// SPDX-License-Identifier: GPL-2.0
/*
 * FS-iA6B iBus RC receiver driver
 *
 * This driver provides all 14 channels of the FlySky FS-ia6B RC receiver
 * as analog values.
 *
 * Additionally, the channels can be converted to discrete switch values.
 * By default, it is configured for the offical FS-i6 remote control.
 * If you use a different hardware configuration, you can configure it
 * using the `switch_config` parameter.
 */

#include <linux/device.h>
#include <linux/input.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/serio.h>
#include <linux/slab.h>
#include <linux/types.h>

#define DRIVER_DESC		"FS-iA6B iBus RC receiver"

MODULE_AUTHOR("Markus Koch <markus@notsyncing.net>");
MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_LICENSE("GPL");

#define IBUS_SERVO_COUNT	14

static char *switch_config = "00000022320000";
module_param(switch_config, charp, 0444);
MODULE_PARM_DESC(switch_config,
		 "Amount of switch positions per channel (14 characters, 0-3)");

static int fsia6b_axes[IBUS_SERVO_COUNT] = {
	ABS_X, ABS_Y,
	ABS_Z, ABS_RX,
	ABS_RY, ABS_RZ,
	ABS_HAT0X, ABS_HAT0Y,
	ABS_HAT1X, ABS_HAT1Y,
	ABS_HAT2X, ABS_HAT2Y,
	ABS_HAT3X, ABS_HAT3Y
};

enum ibus_state { SYNC, COLLECT, PROCESS };

struct ibus_packet {
	enum ibus_state state;

	int offset;
	u16 ibuf;
	u16 channel[IBUS_SERVO_COUNT];
};

struct fsia6b {
	struct input_dev *dev;
	struct ibus_packet packet;

	char phys[32];
};

static irqreturn_t fsia6b_serio_irq(struct serio *serio,
				    unsigned char data, unsigned int flags)
{
	struct fsia6b *fsia6b = serio_get_drvdata(serio);
	int i;
	int sw_state;
	int sw_id = BTN_0;

	fsia6b->packet.ibuf = (data << 8) | ((fsia6b->packet.ibuf >> 8) & 0xFF);

	switch (fsia6b->packet.state) {
	case SYNC:
		if (fsia6b->packet.ibuf == 0x4020)
			fsia6b->packet.state = COLLECT;
		break;

	case COLLECT:
		fsia6b->packet.state = PROCESS;
		break;

	case PROCESS:
		fsia6b->packet.channel[fsia6b->packet.offset] =
				fsia6b->packet.ibuf;
		fsia6b->packet.offset++;

		if (fsia6b->packet.offset == IBUS_SERVO_COUNT) {
			fsia6b->packet.offset = 0;
			fsia6b->packet.state = SYNC;
			for (i = 0; i < IBUS_SERVO_COUNT; ++i) {
				input_report_abs(fsia6b->dev, fsia6b_axes[i],
						 fsia6b->packet.channel[i]);

				sw_state = 0;
				if (fsia6b->packet.channel[i] > 1900)
					sw_state = 1;
				else if (fsia6b->packet.channel[i] < 1100)
					sw_state = 2;

				switch (switch_config[i]) {
				case '3':
					input_report_key(fsia6b->dev,
							 sw_id++,
							 sw_state == 0);
					fallthrough;
				case '2':
					input_report_key(fsia6b->dev,
							 sw_id++,
							 sw_state == 1);
					fallthrough;
				case '1':
					input_report_key(fsia6b->dev,
							 sw_id++,
							 sw_state == 2);
				}
			}
			input_sync(fsia6b->dev);
		} else {
			fsia6b->packet.state = COLLECT;
		}
		break;
	}

	return IRQ_HANDLED;
}

static int fsia6b_serio_connect(struct serio *serio, struct serio_driver *drv)
{
	struct fsia6b *fsia6b;
	struct input_dev *input_dev;
	int err;
	int i, j;
	int sw_id = 0;

	fsia6b = kzalloc(sizeof(*fsia6b), GFP_KERNEL);
	if (!fsia6b)
		return -ENOMEM;

	fsia6b->packet.ibuf = 0;
	fsia6b->packet.offset = 0;
	fsia6b->packet.state = SYNC;

	serio_set_drvdata(serio, fsia6b);

	input_dev = input_allocate_device();
	if (!input_dev) {
		err = -ENOMEM;
		goto fail1;
	}
	fsia6b->dev = input_dev;

	snprintf(fsia6b->phys, sizeof(fsia6b->phys), "%s/input0", serio->phys);

	input_dev->name = DRIVER_DESC;
	input_dev->phys = fsia6b->phys;
	input_dev->id.bustype = BUS_RS232;
	input_dev->id.vendor = SERIO_FSIA6B;
	input_dev->id.product = serio->id.id;
	input_dev->id.version = 0x0100;
	input_dev->dev.parent = &serio->dev;

	for (i = 0; i < IBUS_SERVO_COUNT; i++)
		input_set_abs_params(input_dev, fsia6b_axes[i],
				     1000, 2000, 2, 2);

	/* Register switch configuration */
	for (i = 0; i < IBUS_SERVO_COUNT; i++) {
		if (switch_config[i] < '0' || switch_config[i] > '3') {
			dev_err(&fsia6b->dev->dev,
				"Invalid switch configuration supplied for fsia6b.\n");
			err = -EINVAL;
			goto fail2;
		}

		for (j = '1'; j <= switch_config[i]; j++) {
			input_set_capability(input_dev, EV_KEY, BTN_0 + sw_id);
			sw_id++;
		}
	}

	err = serio_open(serio, drv);
	if (err)
		goto fail2;

	err = input_register_device(fsia6b->dev);
	if (err)
		goto fail3;

	return 0;

fail3:	serio_close(serio);
fail2:	input_free_device(input_dev);
fail1:	serio_set_drvdata(serio, NULL);
	kfree(fsia6b);
	return err;
}

static void fsia6b_serio_disconnect(struct serio *serio)
{
	struct fsia6b *fsia6b = serio_get_drvdata(serio);

	serio_close(serio);
	serio_set_drvdata(serio, NULL);
	input_unregister_device(fsia6b->dev);
	kfree(fsia6b);
}

static const struct serio_device_id fsia6b_serio_ids[] = {
	{
		.type	= SERIO_RS232,
		.proto	= SERIO_FSIA6B,
		.id	= SERIO_ANY,
		.extra	= SERIO_ANY,
	},
	{ 0 }
};

MODULE_DEVICE_TABLE(serio, fsia6b_serio_ids);

static struct serio_driver fsia6b_serio_drv = {
	.driver		= {
		.name	= "fsia6b"
	},
	.description	= DRIVER_DESC,
	.id_table	= fsia6b_serio_ids,
	.interrupt	= fsia6b_serio_irq,
	.connect	= fsia6b_serio_connect,
	.disconnect	= fsia6b_serio_disconnect
};

module_serio_driver(fsia6b_serio_drv)