sh_eth: fix EESIPR values for SH77{34|63}

[linux/fpc-iii.git] / 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_slave - Slave configuration
 * @slave_addr: slave memory address
 * @xfer_size: size (in bytes) of hardware transfers
 */
struct rcar_dmac_chan_slave {
        phys_addr_t slave_addr;
        unsigned int xfer_size;
};

/*
 * struct rcar_dmac_chan_map - Map of slave device phys to dma address
 * @addr: slave dma address
 * @dir: direction of mapping
 * @slave: slave configuration that is mapped
 */
struct rcar_dmac_chan_map {
        dma_addr_t addr;
        enum dma_data_direction dir;
        struct rcar_dmac_chan_slave slave;
};

/*
 * 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: slave memory address and size on the source side
 * @dst: slave memory address and size on the destination side
 * @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;

        struct rcar_dmac_chan_slave src;
        struct rcar_dmac_chan_slave dst;
        struct rcar_dmac_chan_map map;
        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));
}

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, GENMASK(dmac->n_channels - 1, 0));
        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(&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);

        rchan->desc.running = NULL;

        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 int rcar_dmac_map_slave_addr(struct dma_chan *chan,
                                    enum dma_transfer_direction dir)
{
        struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
        struct rcar_dmac_chan_map *map = &rchan->map;
        phys_addr_t dev_addr;
        size_t dev_size;
        enum dma_data_direction dev_dir;

        if (dir == DMA_DEV_TO_MEM) {
                dev_addr = rchan->src.slave_addr;
                dev_size = rchan->src.xfer_size;
                dev_dir = DMA_TO_DEVICE;
        } else {
                dev_addr = rchan->dst.slave_addr;
                dev_size = rchan->dst.xfer_size;
                dev_dir = DMA_FROM_DEVICE;
        }

        /* Reuse current map if possible. */
        if (dev_addr == map->slave.slave_addr &&
            dev_size == map->slave.xfer_size &&
            dev_dir == map->dir)
                return 0;

        /* Remove old mapping if present. */
        if (map->slave.xfer_size)
                dma_unmap_resource(chan->device->dev, map->addr,
                                   map->slave.xfer_size, map->dir, 0);
        map->slave.xfer_size = 0;

        /* Create new slave address map. */
        map->addr = dma_map_resource(chan->device->dev, dev_addr, dev_size,
                                     dev_dir, 0);

        if (dma_mapping_error(chan->device->dev, map->addr)) {
                dev_err(chan->device->dev,
                        "chan%u: failed to map %zx@%pap", rchan->index,
                        dev_size, &dev_addr);
                return -EIO;
        }

        dev_dbg(chan->device->dev, "chan%u: map %zx@%pap to %pad dir: %s\n",
                rchan->index, dev_size, &dev_addr, &map->addr,
                dev_dir == DMA_TO_DEVICE ? "DMA_TO_DEVICE" : "DMA_FROM_DEVICE");

        map->slave.slave_addr = dev_addr;
        map->slave.xfer_size = dev_size;
        map->dir = dev_dir;

        return 0;
}

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);

        /* 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;
        }

        if (rcar_dmac_map_slave_addr(chan, dir))
                return NULL;

        return rcar_dmac_chan_prep_sg(rchan, sgl, sg_len, rchan->map.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;
        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;
        }

        if (rcar_dmac_map_slave_addr(chan, dir))
                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;
        }

        desc = rcar_dmac_chan_prep_sg(rchan, sgl, sg_len, rchan->map.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;
        enum dma_status status;
        unsigned int residue = 0;
        unsigned int dptr = 0;

        if (!desc)
                return 0;

        /*
         * If the cookie corresponds to a descriptor that has been completed
         * there is no residue. The same check has already been performed by the
         * caller but without holding the channel lock, so the descriptor could
         * now be complete.
         */
        status = dma_cookie_status(&chan->chan, cookie, NULL);
        if (status == DMA_COMPLETE)
                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) {
                list_for_each_entry(desc, &chan->desc.pending, node) {
                        if (cookie == desc->async_tx.cookie)
                                return desc->size;
                }
                list_for_each_entry(desc, &chan->desc.active, node) {
                        if (cookie == desc->async_tx.cookie)
                                return desc->size;
                }

                /*
                 * No descriptor found for the cookie, there's thus no residue.
                 * This shouldn't happen if the calling driver passes a correct
                 * cookie value.
                 */
                WARN(1, "No descriptor for cookie!");
                return 0;
        }

        /*
         * 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);

        /* if there's no residue, the cookie is complete */
        if (!residue)
                return DMA_COMPLETE;

        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;
        struct dmaengine_desc_callback cb;

        spin_lock_irq(&chan->lock);

        /* For cyclic transfers notify the user after every chunk. */
        if (chan->desc.running && chan->desc.running->cyclic) {
                desc = chan->desc.running;
                dmaengine_desc_get_callback(&desc->async_tx, &cb);

                if (dmaengine_desc_callback_valid(&cb)) {
                        spin_unlock_irq(&chan->lock);
                        dmaengine_desc_callback_invoke(&cb, NULL);
                        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);

                dmaengine_desc_get_callback(&desc->async_tx, &cb);
                if (dmaengine_desc_callback_valid(&cb)) {
                        spin_unlock_irq(&chan->lock);
                        /*
                         * We own the only reference to this descriptor, we can
                         * safely dereference it without holding the channel
                         * lock.
                         */
                        dmaengine_desc_callback_invoke(&cb, NULL);
                        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");