// SPDX-License-Identifier: GPL-2.0+
// ir-imon-decoder.c - handle iMon protocol
//
// Copyright (C) 2018 by Sean Young <sean@mess.org>

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include "rc-core-priv.h"

#define IMON_UNIT		415662 /* ns */
#define IMON_BITS		30
#define IMON_CHKBITS		(BIT(30) | BIT(25) | BIT(24) | BIT(22) | \
				 BIT(21) | BIT(20) | BIT(19) | BIT(18) | \
				 BIT(17) | BIT(16) | BIT(14) | BIT(13) | \
				 BIT(12) | BIT(11) | BIT(10) | BIT(9))

/*
 * This protocol has 30 bits. The format is one IMON_UNIT header pulse,
 * followed by 30 bits. Each bit is one IMON_UNIT check field, and then
 * one IMON_UNIT field with the actual bit (1=space, 0=pulse).
 * The check field is always space for some bits, for others it is pulse if
 * both the preceding and current bit are zero, else space. IMON_CHKBITS
 * defines which bits are of type check.
 *
 * There is no way to distinguish an incomplete message from one where
 * the lower bits are all set, iow. the last pulse is for the lowest
 * bit which is 0.
 */
enum imon_state {
	STATE_INACTIVE,
	STATE_BIT_CHK,
	STATE_BIT_START,
	STATE_FINISHED
};

/**
 * ir_imon_decode() - Decode one iMON pulse or space
 * @dev:	the struct rc_dev descriptor of the device
 * @ev:		the struct ir_raw_event descriptor of the pulse/space
 *
 * This function returns -EINVAL if the pulse violates the state machine
 */
static int ir_imon_decode(struct rc_dev *dev, struct ir_raw_event ev)
{
	struct imon_dec *data = &dev->raw->imon;

	if (!is_timing_event(ev)) {
		if (ev.reset)
			data->state = STATE_INACTIVE;
		return 0;
	}

	dev_dbg(&dev->dev,
		"iMON decode started at state %d bitno %d (%uus %s)\n",
		data->state, data->count, TO_US(ev.duration),
		TO_STR(ev.pulse));

	for (;;) {
		if (!geq_margin(ev.duration, IMON_UNIT, IMON_UNIT / 2))
			return 0;

		decrease_duration(&ev, IMON_UNIT);

		switch (data->state) {
		case STATE_INACTIVE:
			if (ev.pulse) {
				data->state = STATE_BIT_CHK;
				data->bits = 0;
				data->count = IMON_BITS;
			}
			break;
		case STATE_BIT_CHK:
			if (IMON_CHKBITS & BIT(data->count))
				data->last_chk = ev.pulse;
			else if (ev.pulse)
				goto err_out;
			data->state = STATE_BIT_START;
			break;
		case STATE_BIT_START:
			data->bits <<= 1;
			if (!ev.pulse)
				data->bits |= 1;

			if (IMON_CHKBITS & BIT(data->count)) {
				if (data->last_chk != !(data->bits & 3))
					goto err_out;
			}

			if (!data->count--)
				data->state = STATE_FINISHED;
			else
				data->state = STATE_BIT_CHK;
			break;
		case STATE_FINISHED:
			if (ev.pulse)
				goto err_out;
			rc_keydown(dev, RC_PROTO_IMON, data->bits, 0);
			data->state = STATE_INACTIVE;
			break;
		}
	}

err_out:
	dev_dbg(&dev->dev,
		"iMON decode failed at state %d bitno %d (%uus %s)\n",
		data->state, data->count, TO_US(ev.duration),
		TO_STR(ev.pulse));

	data->state = STATE_INACTIVE;

	return -EINVAL;
}

/**
 * ir_imon_encode() - Encode a scancode as a stream of raw events
 *
 * @protocol:	protocol to encode
 * @scancode:	scancode to encode
 * @events:	array of raw ir events to write into
 * @max:	maximum size of @events
 *
 * Returns:	The number of events written.
 *		-ENOBUFS if there isn't enough space in the array to fit the
 *		encoding. In this case all @max events will have been written.
 */
static int ir_imon_encode(enum rc_proto protocol, u32 scancode,
			  struct ir_raw_event *events, unsigned int max)
{
	struct ir_raw_event *e = events;
	int i, pulse;

	if (!max--)
		return -ENOBUFS;
	init_ir_raw_event_duration(e, 1, IMON_UNIT);

	for (i = IMON_BITS; i >= 0; i--) {
		if (BIT(i) & IMON_CHKBITS)
			pulse = !(scancode & (BIT(i) | BIT(i + 1)));
		else
			pulse = 0;

		if (pulse == e->pulse) {
			e->duration += IMON_UNIT;
		} else {
			if (!max--)
				return -ENOBUFS;
			init_ir_raw_event_duration(++e, pulse, IMON_UNIT);
		}

		pulse = !(scancode & BIT(i));

		if (pulse == e->pulse) {
			e->duration += IMON_UNIT;
		} else {
			if (!max--)
				return -ENOBUFS;
			init_ir_raw_event_duration(++e, pulse, IMON_UNIT);
		}
	}

	if (e->pulse)
		e++;

	return e - events;
}

static struct ir_raw_handler imon_handler = {
	.protocols	= RC_PROTO_BIT_IMON,
	.decode		= ir_imon_decode,
	.encode		= ir_imon_encode,
	.carrier	= 38000,
};

static int __init ir_imon_decode_init(void)
{
	ir_raw_handler_register(&imon_handler);

	pr_info("IR iMON protocol handler initialized\n");
	return 0;
}

static void __exit ir_imon_decode_exit(void)
{
	ir_raw_handler_unregister(&imon_handler);
}

module_init(ir_imon_decode_init);
module_exit(ir_imon_decode_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Sean Young <sean@mess.org>");
MODULE_DESCRIPTION("iMON IR protocol decoder");