diff --git a/MAINTAINERS b/MAINTAINERS
index 84c2964ad0b6..66a9e3bec786 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1878,8 +1878,10 @@ M:	Martin Povišer <povik+lin@cutebit.org>
 L:	asahi@lists.linux.dev
 L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
 S:	Maintained
+F:	Documentation/devicetree/bindings/dma/apple,sio.yaml
 F:	Documentation/devicetree/bindings/sound/adi,ssm3515.yaml
 F:	Documentation/devicetree/bindings/sound/apple,*
+F:	drivers/dma/apple-sio.c
 F:	sound/soc/apple/*
 F:	sound/soc/codecs/cs42l83-i2c.c
 F:	sound/soc/codecs/ssm3515.c
diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 70ba506dabab..e82b50584cd4 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -89,10 +89,21 @@ config APPLE_ADMAC
 	tristate "Apple ADMAC support"
 	depends on ARCH_APPLE || COMPILE_TEST
 	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
 	default ARCH_APPLE
 	help
 	  Enable support for Audio DMA Controller found on Apple Silicon SoCs.
 
+config APPLE_SIO
+	tristate "Apple SIO support"
+	depends on ARCH_APPLE || COMPILE_TEST
+	depends on APPLE_RTKIT
+	select DMA_ENGINE
+	default ARCH_APPLE
+	help
+	  Enable support for the SIO coprocessor found on Apple Silicon SoCs
+	  where it provides DMA services.
+
 config AT_HDMAC
 	tristate "Atmel AHB DMA support"
 	depends on ARCH_AT91
diff --git a/drivers/dma/Makefile b/drivers/dma/Makefile
index 83553a97a010..787583ff2d45 100644
--- a/drivers/dma/Makefile
+++ b/drivers/dma/Makefile
@@ -18,6 +18,7 @@ obj-$(CONFIG_AMBA_PL08X) += amba-pl08x.o
 obj-$(CONFIG_AMCC_PPC440SPE_ADMA) += ppc4xx/
 obj-$(CONFIG_AMD_PTDMA) += ptdma/
 obj-$(CONFIG_APPLE_ADMAC) += apple-admac.o
+obj-$(CONFIG_APPLE_SIO) += apple-sio.o
 obj-$(CONFIG_AT_HDMAC) += at_hdmac.o
 obj-$(CONFIG_AT_XDMAC) += at_xdmac.o
 obj-$(CONFIG_AXI_DMAC) += dma-axi-dmac.o
diff --git a/drivers/dma/apple-sio.c b/drivers/dma/apple-sio.c
new file mode 100644
index 000000000000..2278388d9053
--- /dev/null
+++ b/drivers/dma/apple-sio.c
@@ -0,0 +1,907 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Driver for SIO coprocessor on t8103 (M1) and other Apple SoCs
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/completion.h>
+#include <linux/device.h>
+#include <linux/dma-mapping.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/of_dma.h>
+#include <linux/soc/apple/rtkit.h>
+
+#include "dmaengine.h"
+#include "virt-dma.h"
+
+#define NCHANNELS_MAX	0x80
+
+#define REG_CPU_CONTROL	0x44
+#define CPU_CONTROL_RUN BIT(4)
+
+#define SIOMSG_DATA	GENMASK(63, 32)
+#define SIOMSG_TYPE	GENMASK(23, 16)
+#define SIOMSG_PARAM	GENMASK(31, 24)
+#define SIOMSG_TAG	GENMASK(13, 8)
+#define SIOMSG_EP	GENMASK(7, 0)
+
+#define EP_SIO		0x20
+
+#define MSG_START	0x2
+#define MSG_SETUP	0x3
+#define MSG_CONFIGURE	0x5
+#define MSG_ISSUE	0x6
+#define MSG_TERMINATE	0x8
+#define MSG_ACK		0x65
+#define MSG_NACK	0x66
+#define MSG_STARTED	0x67
+#define MSG_REPORT	0x68
+
+#define SIO_CALL_TIMEOUT_MS	100
+#define SIO_SHMEM_SIZE		0x1000
+#define SIO_NO_DESC_SLOTS	64
+
+/*
+ * There are two kinds of 'transaction descriptors' in play here.
+ *
+ * There's the struct sio_tx, and the struct dma_async_tx_descriptor embedded
+ * inside, which jointly represent a transaction to the dmaengine subsystem.
+ * At this time we only support those transactions to be cyclic.
+ *
+ * Then there are the coprocessor descriptors, which is what the coprocessor
+ * knows and understands. These don't seem to have a cyclic regime, so we can't
+ * map the dmaengine transaction on an exact coprocessor counterpart. Instead
+ * we continually queue up many coprocessor descriptors to implement a cyclic
+ * transaction.
+ *
+ * The number below is the maximum of how far ahead (how many) coprocessor
+ * descriptors we should be queuing up, per channel, for a cyclic transaction.
+ * Basically it's a made-up number.
+ */
+#define SIO_MAX_NINFLIGHT	4
+
+struct sio_coproc_desc {
+	u32 pad1;
+	u32 flag;
+	u64 unk;
+	u64 iova;
+	u64 size;
+	u64 pad2;
+	u64 pad3;
+} __packed;
+static_assert(sizeof(struct sio_coproc_desc) == 48);
+
+struct sio_shmem_chan_config {
+	u32 datashape;
+	u32 timeout;
+	u32 fifo;
+	u32 threshold;
+	u32 limit;
+} __packed;
+
+struct sio_data;
+struct sio_tx;
+
+struct sio_chan {
+	unsigned int no;
+	struct sio_data *host;
+	struct virt_dma_chan vc;
+	struct work_struct terminate_wq;
+
+	bool configured;
+	struct sio_shmem_chan_config cfg;
+
+	struct sio_tx *current_tx;
+};
+
+#define SIO_NTAGS		16
+
+typedef void (*sio_ack_callback)(struct sio_chan *, void *, bool);
+
+struct sio_data {
+	void __iomem *base;
+	struct dma_device dma;
+	struct device *dev;
+	struct apple_rtkit *rtk;
+	void *shmem;
+	struct sio_coproc_desc *shmem_desc_base;
+	unsigned long *desc_allocated;
+
+	struct sio_tagdata {
+		DECLARE_BITMAP(allocated, SIO_NTAGS);
+		int last_tag;
+
+		struct completion completions[SIO_NTAGS];
+		bool atomic[SIO_NTAGS];
+		bool acked[SIO_NTAGS];
+
+		sio_ack_callback ack_callback[SIO_NTAGS];
+		void *cookie[SIO_NTAGS];
+	} tags;
+
+	int nchannels;
+	struct sio_chan channels[];
+};
+
+struct sio_tx {
+	struct virt_dma_desc vd;
+	struct completion done;
+
+	bool terminated;
+	size_t period_len;
+	int nperiods;
+	int ninflight;
+	int next;
+
+	struct sio_coproc_desc *siodesc[];
+};
+
+static int sio_send_siomsg(struct sio_data *sio, u64 msg);
+static int sio_send_siomsg_atomic(struct sio_data *sio, u64 msg,
+				  sio_ack_callback ack_callback,
+				  void *cookie);
+static int sio_call(struct sio_data *sio, u64 msg);
+
+static struct sio_chan *to_sio_chan(struct dma_chan *chan)
+{
+	return container_of(chan, struct sio_chan, vc.chan);
+}
+
+static struct sio_tx *to_sio_tx(struct dma_async_tx_descriptor *tx)
+{
+	return container_of(tx, struct sio_tx, vd.tx);
+}
+
+static int sio_alloc_tag(struct sio_data *sio)
+{
+	struct sio_tagdata *tags = &sio->tags;
+	int tag, i;
+
+	/*
+	 * Because tag number 0 is special, the usable tag range
+	 * is 1...(SIO_NTAGS - 1). So, to pick the next usable tag,
+	 * we do modulo (SIO_NTAGS - 1) *then* plus one.
+	 */
+
+#define SIO_USABLE_TAGS (SIO_NTAGS - 1)
+	tag = (READ_ONCE(tags->last_tag) % SIO_USABLE_TAGS) + 1;
+
+	for (i = 0; i < SIO_USABLE_TAGS; i++) {
+		if (!test_and_set_bit(tag, tags->allocated))
+			break;
+
+		tag = (tag % SIO_USABLE_TAGS) + 1;
+	}
+
+	WRITE_ONCE(tags->last_tag, tag);
+
+	if (i < SIO_USABLE_TAGS)
+		return tag;
+	else
+		return -EBUSY;
+#undef SIO_USABLE_TAGS
+}
+
+static void sio_free_tag(struct sio_data *sio, int tag)
+{
+	struct sio_tagdata *tags = &sio->tags;
+
+	if (WARN_ON(tag >= SIO_NTAGS))
+		return;
+
+	tags->atomic[tag] = false;
+	tags->ack_callback[tag] = NULL;
+
+	WARN_ON(!test_and_clear_bit(tag, tags->allocated));
+}
+
+static void sio_set_tag_atomic(struct sio_data *sio, int tag,
+			       sio_ack_callback ack_callback,
+			       void *cookie)
+{
+	struct sio_tagdata *tags = &sio->tags;
+
+	tags->atomic[tag] = true;
+	tags->ack_callback[tag] = ack_callback;
+	tags->cookie[tag] = cookie;
+}
+
+static struct sio_coproc_desc *sio_alloc_desc(struct sio_data *sio)
+{
+	int i;
+
+	for (i = 0; i < SIO_NO_DESC_SLOTS; i++)
+		if (!test_and_set_bit(i, sio->desc_allocated))
+			return sio->shmem_desc_base + i;
+
+	return NULL;
+}
+
+static void sio_free_desc(struct sio_data *sio, struct sio_coproc_desc *desc)
+{
+	clear_bit(desc - sio->shmem_desc_base, sio->desc_allocated);
+}
+
+static int sio_coproc_desc_slot(struct sio_data *sio, struct sio_coproc_desc *desc)
+{
+	return (desc - sio->shmem_desc_base) * 4;
+}
+
+static enum dma_transfer_direction sio_chan_direction(int channo)
+{
+	/* Channel directions are fixed based on channel number */
+	return (channo & 1) ? DMA_DEV_TO_MEM : DMA_MEM_TO_DEV;
+}
+
+static void sio_tx_free(struct virt_dma_desc *vd)
+{
+	struct sio_data *sio = to_sio_chan(vd->tx.chan)->host;
+	struct sio_tx *siotx = to_sio_tx(&vd->tx);
+	int i;
+
+	for (i = 0; i < siotx->nperiods; i++)
+		if (siotx->siodesc[i])
+			sio_free_desc(sio, siotx->siodesc[i]);
+	kfree(siotx);
+}
+
+static struct dma_async_tx_descriptor *sio_prep_dma_cyclic(
+		struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
+		size_t period_len, enum dma_transfer_direction direction,
+		unsigned long flags)
+{
+	struct sio_chan *siochan = to_sio_chan(chan);
+	struct sio_tx *siotx = NULL;
+	int i, nperiods = buf_len / period_len;
+
+	if (direction != sio_chan_direction(siochan->no))
+		return NULL;
+
+	siotx = kzalloc(struct_size(siotx, siodesc, nperiods), GFP_NOWAIT);
+	if (!siotx)
+		return NULL;
+
+	init_completion(&siotx->done);
+	siotx->period_len = period_len;
+	siotx->nperiods = nperiods;
+
+	for (i = 0; i < nperiods; i++) {
+		struct sio_coproc_desc *d;
+
+		siotx->siodesc[i] = d = sio_alloc_desc(siochan->host);
+		if (!d) {
+			sio_tx_free(&siotx->vd);
+			return NULL;
+		}
+
+		d->flag = 1; /* not sure what's up with this */
+		d->iova = buf_addr + period_len * i;
+		d->size = period_len;
+	}
+	dma_wmb();
+
+	return vchan_tx_prep(&siochan->vc, &siotx->vd, flags);
+}
+
+static enum dma_status sio_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
+				     struct dma_tx_state *txstate)
+{
+	struct sio_chan *siochan = to_sio_chan(chan);
+	struct virt_dma_desc *vd;
+	struct sio_tx *siotx;
+	enum dma_status ret;
+	unsigned long flags;
+	int periods_residue;
+	size_t residue;
+
+	ret = dma_cookie_status(chan, cookie, txstate);
+	if (ret == DMA_COMPLETE || !txstate)
+		return ret;
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	siotx = siochan->current_tx;
+
+	if (siotx && siotx->vd.tx.cookie == cookie) {
+		ret = DMA_IN_PROGRESS;
+		periods_residue = siotx->next - siotx->ninflight;
+		while (periods_residue < 0)
+			periods_residue += siotx->nperiods;
+		residue = (siotx->nperiods - periods_residue) * siotx->period_len;
+	} else {
+		ret = DMA_IN_PROGRESS;
+		residue = 0;
+		vd = vchan_find_desc(&siochan->vc, cookie);
+		if (vd) {
+			siotx = to_sio_tx(&vd->tx);
+			residue = siotx->period_len * siotx->nperiods;
+		}
+	}
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+	dma_set_residue(txstate, residue);
+
+	return ret;
+}
+
+static bool sio_fill_in_locked(struct sio_chan *siochan);
+
+static void sio_handle_issue_ack(struct sio_chan *siochan, void *cookie, bool ok)
+{
+	dma_cookie_t tx_cookie = (unsigned long) cookie;
+	unsigned long flags;
+	struct sio_tx *tx;
+
+	if (!ok) {
+		dev_err(siochan->host->dev, "nacked issue on chan %d\n", siochan->no);
+		return;
+	}
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	if (!siochan->current_tx || tx_cookie != siochan->current_tx->vd.tx.cookie ||
+			siochan->current_tx->terminated)
+		goto out;
+
+	tx = siochan->current_tx;
+	tx->next = (tx->next + 1) % tx->nperiods;
+	tx->ninflight++;
+	sio_fill_in_locked(siochan);
+
+out:
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+}
+
+static bool sio_fill_in_locked(struct sio_chan *siochan)
+{
+	struct sio_data *sio = siochan->host;
+	struct sio_tx *tx = siochan->current_tx;
+	struct sio_coproc_desc *d = tx->siodesc[tx->next];
+	int ret;
+
+	if (tx->ninflight >= SIO_MAX_NINFLIGHT || tx->terminated)
+		return false;
+
+	static_assert(sizeof(dma_cookie_t) <= sizeof(void *));
+	ret = sio_send_siomsg_atomic(sio, FIELD_PREP(SIOMSG_EP, siochan->no) |
+				     FIELD_PREP(SIOMSG_TYPE, MSG_ISSUE) |
+				     FIELD_PREP(SIOMSG_DATA, sio_coproc_desc_slot(sio, d)),
+				     sio_handle_issue_ack, (void *) (uintptr_t) tx->vd.tx.cookie);
+	if (ret < 0)
+		dev_err_ratelimited(sio->dev, "can't issue on chan %d ninflight %d: %d\n",
+				    siochan->no, tx->ninflight, ret);
+	return true;
+}
+
+static void sio_update_current_tx_locked(struct sio_chan *siochan)
+{
+	struct virt_dma_desc *vd = vchan_next_desc(&siochan->vc);
+
+	if (vd && !siochan->current_tx) {
+		list_del(&vd->node);
+		siochan->current_tx = to_sio_tx(&vd->tx);
+		sio_fill_in_locked(siochan);
+	}
+}
+
+static void sio_issue_pending(struct dma_chan *chan)
+{
+	struct sio_chan *siochan = to_sio_chan(chan);
+	unsigned long flags;
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	vchan_issue_pending(&siochan->vc);
+	sio_update_current_tx_locked(siochan);
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+}
+
+static int sio_terminate_all(struct dma_chan *chan)
+{
+	struct sio_chan *siochan = to_sio_chan(chan);
+	unsigned long flags;
+	LIST_HEAD(to_free);
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	if (siochan->current_tx && !siochan->current_tx->terminated) {
+		dma_cookie_complete(&siochan->current_tx->vd.tx);
+		siochan->current_tx->terminated = true;
+		schedule_work(&siochan->terminate_wq);
+	}
+	vchan_get_all_descriptors(&siochan->vc, &to_free);
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+
+	vchan_dma_desc_free_list(&siochan->vc, &to_free);
+
+	return 0;
+}
+
+static void sio_terminate_work(struct work_struct *wq)
+{
+	struct sio_chan *siochan = container_of(wq, struct sio_chan, terminate_wq);
+	struct sio_tx *tx;
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	tx = siochan->current_tx;
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+
+	if (WARN_ON(!tx))
+		return;
+
+	ret = sio_call(siochan->host, FIELD_PREP(SIOMSG_EP, siochan->no) |
+				      FIELD_PREP(SIOMSG_TYPE, MSG_TERMINATE));
+	if (ret < 0)
+		dev_err(siochan->host->dev, "terminate call on chan %d failed: %d\n",
+			siochan->no, ret);
+
+	ret = wait_for_completion_timeout(&tx->done, msecs_to_jiffies(500));
+	if (!ret)
+		dev_err(siochan->host->dev, "terminate descriptor wait timed out\n");
+
+	tasklet_kill(&siochan->vc.task);
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	WARN_ON(siochan->current_tx != tx);
+	siochan->current_tx = NULL;
+	sio_update_current_tx_locked(siochan);
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+
+	sio_tx_free(&tx->vd);
+}
+
+static void sio_synchronize(struct dma_chan *chan)
+{
+	struct sio_chan *siochan = to_sio_chan(chan);
+
+	flush_work(&siochan->terminate_wq);
+}
+
+static void sio_free_chan_resources(struct dma_chan *chan)
+{
+	sio_terminate_all(chan);
+	sio_synchronize(chan);
+	vchan_free_chan_resources(&to_sio_chan(chan)->vc);
+}
+
+static struct dma_chan *sio_dma_of_xlate(struct of_phandle_args *dma_spec,
+					 struct of_dma *ofdma)
+{
+	struct sio_data *sio = (struct sio_data *) ofdma->of_dma_data;
+	unsigned int index = dma_spec->args[0];
+
+	if (dma_spec->args_count != 1 || index >= sio->nchannels)
+		return ERR_PTR(-EINVAL);
+
+	return dma_get_slave_channel(&sio->channels[index].vc.chan);
+}
+
+static void sio_rtk_crashed(void *cookie)
+{
+	struct sio_data *sio = cookie;
+
+	dev_err(sio->dev, "SIO down (crashed)");
+}
+
+static void sio_process_report(struct sio_chan *siochan)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&siochan->vc.lock, flags);
+	if (siochan->current_tx) {
+		struct sio_tx *tx = siochan->current_tx;
+
+		if (tx->ninflight)
+			tx->ninflight--;
+		vchan_cyclic_callback(&tx->vd);
+		if (!sio_fill_in_locked(siochan) && !tx->ninflight)
+			complete(&tx->done);
+	}
+	spin_unlock_irqrestore(&siochan->vc.lock, flags);
+}
+
+static void sio_recv_msg(void *cookie, u8 ep, u64 msg)
+{
+	struct sio_data *sio = cookie;
+	struct sio_tagdata *tags = &sio->tags;
+	u32 data;
+	u8 param, type, tag, sioep;
+
+	if (ep != EP_SIO)
+		goto unknown;
+
+	data  = FIELD_GET(SIOMSG_DATA, msg);
+	param = FIELD_GET(SIOMSG_PARAM, msg);
+	type  = FIELD_GET(SIOMSG_TYPE, msg);
+	tag   = FIELD_GET(SIOMSG_TAG, msg);
+	sioep = FIELD_GET(SIOMSG_EP, msg);
+
+	switch (type) {
+	case MSG_STARTED:
+		dev_info(sio->dev, "SIO protocol v%u\n", data);
+		type = MSG_ACK; /* Pretend this is an ACK */
+		fallthrough;
+	case MSG_ACK:
+	case MSG_NACK:
+		if (WARN_ON(tag >= SIO_NTAGS))
+			break;
+
+		if (tags->atomic[tag]) {
+			sio_ack_callback callback = tags->ack_callback[tag];
+
+			if (callback && !WARN_ON(sioep >= sio->nchannels))
+				callback(&sio->channels[sioep],
+					 tags->cookie[tag], type == MSG_ACK);
+			if (type == MSG_NACK)
+				dev_err(sio->dev, "got a NACK on channel %d\n", sioep);
+			sio_free_tag(sio, tag);
+		} else {
+			tags->acked[tag] = (type == MSG_ACK);
+			complete(&tags->completions[tag]);
+		}
+		break;
+
+	case MSG_REPORT:
+		if (WARN_ON(sioep >= sio->nchannels))
+			break;
+
+		sio_process_report(&sio->channels[sioep]);
+		break;
+
+	default:
+		goto unknown;
+	}
+	return;
+
+unknown:
+	dev_warn(sio->dev, "received unknown message: ep %x data %016llx\n",
+		 ep, msg);
+}
+
+static int _sio_send_siomsg(struct sio_data *sio, u64 msg, bool atomic,
+			    sio_ack_callback ack_callback, void *cookie)
+{
+	int tag, ret;
+
+	tag = sio_alloc_tag(sio);
+	if (tag < 0)
+		return tag;
+
+	if (atomic)
+		sio_set_tag_atomic(sio, tag, ack_callback, cookie);
+	else
+		reinit_completion(&sio->tags.completions[tag]);
+
+	msg &= ~SIOMSG_TAG;
+	msg |= FIELD_PREP(SIOMSG_TAG, tag);
+	ret = apple_rtkit_send_message(sio->rtk, EP_SIO, msg, NULL,
+				       atomic);
+	if (ret < 0) {
+		sio_free_tag(sio, tag);
+		return ret;
+	}
+
+	return tag;
+}
+
+static int sio_send_siomsg(struct sio_data *sio, u64 msg)
+{
+	return _sio_send_siomsg(sio, msg, false, NULL, NULL);
+}
+
+static int sio_send_siomsg_atomic(struct sio_data *sio, u64 msg,
+				  sio_ack_callback ack_callback,
+				  void *cookie)
+{
+	return _sio_send_siomsg(sio, msg, true, ack_callback, cookie);
+}
+
+static int sio_call(struct sio_data *sio, u64 msg)
+{
+	int tag, ret;
+
+	tag = sio_send_siomsg(sio, msg);
+	if (tag < 0)
+		return tag;
+
+	ret = wait_for_completion_timeout(&sio->tags.completions[tag],
+					  msecs_to_jiffies(SIO_CALL_TIMEOUT_MS));
+	if (!ret) {
+		dev_warn(sio->dev, "call %8x timed out\n", msg);
+		sio_free_tag(sio, tag);
+		return -ETIME;
+	}
+
+	ret = sio->tags.acked[tag];
+	sio_free_tag(sio, tag);
+
+	return ret;
+}
+
+static const struct apple_rtkit_ops sio_rtkit_ops = {
+	.crashed = sio_rtk_crashed,
+	.recv_message = sio_recv_msg,
+};
+
+static int sio_device_config(struct dma_chan *chan,
+			     struct dma_slave_config *config)
+{
+	struct sio_chan *siochan = to_sio_chan(chan);
+	struct sio_data *sio = siochan->host;
+	bool is_tx = sio_chan_direction(siochan->no) == DMA_MEM_TO_DEV;
+	struct sio_shmem_chan_config *cfg_shmem = sio->shmem;
+	struct sio_shmem_chan_config cfg;
+	int ret;
+
+	switch (is_tx ? config->dst_addr_width : config->src_addr_width) {
+	case DMA_SLAVE_BUSWIDTH_1_BYTE:
+		cfg.datashape = 0;
+		break;
+	case DMA_SLAVE_BUSWIDTH_2_BYTES:
+		cfg.datashape = 1;
+		break;
+	case DMA_SLAVE_BUSWIDTH_4_BYTES:
+		cfg.datashape = 2;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	cfg.fifo = 0x800;
+	cfg.limit = 0x800;
+	cfg.threshold = 0x800;
+
+	/*
+	 * Dmaengine prescribes we ought to apply the new configuration only
+	 * to newly-queued descriptors.
+	 *
+	 * To comply with dmaengine's interface we take the lazy path here:
+	 * we apply the configuration right away, we only allow the channel
+	 * to be configured once, which means subsequent calls to `device_config`
+	 * either return -EBUSY if the configuration differs, or they are
+	 * a no-op if the configuration is the same as the starting one.
+	 *
+	 * This is the reasonable thing to do given that these sio channels
+	 * are tied to fixed peripherals, and what's more given that the
+	 * only planned consumer of this dmaengine driver in the kernel is
+	 * diplayport audio support, where the DMA configuration is fixed,
+	 * and no more than a single descriptor (a cyclic one) gets ever issued
+	 * at the same time.
+	 *
+	 * The code complexity cost of tracking to which descriptor
+	 * the configuration relates would be significant here, especially
+	 * since we need to do a non-atomic operation to apply it (a call to
+	 * the coprocessor) and dmaengine has its bunch of atomicity
+	 * restrictions. And this complexity would be for naught since it
+	 * doesn't even get exercised by the only planned consumer.
+	 */
+	if (siochan->configured && memcmp(&siochan->cfg, &cfg, sizeof(cfg)))
+		return -EBUSY;
+
+	*cfg_shmem = cfg;
+	dma_wmb();
+
+	ret = sio_call(sio, FIELD_PREP(SIOMSG_TYPE, MSG_CONFIGURE) |
+			    FIELD_PREP(SIOMSG_EP, siochan->no));
+
+	if (ret == 1)
+		ret = 0;
+	else if (ret == 0)
+		ret = -EINVAL;
+
+	if (ret == 0) {
+		siochan->configured = true;
+		siochan->cfg = cfg;
+	}
+
+	return ret;
+}
+
+static int sio_alloc_shmem(struct sio_data *sio)
+{
+	dma_addr_t iova;
+	int err;
+
+	sio->shmem = dma_alloc_coherent(sio->dev, SIO_SHMEM_SIZE,
+					&iova, GFP_KERNEL);
+	if (!sio->shmem)
+		return -ENOMEM;
+
+	sio->shmem_desc_base = (struct sio_coproc_desc *) (sio->shmem + 56);
+	sio->desc_allocated = devm_kzalloc(sio->dev, SIO_NO_DESC_SLOTS / 32,
+					   GFP_KERNEL);
+	if (!sio->desc_allocated)
+		return -ENOMEM;
+
+	err = sio_call(sio, FIELD_PREP(SIOMSG_TYPE, MSG_SETUP) |
+			    FIELD_PREP(SIOMSG_PARAM, 1) |
+			    FIELD_PREP(SIOMSG_DATA, iova >> 12));
+	if (err != 1) {
+		if (err == 0)
+			err = -EINVAL;
+		return err;
+	}
+
+	err = sio_call(sio, FIELD_PREP(SIOMSG_TYPE, MSG_SETUP) |
+			    FIELD_PREP(SIOMSG_PARAM, 2) |
+			    FIELD_PREP(SIOMSG_DATA, SIO_SHMEM_SIZE));
+	if (err != 1) {
+		if (err == 0)
+			err = -EINVAL;
+		return err;
+	}
+
+	return 0;
+}
+
+static int sio_send_dt_params(struct sio_data *sio)
+{
+	struct device_node *np = sio->dev->of_node;
+	const char *propname = "apple,sio-firmware-params";
+	int nparams, err, i;
+
+	nparams = of_property_count_u32_elems(np, propname);
+	if (nparams < 0) {
+		err = nparams;
+		goto badprop;
+	}
+
+	for (i = 0; i < nparams / 2; i++) {
+		u32 key, val;
+
+		err = of_property_read_u32_index(np, propname, 2 * i, &key);
+		if (err)
+			goto badprop;
+		err = of_property_read_u32_index(np, propname, 2 * i + 1, &val);
+		if (err)
+			goto badprop;
+
+		err = sio_call(sio, FIELD_PREP(SIOMSG_TYPE, MSG_SETUP) |
+				    FIELD_PREP(SIOMSG_PARAM, key & 0xff) |
+				    FIELD_PREP(SIOMSG_EP, key >> 8) |
+				    FIELD_PREP(SIOMSG_DATA, val));
+		if (err < 1) {
+			if (err == 0)
+				err = -ENXIO;
+			return dev_err_probe(sio->dev, err, "sending SIO parameter %#x value %#x\n",
+					     key, val);
+		}
+	}
+
+	return 0;
+
+badprop:
+	return dev_err_probe(sio->dev, err, "failed to read '%s'\n", propname);
+}
+
+static int sio_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct sio_data *sio;
+	struct dma_device *dma;
+	int nchannels;
+	int err, i;
+
+	err = of_property_read_u32(np, "dma-channels", &nchannels);
+	if (err || nchannels > NCHANNELS_MAX)
+		return dev_err_probe(&pdev->dev, -EINVAL,
+				     "missing or invalid dma-channels property\n");
+
+	sio = devm_kzalloc(&pdev->dev, struct_size(sio, channels, nchannels), GFP_KERNEL);
+	if (!sio)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, sio);
+	sio->dev = &pdev->dev;
+	sio->nchannels = nchannels;
+
+	sio->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(sio->base))
+		return PTR_ERR(sio->base);
+
+	sio->rtk = devm_apple_rtkit_init(&pdev->dev, sio, NULL, 0, &sio_rtkit_ops);
+	if (IS_ERR(sio->rtk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(sio->rtk),
+				     "couldn't initialize rtkit\n");
+	for (i = 1; i < SIO_NTAGS; i++)
+		init_completion(&sio->tags.completions[i]);
+
+	dma = &sio->dma;
+	dma_cap_set(DMA_PRIVATE, dma->cap_mask);
+	dma_cap_set(DMA_CYCLIC, dma->cap_mask);
+
+	dma->dev = &pdev->dev;
+	dma->device_free_chan_resources = sio_free_chan_resources;
+	dma->device_tx_status = sio_tx_status;
+	dma->device_issue_pending = sio_issue_pending;
+	dma->device_terminate_all = sio_terminate_all;
+	dma->device_synchronize = sio_synchronize;
+	dma->device_prep_dma_cyclic = sio_prep_dma_cyclic;
+	dma->device_config = sio_device_config;
+
+	dma->directions = BIT(DMA_MEM_TO_DEV);
+	dma->residue_granularity = DMA_RESIDUE_GRANULARITY_SEGMENT;
+	dma->dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
+			       BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
+			       BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
+
+	INIT_LIST_HEAD(&dma->channels);
+	for (i = 0; i < nchannels; i++) {
+		struct sio_chan *siochan = &sio->channels[i];
+
+		siochan->host = sio;
+		siochan->no = i;
+		siochan->vc.desc_free = sio_tx_free;
+		INIT_WORK(&siochan->terminate_wq, sio_terminate_work);
+		vchan_init(&siochan->vc, dma);
+	}
+
+	writel(CPU_CONTROL_RUN, sio->base + REG_CPU_CONTROL);
+
+	err = apple_rtkit_boot(sio->rtk);
+	if (err)
+		return dev_err_probe(&pdev->dev, err, "SIO did not boot\n");
+
+	err = apple_rtkit_start_ep(sio->rtk, EP_SIO);
+	if (err)
+		return dev_err_probe(&pdev->dev, err, "starting SIO endpoint\n");
+
+	err = sio_call(sio, FIELD_PREP(SIOMSG_TYPE, MSG_START));
+	if (err < 1) {
+		if (err == 0)
+			err = -ENXIO;
+		return dev_err_probe(&pdev->dev, err, "starting SIO service\n");
+	}
+
+	err = sio_send_dt_params(sio);
+	if (err < 0)
+		return dev_err_probe(&pdev->dev, err, "failed to send boot-up parameters\n");
+
+	err = sio_alloc_shmem(sio);
+	if (err < 0)
+		return err;
+
+	err = dma_async_device_register(&sio->dma);
+	if (err)
+		return dev_err_probe(&pdev->dev, err, "failed to register DMA device\n");
+
+	err = of_dma_controller_register(pdev->dev.of_node, sio_dma_of_xlate, sio);
+	if (err) {
+		dma_async_device_unregister(&sio->dma);
+		return dev_err_probe(&pdev->dev, err, "failed to register with OF\n");
+	}
+
+	return 0;
+}
+
+static int sio_remove(struct platform_device *pdev)
+{
+	struct sio_data *sio = platform_get_drvdata(pdev);
+
+	of_dma_controller_free(pdev->dev.of_node);
+	dma_async_device_unregister(&sio->dma);
+	return 0;
+}
+
+static const struct of_device_id sio_of_match[] = {
+	{ .compatible = "apple,sio", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, sio_of_match);
+
+static struct platform_driver apple_sio_driver = {
+	.driver = {
+		.name = "apple-sio",
+		.of_match_table = sio_of_match,
+	},
+	.probe = sio_probe,
+	.remove = sio_remove,
+};
+module_platform_driver(apple_sio_driver);
+
+MODULE_AUTHOR("Martin Povišer <povik+lin@cutebit.org>");
+MODULE_DESCRIPTION("Driver for SIO coprocessor on Apple SoCs");
+MODULE_LICENSE("Dual MIT/GPL");
