Compilation and testing of raspberry pie driver code

First, find a simplified driver code

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <asm/io.h>

static struct class *pin4_class;
static struct device *pin4_class_dev;


static dev_t devno;           // Device number 
static int major = 231;       // The main equipment, 
static int minor = 0;         // Secondary device number 
static char *module_name = "pin4"; // Module name 

static int pin4_read (struct file *file1,char __user *buf,size_t size,loff_t *ppos)
{
        printk("pin4_read\n");
        return 0;
}

static int pin4_open(struct inode *inode,struct file *file)
{
        printk("pin4_open\n");
        return 0;
}

static ssize_t pin4_write(struct file *file,const char __user *buf,size_t count,loff_t *ppos)
{
        printk("pin4_write\n");
        return 0;
}

static struct file_operations pin4_fops = {
        .owner = THIS_MODULE,
        .open  = pin4_open,
        .write = pin4_write,
        .read  = pin4_read,
};

int __init pin4_drv_init(void)
{
        int ret;
        devno = MKDEV(major,minor);
        ret = register_chrdev(major,module_name,&pin4_fops);  // Registration drive    Tell the kernel , Add this driver to the linked list of kernel drivers 

        pin4_class = class_create(THIS_MODULE,"myfirstdemo");
        pin4_class_dev = device_create(pin4_class,NULL,devno,NULL,module_name); // Create device files 

        return 0;
}

void __exit pin4_drv_exit(void)
{
        device_destroy(pin4_class,devno);
        class_destroy(pin4_class);
        unregister_chrdev(major,module_name);   // Unload the drive 
}

module_init(pin4_drv_init);
module_exit(pin4_drv_exit);
MODULE_LICENSE("GPL v2");

Write another piece of code for test drive

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

int main()
{
        int fd;

        fd = open("/dev/pin4",O_RDWR);
        if(fd < 0){
                printf("open failed\n");
                perror("reason:");
        }else{
                printf("open success\n");
        }
        fd = write(fd,'1',1);
}

Then you can start compiling the driver code

1. open Linux Kernel source tree directory , Get into linux-rpi-4.14.y/drivers/char, Copy the driver code . 

2. Get into Makefile , And modify

3. Go back to the kernel and compile the module driver , Will generate a .ko file .

ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KERNEL=kernel7 make modules

 4. Put this .ko Upload the file to raspberry pie （ It can also be used here FileZilla Upload ）

scp pin4test.ko [email protected]:/home/pi

5. Compile test code

arm-linux-gnueabihf-gcc pin4demo.c -o pin4demo

Upload the generated executable file to raspberry pie . 

  When raspberry pie gets these two documents , Next, load the kernel driver . 

6. Load the kernel driver

sudo insmod pin4text.ko

After loading successfully, you can see the device number  

  Or use lsmod Look at the driver , Found that the driver was loaded successfully .

 7. Add a permission to the driver that everyone can view

sudo chmod 666 /dev/pin4

8. Call the upper test program  

 9. At this time, we can't see any information on the top , Because we use printk Print information ,printk Print the data in kernel mode . So we use dmesg Check the contents in kernel mode , Find out pin4_open And pin4_write All called , Successful test ！