// SPDX-License-Identifier: GPL-2.0-only
/* ir-rc6-decoder.c - A decoder for the RC6 IR protocol
 *
 * Copyright (C) 2010 by David Härdeman <david@hardeman.nu>
 */

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

/*
 * This decoder currently supports:
 * RC6-0-16     (standard toggle bit in header)
 * RC6-6A-20    (no toggle bit)
 * RC6-6A-24    (no toggle bit)
 * RC6-6A-32    (MCE version with toggle bit in body)
 */

#define RC6_UNIT                444     /* microseconds */
#define RC6_HEADER_NBITS        4       /* not including toggle bit */
#define RC6_0_NBITS             16
#define RC6_6A_32_NBITS         32
#define RC6_6A_NBITS            128     /* Variable 8..128 */
#define RC6_PREFIX_PULSE        (6 * RC6_UNIT)
#define RC6_PREFIX_SPACE        (2 * RC6_UNIT)
#define RC6_BIT_START           (1 * RC6_UNIT)
#define RC6_BIT_END             (1 * RC6_UNIT)
#define RC6_TOGGLE_START        (2 * RC6_UNIT)
#define RC6_TOGGLE_END          (2 * RC6_UNIT)
#define RC6_SUFFIX_SPACE        (6 * RC6_UNIT)
#define RC6_MODE_MASK           0x07    /* for the header bits */
#define RC6_STARTBIT_MASK       0x08    /* for the header bits */
#define RC6_6A_MCE_TOGGLE_MASK  0x8000  /* for the body bits */
#define RC6_6A_LCC_MASK         0xffff0000 /* RC6-6A-32 long customer code mask */
#define RC6_6A_MCE_CC           0x800f0000 /* MCE customer code */
#define RC6_6A_ZOTAC_CC         0x80340000 /* Zotac customer code */
#define RC6_6A_KATHREIN_CC      0x80460000 /* Kathrein RCU-676 customer code */
#ifndef CHAR_BIT
#define CHAR_BIT 8      /* Normally in <limits.h> */
#endif

enum rc6_mode {
        RC6_MODE_0,
        RC6_MODE_6A,
        RC6_MODE_UNKNOWN,
};

enum rc6_state {
        STATE_INACTIVE,
        STATE_PREFIX_SPACE,
        STATE_HEADER_BIT_START,
        STATE_HEADER_BIT_END,
        STATE_TOGGLE_START,
        STATE_TOGGLE_END,
        STATE_BODY_BIT_START,
        STATE_BODY_BIT_END,
        STATE_FINISHED,
};

static enum rc6_mode rc6_mode(struct rc6_dec *data)
{
        switch (data->header & RC6_MODE_MASK) {
        case 0:
                return RC6_MODE_0;
        case 6:
                if (!data->toggle)
                        return RC6_MODE_6A;
                fallthrough;
        default:
                return RC6_MODE_UNKNOWN;
        }
}

/**
 * ir_rc6_decode() - Decode one RC6 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_rc6_decode(struct rc_dev *dev, struct ir_raw_event ev)
{
        struct rc6_dec *data = &dev->raw->rc6;
        u32 scancode;
        u8 toggle;
        enum rc_proto protocol;

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

        if (!geq_margin(ev.duration, RC6_UNIT, RC6_UNIT / 2))
                goto out;

again:
        dev_dbg(&dev->dev, "RC6 decode started at state %i (%uus %s)\n",
                data->state, ev.duration, TO_STR(ev.pulse));

        if (!geq_margin(ev.duration, RC6_UNIT, RC6_UNIT / 2))
                return 0;

        switch (data->state) {

        case STATE_INACTIVE:
                if (!ev.pulse)
                        break;

                /* Note: larger margin on first pulse since each RC6_UNIT
                   is quite short and some hardware takes some time to
                   adjust to the signal */
                if (!eq_margin(ev.duration, RC6_PREFIX_PULSE, RC6_UNIT))
                        break;

                data->state = STATE_PREFIX_SPACE;
                data->count = 0;
                return 0;

        case STATE_PREFIX_SPACE:
                if (ev.pulse)
                        break;

                if (!eq_margin(ev.duration, RC6_PREFIX_SPACE, RC6_UNIT / 2))
                        break;

                data->state = STATE_HEADER_BIT_START;
                data->header = 0;
                return 0;

        case STATE_HEADER_BIT_START:
                if (!eq_margin(ev.duration, RC6_BIT_START, RC6_UNIT / 2))
                        break;

                data->header <<= 1;
                if (ev.pulse)
                        data->header |= 1;
                data->count++;
                data->state = STATE_HEADER_BIT_END;
                return 0;

        case STATE_HEADER_BIT_END:
                if (data->count == RC6_HEADER_NBITS)
                        data->state = STATE_TOGGLE_START;
                else
                        data->state = STATE_HEADER_BIT_START;

                decrease_duration(&ev, RC6_BIT_END);
                goto again;

        case STATE_TOGGLE_START:
                if (!eq_margin(ev.duration, RC6_TOGGLE_START, RC6_UNIT / 2))
                        break;

                data->toggle = ev.pulse;
                data->state = STATE_TOGGLE_END;
                return 0;

        case STATE_TOGGLE_END:
                if (!(data->header & RC6_STARTBIT_MASK)) {
                        dev_dbg(&dev->dev, "RC6 invalid start bit\n");
                        break;
                }

                data->state = STATE_BODY_BIT_START;
                decrease_duration(&ev, RC6_TOGGLE_END);
                data->count = 0;
                data->body = 0;

                switch (rc6_mode(data)) {
                case RC6_MODE_0:
                        data->wanted_bits = RC6_0_NBITS;
                        break;
                case RC6_MODE_6A:
                        data->wanted_bits = RC6_6A_NBITS;
                        break;
                default:
                        dev_dbg(&dev->dev, "RC6 unknown mode\n");
                        goto out;
                }
                goto again;

        case STATE_BODY_BIT_START:
                if (eq_margin(ev.duration, RC6_BIT_START, RC6_UNIT / 2)) {
                        /* Discard LSB's that won't fit in data->body */
                        if (data->count++ < CHAR_BIT * sizeof data->body) {
                                data->body <<= 1;
                                if (ev.pulse)
                                        data->body |= 1;
                        }
                        data->state = STATE_BODY_BIT_END;
                        return 0;
                } else if (RC6_MODE_6A == rc6_mode(data) && !ev.pulse &&
                                geq_margin(ev.duration, RC6_SUFFIX_SPACE, RC6_UNIT / 2)) {
                        data->state = STATE_FINISHED;
                        goto again;
                }
                break;

        case STATE_BODY_BIT_END:
                if (data->count == data->wanted_bits)
                        data->state = STATE_FINISHED;
                else
                        data->state = STATE_BODY_BIT_START;

                decrease_duration(&ev, RC6_BIT_END);
                goto again;

        case STATE_FINISHED:
                if (ev.pulse)
                        break;

                switch (rc6_mode(data)) {
                case RC6_MODE_0:
                        scancode = data->body;
                        toggle = data->toggle;
                        protocol = RC_PROTO_RC6_0;
                        dev_dbg(&dev->dev, "RC6(0) scancode 0x%04x (toggle: %u)\n",
                                scancode, toggle);
                        break;

                case RC6_MODE_6A:
                        if (data->count > CHAR_BIT * sizeof data->body) {
                                dev_dbg(&dev->dev, "RC6 too many (%u) data bits\n",
                                        data->count);
                                goto out;
                        }

                        scancode = data->body;
                        switch (data->count) {
                        case 20:
                                protocol = RC_PROTO_RC6_6A_20;
                                toggle = 0;
                                break;
                        case 24:
                                protocol = RC_PROTO_RC6_6A_24;
                                toggle = 0;
                                break;
                        case 32:
                                switch (scancode & RC6_6A_LCC_MASK) {
                                case RC6_6A_MCE_CC:
                                case RC6_6A_KATHREIN_CC:
                                case RC6_6A_ZOTAC_CC:
                                        protocol = RC_PROTO_RC6_MCE;
                                        toggle = !!(scancode & RC6_6A_MCE_TOGGLE_MASK);
                                        scancode &= ~RC6_6A_MCE_TOGGLE_MASK;
                                        break;
                                default:
                                        protocol = RC_PROTO_RC6_6A_32;
                                        toggle = 0;
                                        break;
                                }
                                break;
                        default:
                                dev_dbg(&dev->dev, "RC6(6A) unsupported length\n");
                                goto out;
                        }

                        dev_dbg(&dev->dev, "RC6(6A) proto 0x%04x, scancode 0x%08x (toggle: %u)\n",
                                protocol, scancode, toggle);
                        break;
                default:
                        dev_dbg(&dev->dev, "RC6 unknown mode\n");
                        goto out;
                }

                rc_keydown(dev, protocol, scancode, toggle);
                data->state = STATE_INACTIVE;
                return 0;
        }

out:
        dev_dbg(&dev->dev, "RC6 decode failed at state %i (%uus %s)\n",
                data->state, ev.duration, TO_STR(ev.pulse));
        data->state = STATE_INACTIVE;
        return -EINVAL;
}

static const struct ir_raw_timings_manchester ir_rc6_timings[4] = {
        {
                .leader_pulse           = RC6_PREFIX_PULSE,
                .leader_space           = RC6_PREFIX_SPACE,
                .clock                  = RC6_UNIT,
                .invert                 = 1,
        },
        {
                .clock                  = RC6_UNIT * 2,
                .invert                 = 1,
        },
        {
                .clock                  = RC6_UNIT,
                .invert                 = 1,
                .trailer_space          = RC6_SUFFIX_SPACE,
        },
};

/**
 * ir_rc6_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.
 *              -EINVAL if the scancode is ambiguous or invalid.
 */
static int ir_rc6_encode(enum rc_proto protocol, u32 scancode,
                         struct ir_raw_event *events, unsigned int max)
{
        int ret;
        struct ir_raw_event *e = events;

        if (protocol == RC_PROTO_RC6_0) {
                /* Modulate the header (Start Bit & Mode-0) */
                ret = ir_raw_gen_manchester(&e, max - (e - events),
                                            &ir_rc6_timings[0],
                                            RC6_HEADER_NBITS, (1 << 3));
                if (ret < 0)
                        return ret;

                /* Modulate Trailer Bit */
                ret = ir_raw_gen_manchester(&e, max - (e - events),
                                            &ir_rc6_timings[1], 1, 0);
                if (ret < 0)
                        return ret;

                /* Modulate rest of the data */
                ret = ir_raw_gen_manchester(&e, max - (e - events),
                                            &ir_rc6_timings[2], RC6_0_NBITS,
                                            scancode);
                if (ret < 0)
                        return ret;

        } else {
                int bits;

                switch (protocol) {
                case RC_PROTO_RC6_MCE:
                case RC_PROTO_RC6_6A_32:
                        bits = 32;
                        break;
                case RC_PROTO_RC6_6A_24:
                        bits = 24;
                        break;
                case RC_PROTO_RC6_6A_20:
                        bits = 20;
                        break;
                default:
                        return -EINVAL;
                }

                /* Modulate the header (Start Bit & Header-version 6 */
                ret = ir_raw_gen_manchester(&e, max - (e - events),
                                            &ir_rc6_timings[0],
                                            RC6_HEADER_NBITS, (1 << 3 | 6));
                if (ret < 0)
                        return ret;

                /* Modulate Trailer Bit */
                ret = ir_raw_gen_manchester(&e, max - (e - events),
                                            &ir_rc6_timings[1], 1, 0);
                if (ret < 0)
                        return ret;

                /* Modulate rest of the data */
                ret = ir_raw_gen_manchester(&e, max - (e - events),
                                            &ir_rc6_timings[2],
                                            bits,
                                            scancode);
                if (ret < 0)
                        return ret;
        }

        return e - events;
}

static struct ir_raw_handler rc6_handler = {
        .protocols      = RC_PROTO_BIT_RC6_0 | RC_PROTO_BIT_RC6_6A_20 |
                          RC_PROTO_BIT_RC6_6A_24 | RC_PROTO_BIT_RC6_6A_32 |
                          RC_PROTO_BIT_RC6_MCE,
        .decode         = ir_rc6_decode,
        .encode         = ir_rc6_encode,
        .carrier        = 36000,
        .min_timeout    = RC6_SUFFIX_SPACE,
};

static int __init ir_rc6_decode_init(void)
{
        ir_raw_handler_register(&rc6_handler);

        printk(KERN_INFO "IR RC6 protocol handler initialized\n");
        return 0;
}

static void __exit ir_rc6_decode_exit(void)
{
        ir_raw_handler_unregister(&rc6_handler);
}

module_init(ir_rc6_decode_init);
module_exit(ir_rc6_decode_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("David Härdeman <david@hardeman.nu>");
MODULE_DESCRIPTION("RC6 IR protocol decoder");