// 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               416 /* us */
#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,
        STATE_ERROR,
};

static void ir_imon_decode_scancode(struct rc_dev *dev)
{
        struct imon_dec *imon = &dev->raw->imon;

        /* Keyboard/Mouse toggle */
        if (imon->bits == 0x299115b7)
                imon->stick_keyboard = !imon->stick_keyboard;

        if ((imon->bits & 0xfc0000ff) == 0x680000b7) {
                int rel_x, rel_y;
                u8 buf;

                buf = imon->bits >> 16;
                rel_x = (buf & 0x08) | (buf & 0x10) >> 2 |
                        (buf & 0x20) >> 4 | (buf & 0x40) >> 6;
                if (imon->bits & 0x02000000)
                        rel_x |= ~0x0f;
                buf = imon->bits >> 8;
                rel_y = (buf & 0x08) | (buf & 0x10) >> 2 |
                        (buf & 0x20) >> 4 | (buf & 0x40) >> 6;
                if (imon->bits & 0x01000000)
                        rel_y |= ~0x0f;

                if (rel_x && rel_y && imon->stick_keyboard) {
                        if (abs(rel_y) > abs(rel_x))
                                imon->bits = rel_y > 0 ?
                                        0x289515b7 : /* KEY_DOWN */
                                        0x2aa515b7;  /* KEY_UP */
                        else
                                imon->bits = rel_x > 0 ?
                                        0x2ba515b7 : /* KEY_RIGHT */
                                        0x29a515b7;  /* KEY_LEFT */
                }

                if (!imon->stick_keyboard) {
                        input_report_rel(dev->input_dev, REL_X, rel_x);
                        input_report_rel(dev->input_dev, REL_Y, rel_y);

                        input_report_key(dev->input_dev, BTN_LEFT,
                                         (imon->bits & 0x00010000) != 0);
                        input_report_key(dev->input_dev, BTN_RIGHT,
                                         (imon->bits & 0x00040000) != 0);
                }
        }

        rc_keydown(dev, RC_PROTO_IMON, imon->bits, 0);
}

/**
 * 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.overflow)
                        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, ev.duration, TO_STR(ev.pulse));

        /*
         * Since iMON protocol is a series of bits, if at any point
         * we encounter an error, make sure that any remaining bits
         * aren't parsed as a scancode made up of less bits.
         *
         * Note that if the stick is held, then the remote repeats
         * the scancode with about 12ms between them. So, make sure
         * we have at least 10ms of space after an error. That way,
         * we're at a new scancode.
         */
        if (data->state == STATE_ERROR) {
                if (!ev.pulse && ev.duration > MS_TO_US(10))
                        data->state = STATE_INACTIVE;
                return 0;
        }

        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;
                        ir_imon_decode_scancode(dev);
                        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, ev.duration, TO_STR(ev.pulse));

        data->state = STATE_ERROR;

        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 int ir_imon_register(struct rc_dev *dev)
{
        struct imon_dec *imon = &dev->raw->imon;

        imon->stick_keyboard = false;

        return 0;
}

static struct ir_raw_handler imon_handler = {
        .protocols      = RC_PROTO_BIT_IMON,
        .decode         = ir_imon_decode,
        .encode         = ir_imon_encode,
        .carrier        = 38000,
        .raw_register   = ir_imon_register,
        .min_timeout    = IMON_UNIT * IMON_BITS * 2,
};

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");