/*
 * Copyright (C) 2024 LingYun IoT System Studio
 * Author: Guo Wenxue <guowenxue@gmail.com>
 *
 * A character skeleton driver example in linux kernel.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>   /* printk() */
#include <linux/fs.h>       /* everything... */
#include <linux/errno.h>    /* error codes */
#include <linux/types.h>    /* size_t */
#include <linux/cdev.h>     /* cdev */
#include <linux/version.h>  /* kernel version code */
#include <linux/moduleparam.h>

//#define CONFIG_DYNAMIC_ALLOC

/* device name and major number */
#define DEV_NAME         "chrdev"

#ifdef CONFIG_DYNAMIC_ALLOC
#define DEV_MAJOR  0
#else
#define DEV_MAJOR  79
#endif

int dev_major = DEV_MAJOR;
module_param(dev_major, int, S_IRUGO);

#ifdef CONFIG_DYNAMIC_ALLOC
struct cdev   *cdev;
#else
struct cdev    cdev;
#endif

static int chrdev_open (struct inode *inode, struct file *file)
{
    return 0;
}

static int chrdev_close (struct inode *node, struct file *file)
{
    return 0;
}

static struct file_operations chrdev_fops = {
    .owner          = THIS_MODULE,
    .open           = chrdev_open,  /* open()  implementation */
    .release        = chrdev_close, /* close() implementation */
};

static int __init chrdev_init(void)
{
    dev_t      devno;
    int        rv;

    /* 1. Allocate device number */
    if(0 != dev_major)
    {
        devno = MKDEV(dev_major, 0);
        rv = register_chrdev_region(devno, 1, DEV_NAME);
    }
    else
    {
        rv = alloc_chrdev_region(&devno, 0, 1, DEV_NAME);
        dev_major = MAJOR(devno);
    }

    if(rv < 0)
    {
        printk(KERN_ERR "%s driver can't use major %d\n", DEV_NAME, dev_major);
        return -ENODEV;
    }

    /* 2. Allocate and initialize cdev */
#ifdef CONFIG_DYNAMIC_ALLOC
    cdev = cdev_alloc();
    if( !cdev )
    {
         printk(KERN_ERR "Unable to allocate cdev\n");
         goto failed1;
    }
    cdev_init(cdev, &chrdev_fops);
#else
    cdev_init(&cdev, &chrdev_fops);
    cdev.owner = THIS_MODULE;
#endif

    /* 3. Register cdev to linux kernel */
#ifdef CONFIG_DYNAMIC_ALLOC
    rv = cdev_add(cdev, devno, 1);
#else
    rv = cdev_add(&cdev, devno, 1);
#endif
    if( rv )
    {
        rv = -ENODEV;
        printk(KERN_ERR "%s driver regist failed, rv=%d\n", DEV_NAME, rv);
        goto failed1;
    }

    printk(KERN_INFO "%s driver on major[%d] installed.\n", DEV_NAME, dev_major);
    return 0;

failed1:
    unregister_chrdev_region(devno, 1);

    printk(KERN_ERR "%s driver installed failed.\n", DEV_NAME);
    return rv;
}

static void __exit chrdev_exit(void)
{
#ifdef CONFIG_DYNAMIC_ALLOC
    cdev_del(cdev);
#else
    cdev_del(&cdev);
#endif
    unregister_chrdev_region(MKDEV(dev_major,0), 1);

    printk(KERN_INFO "%s driver removed!\n", DEV_NAME);
    return;
}

module_init(chrdev_init);
module_exit(chrdev_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("GuoWenxue <guowenxue@gmail.com>");