENSE("GPL");