// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/cdev.h>
#include <linux/of.h>

struct hello_dev {
	struct device *dev;
	struct cdev cdev;
	unsigned int minor;
};

#define HELLO_MAX_DEVICES 10

static struct class *hello_class;
static dev_t hello_devt;

static int hello_open(struct inode *node, struct file *f)
{
	struct cdev *cd = node->i_cdev;
	struct hello_dev *hello = container_of(cd, struct hello_dev, cdev);
	dev_info(hello->dev, "%s\n", __func__);
	f->private_data = hello;
	return 0;
}

static int hello_release(struct inode *node, struct file *f)
{
	struct hello_dev *hello = f->private_data;
	dev_info(hello->dev, "%s\n", __func__);
	f->private_data = NULL;
	return 0;
}

static ssize_t hello_read(struct file *f, char __user *u, size_t s, loff_t *l)
{
	struct hello_dev *hello = f->private_data;
	char buf[10];
	size_t len;

	dev_info(hello->dev, "%s: size=%zu offset=%llu\n", __func__, s, *l);

	if (*l >= 40)
		return 0;

	len = snprintf(buf, sizeof(buf), "hello:%d\n", hello->minor);

	if (s < len)
		len = s;

	if (copy_to_user(u, buf, len) != 0)
		return -EFAULT;

	*l += len;

	return len;
}

static ssize_t hello_write(struct file *f, const char __user *u, size_t s,
			   loff_t *l)
{
	struct hello_dev *hello = f->private_data;
	dev_info(hello->dev, "%s: size=%zu offset=%llu\n", __func__, s, *l);
	return s;
}

static const struct file_operations hello_fops = {
	.owner = THIS_MODULE,
	.open = hello_open,
	.release = hello_release,
	.read = hello_read,
	.write = hello_write,
};

static int hello_probe(struct platform_device *pdev)
{
	struct hello_dev *hello;
	struct device *dev;
	dev_t devt;
	int ret;

	hello = devm_kzalloc(&pdev->dev, sizeof(*hello), GFP_KERNEL);
	if (!hello) {
		dev_err(&pdev->dev, "devm_kzalloc failed\n");
		return -ENOMEM;
	}

#ifdef CONFIG_OF
	ret = of_property_read_u32(pdev->dev.of_node, "index", &hello->minor);
	if (ret < 0) {
		dev_err(&pdev->dev, "no index specified\n");
		goto err_out;
	}
#else
	hello->minor = (unsigned)pdev->id;
#endif

	if (hello->minor >= HELLO_MAX_DEVICES) {
		dev_err(&pdev->dev, "invalid index: %u\n", hello->minor);
		ret = -EINVAL;
		goto err_out;
	}

	hello->dev = &pdev->dev;
	platform_set_drvdata(pdev, hello);

	devt = MKDEV(MAJOR(hello_devt), hello->minor);

	cdev_init(&hello->cdev, &hello_fops);
	hello->cdev.owner = THIS_MODULE;
	ret = cdev_add(&hello->cdev, devt, 1);
	if (ret != 0) {
		dev_err(&pdev->dev, "cdev_add failed\n");
		goto err_drvdata;
	}

	dev = device_create(hello_class, &pdev->dev, devt, hello,
			    "hello%d", hello->minor);
	if (IS_ERR(dev)) {
		dev_err(&pdev->dev, "device_create failed\n");
		ret = PTR_ERR(dev);
		goto err_cdev;
	}

	dev_info(&pdev->dev, "HELLO! I am hello device %d!\n", hello->minor);

	return 0;

err_cdev:
	cdev_del(&hello->cdev);
err_drvdata:
	platform_set_drvdata(pdev, NULL);
err_out:
	return ret;
}

static int hello_remove(struct platform_device *pdev)
{
	struct hello_dev *hello = platform_get_drvdata(pdev);

	device_destroy(hello_class, MKDEV(MAJOR(hello_devt), hello->minor));
	cdev_del(&hello->cdev);
	platform_set_drvdata(pdev, NULL);

	dev_info(&pdev->dev, "GOODBYE! I was hello device %d!\n", hello->minor);

	return 0;
}

static const struct of_device_id hello_match[] = {
	{ .compatible = "virtual,hello", },
	{ /* end of table */ }
};

static struct platform_driver hello_driver = {
	.driver = {
		.name = "hello",
		.of_match_table = hello_match,
	},
	.probe = hello_probe,
	.remove = hello_remove,
};

#ifndef CONFIG_OF
static struct platform_device *pdevs[3];
#endif

static int __init hello_init(void)
{
	int ret;

	printk(KERN_INFO "%s\n", __func__);

	ret = alloc_chrdev_region(&hello_devt, 0, HELLO_MAX_DEVICES, "hello");
	if (ret < 0)
		return ret;

	hello_class = class_create(THIS_MODULE, "hello");
	if (IS_ERR(hello_class)) {
		printk(KERN_ERR "%s: failed to create class\n", __func__);
		ret = PTR_ERR(hello_class);
		goto err_region;
	}

	ret = platform_driver_register(&hello_driver);
	if (ret != 0)
		goto err_class;

#ifndef CONFIG_OF
	pdevs[0] = platform_device_register_simple("hello", 1, NULL, 0);
	pdevs[1] = platform_device_register_simple("hello", 3, NULL, 0);
	pdevs[2] = platform_device_register_simple("hello", 5, NULL, 0);
#endif

	return 0;

err_class:
	class_destroy(hello_class);
err_region:
	unregister_chrdev_region(hello_devt, HELLO_MAX_DEVICES);
	return ret;
}

static void __exit hello_exit(void)
{
	printk(KERN_INFO "%s\n", __func__);

#ifndef CONFIG_OF
	platform_device_unregister(pdevs[0]);
	platform_device_unregister(pdevs[1]);
	platform_device_unregister(pdevs[2]);
#endif

	platform_driver_unregister(&hello_driver);
	class_destroy(hello_class);
	unregister_chrdev_region(hello_devt, HELLO_MAX_DEVICES);
}

module_init(hello_init);
module_exit(hello_exit);

MODULE_AUTHOR("John Ogness <john.ogness@linutronix.de>");
MODULE_DESCRIPTION("a great module for hello-ing!");
MODULE_LICENSE("GPL v2");
MODULE_VERSION("20190101");