#include <linux/module.h>
#include <linux/init.h>
#include <linux/mod_devicetable.h>
#include <linux/property.h>
#include <linux/platform_device.h>
#include <linux/of_device.h>
#include <linux/gpio/consumer.h>
#include <linux/proc_fs.h>

/* Meta Information */
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Johannes 4 GNU/Linux");
MODULE_DESCRIPTION("A simple LKM to parse the device tree for a specific device and its properties");

/* Declate the probe and remove functions */
static int dt_probe(struct platform_device *pdev);
static void dt_remove(struct platform_device *pdev);

static struct of_device_id my_driver_ids[] = {
	{
		.compatible = "brightlight,mydev",
	}, { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, my_driver_ids);

static struct platform_driver my_driver = {
	.probe = dt_probe,
	.remove = dt_remove,
	.driver = {
		.name = "my_device_driver",
		.of_match_table = my_driver_ids,
	},
};

/* GPIO variable */
static struct gpio_desc *my_led = NULL;

static struct proc_dir_entry *proc_file;

/**
 * @brief Write data to buffer
 */
static ssize_t my_write(struct file *File, const char *user_buffer, size_t count, loff_t *offs) {
	switch (user_buffer[0]) {
		case '0':
		case '1':
			gpiod_set_value(my_led, user_buffer[0] - '0');
		default:
			break;
	}
	return count;
}

static struct proc_ops fops = {
	.proc_write = my_write,
};

/**
 * @brief This function is called on loading the driver 
 */
static int dt_probe(struct platform_device *pdev) {
	struct device *dev = &pdev->dev;
	const char *label;
	int my_value, ret;

	printk("dt_gpio - Now I am in the probe function!\n");

	/* Check for device properties */
	if(!device_property_present(dev, "label")) {
		printk("dt_gpio - Error! Device property 'label' not found!\n");
		return -1;
	}
	if(!device_property_present(dev, "my_value")) {
		printk("dt_gpio - Error! Device property 'my_value' not found!\n");
		return -1;
	}
	if(!device_property_present(dev, "green-led-gpio")) {
		printk("dt_gpio - Error! Device property 'green-led-gpio' not found!\n");
		return -1;
	}

	/* Read device properties */
	ret = device_property_read_string(dev, "label", &label);
	if(ret) {
		printk("dt_gpio - Error! Could not read 'label'\n");
		return -1;
	}
	printk("dt_gpio - label: %s\n", label);
	ret = device_property_read_u32(dev, "my_value", &my_value);
	if(ret) {
		printk("dt_gpio - Error! Could not read 'my_value'\n");
		return -1;
	}
	printk("dt_gpio - my_value: %d\n", my_value);

	/* Init GPIO */
	my_led = gpiod_get(dev, "green-led", GPIOD_OUT_LOW);
	if(IS_ERR(my_led)) {
		printk("dt_gpio - Error! Could not setup the GPIO\n");
		return -1 * IS_ERR(my_led);
	}

	/* Creating procfs file */
	proc_file = proc_create("my-led", 0666, NULL, &fops);
	if(proc_file == NULL) {
		printk("procfs_test - Error creating /proc/my-led\n");
		gpiod_put(my_led);
		return -ENOMEM;
	}


	return 0;
}

/**
 * @brief This function is called on unloading the driver 
 */
static void dt_remove(struct platform_device *pdev) {
	printk("dt_gpio - Now I am in the remove function\n");
	gpiod_put(my_led);
	proc_remove(proc_file);
}

/**
 * @brief This function is called, when the module is loaded into the kernel
 */
static int __init my_init(void) {
	printk("dt_gpio - Loading the driver...\n");
	if(platform_driver_register(&my_driver)) {
		printk("dt_gpio - Error! Could not load driver\n");
		return -1;
	}
	return 0;
}

/**
 * @brief This function is called, when the module is removed from the kernel
 */
static void __exit my_exit(void) {
	printk("dt_gpio - Unload driver");
	platform_driver_unregister(&my_driver);
}

module_init(my_init);
module_exit(my_exit);