编写驱动，实现应用层自由控制哪个数码管显示及显示内容

驱动程序：

#include <linux/init.h>
#include <linux/module.h>
#include<linux/spi/spi.h>
int major;
char kbuf[128]={0};
struct class *cls;  //句柄
struct device *dev;
struct spi_device *spi_wr;//spi结构体指针,用于向芯片写入数据
int mycdev_open(struct inode *inode, struct file *file)//对应应用层open
{
      printk("%s:%s:%d\n",__FILE__,__func__,__LINE__);
      return 0;
}
ssize_t mycdev_write(struct file *file, const char __user *ubuf, size_t size, loff_t *loff)//对应应用层write
{
    int ret;
    if(size>sizeof(kbuf))
    size=sizeof(kbuf);
    ret=copy_from_user(kbuf,ubuf,size);
    if(ret)
    {
        printk("数据从内核向用户拷贝失败\n");
        return -EIO;
    }
    spi_write(spi_wr,kbuf,2); //写入芯片
    return size;
}
int mycdev_close(struct inode *inode, struct file *file)//对应应用层close
{
      printk("%s:%s:%d\n",__FILE__,__func__,__LINE__);
       return 0;
}
//操作方法结构体的初始化
struct file_operations fops={
    .open=mycdev_open,
    .write=mycdev_write,
    .release=mycdev_close,
};
int m74hc595_probe(struct spi_device *spi)
{
    //动态注册字符设备驱动
    major = register_chrdev(0,"myspi",&fops);
    if(major<0)
    {
        printk("字符设备驱动注册失败\n");
        return major;
    }
    printk("字符设备驱动注册成功major=%d\n",major);
    //向上提交节点目录
    cls = class_create(THIS_MODULE,"MYSPI");
    if(IS_ERR(cls))
    {
        printk("向上提交目录失败\n");
        return PTR_ERR(cls);
    }
     printk("向上提交目录成功\n");
     //创建设备节点
    dev = device_create(cls,NULL,MKDEV(major,0),NULL,"myspi");
    if(IS_ERR(dev))
    {
        printk("创建节点失败\n");
        return PTR_ERR(dev);
    }
    printk("创建节点成功\n");
    //将连接成功得到的spi给spi_write
    spi_wr = spi;
    return 0;
}

int m74hc595_remove(struct spi_device *spi)
{
    //关闭所有数码管
    kbuf[0]=0;
    spi_write(spi_wr,kbuf,2); //写入芯片
    device_destroy(cls,MKDEV(major,0));  //销毁节点
    class_destroy(cls);   //销毁目录
    unregister_chrdev(major,"myspi"); //注销字符设备驱动  
     printk("模块卸载成功\n");
    return 0;
}

//设备树匹配表
struct of_device_id of_table[]={
    {.compatible="hqyj,m74hc595"},
    {},
};
MODULE_DEVICE_TABLE(of,of_table);
//定义SPI对象并且初始化
struct spi_driver m74hc595 ={ 
    .probe=m74hc595_probe,
    .remove=m74hc595_remove,
    .driver={
        .name="m74hc595",
        .of_match_table=of_table,
    },
};
//一键注册宏
module_spi_driver(m74hc595); 
MODULE_LICENSE("GPL"); 

应用层程序：

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char const *argv[])
{
    //led显示数字0-9
    char ledmu[10]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f};
    int fd=open("/dev/myspi",O_RDWR);
    if(fd<0)
    {

        printf("打开设备文件失败\n");
        exit(-1);
    }
    printf("设备文件打开成功\n");
    char nss;//选择使用那些数码管
    char buf[10]; //发送数据到内核层
    int i=0;
    /*
    //循环打印数值,数码管0显示1秒0，然后数码管1显示1秒1，然后数码管2显示1秒2，然后数码管3显示1秒3，然后数码管0显示1秒4
    int j=0;
    while(1)
    {
        nss = 1;
        nss <<= i++;
        sprintf(buf, "%c%c",nss, ledmu[j++]);
        write(fd,buf,2);
         if(i==4)
            i=0;
        if(j==10)
            j=0;
        sleep(1);
    }
    */
    //自由控制哪个数码管显示及显示的数字
    while(1)
    {
        nss = 0;
        bzero(buf,sizeof(buf));
        printf("请选择要显示数字的数码, 显示:1, 不显示:0 例2,3显示:(0110)   输入非0,1退出\n");
        fgets(buf,sizeof(buf),stdin);
        if(buf[0]!='0' && buf[0]!='1')
        {
            break;
        }
        for(i=0; i<4; i++)
        {
            nss <<= 1;
            if(buf[i]=='1')
            {
                nss |= 1;
            }
        }
        printf("请输入要显示的数字:");
        scanf("%d",&i);
        while(getchar()!='\n');//吸收垃圾字符
        sprintf(buf, "%c%c",nss, ledmu[i]);
        write(fd, buf, 2);
    }
    close(fd);
    return 0;
}

测试结果：