/*
 * BCM2835 SPI Master Controller
 *
 * Copyright (c) 2024 Rayhan Faizel <rayhan.faizel@gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu/osdep.h"
#include "qemu/log.h"
#include "qemu/fifo8.h"
#include "hw/ssi/bcm2835_spi.h"
#include "hw/irq.h"
#include "migration/vmstate.h"

static void bcm2835_spi_update_int(BCM2835SPIState *s)
{
    int do_interrupt = 0;

    /* Interrupt on DONE */
    if (s->cs & BCM2835_SPI_CS_INTD && s->cs & BCM2835_SPI_CS_DONE) {
        do_interrupt = 1;
    }
    /* Interrupt on RXR */
    if (s->cs & BCM2835_SPI_CS_INTR && s->cs & BCM2835_SPI_CS_RXR) {
        do_interrupt = 1;
    }
    qemu_set_irq(s->irq, do_interrupt);
}

static void bcm2835_spi_update_rx_flags(BCM2835SPIState *s)
{
    /* Set RXD if RX FIFO is non empty */
    if (!fifo8_is_empty(&s->rx_fifo)) {
        s->cs |= BCM2835_SPI_CS_RXD;
    } else {
        s->cs &= ~BCM2835_SPI_CS_RXD;
    }

    /* Set RXF if RX FIFO is full */
    if (fifo8_is_full(&s->rx_fifo)) {
        s->cs |= BCM2835_SPI_CS_RXF;
    } else {
        s->cs &= ~BCM2835_SPI_CS_RXF;
    }

    /* Set RXR if RX FIFO is 3/4th used or above */
    if (fifo8_num_used(&s->rx_fifo) >= FIFO_SIZE_3_4) {
        s->cs |= BCM2835_SPI_CS_RXR;
    } else {
        s->cs &= ~BCM2835_SPI_CS_RXR;
    }
}

static void bcm2835_spi_update_tx_flags(BCM2835SPIState *s)
{
    /* Set TXD if TX FIFO is not full */
    if (fifo8_is_full(&s->tx_fifo)) {
        s->cs &= ~BCM2835_SPI_CS_TXD;
    } else {
        s->cs |= BCM2835_SPI_CS_TXD;
    }

    /* Set DONE if in TA mode and TX FIFO is empty */
    if (fifo8_is_empty(&s->tx_fifo) && s->cs & BCM2835_SPI_CS_TA) {
        s->cs |= BCM2835_SPI_CS_DONE;
    } else {
        s->cs &= ~BCM2835_SPI_CS_DONE;
    }
}

static void bcm2835_spi_flush_tx_fifo(BCM2835SPIState *s)
{
    uint8_t tx_byte, rx_byte;

    while (!fifo8_is_empty(&s->tx_fifo) && !fifo8_is_full(&s->rx_fifo)) {
        tx_byte = fifo8_pop(&s->tx_fifo);
        rx_byte = ssi_transfer(s->bus, tx_byte);
        fifo8_push(&s->rx_fifo, rx_byte);
    }

    bcm2835_spi_update_tx_flags(s);
    bcm2835_spi_update_rx_flags(s);
}

static uint64_t bcm2835_spi_read(void *opaque, hwaddr addr, unsigned size)
{
    BCM2835SPIState *s = opaque;
    uint32_t readval = 0;

    switch (addr) {
    case BCM2835_SPI_CS:
        readval = s->cs & 0xffffffff;
        break;
    case BCM2835_SPI_FIFO:
        bcm2835_spi_flush_tx_fifo(s);
        if (s->cs & BCM2835_SPI_CS_RXD) {
            readval = fifo8_pop(&s->rx_fifo);
            bcm2835_spi_update_rx_flags(s);
        }

        bcm2835_spi_update_int(s);
        break;
    case BCM2835_SPI_CLK:
        readval = s->clk & 0xffff;
        break;
    case BCM2835_SPI_DLEN:
        readval = s->dlen & 0xffff;
        break;
    case BCM2835_SPI_LTOH:
        readval = s->ltoh & 0xf;
        break;
    case BCM2835_SPI_DC:
        readval = s->dc & 0xffffffff;
        break;
    default:
        qemu_log_mask(LOG_GUEST_ERROR,
                      "%s: Bad offset 0x%" HWADDR_PRIx "\n", __func__, addr);
    }
    return readval;
}

static void bcm2835_spi_write(void *opaque, hwaddr addr,
                              uint64_t value, unsigned int size)
{
    BCM2835SPIState *s = opaque;

    switch (addr) {
    case BCM2835_SPI_CS:
        s->cs = (value & ~RO_MASK) | (s->cs & RO_MASK);
        if (!(s->cs & BCM2835_SPI_CS_TA)) {
            /* Clear DONE and RXR if TA is off */
            s->cs &= ~(BCM2835_SPI_CS_DONE);
            s->cs &= ~(BCM2835_SPI_CS_RXR);
        }

        /* Clear RX FIFO */
        if (s->cs & BCM2835_SPI_CLEAR_RX) {
            fifo8_reset(&s->rx_fifo);
            bcm2835_spi_update_rx_flags(s);
        }

        /* Clear TX FIFO*/
        if (s->cs & BCM2835_SPI_CLEAR_TX) {
            fifo8_reset(&s->tx_fifo);
            bcm2835_spi_update_tx_flags(s);
        }

        /* Set Transfer Active */
        if (s->cs & BCM2835_SPI_CS_TA) {
            bcm2835_spi_update_tx_flags(s);
        }

        if (s->cs & BCM2835_SPI_CS_DMAEN) {
            qemu_log_mask(LOG_UNIMP, "%s: " \
                          "DMA not supported\n", __func__);
        }

        if (s->cs & BCM2835_SPI_CS_LEN) {
            qemu_log_mask(LOG_UNIMP, "%s: " \
                          "LoSSI not supported\n", __func__);
        }

        bcm2835_spi_update_int(s);
        break;
    case BCM2835_SPI_FIFO:
        /*
         * According to documentation, writes to FIFO without TA controls
         * CS and DLEN registers. This is supposed to be used in DMA mode
         * which is currently unimplemented. Moreover, Linux does not make
         * use of this and directly modifies the CS and DLEN registers.
         */
        if (s->cs & BCM2835_SPI_CS_TA) {
            if (s->cs & BCM2835_SPI_CS_TXD) {
                fifo8_push(&s->tx_fifo, value & 0xff);
                bcm2835_spi_update_tx_flags(s);
            }

            bcm2835_spi_flush_tx_fifo(s);
            bcm2835_spi_update_int(s);
        }
        break;
    case BCM2835_SPI_CLK:
        s->clk = value & 0xffff;
        break;
    case BCM2835_SPI_DLEN:
        s->dlen = value & 0xffff;
        break;
    case BCM2835_SPI_LTOH:
        s->ltoh = value & 0xf;
        break;
    case BCM2835_SPI_DC:
        s->dc = value & 0xffffffff;
        break;
    default:
        qemu_log_mask(LOG_GUEST_ERROR,
                      "%s: Bad offset 0x%" HWADDR_PRIx "\n", __func__, addr);
    }
}

static const MemoryRegionOps bcm2835_spi_ops = {
    .read = bcm2835_spi_read,
    .write = bcm2835_spi_write,
    .endianness = DEVICE_NATIVE_ENDIAN,
};

static void bcm2835_spi_realize(DeviceState *dev, Error **errp)
{
    BCM2835SPIState *s = BCM2835_SPI(dev);
    s->bus = ssi_create_bus(dev, "spi");

    memory_region_init_io(&s->iomem, OBJECT(dev), &bcm2835_spi_ops, s,
                          TYPE_BCM2835_SPI, 0x18);
    sysbus_init_mmio(SYS_BUS_DEVICE(dev), &s->iomem);
    sysbus_init_irq(SYS_BUS_DEVICE(dev), &s->irq);

    fifo8_create(&s->tx_fifo, FIFO_SIZE);
    fifo8_create(&s->rx_fifo, FIFO_SIZE);
}
static void bcm2835_spi_reset(DeviceState *dev)
{
    BCM2835SPIState *s = BCM2835_SPI(dev);

    fifo8_reset(&s->tx_fifo);
    fifo8_reset(&s->rx_fifo);

    /* Reset values according to BCM2835 Peripheral Documentation */
    s->cs = BCM2835_SPI_CS_TXD | BCM2835_SPI_CS_REN;
    s->clk = 0;
    s->dlen = 0;
    s->ltoh = 0x1;
    s->dc = 0x30201020;
}

static const VMStateDescription vmstate_bcm2835_spi = {
    .name = TYPE_BCM2835_SPI,
    .version_id = 1,
    .minimum_version_id = 1,
    .fields = (const VMStateField[]) {
        VMSTATE_FIFO8(tx_fifo, BCM2835SPIState),
        VMSTATE_FIFO8(rx_fifo, BCM2835SPIState),
        VMSTATE_UINT32(cs, BCM2835SPIState),
        VMSTATE_UINT32(clk, BCM2835SPIState),
        VMSTATE_UINT32(dlen, BCM2835SPIState),
        VMSTATE_UINT32(ltoh, BCM2835SPIState),
        VMSTATE_UINT32(dc, BCM2835SPIState),
        VMSTATE_END_OF_LIST()
    }
};

static void bcm2835_spi_class_init(ObjectClass *klass, void *data)
{
    DeviceClass *dc = DEVICE_CLASS(klass);

    device_class_set_legacy_reset(dc, bcm2835_spi_reset);
    dc->realize = bcm2835_spi_realize;
    dc->vmsd = &vmstate_bcm2835_spi;
}

static const TypeInfo bcm2835_spi_info = {
    .name = TYPE_BCM2835_SPI,
    .parent = TYPE_SYS_BUS_DEVICE,
    .instance_size = sizeof(BCM2835SPIState),
    .class_init = bcm2835_spi_class_init,
};

static void bcm2835_spi_register_types(void)
{
    type_register_static(&bcm2835_spi_info);
}

type_init(bcm2835_spi_register_types)