sound: Add n64 driver

This adds support for the Nintendo 64 console's sound.
Signed-off-by: Lauri Kasanen <cand@gmx.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

sound/mips/Kconfig

@@ -24,5 +24,12 @@ config SND_SGI_HAL2
 	help
 	  Sound support for the SGI Indy and Indigo2 Workstation.
 
+config SND_N64
+	bool "N64 Audio"
+	depends on MACH_NINTENDO64 && SND=y
+	select SND_PCM
+	help
+	  Sound support for the N64.
+
 endif	# SND_MIPS
 

sound/mips/Makefile

@@ -9,3 +9,4 @@ snd-sgi-hal2-objs := hal2.o
 # Toplevel Module Dependency
 obj-$(CONFIG_SND_SGI_O2) += snd-sgi-o2.o
 obj-$(CONFIG_SND_SGI_HAL2) += snd-sgi-hal2.o
+obj-$(CONFIG_SND_N64) += snd-n64.o

sound/mips/snd-n64.c

+// 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 <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;
+	unsigned long flags;
+	u32 count;
+
+	spin_lock_irqsave(&priv->chan.lock, flags);
+
+	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;
+
+	spin_unlock_irqrestore(&priv->chan.lock, flags);
+}
+
+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);
+	unsigned long flags;
+
+	// 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)) {
+		spin_lock_irqsave(&priv->chan.lock, flags);
+
+		priv->chan.pos = priv->chan.nextpos;
+
+		spin_unlock_irqrestore(&priv->chan.lock, flags);
+
+		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);
+
+	spin_lock_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);
+
+	spin_unlock_irq(&priv->chan.lock);
+	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;
+	struct resource *res;
+	int err;
+
+	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 (!priv->mi_reg_base) {
+		err = -EINVAL;
+		goto fail_dma_alloc;
+	}
+
+	priv->ai_reg_base = devm_platform_ioremap_resource(pdev, 1);
+	if (!priv->ai_reg_base) {
+		err = -EINVAL;
+		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;
+	strcpy(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);
+
+	strcpy(card->driver, "N64 Audio");
+	strcpy(card->shortname, "N64 Audio");
+	strcpy(card->longname, "N64 Audio");
+
+	res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
+	if (devm_request_irq(&pdev->dev, res->start, 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);