linux/drivers/dma/sh/rcar-dmac.c

/*
 * Renesas R-Car Gen2 DMA Controller Driver
 *
 * Copyright (C) 2014 Renesas Electronics Inc.
 *
 * Author: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
 *
 * This is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 */

#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/interrupt.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/of_dma.h>
#include <linux/of_platform.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

#include "../dmaengine.h"

/*
 * struct rcar_dmac_xfer_chunk - Descriptor for a hardware transfer
 * @node: entry in the parent's chunks list
 * @src_addr: device source address
 * @dst_addr: device destination address
 * @size: transfer size in bytes
 */
struct rcar_dmac_xfer_chunk {
	struct list_head node;

	dma_addr_t src_addr;
	dma_addr_t dst_addr;
	u32 size;
};

/*
 * struct rcar_dmac_hw_desc - Hardware descriptor for a transfer chunk
 * @sar: value of the SAR register (source address)
 * @dar: value of the DAR register (destination address)
 * @tcr: value of the TCR register (transfer count)
 */
struct rcar_dmac_hw_desc {
	u32 sar;
	u32 dar;
	u32 tcr;
	u32 reserved;
} __attribute__((__packed__));

/*
 * struct rcar_dmac_desc - R-Car Gen2 DMA Transfer Descriptor
 * @async_tx: base DMA asynchronous transaction descriptor
 * @direction: direction of the DMA transfer
 * @xfer_shift: log2 of the transfer size
 * @chcr: value of the channel configuration register for this transfer
 * @node: entry in the channel's descriptors lists
 * @chunks: list of transfer chunks for this transfer
 * @running: the transfer chunk being currently processed
 * @nchunks: number of transfer chunks for this transfer
 * @hwdescs.use: whether the transfer descriptor uses hardware descriptors
 * @hwdescs.mem: hardware descriptors memory for the transfer
 * @hwdescs.dma: device address of the hardware descriptors memory
 * @hwdescs.size: size of the hardware descriptors in bytes
 * @size: transfer size in bytes
 * @cyclic: when set indicates that the DMA transfer is cyclic
 */
struct rcar_dmac_desc {
	struct dma_async_tx_descriptor async_tx;
	enum dma_transfer_direction direction;
	unsigned int xfer_shift;
	u32 chcr;

	struct list_head node;
	struct list_head chunks;
	struct rcar_dmac_xfer_chunk *running;
	unsigned int nchunks;

	struct {
		bool use;
		struct rcar_dmac_hw_desc *mem;
		dma_addr_t dma;
		size_t size;
	} hwdescs;

	unsigned int size;
	bool cyclic;
};

#define to_rcar_dmac_desc(d)	container_of(d, struct rcar_dmac_desc, async_tx)

/*
 * struct rcar_dmac_desc_page - One page worth of descriptors
 * @node: entry in the channel's pages list
 * @descs: array of DMA descriptors
 * @chunks: array of transfer chunk descriptors
 */
struct rcar_dmac_desc_page {
	struct list_head node;

	union {
		struct rcar_dmac_desc descs[0];
		struct rcar_dmac_xfer_chunk chunks[0];
	};
};

#define RCAR_DMAC_DESCS_PER_PAGE					\
	((PAGE_SIZE - offsetof(struct rcar_dmac_desc_page, descs)) /	\
	sizeof(struct rcar_dmac_desc))
#define RCAR_DMAC_XFER_CHUNKS_PER_PAGE					\
	((PAGE_SIZE - offsetof(struct rcar_dmac_desc_page, chunks)) /	\
	sizeof(struct rcar_dmac_xfer_chunk))

/*
 * struct rcar_dmac_chan - R-Car Gen2 DMA Controller Channel
 * @chan: base DMA channel object
 * @iomem: channel I/O memory base
 * @index: index of this channel in the controller
 * @src_xfer_size: size (in bytes) of hardware transfers on the source side
 * @dst_xfer_size: size (in bytes) of hardware transfers on the destination side
 * @src_slave_addr: slave source memory address
 * @dst_slave_addr: slave destination memory address
 * @mid_rid: hardware MID/RID for the DMA client using this channel
 * @lock: protects the channel CHCR register and the desc members
 * @desc.free: list of free descriptors
 * @desc.pending: list of pending descriptors (submitted with tx_submit)
 * @desc.active: list of active descriptors (activated with issue_pending)
 * @desc.done: list of completed descriptors
 * @desc.wait: list of descriptors waiting for an ack
 * @desc.running: the descriptor being processed (a member of the active list)
 * @desc.chunks_free: list of free transfer chunk descriptors
 * @desc.pages: list of pages used by allocated descriptors
 */
struct rcar_dmac_chan {
	struct dma_chan chan;
	void __iomem *iomem;
	unsigned int index;

	unsigned int src_xfer_size;
	unsigned int dst_xfer_size;
	dma_addr_t src_slave_addr;
	dma_addr_t dst_slave_addr;
	int mid_rid;

	spinlock_t lock;

	struct {
		struct list_head free;
		struct list_head pending;
		struct list_head active;
		struct list_head done;
		struct list_head wait;
		struct rcar_dmac_desc *running;

		struct list_head chunks_free;

		struct list_head pages;
	} desc;
};

#define to_rcar_dmac_chan(c)	container_of(c, struct rcar_dmac_chan, chan)

/*
 * struct rcar_dmac - R-Car Gen2 DMA Controller
 * @engine: base DMA engine object
 * @dev: the hardware device
 * @iomem: remapped I/O memory base
 * @n_channels: number of available channels
 * @channels: array of DMAC channels
 * @modules: bitmask of client modules in use
 */
struct rcar_dmac {
	struct dma_device engine;
	struct device *dev;
	void __iomem *iomem;

	unsigned int n_channels;
	struct rcar_dmac_chan *channels;

	DECLARE_BITMAP(modules, 256);
};

#define to_rcar_dmac(d)		container_of(d, struct rcar_dmac, engine)

/* -----------------------------------------------------------------------------
 * Registers
 */

#define RCAR_DMAC_CHAN_OFFSET(i)	(0x8000 + 0x80 * (i))

#define RCAR_DMAISTA			0x0020
#define RCAR_DMASEC			0x0030
#define RCAR_DMAOR			0x0060
#define RCAR_DMAOR_PRI_FIXED		(0 << 8)
#define RCAR_DMAOR_PRI_ROUND_ROBIN	(3 << 8)
#define RCAR_DMAOR_AE			(1 << 2)
#define RCAR_DMAOR_DME			(1 << 0)
#define RCAR_DMACHCLR			0x0080
#define RCAR_DMADPSEC			0x00a0

#define RCAR_DMASAR			0x0000
#define RCAR_DMADAR			0x0004
#define RCAR_DMATCR			0x0008
#define RCAR_DMATCR_MASK		0x00ffffff
#define RCAR_DMATSR			0x0028
#define RCAR_DMACHCR			0x000c
#define RCAR_DMACHCR_CAE		(1 << 31)
#define RCAR_DMACHCR_CAIE		(1 << 30)
#define RCAR_DMACHCR_DPM_DISABLED	(0 << 28)
#define RCAR_DMACHCR_DPM_ENABLED	(1 << 28)
#define RCAR_DMACHCR_DPM_REPEAT		(2 << 28)
#define RCAR_DMACHCR_DPM_INFINITE	(3 << 28)
#define RCAR_DMACHCR_RPT_SAR		(1 << 27)
#define RCAR_DMACHCR_RPT_DAR		(1 << 26)
#define RCAR_DMACHCR_RPT_TCR		(1 << 25)
#define RCAR_DMACHCR_DPB		(1 << 22)
#define RCAR_DMACHCR_DSE		(1 << 19)
#define RCAR_DMACHCR_DSIE		(1 << 18)
#define RCAR_DMACHCR_TS_1B		((0 << 20) | (0 << 3))
#define RCAR_DMACHCR_TS_2B		((0 << 20) | (1 << 3))
#define RCAR_DMACHCR_TS_4B		((0 << 20) | (2 << 3))
#define RCAR_DMACHCR_TS_16B		((0 << 20) | (3 << 3))
#define RCAR_DMACHCR_TS_32B		((1 << 20) | (0 << 3))
#define RCAR_DMACHCR_TS_64B		((1 << 20) | (1 << 3))
#define RCAR_DMACHCR_TS_8B		((1 << 20) | (3 << 3))
#define RCAR_DMACHCR_DM_FIXED		(0 << 14)
#define RCAR_DMACHCR_DM_INC		(1 << 14)
#define RCAR_DMACHCR_DM_DEC		(2 << 14)
#define RCAR_DMACHCR_SM_FIXED		(0 << 12)
#define RCAR_DMACHCR_SM_INC		(1 << 12)
#define RCAR_DMACHCR_SM_DEC		(2 << 12)
#define RCAR_DMACHCR_RS_AUTO		(4 << 8)
#define RCAR_DMACHCR_RS_DMARS		(8 << 8)
#define RCAR_DMACHCR_IE			(1 << 2)
#define RCAR_DMACHCR_TE			(1 << 1)
#define RCAR_DMACHCR_DE			(1 << 0)
#define RCAR_DMATCRB			0x0018
#define RCAR_DMATSRB			0x0038
#define RCAR_DMACHCRB			0x001c
#define RCAR_DMACHCRB_DCNT(n)		((n) << 24)
#define RCAR_DMACHCRB_DPTR_MASK		(0xff << 16)
#define RCAR_DMACHCRB_DPTR_SHIFT	16
#define RCAR_DMACHCRB_DRST		(1 << 15)
#define RCAR_DMACHCRB_DTS		(1 << 8)
#define RCAR_DMACHCRB_SLM_NORMAL	(0 << 4)
#define RCAR_DMACHCRB_SLM_CLK(n)	((8 | (n)) << 4)
#define RCAR_DMACHCRB_PRI(n)		((n) << 0)
#define RCAR_DMARS			0x0040
#define RCAR_DMABUFCR			0x0048
#define RCAR_DMABUFCR_MBU(n)		((n) << 16)
#define RCAR_DMABUFCR_ULB(n)		((n) << 0)
#define RCAR_DMADPBASE			0x0050
#define RCAR_DMADPBASE_MASK		0xfffffff0
#define RCAR_DMADPBASE_SEL		(1 << 0)
#define RCAR_DMADPCR			0x0054
#define RCAR_DMADPCR_DIPT(n)		((n) << 24)
#define RCAR_DMAFIXSAR			0x0010
#define RCAR_DMAFIXDAR			0x0014
#define RCAR_DMAFIXDPBASE		0x0060

/* Hardcode the MEMCPY transfer size to 4 bytes. */
#define RCAR_DMAC_MEMCPY_XFER_SIZE	4

/* -----------------------------------------------------------------------------
 * Device access
 */

static void rcar_dmac_write(struct rcar_dmac *dmac, u32 reg, u32 data)
{
	if (reg == RCAR_DMAOR)
		writew(data, dmac->iomem + reg);
	else
		writel(data, dmac->iomem + reg);
}

static u32 rcar_dmac_read(struct rcar_dmac *dmac, u32 reg)
{
	if (reg == RCAR_DMAOR)
		return readw(dmac->iomem + reg);
	else
		return readl(dmac->iomem + reg);
}

static u32 rcar_dmac_chan_read(struct rcar_dmac_chan *chan, u32 reg)
{
	if (reg == RCAR_DMARS)
		return readw(chan->iomem + reg);
	else
		return readl(chan->iomem + reg);
}

static void rcar_dmac_chan_write(struct rcar_dmac_chan *chan, u32 reg, u32 data)
{
	if (reg == RCAR_DMARS)
		writew(data, chan->iomem + reg);
	else
		writel(data, chan->iomem + reg);
}

/* -----------------------------------------------------------------------------
 * Initialization and configuration
 */

static bool rcar_dmac_chan_is_busy(struct rcar_dmac_chan *chan)
{
	u32 chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);

	return (chcr & (RCAR_DMACHCR_DE | RCAR_DMACHCR_TE)) == RCAR_DMACHCR_DE;
}

static void rcar_dmac_chan_start_xfer(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_desc *desc = chan->desc.running;
	u32 chcr = desc->chcr;

	WARN_ON_ONCE(rcar_dmac_chan_is_busy(chan));

	if (chan->mid_rid >= 0)
		rcar_dmac_chan_write(chan, RCAR_DMARS, chan->mid_rid);

	if (desc->hwdescs.use) {
		struct rcar_dmac_xfer_chunk *chunk;

		dev_dbg(chan->chan.device->dev,
			"chan%u: queue desc %p: %u@%pad\n",
			chan->index, desc, desc->nchunks, &desc->hwdescs.dma);

#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
		rcar_dmac_chan_write(chan, RCAR_DMAFIXDPBASE,
				     desc->hwdescs.dma >> 32);
#endif
		rcar_dmac_chan_write(chan, RCAR_DMADPBASE,
				     (desc->hwdescs.dma & 0xfffffff0) |
				     RCAR_DMADPBASE_SEL);
		rcar_dmac_chan_write(chan, RCAR_DMACHCRB,
				     RCAR_DMACHCRB_DCNT(desc->nchunks - 1) |
				     RCAR_DMACHCRB_DRST);

		/*
		 * Errata: When descriptor memory is accessed through an IOMMU
		 * the DMADAR register isn't initialized automatically from the
		 * first descriptor at beginning of transfer by the DMAC like it
		 * should. Initialize it manually with the destination address
		 * of the first chunk.
		 */
		chunk = list_first_entry(&desc->chunks,
					 struct rcar_dmac_xfer_chunk, node);
		rcar_dmac_chan_write(chan, RCAR_DMADAR,
				     chunk->dst_addr & 0xffffffff);

		/*
		 * Program the descriptor stage interrupt to occur after the end
		 * of the first stage.
		 */
		rcar_dmac_chan_write(chan, RCAR_DMADPCR, RCAR_DMADPCR_DIPT(1));

		chcr |= RCAR_DMACHCR_RPT_SAR | RCAR_DMACHCR_RPT_DAR
		     |  RCAR_DMACHCR_RPT_TCR | RCAR_DMACHCR_DPB;

		/*
		 * If the descriptor isn't cyclic enable normal descriptor mode
		 * and the transfer completion interrupt.
		 */
		if (!desc->cyclic)
			chcr |= RCAR_DMACHCR_DPM_ENABLED | RCAR_DMACHCR_IE;
		/*
		 * If the descriptor is cyclic and has a callback enable the
		 * descriptor stage interrupt in infinite repeat mode.
		 */
		else if (desc->async_tx.callback)
			chcr |= RCAR_DMACHCR_DPM_INFINITE | RCAR_DMACHCR_DSIE;
		/*
		 * Otherwise just select infinite repeat mode without any
		 * interrupt.
		 */
		else
			chcr |= RCAR_DMACHCR_DPM_INFINITE;
	} else {
		struct rcar_dmac_xfer_chunk *chunk = desc->running;

		dev_dbg(chan->chan.device->dev,
			"chan%u: queue chunk %p: %u@%pad -> %pad\n",
			chan->index, chunk, chunk->size, &chunk->src_addr,
			&chunk->dst_addr);

#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
		rcar_dmac_chan_write(chan, RCAR_DMAFIXSAR,
				     chunk->src_addr >> 32);
		rcar_dmac_chan_write(chan, RCAR_DMAFIXDAR,
				     chunk->dst_addr >> 32);
#endif
		rcar_dmac_chan_write(chan, RCAR_DMASAR,
				     chunk->src_addr & 0xffffffff);
		rcar_dmac_chan_write(chan, RCAR_DMADAR,
				     chunk->dst_addr & 0xffffffff);
		rcar_dmac_chan_write(chan, RCAR_DMATCR,
				     chunk->size >> desc->xfer_shift);

		chcr |= RCAR_DMACHCR_DPM_DISABLED | RCAR_DMACHCR_IE;
	}

	rcar_dmac_chan_write(chan, RCAR_DMACHCR, chcr | RCAR_DMACHCR_DE);
}

static int rcar_dmac_init(struct rcar_dmac *dmac)
{
	u16 dmaor;

	/* Clear all channels and enable the DMAC globally. */
	rcar_dmac_write(dmac, RCAR_DMACHCLR, 0x7fff);
	rcar_dmac_write(dmac, RCAR_DMAOR,
			RCAR_DMAOR_PRI_FIXED | RCAR_DMAOR_DME);

	dmaor = rcar_dmac_read(dmac, RCAR_DMAOR);
	if ((dmaor & (RCAR_DMAOR_AE | RCAR_DMAOR_DME)) != RCAR_DMAOR_DME) {
		dev_warn(dmac->dev, "DMAOR initialization failed.\n");
		return -EIO;
	}

	return 0;
}

/* -----------------------------------------------------------------------------
 * Descriptors submission
 */

static dma_cookie_t rcar_dmac_tx_submit(struct dma_async_tx_descriptor *tx)
{
	struct rcar_dmac_chan *chan = to_rcar_dmac_chan(tx->chan);
	struct rcar_dmac_desc *desc = to_rcar_dmac_desc(tx);
	unsigned long flags;
	dma_cookie_t cookie;

	spin_lock_irqsave(&chan->lock, flags);

	cookie = dma_cookie_assign(tx);

	dev_dbg(chan->chan.device->dev, "chan%u: submit #%d@%p\n",
		chan->index, tx->cookie, desc);

	list_add_tail(&desc->node, &chan->desc.pending);
	desc->running = list_first_entry(&desc->chunks,
					 struct rcar_dmac_xfer_chunk, node);

	spin_unlock_irqrestore(&chan->lock, flags);

	return cookie;
}

/* -----------------------------------------------------------------------------
 * Descriptors allocation and free
 */

/*
 * rcar_dmac_desc_alloc - Allocate a page worth of DMA descriptors
 * @chan: the DMA channel
 * @gfp: allocation flags
 */
static int rcar_dmac_desc_alloc(struct rcar_dmac_chan *chan, gfp_t gfp)
{
	struct rcar_dmac_desc_page *page;
	unsigned long flags;
	LIST_HEAD(list);
	unsigned int i;

	page = (void *)get_zeroed_page(gfp);
	if (!page)
		return -ENOMEM;

	for (i = 0; i < RCAR_DMAC_DESCS_PER_PAGE; ++i) {
		struct rcar_dmac_desc *desc = &page->descs[i];

		dma_async_tx_descriptor_init(&desc->async_tx, &chan->chan);
		desc->async_tx.tx_submit = rcar_dmac_tx_submit;
		INIT_LIST_HEAD(&desc->chunks);

		list_add_tail(&desc->node, &list);
	}

	spin_lock_irqsave(&chan->lock, flags);
	list_splice_tail(&list, &chan->desc.free);
	list_add_tail(&page->node, &chan->desc.pages);
	spin_unlock_irqrestore(&chan->lock, flags);

	return 0;
}

/*
 * rcar_dmac_desc_put - Release a DMA transfer descriptor
 * @chan: the DMA channel
 * @desc: the descriptor
 *
 * Put the descriptor and its transfer chunk descriptors back in the channel's
 * free descriptors lists. The descriptor's chunks list will be reinitialized to
 * an empty list as a result.
 *
 * The descriptor must have been removed from the channel's lists before calling
 * this function.
 */
static void rcar_dmac_desc_put(struct rcar_dmac_chan *chan,
			       struct rcar_dmac_desc *desc)
{
	unsigned long flags;

	spin_lock_irqsave(&chan->lock, flags);
	list_splice_tail_init(&desc->chunks, &chan->desc.chunks_free);
	list_add_tail(&desc->node, &chan->desc.free);
	spin_unlock_irqrestore(&chan->lock, flags);
}

static void rcar_dmac_desc_recycle_acked(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_desc *desc, *_desc;
	unsigned long flags;
	LIST_HEAD(list);

	/*
	 * We have to temporarily move all descriptors from the wait list to a
	 * local list as iterating over the wait list, even with
	 * list_for_each_entry_safe, isn't safe if we release the channel lock
	 * around the rcar_dmac_desc_put() call.
	 */
	spin_lock_irqsave(&chan->lock, flags);
	list_splice_init(&chan->desc.wait, &list);
	spin_unlock_irqrestore(&chan->lock, flags);

	list_for_each_entry_safe(desc, _desc, &list, node) {
		if (async_tx_test_ack(&desc->async_tx)) {
			list_del(&desc->node);
			rcar_dmac_desc_put(chan, desc);
		}
	}

	if (list_empty(&list))
		return;

	/* Put the remaining descriptors back in the wait list. */
	spin_lock_irqsave(&chan->lock, flags);
	list_splice(&list, &chan->desc.wait);
	spin_unlock_irqrestore(&chan->lock, flags);
}

/*
 * rcar_dmac_desc_get - Allocate a descriptor for a DMA transfer
 * @chan: the DMA channel
 *
 * Locking: This function must be called in a non-atomic context.
 *
 * Return: A pointer to the allocated descriptor or NULL if no descriptor can
 * be allocated.
 */
static struct rcar_dmac_desc *rcar_dmac_desc_get(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_desc *desc;
	unsigned long flags;
	int ret;

	/* Recycle acked descriptors before attempting allocation. */
	rcar_dmac_desc_recycle_acked(chan);

	spin_lock_irqsave(&chan->lock, flags);

	while (list_empty(&chan->desc.free)) {
		/*
		 * No free descriptors, allocate a page worth of them and try
		 * again, as someone else could race us to get the newly
		 * allocated descriptors. If the allocation fails return an
		 * error.
		 */
		spin_unlock_irqrestore(&chan->lock, flags);
		ret = rcar_dmac_desc_alloc(chan, GFP_NOWAIT);
		if (ret < 0)
			return NULL;
		spin_lock_irqsave(&chan->lock, flags);
	}

	desc = list_first_entry(&chan->desc.free, struct rcar_dmac_desc, node);
	list_del(&desc->node);

	spin_unlock_irqrestore(&chan->lock, flags);

	return desc;
}

/*
 * rcar_dmac_xfer_chunk_alloc - Allocate a page worth of transfer chunks
 * @chan: the DMA channel
 * @gfp: allocation flags
 */
static int rcar_dmac_xfer_chunk_alloc(struct rcar_dmac_chan *chan, gfp_t gfp)
{
	struct rcar_dmac_desc_page *page;
	unsigned long flags;
	LIST_HEAD(list);
	unsigned int i;

	page = (void *)get_zeroed_page(gfp);
	if (!page)
		return -ENOMEM;

	for (i = 0; i < RCAR_DMAC_XFER_CHUNKS_PER_PAGE; ++i) {
		struct rcar_dmac_xfer_chunk *chunk = &page->chunks[i];

		list_add_tail(&chunk->node, &list);
	}

	spin_lock_irqsave(&chan->lock, flags);
	list_splice_tail(&list, &chan->desc.chunks_free);
	list_add_tail(&page->node, &chan->desc.pages);
	spin_unlock_irqrestore(&chan->lock, flags);

	return 0;
}

/*
 * rcar_dmac_xfer_chunk_get - Allocate a transfer chunk for a DMA transfer
 * @chan: the DMA channel
 *
 * Locking: This function must be called in a non-atomic context.
 *
 * Return: A pointer to the allocated transfer chunk descriptor or NULL if no
 * descriptor can be allocated.
 */
static struct rcar_dmac_xfer_chunk *
rcar_dmac_xfer_chunk_get(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_xfer_chunk *chunk;
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&chan->lock, flags);

	while (list_empty(&chan->desc.chunks_free)) {
		/*
		 * No free descriptors, allocate a page worth of them and try
		 * again, as someone else could race us to get the newly
		 * allocated descriptors. If the allocation fails return an
		 * error.
		 */
		spin_unlock_irqrestore(&chan->lock, flags);
		ret = rcar_dmac_xfer_chunk_alloc(chan, GFP_NOWAIT);
		if (ret < 0)
			return NULL;
		spin_lock_irqsave(&chan->lock, flags);
	}

	chunk = list_first_entry(&chan->desc.chunks_free,
				 struct rcar_dmac_xfer_chunk, node);
	list_del(&chunk->node);

	spin_unlock_irqrestore(&chan->lock, flags);

	return chunk;
}

static void rcar_dmac_realloc_hwdesc(struct rcar_dmac_chan *chan,
				     struct rcar_dmac_desc *desc, size_t size)
{
	/*
	 * dma_alloc_coherent() allocates memory in page size increments. To
	 * avoid reallocating the hardware descriptors when the allocated size
	 * wouldn't change align the requested size to a multiple of the page
	 * size.
	 */
	size = PAGE_ALIGN(size);

	if (desc->hwdescs.size == size)
		return;

	if (desc->hwdescs.mem) {
		dma_free_coherent(chan->chan.device->dev, desc->hwdescs.size,
				  desc->hwdescs.mem, desc->hwdescs.dma);
		desc->hwdescs.mem = NULL;
		desc->hwdescs.size = 0;
	}

	if (!size)
		return;

	desc->hwdescs.mem = dma_alloc_coherent(chan->chan.device->dev, size,
					       &desc->hwdescs.dma, GFP_NOWAIT);
	if (!desc->hwdescs.mem)
		return;

	desc->hwdescs.size = size;
}

static int rcar_dmac_fill_hwdesc(struct rcar_dmac_chan *chan,
				 struct rcar_dmac_desc *desc)
{
	struct rcar_dmac_xfer_chunk *chunk;
	struct rcar_dmac_hw_desc *hwdesc;

	rcar_dmac_realloc_hwdesc(chan, desc, desc->nchunks * sizeof(*hwdesc));

	hwdesc = desc->hwdescs.mem;
	if (!hwdesc)
		return -ENOMEM;

	list_for_each_entry(chunk, &desc->chunks, node) {
		hwdesc->sar = chunk->src_addr;
		hwdesc->dar = chunk->dst_addr;
		hwdesc->tcr = chunk->size >> desc->xfer_shift;
		hwdesc++;
	}

	return 0;
}

/* -----------------------------------------------------------------------------
 * Stop and reset
 */

static void rcar_dmac_chan_halt(struct rcar_dmac_chan *chan)
{
	u32 chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);

	chcr &= ~(RCAR_DMACHCR_DSE | RCAR_DMACHCR_DSIE | RCAR_DMACHCR_IE |
		  RCAR_DMACHCR_TE | RCAR_DMACHCR_DE);
	rcar_dmac_chan_write(chan, RCAR_DMACHCR, chcr);
}

static void rcar_dmac_chan_reinit(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_desc *desc, *_desc;
	unsigned long flags;
	LIST_HEAD(descs);

	spin_lock_irqsave(&chan->lock, flags);

	/* Move all non-free descriptors to the local lists. */
	list_splice_init(&chan->desc.pending, &descs);
	list_splice_init(&chan->desc.active, &descs);
	list_splice_init(&chan->desc.done, &descs);
	list_splice_init(&chan->desc.wait, &descs);

	chan->desc.running = NULL;

	spin_unlock_irqrestore(&chan->lock, flags);

	list_for_each_entry_safe(desc, _desc, &descs, node) {
		list_del(&desc->node);
		rcar_dmac_desc_put(chan, desc);
	}
}

static void rcar_dmac_stop(struct rcar_dmac *dmac)
{
	rcar_dmac_write(dmac, RCAR_DMAOR, 0);
}

static void rcar_dmac_abort(struct rcar_dmac *dmac)
{
	unsigned int i;

	/* Stop all channels. */
	for (i = 0; i < dmac->n_channels; ++i) {
		struct rcar_dmac_chan *chan = &dmac->channels[i];

		/* Stop and reinitialize the channel. */
		spin_lock(&chan->lock);
		rcar_dmac_chan_halt(chan);
		spin_unlock(&chan->lock);

		rcar_dmac_chan_reinit(chan);
	}
}

/* -----------------------------------------------------------------------------
 * Descriptors preparation
 */

static void rcar_dmac_chan_configure_desc(struct rcar_dmac_chan *chan,
					  struct rcar_dmac_desc *desc)
{
	static const u32 chcr_ts[] = {
		RCAR_DMACHCR_TS_1B, RCAR_DMACHCR_TS_2B,
		RCAR_DMACHCR_TS_4B, RCAR_DMACHCR_TS_8B,
		RCAR_DMACHCR_TS_16B, RCAR_DMACHCR_TS_32B,
		RCAR_DMACHCR_TS_64B,
	};

	unsigned int xfer_size;
	u32 chcr;

	switch (desc->direction) {
	case DMA_DEV_TO_MEM:
		chcr = RCAR_DMACHCR_DM_INC | RCAR_DMACHCR_SM_FIXED
		     | RCAR_DMACHCR_RS_DMARS;
		xfer_size = chan->src_xfer_size;
		break;

	case DMA_MEM_TO_DEV:
		chcr = RCAR_DMACHCR_DM_FIXED | RCAR_DMACHCR_SM_INC
		     | RCAR_DMACHCR_RS_DMARS;
		xfer_size = chan->dst_xfer_size;
		break;

	case DMA_MEM_TO_MEM:
	default:
		chcr = RCAR_DMACHCR_DM_INC | RCAR_DMACHCR_SM_INC
		     | RCAR_DMACHCR_RS_AUTO;
		xfer_size = RCAR_DMAC_MEMCPY_XFER_SIZE;
		break;
	}

	desc->xfer_shift = ilog2(xfer_size);
	desc->chcr = chcr | chcr_ts[desc->xfer_shift];
}

/*
 * rcar_dmac_chan_prep_sg - prepare transfer descriptors from an SG list
 *
 * Common routine for public (MEMCPY) and slave DMA. The MEMCPY case is also
 * converted to scatter-gather to guarantee consistent locking and a correct
 * list manipulation. For slave DMA direction carries the usual meaning, and,
 * logically, the SG list is RAM and the addr variable contains slave address,
 * e.g., the FIFO I/O register. For MEMCPY direction equals DMA_MEM_TO_MEM
 * and the SG list contains only one element and points at the source buffer.
 */
static struct dma_async_tx_descriptor *
rcar_dmac_chan_prep_sg(struct rcar_dmac_chan *chan, struct scatterlist *sgl,
		       unsigned int sg_len, dma_addr_t dev_addr,
		       enum dma_transfer_direction dir, unsigned long dma_flags,
		       bool cyclic)
{
	struct rcar_dmac_xfer_chunk *chunk;
	struct rcar_dmac_desc *desc;
	struct scatterlist *sg;
	unsigned int nchunks = 0;
	unsigned int max_chunk_size;
	unsigned int full_size = 0;
	bool highmem = false;
	unsigned int i;

	desc = rcar_dmac_desc_get(chan);
	if (!desc)
		return NULL;

	desc->async_tx.flags = dma_flags;
	desc->async_tx.cookie = -EBUSY;

	desc->cyclic = cyclic;
	desc->direction = dir;

	rcar_dmac_chan_configure_desc(chan, desc);

	max_chunk_size = (RCAR_DMATCR_MASK + 1) << desc->xfer_shift;

	/*
	 * Allocate and fill the transfer chunk descriptors. We own the only
	 * reference to the DMA descriptor, there's no need for locking.
	 */
	for_each_sg(sgl, sg, sg_len, i) {
		dma_addr_t mem_addr = sg_dma_address(sg);
		unsigned int len = sg_dma_len(sg);

		full_size += len;

		while (len) {
			unsigned int size = min(len, max_chunk_size);

#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
			/*
			 * Prevent individual transfers from crossing 4GB
			 * boundaries.
			 */
			if (dev_addr >> 32 != (dev_addr + size - 1) >> 32)
				size = ALIGN(dev_addr, 1ULL << 32) - dev_addr;
			if (mem_addr >> 32 != (mem_addr + size - 1) >> 32)
				size = ALIGN(mem_addr, 1ULL << 32) - mem_addr;

			/*
			 * Check if either of the source or destination address
			 * can't be expressed in 32 bits. If so we can't use
			 * hardware descriptor lists.
			 */
			if (dev_addr >> 32 || mem_addr >> 32)
				highmem = true;
#endif

			chunk = rcar_dmac_xfer_chunk_get(chan);
			if (!chunk) {
				rcar_dmac_desc_put(chan, desc);
				return NULL;
			}

			if (dir == DMA_DEV_TO_MEM) {
				chunk->src_addr = dev_addr;
				chunk->dst_addr = mem_addr;
			} else {
				chunk->src_addr = mem_addr;
				chunk->dst_addr = dev_addr;
			}

			chunk->size = size;

			dev_dbg(chan->chan.device->dev,
				"chan%u: chunk %p/%p sgl %u@%p, %u/%u %pad -> %pad\n",
				chan->index, chunk, desc, i, sg, size, len,
				&chunk->src_addr, &chunk->dst_addr);

			mem_addr += size;
			if (dir == DMA_MEM_TO_MEM)
				dev_addr += size;

			len -= size;

			list_add_tail(&chunk->node, &desc->chunks);
			nchunks++;
		}
	}

	desc->nchunks = nchunks;
	desc->size = full_size;

	/*
	 * Use hardware descriptor lists if possible when more than one chunk
	 * needs to be transferred (otherwise they don't make much sense).
	 *
	 * The highmem check currently covers the whole transfer. As an
	 * optimization we could use descriptor lists for consecutive lowmem
	 * chunks and direct manual mode for highmem chunks. Whether the
	 * performance improvement would be significant enough compared to the
	 * additional complexity remains to be investigated.
	 */
	desc->hwdescs.use = !highmem && nchunks > 1;
	if (desc->hwdescs.use) {
		if (rcar_dmac_fill_hwdesc(chan, desc) < 0)
			desc->hwdescs.use = false;
	}

	return &desc->async_tx;
}

/* -----------------------------------------------------------------------------
 * DMA engine operations
 */

static int rcar_dmac_alloc_chan_resources(struct dma_chan *chan)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	int ret;

	INIT_LIST_HEAD(&rchan->desc.chunks_free);
	INIT_LIST_HEAD(&rchan->desc.pages);

	/* Preallocate descriptors. */
	ret = rcar_dmac_xfer_chunk_alloc(rchan, GFP_KERNEL);
	if (ret < 0)
		return -ENOMEM;

	ret = rcar_dmac_desc_alloc(rchan, GFP_KERNEL);
	if (ret < 0)
		return -ENOMEM;

	return pm_runtime_get_sync(chan->device->dev);
}

static void rcar_dmac_free_chan_resources(struct dma_chan *chan)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	struct rcar_dmac *dmac = to_rcar_dmac(chan->device);
	struct rcar_dmac_desc_page *page, *_page;
	struct rcar_dmac_desc *desc;
	LIST_HEAD(list);

	/* Protect against ISR */
	spin_lock_irq(&rchan->lock);
	rcar_dmac_chan_halt(rchan);
	spin_unlock_irq(&rchan->lock);

	/* Now no new interrupts will occur */

	if (rchan->mid_rid >= 0) {
		/* The caller is holding dma_list_mutex */
		clear_bit(rchan->mid_rid, dmac->modules);
		rchan->mid_rid = -EINVAL;
	}

	list_splice_init(&rchan->desc.free, &list);
	list_splice_init(&rchan->desc.pending, &list);
	list_splice_init(&rchan->desc.active, &list);
	list_splice_init(&rchan->desc.done, &list);
	list_splice_init(&rchan->desc.wait, &list);

	list_for_each_entry(desc, &list, node)
		rcar_dmac_realloc_hwdesc(rchan, desc, 0);

	list_for_each_entry_safe(page, _page, &rchan->desc.pages, node) {
		list_del(&page->node);
		free_page((unsigned long)page);
	}

	pm_runtime_put(chan->device->dev);
}

static struct dma_async_tx_descriptor *
rcar_dmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dma_dest,
			  dma_addr_t dma_src, size_t len, unsigned long flags)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	struct scatterlist sgl;

	if (!len)
		return NULL;

	sg_init_table(&sgl, 1);
	sg_set_page(&sgl, pfn_to_page(PFN_DOWN(dma_src)), len,
		    offset_in_page(dma_src));
	sg_dma_address(&sgl) = dma_src;
	sg_dma_len(&sgl) = len;

	return rcar_dmac_chan_prep_sg(rchan, &sgl, 1, dma_dest,
				      DMA_MEM_TO_MEM, flags, false);
}

static struct dma_async_tx_descriptor *
rcar_dmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
			unsigned int sg_len, enum dma_transfer_direction dir,
			unsigned long flags, void *context)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	dma_addr_t dev_addr;

	/* Someone calling slave DMA on a generic channel? */
	if (rchan->mid_rid < 0 || !sg_len) {
		dev_warn(chan->device->dev,
			 "%s: bad parameter: len=%d, id=%d\n",
			 __func__, sg_len, rchan->mid_rid);
		return NULL;
	}

	dev_addr = dir == DMA_DEV_TO_MEM
		 ? rchan->src_slave_addr : rchan->dst_slave_addr;
	return rcar_dmac_chan_prep_sg(rchan, sgl, sg_len, dev_addr,
				      dir, flags, false);
}

#define RCAR_DMAC_MAX_SG_LEN	32

static struct dma_async_tx_descriptor *
rcar_dmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
			  size_t buf_len, size_t period_len,
			  enum dma_transfer_direction dir, unsigned long flags)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	struct dma_async_tx_descriptor *desc;
	struct scatterlist *sgl;
	dma_addr_t dev_addr;
	unsigned int sg_len;
	unsigned int i;

	/* Someone calling slave DMA on a generic channel? */
	if (rchan->mid_rid < 0 || buf_len < period_len) {
		dev_warn(chan->device->dev,
			"%s: bad parameter: buf_len=%zu, period_len=%zu, id=%d\n",
			__func__, buf_len, period_len, rchan->mid_rid);
		return NULL;
	}

	sg_len = buf_len / period_len;
	if (sg_len > RCAR_DMAC_MAX_SG_LEN) {
		dev_err(chan->device->dev,
			"chan%u: sg length %d exceds limit %d",
			rchan->index, sg_len, RCAR_DMAC_MAX_SG_LEN);
		return NULL;
	}

	/*
	 * Allocate the sg list dynamically as it would consume too much stack
	 * space.
	 */
	sgl = kcalloc(sg_len, sizeof(*sgl), GFP_NOWAIT);
	if (!sgl)
		return NULL;

	sg_init_table(sgl, sg_len);

	for (i = 0; i < sg_len; ++i) {
		dma_addr_t src = buf_addr + (period_len * i);

		sg_set_page(&sgl[i], pfn_to_page(PFN_DOWN(src)), period_len,
			    offset_in_page(src));
		sg_dma_address(&sgl[i]) = src;
		sg_dma_len(&sgl[i]) = period_len;
	}

	dev_addr = dir == DMA_DEV_TO_MEM
		 ? rchan->src_slave_addr : rchan->dst_slave_addr;
	desc = rcar_dmac_chan_prep_sg(rchan, sgl, sg_len, dev_addr,
				      dir, flags, true);

	kfree(sgl);
	return desc;
}

static int rcar_dmac_device_config(struct dma_chan *chan,
				   struct dma_slave_config *cfg)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);

	/*
	 * We could lock this, but you shouldn't be configuring the
	 * channel, while using it...
	 */
	rchan->src_slave_addr = cfg->src_addr;
	rchan->dst_slave_addr = cfg->dst_addr;
	rchan->src_xfer_size = cfg->src_addr_width;
	rchan->dst_xfer_size = cfg->dst_addr_width;

	return 0;
}

static int rcar_dmac_chan_terminate_all(struct dma_chan *chan)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	unsigned long flags;

	spin_lock_irqsave(&rchan->lock, flags);
	rcar_dmac_chan_halt(rchan);
	spin_unlock_irqrestore(&rchan->lock, flags);

	/*
	 * FIXME: No new interrupt can occur now, but the IRQ thread might still
	 * be running.
	 */

	rcar_dmac_chan_reinit(rchan);

	return 0;
}

static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
					       dma_cookie_t cookie)
{
	struct rcar_dmac_desc *desc = chan->desc.running;
	struct rcar_dmac_xfer_chunk *running = NULL;
	struct rcar_dmac_xfer_chunk *chunk;
	unsigned int residue = 0;
	unsigned int dptr = 0;

	if (!desc)
		return 0;

	/*
	 * If the cookie doesn't correspond to the currently running transfer
	 * then the descriptor hasn't been processed yet, and the residue is
	 * equal to the full descriptor size.
	 */
	if (cookie != desc->async_tx.cookie)
		return desc->size;

	/*
	 * In descriptor mode the descriptor running pointer is not maintained
	 * by the interrupt handler, find the running descriptor from the
	 * descriptor pointer field in the CHCRB register. In non-descriptor
	 * mode just use the running descriptor pointer.
	 */
	if (desc->hwdescs.use) {
		dptr = (rcar_dmac_chan_read(chan, RCAR_DMACHCRB) &
			RCAR_DMACHCRB_DPTR_MASK) >> RCAR_DMACHCRB_DPTR_SHIFT;
		WARN_ON(dptr >= desc->nchunks);
	} else {
		running = desc->running;
	}

	/* Compute the size of all chunks still to be transferred. */
	list_for_each_entry_reverse(chunk, &desc->chunks, node) {
		if (chunk == running || ++dptr == desc->nchunks)
			break;

		residue += chunk->size;
	}

	/* Add the residue for the current chunk. */
	residue += rcar_dmac_chan_read(chan, RCAR_DMATCR) << desc->xfer_shift;

	return residue;
}

static enum dma_status rcar_dmac_tx_status(struct dma_chan *chan,
					   dma_cookie_t cookie,
					   struct dma_tx_state *txstate)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	enum dma_status status;
	unsigned long flags;
	unsigned int residue;

	status = dma_cookie_status(chan, cookie, txstate);
	if (status == DMA_COMPLETE || !txstate)
		return status;

	spin_lock_irqsave(&rchan->lock, flags);
	residue = rcar_dmac_chan_get_residue(rchan, cookie);
	spin_unlock_irqrestore(&rchan->lock, flags);

	dma_set_residue(txstate, residue);

	return status;
}

static void rcar_dmac_issue_pending(struct dma_chan *chan)
{
	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
	unsigned long flags;

	spin_lock_irqsave(&rchan->lock, flags);

	if (list_empty(&rchan->desc.pending))
		goto done;

	/* Append the pending list to the active list. */
	list_splice_tail_init(&rchan->desc.pending, &rchan->desc.active);

	/*
	 * If no transfer is running pick the first descriptor from the active
	 * list and start the transfer.
	 */
	if (!rchan->desc.running) {
		struct rcar_dmac_desc *desc;

		desc = list_first_entry(&rchan->desc.active,
					struct rcar_dmac_desc, node);
		rchan->desc.running = desc;

		rcar_dmac_chan_start_xfer(rchan);
	}

done:
	spin_unlock_irqrestore(&rchan->lock, flags);
}

/* -----------------------------------------------------------------------------
 * IRQ handling
 */

static irqreturn_t rcar_dmac_isr_desc_stage_end(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_desc *desc = chan->desc.running;
	unsigned int stage;

	if (WARN_ON(!desc || !desc->cyclic)) {
		/*
		 * This should never happen, there should always be a running
		 * cyclic descriptor when a descriptor stage end interrupt is
		 * triggered. Warn and return.
		 */
		return IRQ_NONE;
	}

	/* Program the interrupt pointer to the next stage. */
	stage = (rcar_dmac_chan_read(chan, RCAR_DMACHCRB) &
		 RCAR_DMACHCRB_DPTR_MASK) >> RCAR_DMACHCRB_DPTR_SHIFT;
	rcar_dmac_chan_write(chan, RCAR_DMADPCR, RCAR_DMADPCR_DIPT(stage));

	return IRQ_WAKE_THREAD;
}

static irqreturn_t rcar_dmac_isr_transfer_end(struct rcar_dmac_chan *chan)
{
	struct rcar_dmac_desc *desc = chan->desc.running;
	irqreturn_t ret = IRQ_WAKE_THREAD;

	if (WARN_ON_ONCE(!desc)) {
		/*
		 * This should never happen, there should always be a running
		 * descriptor when a transfer end interrupt is triggered. Warn
		 * and return.
		 */
		return IRQ_NONE;
	}

	/*
	 * The transfer end interrupt isn't generated for each chunk when using
	 * descriptor mode. Only update the running chunk pointer in
	 * non-descriptor mode.
	 */
	if (!desc->hwdescs.use) {
		/*
		 * If we haven't completed the last transfer chunk simply move
		 * to the next one. Only wake the IRQ thread if the transfer is
		 * cyclic.
		 */
		if (!list_is_last(&desc->running->node, &desc->chunks)) {
			desc->running = list_next_entry(desc->running, node);
			if (!desc->cyclic)
				ret = IRQ_HANDLED;
			goto done;
		}

		/*
		 * We've completed the last transfer chunk. If the transfer is
		 * cyclic, move back to the first one.
		 */
		if (desc->cyclic) {
			desc->running =
				list_first_entry(&desc->chunks,
						 struct rcar_dmac_xfer_chunk,
						 node);
			goto done;
		}
	}

	/* The descriptor is complete, move it to the done list. */
	list_move_tail(&desc->node, &chan->desc.done);

	/* Queue the next descriptor, if any. */
	if (!list_empty(&chan->desc.active))
		chan->desc.running = list_first_entry(&chan->desc.active,
						      struct rcar_dmac_desc,
						      node);
	else
		chan->desc.running = NULL;

done:
	if (chan->desc.running)
		rcar_dmac_chan_start_xfer(chan);

	return ret;
}

static irqreturn_t rcar_dmac_isr_channel(int irq, void *dev)
{
	u32 mask = RCAR_DMACHCR_DSE | RCAR_DMACHCR_TE;
	struct rcar_dmac_chan *chan = dev;
	irqreturn_t ret = IRQ_NONE;
	u32 chcr;

	spin_lock(&chan->lock);

	chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
	if (chcr & RCAR_DMACHCR_TE)
		mask |= RCAR_DMACHCR_DE;
	rcar_dmac_chan_write(chan, RCAR_DMACHCR, chcr & ~mask);

	if (chcr & RCAR_DMACHCR_DSE)
		ret |= rcar_dmac_isr_desc_stage_end(chan);

	if (chcr & RCAR_DMACHCR_TE)
		ret |= rcar_dmac_isr_transfer_end(chan);

	spin_unlock(&chan->lock);

	return ret;
}

static irqreturn_t rcar_dmac_isr_channel_thread(int irq, void *dev)
{
	struct rcar_dmac_chan *chan = dev;
	struct rcar_dmac_desc *desc;

	spin_lock_irq(&chan->lock);

	/* For cyclic transfers notify the user after every chunk. */
	if (chan->desc.running && chan->desc.running->cyclic) {
		dma_async_tx_callback callback;
		void *callback_param;

		desc = chan->desc.running;
		callback = desc->async_tx.callback;
		callback_param = desc->async_tx.callback_param;

		if (callback) {
			spin_unlock_irq(&chan->lock);
			callback(callback_param);
			spin_lock_irq(&chan->lock);
		}
	}

	/*
	 * Call the callback function for all descriptors on the done list and
	 * move them to the ack wait list.
	 */
	while (!list_empty(&chan->desc.done)) {
		desc = list_first_entry(&chan->desc.done, struct rcar_dmac_desc,
					node);
		dma_cookie_complete(&desc->async_tx);
		list_del(&desc->node);

		if (desc->async_tx.callback) {
			spin_unlock_irq(&chan->lock);
			/*
			 * We own the only reference to this descriptor, we can
			 * safely dereference it without holding the channel
			 * lock.
			 */
			desc->async_tx.callback(desc->async_tx.callback_param);
			spin_lock_irq(&chan->lock);
		}

		list_add_tail(&desc->node, &chan->desc.wait);
	}

	spin_unlock_irq(&chan->lock);

	/* Recycle all acked descriptors. */
	rcar_dmac_desc_recycle_acked(chan);

	return IRQ_HANDLED;
}

static irqreturn_t rcar_dmac_isr_error(int irq, void *data)
{
	struct rcar_dmac *dmac = data;

	if (!(rcar_dmac_read(dmac, RCAR_DMAOR) & RCAR_DMAOR_AE))
		return IRQ_NONE;

	/*
	 * An unrecoverable error occurred on an unknown channel. Halt the DMAC,
	 * abort transfers on all channels, and reinitialize the DMAC.
	 */
	rcar_dmac_stop(dmac);
	rcar_dmac_abort(dmac);
	rcar_dmac_init(dmac);

	return IRQ_HANDLED;
}

/* -----------------------------------------------------------------------------
 * OF xlate and channel filter
 */

static bool rcar_dmac_chan_filter(struct dma_chan *chan, void *arg)
{
	struct rcar_dmac *dmac = to_rcar_dmac(chan->device);
	struct of_phandle_args *dma_spec = arg;

	/*
	 * FIXME: Using a filter on OF platforms is a nonsense. The OF xlate
	 * function knows from which device it wants to allocate a channel from,
	 * and would be perfectly capable of selecting the channel it wants.
	 * Forcing it to call dma_request_channel() and iterate through all
	 * channels from all controllers is just pointless.
	 */
	if (chan->device->device_config != rcar_dmac_device_config ||
	    dma_spec->np != chan->device->dev->of_node)
		return false;

	return !test_and_set_bit(dma_spec->args[0], dmac->modules);
}

static struct dma_chan *rcar_dmac_of_xlate(struct of_phandle_args *dma_spec,
					   struct of_dma *ofdma)
{
	struct rcar_dmac_chan *rchan;
	struct dma_chan *chan;
	dma_cap_mask_t mask;

	if (dma_spec->args_count != 1)
		return NULL;

	/* Only slave DMA channels can be allocated via DT */
	dma_cap_zero(mask);
	dma_cap_set(DMA_SLAVE, mask);

	chan = dma_request_channel(mask, rcar_dmac_chan_filter, dma_spec);
	if (!chan)
		return NULL;

	rchan = to_rcar_dmac_chan(chan);
	rchan->mid_rid = dma_spec->args[0];

	return chan;
}

/* -----------------------------------------------------------------------------
 * Power management
 */

#ifdef CONFIG_PM_SLEEP
static int rcar_dmac_sleep_suspend(struct device *dev)
{
	/*
	 * TODO: Wait for the current transfer to complete and stop the device.
	 */
	return 0;
}

static int rcar_dmac_sleep_resume(struct device *dev)
{
	/* TODO: Resume transfers, if any. */
	return 0;
}
#endif

#ifdef CONFIG_PM
static int rcar_dmac_runtime_suspend(struct device *dev)
{
	return 0;
}

static int rcar_dmac_runtime_resume(struct device *dev)
{
	struct rcar_dmac *dmac = dev_get_drvdata(dev);

	return rcar_dmac_init(dmac);
}
#endif

static const struct dev_pm_ops rcar_dmac_pm = {
	SET_SYSTEM_SLEEP_PM_OPS(rcar_dmac_sleep_suspend, rcar_dmac_sleep_resume)
	SET_RUNTIME_PM_OPS(rcar_dmac_runtime_suspend, rcar_dmac_runtime_resume,
			   NULL)
};

/* -----------------------------------------------------------------------------
 * Probe and remove
 */

static int rcar_dmac_chan_probe(struct rcar_dmac *dmac,
				struct rcar_dmac_chan *rchan,
				unsigned int index)
{
	struct platform_device *pdev = to_platform_device(dmac->dev);
	struct dma_chan *chan = &rchan->chan;
	char pdev_irqname[5];
	char *irqname;
	int irq;
	int ret;

	rchan->index = index;
	rchan->iomem = dmac->iomem + RCAR_DMAC_CHAN_OFFSET(index);
	rchan->mid_rid = -EINVAL;

	spin_lock_init(&rchan->lock);

	INIT_LIST_HEAD(&rchan->desc.free);
	INIT_LIST_HEAD(&rchan->desc.pending);
	INIT_LIST_HEAD(&rchan->desc.active);
	INIT_LIST_HEAD(&rchan->desc.done);
	INIT_LIST_HEAD(&rchan->desc.wait);

	/* Request the channel interrupt. */
	sprintf(pdev_irqname, "ch%u", index);
	irq = platform_get_irq_byname(pdev, pdev_irqname);
	if (irq < 0) {
		dev_err(dmac->dev, "no IRQ specified for channel %u\n", index);
		return -ENODEV;
	}

	irqname = devm_kasprintf(dmac->dev, GFP_KERNEL, "%s:%u",
				 dev_name(dmac->dev), index);
	if (!irqname)
		return -ENOMEM;

	ret = devm_request_threaded_irq(dmac->dev, irq, rcar_dmac_isr_channel,
					rcar_dmac_isr_channel_thread, 0,
					irqname, rchan);
	if (ret) {
		dev_err(dmac->dev, "failed to request IRQ %u (%d)\n", irq, ret);
		return ret;
	}

	/*
	 * Initialize the DMA engine channel and add it to the DMA engine
	 * channels list.
	 */
	chan->device = &dmac->engine;
	dma_cookie_init(chan);

	list_add_tail(&chan->device_node, &dmac->engine.channels);

	return 0;
}

static int rcar_dmac_parse_of(struct device *dev, struct rcar_dmac *dmac)
{
	struct device_node *np = dev->of_node;
	int ret;

	ret = of_property_read_u32(np, "dma-channels", &dmac->n_channels);
	if (ret < 0) {
		dev_err(dev, "unable to read dma-channels property\n");
		return ret;
	}

	if (dmac->n_channels <= 0 || dmac->n_channels >= 100) {
		dev_err(dev, "invalid number of channels %u\n",
			dmac->n_channels);
		return -EINVAL;
	}

	return 0;
}

static int rcar_dmac_probe(struct platform_device *pdev)
{
	const enum dma_slave_buswidth widths = DMA_SLAVE_BUSWIDTH_1_BYTE |
		DMA_SLAVE_BUSWIDTH_2_BYTES | DMA_SLAVE_BUSWIDTH_4_BYTES |
		DMA_SLAVE_BUSWIDTH_8_BYTES | DMA_SLAVE_BUSWIDTH_16_BYTES |
		DMA_SLAVE_BUSWIDTH_32_BYTES | DMA_SLAVE_BUSWIDTH_64_BYTES;
	unsigned int channels_offset = 0;
	struct dma_device *engine;
	struct rcar_dmac *dmac;
	struct resource *mem;
	unsigned int i;
	char *irqname;
	int irq;
	int ret;

	dmac = devm_kzalloc(&pdev->dev, sizeof(*dmac), GFP_KERNEL);
	if (!dmac)
		return -ENOMEM;

	dmac->dev = &pdev->dev;
	platform_set_drvdata(pdev, dmac);

	ret = rcar_dmac_parse_of(&pdev->dev, dmac);
	if (ret < 0)
		return ret;

	/*
	 * A still unconfirmed hardware bug prevents the IPMMU microTLB 0 to be
	 * flushed correctly, resulting in memory corruption. DMAC 0 channel 0
	 * is connected to microTLB 0 on currently supported platforms, so we
	 * can't use it with the IPMMU. As the IOMMU API operates at the device
	 * level we can't disable it selectively, so ignore channel 0 for now if
	 * the device is part of an IOMMU group.
	 */
	if (pdev->dev.iommu_group) {
		dmac->n_channels--;
		channels_offset = 1;
	}

	dmac->channels = devm_kcalloc(&pdev->dev, dmac->n_channels,
				      sizeof(*dmac->channels), GFP_KERNEL);
	if (!dmac->channels)
		return -ENOMEM;

	/* Request resources. */
	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	dmac->iomem = devm_ioremap_resource(&pdev->dev, mem);
	if (IS_ERR(dmac->iomem))
		return PTR_ERR(dmac->iomem);

	irq = platform_get_irq_byname(pdev, "error");
	if (irq < 0) {
		dev_err(&pdev->dev, "no error IRQ specified\n");
		return -ENODEV;
	}

	irqname = devm_kasprintf(dmac->dev, GFP_KERNEL, "%s:error",
				 dev_name(dmac->dev));
	if (!irqname)
		return -ENOMEM;

	ret = devm_request_irq(&pdev->dev, irq, rcar_dmac_isr_error, 0,
			       irqname, dmac);
	if (ret) {
		dev_err(&pdev->dev, "failed to request IRQ %u (%d)\n",
			irq, ret);
		return ret;
	}

	/* Enable runtime PM and initialize the device. */
	pm_runtime_enable(&pdev->dev);
	ret = pm_runtime_get_sync(&pdev->dev);
	if (ret < 0) {
		dev_err(&pdev->dev, "runtime PM get sync failed (%d)\n", ret);
		return ret;
	}

	ret = rcar_dmac_init(dmac);
	pm_runtime_put(&pdev->dev);

	if (ret) {
		dev_err(&pdev->dev, "failed to reset device\n");
		goto error;
	}

	/* Initialize the channels. */
	INIT_LIST_HEAD(&dmac->engine.channels);

	for (i = 0; i < dmac->n_channels; ++i) {
		ret = rcar_dmac_chan_probe(dmac, &dmac->channels[i],
					   i + channels_offset);
		if (ret < 0)
			goto error;
	}

	/* Register the DMAC as a DMA provider for DT. */
	ret = of_dma_controller_register(pdev->dev.of_node, rcar_dmac_of_xlate,
					 NULL);
	if (ret < 0)
		goto error;

	/*
	 * Register the DMA engine device.
	 *
	 * Default transfer size of 32 bytes requires 32-byte alignment.
	 */
	engine = &dmac->engine;
	dma_cap_set(DMA_MEMCPY, engine->cap_mask);
	dma_cap_set(DMA_SLAVE, engine->cap_mask);

	engine->dev = &pdev->dev;
	engine->copy_align = ilog2(RCAR_DMAC_MEMCPY_XFER_SIZE);

	engine->src_addr_widths = widths;
	engine->dst_addr_widths = widths;
	engine->directions = BIT(DMA_MEM_TO_DEV) | BIT(DMA_DEV_TO_MEM);
	engine->residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;

	engine->device_alloc_chan_resources = rcar_dmac_alloc_chan_resources;
	engine->device_free_chan_resources = rcar_dmac_free_chan_resources;
	engine->device_prep_dma_memcpy = rcar_dmac_prep_dma_memcpy;
	engine->device_prep_slave_sg = rcar_dmac_prep_slave_sg;
	engine->device_prep_dma_cyclic = rcar_dmac_prep_dma_cyclic;
	engine->device_config = rcar_dmac_device_config;
	engine->device_terminate_all = rcar_dmac_chan_terminate_all;
	engine->device_tx_status = rcar_dmac_tx_status;
	engine->device_issue_pending = rcar_dmac_issue_pending;

	ret = dma_async_device_register(engine);
	if (ret < 0)
		goto error;

	return 0;

error:
	of_dma_controller_free(pdev->dev.of_node);
	pm_runtime_disable(&pdev->dev);
	return ret;
}

static int rcar_dmac_remove(struct platform_device *pdev)
{
	struct rcar_dmac *dmac = platform_get_drvdata(pdev);

	of_dma_controller_free(pdev->dev.of_node);
	dma_async_device_unregister(&dmac->engine);

	pm_runtime_disable(&pdev->dev);

	return 0;
}

static void rcar_dmac_shutdown(struct platform_device *pdev)
{
	struct rcar_dmac *dmac = platform_get_drvdata(pdev);

	rcar_dmac_stop(dmac);
}

static const struct of_device_id rcar_dmac_of_ids[] = {
	{ .compatible = "renesas,rcar-dmac", },
	{ /* Sentinel */ }
};
MODULE_DEVICE_TABLE(of, rcar_dmac_of_ids);

static struct platform_driver rcar_dmac_driver = {
	.driver		= {
		.pm	= &rcar_dmac_pm,
		.name	= "rcar-dmac",
		.of_match_table = rcar_dmac_of_ids,
	},
	.probe		= rcar_dmac_probe,
	.remove		= rcar_dmac_remove,
	.shutdown	= rcar_dmac_shutdown,
};

module_platform_driver(rcar_dmac_driver);

MODULE_DESCRIPTION("R-Car Gen2 DMA Controller Driver");
MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
MODULE_LICENSE("GPL v2");