/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2024 Jessica Clarke <jrtc27@FreeBSD.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>

#include <assert.h>
#include <limits.h>
#include <pthread.h>
#include <stdlib.h>
#include <time.h>

#include "config.h"
#include "mevent.h"
#include "rtc_pl031.h"

#define RTCDR           0x000
#define RTCMR           0x004
#define RTCLR           0x008
#define RTCCR           0x00C
#define RTCIMSC         0x010
#define RTCRIS          0x014
#define RTCMIS          0x018
#define RTCICR          0x01C

#define RTCPeriphID0    0xFE0
#define RTCPeriphID1    0xFE4
#define RTCPeriphID2    0xFE8
#define RTCPeriphID3    0xFEC
#define  _RTCPeriphID_VAL       0x00141031
#define  RTCPeriphID_VAL(_n)    ((_RTCPeriphID_VAL >> (8 * (_n))) & 0xff)

#define RTCCellID0      0xFF0
#define RTCCellID1      0xFF4
#define RTCCellID2      0xFF8
#define RTCCellID3      0xFFC
#define  _RTCCellID_VAL         0xb105f00d
#define  RTCCellID_VAL(_n)      ((_RTCCellID_VAL >> (8 * (_n))) & 0xff)

struct rtc_pl031_softc {
        pthread_mutex_t         mtx;

        time_t                  last_tick;
        uint32_t                dr;
        uint32_t                mr;
        uint32_t                lr;
        uint8_t                 imsc;
        uint8_t                 ris;
        uint8_t                 prev_mis;

        struct mevent           *mevp;

        void                    *arg;
        rtc_pl031_intr_func_t   intr_assert;
        rtc_pl031_intr_func_t   intr_deassert;
};

static void     rtc_pl031_callback(int fd, enum ev_type type, void *param);

/*
 * Returns the current RTC time as number of seconds since 00:00:00 Jan 1, 1970
 */
static time_t
rtc_pl031_time(void)
{
        struct tm tm;
        time_t t;

        time(&t);
        if (get_config_bool_default("rtc.use_localtime", false)) {
                localtime_r(&t, &tm);
                t = timegm(&tm);
        }
        return (t);
}

static void
rtc_pl031_update_mis(struct rtc_pl031_softc *sc)
{
        uint8_t mis;

        mis = sc->ris & sc->imsc;
        if (mis == sc->prev_mis)
                return;

        sc->prev_mis = mis;
        if (mis)
                (*sc->intr_assert)(sc->arg);
        else
                (*sc->intr_deassert)(sc->arg);
}

static uint64_t
rtc_pl031_next_match_ticks(struct rtc_pl031_softc *sc)
{
        uint32_t ticks;

        ticks = sc->mr - sc->dr;
        if (ticks == 0)
                return ((uint64_t)1 << 32);

        return (ticks);
}

static int
rtc_pl031_next_timer_msecs(struct rtc_pl031_softc *sc)
{
        uint64_t ticks;

        ticks = rtc_pl031_next_match_ticks(sc);
        return (MIN(ticks * 1000, INT_MAX));
}

static void
rtc_pl031_update_timer(struct rtc_pl031_softc *sc)
{
        mevent_timer_update(sc->mevp, rtc_pl031_next_timer_msecs(sc));
}

static void
rtc_pl031_tick(struct rtc_pl031_softc *sc, bool from_timer)
{
        bool match;
        time_t now, ticks;

        now = rtc_pl031_time();
        ticks = now - sc->last_tick;
        match = ticks >= 0 &&
            (uint64_t)ticks >= rtc_pl031_next_match_ticks(sc);
        sc->dr += ticks;
        sc->last_tick = now;

        if (match) {
                sc->ris = 1;
                rtc_pl031_update_mis(sc);
        }

        if (match || from_timer || ticks < 0)
                rtc_pl031_update_timer(sc);
}

static void
rtc_pl031_callback(int fd __unused, enum ev_type type __unused, void *param)
{
        struct rtc_pl031_softc *sc = param;

        pthread_mutex_lock(&sc->mtx);
        rtc_pl031_tick(sc, true);
        pthread_mutex_unlock(&sc->mtx);
}

void
rtc_pl031_write(struct rtc_pl031_softc *sc, int offset, uint32_t value)
{
        pthread_mutex_lock(&sc->mtx);
        rtc_pl031_tick(sc, false);
        switch (offset) {
        case RTCMR:
                sc->mr = value;
                rtc_pl031_update_timer(sc);
                break;
        case RTCLR:
                sc->lr = value;
                sc->dr = sc->lr;
                rtc_pl031_update_timer(sc);
                break;
        case RTCIMSC:
                sc->imsc = value & 1;
                rtc_pl031_update_mis(sc);
                break;
        case RTCICR:
                sc->ris &= ~value;
                rtc_pl031_update_mis(sc);
                break;
        default:
                /* Ignore writes to read-only/unassigned/ID registers */
                break;
        }
        pthread_mutex_unlock(&sc->mtx);
}

uint32_t
rtc_pl031_read(struct rtc_pl031_softc *sc, int offset)
{
        uint32_t reg;

        pthread_mutex_lock(&sc->mtx);
        rtc_pl031_tick(sc, false);
        switch (offset) {
        case RTCDR:
                reg = sc->dr;
                break;
        case RTCMR:
                reg = sc->mr;
                break;
        case RTCLR:
                reg = sc->lr;
                break;
        case RTCCR:
                /* RTC enabled from reset */
                reg = 1;
                break;
        case RTCIMSC:
                reg = sc->imsc;
                break;
        case RTCRIS:
                reg = sc->ris;
                break;
        case RTCMIS:
                reg = sc->ris & sc->imsc;
                break;
        case RTCPeriphID0:
        case RTCPeriphID1:
        case RTCPeriphID2:
        case RTCPeriphID3:
                reg = RTCPeriphID_VAL(offset - RTCPeriphID0);
                break;
        case RTCCellID0:
        case RTCCellID1:
        case RTCCellID2:
        case RTCCellID3:
                reg = RTCCellID_VAL(offset - RTCCellID0);
                break;
        default:
                /* Return 0 in reads from unasigned registers */
                reg = 0;
                break;
        }
        pthread_mutex_unlock(&sc->mtx);

        return (reg);
}

struct rtc_pl031_softc *
rtc_pl031_init(rtc_pl031_intr_func_t intr_assert,
    rtc_pl031_intr_func_t intr_deassert, void *arg)
{
        struct rtc_pl031_softc *sc;
        time_t now;

        sc = calloc(1, sizeof(struct rtc_pl031_softc));

        pthread_mutex_init(&sc->mtx, NULL);

        now = rtc_pl031_time();
        sc->dr = now;
        sc->last_tick = now;
        sc->arg = arg;
        sc->intr_assert = intr_assert;
        sc->intr_deassert = intr_deassert;

        sc->mevp = mevent_add(rtc_pl031_next_timer_msecs(sc), EVF_TIMER,
            rtc_pl031_callback, sc);

        return (sc);
}