146 彻底掌握POLL机制：动手设计一个POLL实验

实验设计

• App应用程序调用poll函数检测 /dev/dtsled 设备文件的可写事件
  无可写事件，进程一直休眠(poll)
  有可写事件，写入字符 ‘1’，点亮led

• file_operations->poll：
  监视write_data全局变量值
  值为0，无事件发生
  值为1，返回可写事件

• 指定唤醒App进程的等待队列头
  poll_wait（唤醒操作）

• file_operations->write：判断write_data全局变量值

  • 值为0，点亮rgb红灯
  • 值为1，唤醒poll函数引起休眠的App进程

实验操作

1. 后台执行App应用程序，往设备文件写入字符’0’

   ./App 0& 
   

   设备文件没有可写事件产生，poll函数使当前App进程休眠

2. 借助‘echo’应用程序，往设备文件写入字符’1’

   sudo sh -c "echo '1'>/dev/rgb_led"
   

   唤醒之前休眠的App应用程序

实验现象

• 设备文件产生可写事件
• App应用程序写入字符’0’
• rgb红灯被点亮

源文件

1、驱动源文件

#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/init.h>
#include <linux/fs.h>
#include<linux/slab.h>
#include<linux/io.h>
#include<linux/uaccess.h>
#include<linux/cdev.h>
#include<linux/device.h>
#include<linux/of.h>
#include<linux/of_address.h>
#include<linux/of_irq.h>
#include<linux/gpio.h>
#include<linux/of_gpio.h>
#include<linux/atomic.h>
#include<linux/timer.h>
#include<linux/jiffies.h>
#include<linux/interrupt.h>
#include<linux/wait.h>
#include<linux/ide.h>
#include <linux/poll.h>

#define DTSLED_NAME "dtsled"
#define LED_OFF 0
#define LED_ON 1

// 定义一组全局变量，用于存放内存映射得到的虚拟地址
static void __iomem *IMX6U_CCM_CCGR1;
static void __iomem *SW_MUX_GPIO1_IO03;
static void __iomem *SW_PAD_GPIO1_IO03;
static void __iomem *GPIO1_DR;
static void __iomem *GPIO1_GDIR;

// 定义一个等待队列头
wait_queue_head_t wait_queue;
static unsigned int write_data;

extern struct dtsled_dev dtsled;

static void led_switch(u8 state)
{
    u32 val = 0;
    if(state == LED_ON)
    {
        val = readl(GPIO1_DR);
        val &= (~(1<<3));
        writel(val, GPIO1_DR);
    }
    else if(state == LED_OFF)
    {
        val = readl(GPIO1_DR);
        val |= (1<<3);
        writel(val, GPIO1_DR);
    }
}


static int dtsled_open(struct inode *inode, struct file *filp)
{
    int ret;

    if(filp->f_flags & O_NONBLOCK)
    {
        ;
    }
    else
    {
        ;
    }
    
	// struct file 结构体定义在 include/linux/fs.h 中
	// struct file 有一个成员（空指针）：void *private_data
    filp->private_data = &dtsled;
    return 0;
}

static int dtsled_release(struct inode *inode, struct file *filp)
{
    //struct dtsled_dev *dev = (struct dtsled_dev *)filp->private_data;
    return 0;
}

static unsigned int dtsled_poll(struct file *filp, struct poll_table_struct *wait)
{
    unsigned int mask = 0;
	// 详见下，注意第二个参数就是等待队列头
    // zhiding xiaoxiduilie tou
	poll_wait(filp, &wait_queue, wait);

	// 判断驱动程序里面发生了哪些条件，这些条件对应哪些文件的事件，设置好事件后，return回去
	if(write_data)
	{
		mask |= POLLOUT;
	}
	return mask;
}

static ssize_t dtsled_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{
    int ret;
    u8 databuf[32] = {0};
    //struct dtsled_dev *dev = (struct dtsled_dev *)filp->private_data;
    printk("%s(%d):buf=(%s), count=%d\n", __FILE__, __LINE__, buf, count);
    ret = copy_from_user(databuf, buf, count);
    printk("%s(%d):databuf=(%s)\n", __FILE__, __LINE__, databuf);
    if(ret < 0)
    {
        printk("%s(%d):Kernel write failed.\r\n", __FILE__, __LINE__);
        return -1;
    }
	// s是输入字符串,base可以是10(10进制)或16(16进制),或者是0自动识别,res存放转换后的整形值
	// kstrtox.c
    ret = kstrtoint(databuf, 16, &write_data);
    printk("%s(%d):write_data=%d", __FILE__, __LINE__, write_data);
    if(write_data)
    {
        wake_up(&wait_queue);
        printk("%s(%d):have woken up.\n", __FILE__, __LINE__);
        return count;
    }
    else
    {
        led_switch(LED_OFF);
    }
    
    
    return 0;
}



// 操作集结构体，是 struct cdev 的成员
static const struct file_operations dtsled_fops =
{
    .owner = THIS_MODULE,
    .write = dtsled_write,
    .open = dtsled_open,
    .release = dtsled_release,
    //unsigned int (*poll) (struct file *, struct poll_table_struct *);
    .poll = dtsled_poll, 
};

// 自定义结构体类型来描述 LED
struct dtsled_dev
{
   dev_t devid;
   struct cdev cdev; // 用于注册字符设备，操作集结构体是其成员变量
   struct file_operations dtsled_fops; // 操作集结构体
   struct class *class; // 用于自动创建设备节点
   struct device *device; // 用于自动创建设备节点
   u32 major;
   u32 minor;
   struct device_node *nd; // 设备树结点，用来表示 LED 设备节点
};

// 自定结构体来描述 LED 
struct dtsled_dev dtsled;

// 驱动入口函数
static int __init dtsled_init(void)
{
    int ret = 0;
    int val = 0;
    const char *str;
    u32 regdata[10];
    u8 i;

    // 1、使用新方法来获取设备号
    dtsled.major = 0;
    if(dtsled.major)
    {
        dtsled.devid = MKDEV(dtsled.major, 0);
        ret = register_chrdev_region(dtsled.devid, 1, DTSLED_NAME);
    }
    else
    {
        ret = alloc_chrdev_region(&dtsled.devid, 0, 1, DTSLED_NAME);
        dtsled.major = MAJOR(dtsled.devid);
        dtsled.minor = MINOR(dtsled.devid);
    }
    if(ret < 0)
    {
        printk("%d:Register char dev error.\r\n", __LINE__);
        goto fail_devid;
    }
    
    // 2、添加（注册）字符设备
    dtsled.cdev.owner = THIS_MODULE;
    // zhu yi liang ge qu di zhi fu !
    cdev_init(&dtsled.cdev, &dtsled_fops);
    ret = cdev_add(&dtsled.cdev, dtsled.devid, 1);
    if(ret < 0)
    {
        goto fail_cdev;
    }
    
    // 3、自动创建设备节点，需要一个 struct class，一个 struct device
    dtsled.class = class_create(THIS_MODULE, DTSLED_NAME);
    if(IS_ERR(dtsled.class))
    {
        ret = PTR_ERR(dtsled.class);
        goto fail_class;
    }
    
    //  第一个 NULL 表示副设备,  第二个 NULL 表示 drvdata
    dtsled.device = device_create(dtsled.class, NULL, dtsled.devid, NULL, DTSLED_NAME);
    if(IS_ERR(dtsled.device))
    {
        ret = PTR_ERR(dtsled.device);
        goto fail_device;
    }
    
    // 4、设备树相关，读取属性值
    dtsled.nd = of_find_node_by_path("/alpha_led");
    if(dtsled.nd == NULL)
    {
        goto fail_findnd;
    }
    // 获取状态属性，注意是指针的指针
    ret = of_property_read_string(dtsled.nd, "status", &str);
    if(ret)
    {
        printk("%d:fail\r\n", __LINE__);
        goto fail_rs;
    }
    else
    {
        printk("%d:status = \"%s\"\r\n", __LINE__, str);
    }
    //huoqu shuxing
    ret = of_property_read_string(dtsled.nd, "compatible", &str);
    if(ret)
    {
        printk("%d:fail\r\n", __LINE__);
        goto fail_rs;
    }
    else
    {
        printk("%d:compatible = \"%s\"\r\n", __LINE__, str);
    }
    // 获取 reg 属性, 也就是获取 u32 类型属性值的方法
    ret = of_property_read_u32_array(dtsled.nd, "reg", regdata, 10);
    if(ret < 0)
    {
        printk("%d:fail\r\n", __LINE__);
        goto fail_rs;
    }
    else
    {
        printk("< reg > = < ");
        for(i=0; i<10; i++)
        {
            printk("%#X ", regdata[i]);
        }
        printk(">\r\n");
    }

    // 5、初始化 LED
    IMX6U_CCM_CCGR1 = of_iomap(dtsled.nd, 0);
    SW_MUX_GPIO1_IO03 = of_iomap(dtsled.nd, 1);
    SW_PAD_GPIO1_IO03 = of_iomap(dtsled.nd, 2);
    GPIO1_DR = of_iomap(dtsled.nd, 3);
    GPIO1_GDIR = of_iomap(dtsled.nd, 4);

    // 初始化 LED 相关寄存器
    val = readl(IMX6U_CCM_CCGR1);
    val &= (~(3<<26));
    val |= (3<<26);
    writel(val, IMX6U_CCM_CCGR1);
   
    writel(0X5, SW_MUX_GPIO1_IO03);//io mux
    writel(0X10B0, SW_PAD_GPIO1_IO03); // set electrical properity
   
    val = readl(GPIO1_GDIR); // set bit3, out
    val |= (1<<3); 
    writel(val, GPIO1_GDIR);

    val = readl(GPIO1_DR);
    val &= (~(1<<3));//turn on led 
    writel(val, GPIO1_DR);

    // 6、初始化等待队列头
    init_waitqueue_head(&wait_queue);

    return 0;

fail_rs:
fail_findnd:
    device_destroy(dtsled.class, dtsled.devid);
fail_device:
    class_destroy(dtsled.class);
fail_class:
    cdev_del(&dtsled.cdev);
fail_cdev:
    unregister_chrdev_region(dtsled.devid, 1);
fail_devid:
    return ret;
}

// 出口函数
static void __exit dtsled_exit(void)
{
    unsigned int val = 0;
    val = readl(GPIO1_DR);
    val |= (1<<3); // turn off led
    writel(val, GPIO1_DR);
    // 取消地址映射
    iounmap(IMX6U_CCM_CCGR1);
    iounmap(SW_MUX_GPIO1_IO03);
    iounmap(SW_PAD_GPIO1_IO03);
    iounmap(GPIO1_DR);
    iounmap(GPIO1_GDIR);

    // 删除字符设备
    cdev_del(&dtsled.cdev);
    // 释放设备号
    unregister_chrdev_region(dtsled.devid, 1);
    // 删除设备
    device_destroy(dtsled.class, dtsled.devid);
    // 删除类
    class_destroy(dtsled.class);
}

// 注册出口函数和入口函数
module_init(dtsled_init);
module_exit(dtsled_exit);
MODULE_LICENSE("GPL");

2、测试app 源文件

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <poll.h>

int main(int argc, char *argv[])
{
    int error;
    int fd;
    // jiegouti suoyoude chengyuan junwei0
    struct pollfd fds = {0};
    if(argc != 3)
    {
        printf("%s(%d):command error!\n", __FILE__, __LINE__);
        return -1;
    }

    /*打开文件*/
    fd = open(argv[1], O_RDWR|O_NONBLOCK);
    if(fd < 0)
    {
		printf("%s(%d):fail to open file : %s !!!\n", __FILE__, __LINE__, argv[1]);
		return -1;
	}

    fds.fd = fd;
    fds.events = POLLOUT;
    // -1 biaoshi keyi yizhixiumian
    error = poll(&fds, 1, -1);
    if(error < 0)
    {
        printf("%s(%d):poll error.\n", __FILE__, __LINE__);
    }
    else
    {
        if(fds.revents & POLLOUT)
        {
            error = write(fd,argv[2],strlen(argv[2]));
            if(error < 0)
            {
                printf("%s(%d):write to file error! \n", __FILE__, __LINE__);
            }
            else
            {
                printf("%s(%d):write to file success! \n", __FILE__, __LINE__);
            }
        }
    }

   
    /*关闭文件*/
    error = close(fd);
    if(error < 0)
    {
        printf("%s(%d):close file error! \n", __FILE__, __LINE__);
    }
    return 0;
}

3、实验现象

/lib/modules/4.1.15 # modprobe test.ko 
228:status = "okay"
239:compatible = "alientek, alphaled"
< reg > = < 0X20C406C 0X4 0X20E0068 0X4 0X20E02F4 0X4 0X209C000 0X4 0X209C004 0X4 >
/lib/modules/4.1.15 # 
/lib/modules/4.1.15 # 
/lib/modules/4.1.15 # 
/lib/modules/4.1.15 # 
/lib/modules/4.1.15 # ./app /dev/dtsled 0 &
/lib/modules/4.1.15 # echo 1 > /dev/dtsled 
/home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(103):buf=(1
count=2
/home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(105):databuf=(1
)
/home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(114):write_data=1
/home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(103):buf=(0), count=1
/home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(118):have woken up.
/home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(105):databuf=(0)
/lib/modules/4.1.15 # /home/jl/linux/imx6ull/linux_driver/z_exercise/test.c(114):write_data=0app.c(46):write to file success! 

[1]+  Done                       ./app /dev/dtsled 0
/lib/modules/4.1.15 # 

第一次调用app，进程阻塞
echo 1 唤醒app进程
app进程成功唤醒后熄灯