// SPDX-License-Identifier: GPL-2.0
/*
 *   Sound driver for Nintendo 64.
 *
 *   Copyright 2021 Lauri Kasanen
 */

#include <linux/dma-mapping.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/log2.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/spinlock.h>
#include <linux/string.h>

#include <sound/control.h>
#include <sound/core.h>
#include <sound/initval.h>
#include <sound/pcm.h>
#include <sound/pcm_params.h>

MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
MODULE_DESCRIPTION("N64 Audio");
MODULE_LICENSE("GPL");

#define AI_NTSC_DACRATE 48681812
#define AI_STATUS_BUSY  (1 << 30)
#define AI_STATUS_FULL  (1 << 31)

#define AI_ADDR_REG 0
#define AI_LEN_REG 1
#define AI_CONTROL_REG 2
#define AI_STATUS_REG 3
#define AI_RATE_REG 4
#define AI_BITCLOCK_REG 5

#define MI_INTR_REG 2
#define MI_MASK_REG 3

#define MI_INTR_AI 0x04

#define MI_MASK_CLR_AI 0x0010
#define MI_MASK_SET_AI 0x0020


struct n64audio {
        u32 __iomem *ai_reg_base;
        u32 __iomem *mi_reg_base;

        void *ring_base;
        dma_addr_t ring_base_dma;

        struct snd_card *card;

        struct {
                struct snd_pcm_substream *substream;
                int pos, nextpos;
                u32 writesize;
                u32 bufsize;
                spinlock_t lock;
        } chan;
};

static void n64audio_write_reg(struct n64audio *priv, const u8 reg, const u32 value)
{
        writel(value, priv->ai_reg_base + reg);
}

static void n64mi_write_reg(struct n64audio *priv, const u8 reg, const u32 value)
{
        writel(value, priv->mi_reg_base + reg);
}

static u32 n64mi_read_reg(struct n64audio *priv, const u8 reg)
{
        return readl(priv->mi_reg_base + reg);
}

static void n64audio_push(struct n64audio *priv)
{
        struct snd_pcm_runtime *runtime = priv->chan.substream->runtime;
        u32 count;

        guard(spinlock_irqsave)(&priv->chan.lock);

        count = priv->chan.writesize;

        memcpy(priv->ring_base + priv->chan.nextpos,
               runtime->dma_area + priv->chan.nextpos, count);

        /*
         * The hw registers are double-buffered, and the IRQ fires essentially
         * one period behind. The core only allows one period's distance, so we
         * keep a private DMA buffer to afford two.
         */
        n64audio_write_reg(priv, AI_ADDR_REG, priv->ring_base_dma + priv->chan.nextpos);
        barrier();
        n64audio_write_reg(priv, AI_LEN_REG, count);

        priv->chan.nextpos += count;
        priv->chan.nextpos %= priv->chan.bufsize;

        runtime->delay = runtime->period_size;
}

static irqreturn_t n64audio_isr(int irq, void *dev_id)
{
        struct n64audio *priv = dev_id;
        const u32 intrs = n64mi_read_reg(priv, MI_INTR_REG);

        // Check it's ours
        if (!(intrs & MI_INTR_AI))
                return IRQ_NONE;

        n64audio_write_reg(priv, AI_STATUS_REG, 1);

        if (priv->chan.substream && snd_pcm_running(priv->chan.substream)) {
                scoped_guard(spinlock_irqsave, &priv->chan.lock) {
                        priv->chan.pos = priv->chan.nextpos;
                }

                snd_pcm_period_elapsed(priv->chan.substream);
                if (priv->chan.substream && snd_pcm_running(priv->chan.substream))
                        n64audio_push(priv);
        }

        return IRQ_HANDLED;
}

static const struct snd_pcm_hardware n64audio_pcm_hw = {
        .info = (SNDRV_PCM_INFO_MMAP |
                 SNDRV_PCM_INFO_MMAP_VALID |
                 SNDRV_PCM_INFO_INTERLEAVED |
                 SNDRV_PCM_INFO_BLOCK_TRANSFER),
        .formats =          SNDRV_PCM_FMTBIT_S16_BE,
        .rates =            SNDRV_PCM_RATE_8000_48000,
        .rate_min =         8000,
        .rate_max =         48000,
        .channels_min =     2,
        .channels_max =     2,
        .buffer_bytes_max = 32768,
        .period_bytes_min = 1024,
        .period_bytes_max = 32768,
        .periods_min =      3,
        // 3 periods lets the double-buffering hw read one buffer behind safely
        .periods_max =      128,
};

static int hw_rule_period_size(struct snd_pcm_hw_params *params,
                               struct snd_pcm_hw_rule *rule)
{
        struct snd_interval *c = hw_param_interval(params,
                                                   SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
        int changed = 0;

        /*
         * The DMA unit has errata on (start + len) & 0x3fff == 0x2000.
         * This constraint makes sure that the period size is not a power of two,
         * which combined with dma_alloc_coherent aligning the buffer to the largest
         * PoT <= size guarantees it won't be hit.
         */

        if (is_power_of_2(c->min)) {
                c->min += 2;
                changed = 1;
        }
        if (is_power_of_2(c->max)) {
                c->max -= 2;
                changed = 1;
        }
        if (snd_interval_checkempty(c)) {
                c->empty = 1;
                return -EINVAL;
        }

        return changed;
}

static int n64audio_pcm_open(struct snd_pcm_substream *substream)
{
        struct snd_pcm_runtime *runtime = substream->runtime;
        int err;

        runtime->hw = n64audio_pcm_hw;
        err = snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
        if (err < 0)
                return err;

        err = snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 2);
        if (err < 0)
                return err;

        err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
                            hw_rule_period_size, NULL, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
        if (err < 0)
                return err;

        return 0;
}

static int n64audio_pcm_prepare(struct snd_pcm_substream *substream)
{
        struct snd_pcm_runtime *runtime = substream->runtime;
        struct n64audio *priv = substream->pcm->private_data;
        u32 rate;

        rate = ((2 * AI_NTSC_DACRATE / runtime->rate) + 1) / 2 - 1;

        n64audio_write_reg(priv, AI_RATE_REG, rate);

        rate /= 66;
        if (rate > 16)
                rate = 16;
        n64audio_write_reg(priv, AI_BITCLOCK_REG, rate - 1);

        guard(spinlock_irq)(&priv->chan.lock);

        /* Setup the pseudo-dma transfer pointers.  */
        priv->chan.pos = 0;
        priv->chan.nextpos = 0;
        priv->chan.substream = substream;
        priv->chan.writesize = snd_pcm_lib_period_bytes(substream);
        priv->chan.bufsize = snd_pcm_lib_buffer_bytes(substream);

        return 0;
}

static int n64audio_pcm_trigger(struct snd_pcm_substream *substream,
                                int cmd)
{
        struct n64audio *priv = substream->pcm->private_data;

        switch (cmd) {
        case SNDRV_PCM_TRIGGER_START:
                n64audio_push(substream->pcm->private_data);
                n64audio_write_reg(priv, AI_CONTROL_REG, 1);
                n64mi_write_reg(priv, MI_MASK_REG, MI_MASK_SET_AI);
                break;
        case SNDRV_PCM_TRIGGER_STOP:
                n64audio_write_reg(priv, AI_CONTROL_REG, 0);
                n64mi_write_reg(priv, MI_MASK_REG, MI_MASK_CLR_AI);
                break;
        default:
                return -EINVAL;
        }
        return 0;
}

static snd_pcm_uframes_t n64audio_pcm_pointer(struct snd_pcm_substream *substream)
{
        struct n64audio *priv = substream->pcm->private_data;

        return bytes_to_frames(substream->runtime,
                               priv->chan.pos);
}

static int n64audio_pcm_close(struct snd_pcm_substream *substream)
{
        struct n64audio *priv = substream->pcm->private_data;

        priv->chan.substream = NULL;

        return 0;
}

static const struct snd_pcm_ops n64audio_pcm_ops = {
        .open =         n64audio_pcm_open,
        .prepare =      n64audio_pcm_prepare,
        .trigger =      n64audio_pcm_trigger,
        .pointer =      n64audio_pcm_pointer,
        .close =        n64audio_pcm_close,
};

/*
 * The target device is embedded and RAM-constrained. We save RAM
 * by initializing in __init code that gets dropped late in boot.
 * For the same reason there is no module or unloading support.
 */
static int __init n64audio_probe(struct platform_device *pdev)
{
        struct snd_card *card;
        struct snd_pcm *pcm;
        struct n64audio *priv;
        int err, irq;

        err = snd_card_new(&pdev->dev, SNDRV_DEFAULT_IDX1,
                           SNDRV_DEFAULT_STR1,
                           THIS_MODULE, sizeof(*priv), &card);
        if (err < 0)
                return err;

        priv = card->private_data;

        spin_lock_init(&priv->chan.lock);

        priv->card = card;

        priv->ring_base = dma_alloc_coherent(card->dev, 32 * 1024, &priv->ring_base_dma,
                                             GFP_DMA|GFP_KERNEL);
        if (!priv->ring_base) {
                err = -ENOMEM;
                goto fail_card;
        }

        priv->mi_reg_base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(priv->mi_reg_base)) {
                err = PTR_ERR(priv->mi_reg_base);
                goto fail_dma_alloc;
        }

        priv->ai_reg_base = devm_platform_ioremap_resource(pdev, 1);
        if (IS_ERR(priv->ai_reg_base)) {
                err = PTR_ERR(priv->ai_reg_base);
                goto fail_dma_alloc;
        }

        err = snd_pcm_new(card, "N64 Audio", 0, 1, 0, &pcm);
        if (err < 0)
                goto fail_dma_alloc;

        pcm->private_data = priv;
        strscpy(pcm->name, "N64 Audio");

        snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &n64audio_pcm_ops);
        snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC, card->dev, 0, 0);

        strscpy(card->driver, "N64 Audio");
        strscpy(card->shortname, "N64 Audio");
        strscpy(card->longname, "N64 Audio");

        irq = platform_get_irq(pdev, 0);
        if (irq < 0) {
                err = -EINVAL;
                goto fail_dma_alloc;
        }
        if (devm_request_irq(&pdev->dev, irq, n64audio_isr,
                                IRQF_SHARED, "N64 Audio", priv)) {
                err = -EBUSY;
                goto fail_dma_alloc;
        }

        err = snd_card_register(card);
        if (err < 0)
                goto fail_dma_alloc;

        return 0;

fail_dma_alloc:
        dma_free_coherent(card->dev, 32 * 1024, priv->ring_base, priv->ring_base_dma);

fail_card:
        snd_card_free(card);
        return err;
}

static struct platform_driver n64audio_driver = {
        .driver = {
                .name = "n64audio",
        },
};

static int __init n64audio_init(void)
{
        return platform_driver_probe(&n64audio_driver, n64audio_probe);
}

module_init(n64audio_init);