// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2014 Emilio López
 * Emilio López <emilio@elopez.com.ar>
 */

#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/clk.h>
#include <linux/dmaengine.h>
#include <linux/dmapool.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/of_dma.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

#include "virt-dma.h"

/** Common macros to normal and dedicated DMA registers **/

#define SUN4I_DMA_CFG_LOADING                   BIT(31)
#define SUN4I_DMA_CFG_DST_DATA_WIDTH(width)     ((width) << 25)
#define SUN4I_DMA_CFG_DST_BURST_LENGTH(len)     ((len) << 23)
#define SUN4I_DMA_CFG_DST_ADDR_MODE(mode)       ((mode) << 21)
#define SUN4I_DMA_CFG_DST_DRQ_TYPE(type)        ((type) << 16)
#define SUN4I_DMA_CFG_SRC_DATA_WIDTH(width)     ((width) << 9)
#define SUN4I_DMA_CFG_SRC_BURST_LENGTH(len)     ((len) << 7)
#define SUN4I_DMA_CFG_SRC_ADDR_MODE(mode)       ((mode) << 5)
#define SUN4I_DMA_CFG_SRC_DRQ_TYPE(type)        (type)

/** Normal DMA register values **/

/* Normal DMA source/destination data request type values */
#define SUN4I_NDMA_DRQ_TYPE_SDRAM               0x16
#define SUN4I_NDMA_DRQ_TYPE_LIMIT               (0x1F + 1)

/** Normal DMA register layout **/

/* Dedicated DMA source/destination address mode values */
#define SUN4I_NDMA_ADDR_MODE_LINEAR             0
#define SUN4I_NDMA_ADDR_MODE_IO                 1

/* Normal DMA configuration register layout */
#define SUN4I_NDMA_CFG_CONT_MODE                BIT(30)
#define SUN4I_NDMA_CFG_WAIT_STATE(n)            ((n) << 27)
#define SUN4I_NDMA_CFG_DST_NON_SECURE           BIT(22)
#define SUN4I_NDMA_CFG_BYTE_COUNT_MODE_REMAIN   BIT(15)
#define SUN4I_NDMA_CFG_SRC_NON_SECURE           BIT(6)

/** Dedicated DMA register values **/

/* Dedicated DMA source/destination address mode values */
#define SUN4I_DDMA_ADDR_MODE_LINEAR             0
#define SUN4I_DDMA_ADDR_MODE_IO                 1
#define SUN4I_DDMA_ADDR_MODE_HORIZONTAL_PAGE    2
#define SUN4I_DDMA_ADDR_MODE_VERTICAL_PAGE      3

/* Dedicated DMA source/destination data request type values */
#define SUN4I_DDMA_DRQ_TYPE_SDRAM               0x1
#define SUN4I_DDMA_DRQ_TYPE_LIMIT               (0x1F + 1)

/** Dedicated DMA register layout **/

/* Dedicated DMA configuration register layout */
#define SUN4I_DDMA_CFG_BUSY                     BIT(30)
#define SUN4I_DDMA_CFG_CONT_MODE                BIT(29)
#define SUN4I_DDMA_CFG_DST_NON_SECURE           BIT(28)
#define SUN4I_DDMA_CFG_BYTE_COUNT_MODE_REMAIN   BIT(15)
#define SUN4I_DDMA_CFG_SRC_NON_SECURE           BIT(12)

/* Dedicated DMA parameter register layout */
#define SUN4I_DDMA_PARA_DST_DATA_BLK_SIZE(n)    (((n) - 1) << 24)
#define SUN4I_DDMA_PARA_DST_WAIT_CYCLES(n)      (((n) - 1) << 16)
#define SUN4I_DDMA_PARA_SRC_DATA_BLK_SIZE(n)    (((n) - 1) << 8)
#define SUN4I_DDMA_PARA_SRC_WAIT_CYCLES(n)      (((n) - 1) << 0)

/** DMA register offsets **/

/* General register offsets */
#define SUN4I_DMA_IRQ_ENABLE_REG                0x0
#define SUN4I_DMA_IRQ_PENDING_STATUS_REG        0x4

/* Normal DMA register offsets */
#define SUN4I_NDMA_CHANNEL_REG_BASE(n)          (0x100 + (n) * 0x20)
#define SUN4I_NDMA_CFG_REG                      0x0
#define SUN4I_NDMA_SRC_ADDR_REG                 0x4
#define SUN4I_NDMA_DST_ADDR_REG         0x8
#define SUN4I_NDMA_BYTE_COUNT_REG               0xC

/* Dedicated DMA register offsets */
#define SUN4I_DDMA_CHANNEL_REG_BASE(n)          (0x300 + (n) * 0x20)
#define SUN4I_DDMA_CFG_REG                      0x0
#define SUN4I_DDMA_SRC_ADDR_REG                 0x4
#define SUN4I_DDMA_DST_ADDR_REG         0x8
#define SUN4I_DDMA_BYTE_COUNT_REG               0xC
#define SUN4I_DDMA_PARA_REG                     0x18

/** DMA Driver **/

/*
 * Normal DMA has 8 channels, and Dedicated DMA has another 8, so
 * that's 16 channels. As for endpoints, there's 29 and 21
 * respectively. Given that the Normal DMA endpoints (other than
 * SDRAM) can be used as tx/rx, we need 78 vchans in total
 */
#define SUN4I_NDMA_NR_MAX_CHANNELS      8
#define SUN4I_DDMA_NR_MAX_CHANNELS      8
#define SUN4I_DMA_NR_MAX_CHANNELS                                       \
        (SUN4I_NDMA_NR_MAX_CHANNELS + SUN4I_DDMA_NR_MAX_CHANNELS)
#define SUN4I_NDMA_NR_MAX_VCHANS        (29 * 2 - 1)
#define SUN4I_DDMA_NR_MAX_VCHANS        21
#define SUN4I_DMA_NR_MAX_VCHANS                                         \
        (SUN4I_NDMA_NR_MAX_VCHANS + SUN4I_DDMA_NR_MAX_VCHANS)

/* This set of SUN4I_DDMA timing parameters were found experimentally while
 * working with the SPI driver and seem to make it behave correctly */
#define SUN4I_DDMA_MAGIC_SPI_PARAMETERS \
        (SUN4I_DDMA_PARA_DST_DATA_BLK_SIZE(1) |                 \
         SUN4I_DDMA_PARA_SRC_DATA_BLK_SIZE(1) |                         \
         SUN4I_DDMA_PARA_DST_WAIT_CYCLES(2) |                           \
         SUN4I_DDMA_PARA_SRC_WAIT_CYCLES(2))

struct sun4i_dma_pchan {
        /* Register base of channel */
        void __iomem                    *base;
        /* vchan currently being serviced */
        struct sun4i_dma_vchan          *vchan;
        /* Is this a dedicated pchan? */
        int                             is_dedicated;
};

struct sun4i_dma_vchan {
        struct virt_dma_chan            vc;
        struct dma_slave_config         cfg;
        struct sun4i_dma_pchan          *pchan;
        struct sun4i_dma_promise        *processing;
        struct sun4i_dma_contract       *contract;
        u8                              endpoint;
        int                             is_dedicated;
};

struct sun4i_dma_promise {
        u32                             cfg;
        u32                             para;
        dma_addr_t                      src;
        dma_addr_t                      dst;
        size_t                          len;
        struct list_head                list;
};

/* A contract is a set of promises */
struct sun4i_dma_contract {
        struct virt_dma_desc            vd;
        struct list_head                demands;
        struct list_head                completed_demands;
        int                             is_cyclic;
};

struct sun4i_dma_dev {
        DECLARE_BITMAP(pchans_used, SUN4I_DMA_NR_MAX_CHANNELS);
        struct dma_device               slave;
        struct sun4i_dma_pchan          *pchans;
        struct sun4i_dma_vchan          *vchans;
        void __iomem                    *base;
        struct clk                      *clk;
        int                             irq;
        spinlock_t                      lock;
};

static struct sun4i_dma_dev *to_sun4i_dma_dev(struct dma_device *dev)
{
        return container_of(dev, struct sun4i_dma_dev, slave);
}

static struct sun4i_dma_vchan *to_sun4i_dma_vchan(struct dma_chan *chan)
{
        return container_of(chan, struct sun4i_dma_vchan, vc.chan);
}

static struct sun4i_dma_contract *to_sun4i_dma_contract(struct virt_dma_desc *vd)
{
        return container_of(vd, struct sun4i_dma_contract, vd);
}

static struct device *chan2dev(struct dma_chan *chan)
{
        return &chan->dev->device;
}

static int convert_burst(u32 maxburst)
{
        if (maxburst > 8)
                return -EINVAL;

        /* 1 -> 0, 4 -> 1, 8 -> 2 */
        return (maxburst >> 2);
}

static int convert_buswidth(enum dma_slave_buswidth addr_width)
{
        if (addr_width > DMA_SLAVE_BUSWIDTH_4_BYTES)
                return -EINVAL;

        /* 8 (1 byte) -> 0, 16 (2 bytes) -> 1, 32 (4 bytes) -> 2 */
        return (addr_width >> 1);
}

static void sun4i_dma_free_chan_resources(struct dma_chan *chan)
{
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);

        vchan_free_chan_resources(&vchan->vc);
}

static struct sun4i_dma_pchan *find_and_use_pchan(struct sun4i_dma_dev *priv,
                                                  struct sun4i_dma_vchan *vchan)
{
        struct sun4i_dma_pchan *pchan = NULL, *pchans = priv->pchans;
        unsigned long flags;
        int i, max;

        /*
         * pchans 0-SUN4I_NDMA_NR_MAX_CHANNELS are normal, and
         * SUN4I_NDMA_NR_MAX_CHANNELS+ are dedicated ones
         */
        if (vchan->is_dedicated) {
                i = SUN4I_NDMA_NR_MAX_CHANNELS;
                max = SUN4I_DMA_NR_MAX_CHANNELS;
        } else {
                i = 0;
                max = SUN4I_NDMA_NR_MAX_CHANNELS;
        }

        spin_lock_irqsave(&priv->lock, flags);
        for_each_clear_bit_from(i, priv->pchans_used, max) {
                pchan = &pchans[i];
                pchan->vchan = vchan;
                set_bit(i, priv->pchans_used);
                break;
        }
        spin_unlock_irqrestore(&priv->lock, flags);

        return pchan;
}

static void release_pchan(struct sun4i_dma_dev *priv,
                          struct sun4i_dma_pchan *pchan)
{
        unsigned long flags;
        int nr = pchan - priv->pchans;

        spin_lock_irqsave(&priv->lock, flags);

        pchan->vchan = NULL;
        clear_bit(nr, priv->pchans_used);

        spin_unlock_irqrestore(&priv->lock, flags);
}

static void configure_pchan(struct sun4i_dma_pchan *pchan,
                            struct sun4i_dma_promise *d)
{
        /*
         * Configure addresses and misc parameters depending on type
         * SUN4I_DDMA has an extra field with timing parameters
         */
        if (pchan->is_dedicated) {
                writel_relaxed(d->src, pchan->base + SUN4I_DDMA_SRC_ADDR_REG);
                writel_relaxed(d->dst, pchan->base + SUN4I_DDMA_DST_ADDR_REG);
                writel_relaxed(d->len, pchan->base + SUN4I_DDMA_BYTE_COUNT_REG);
                writel_relaxed(d->para, pchan->base + SUN4I_DDMA_PARA_REG);
                writel_relaxed(d->cfg, pchan->base + SUN4I_DDMA_CFG_REG);
        } else {
                writel_relaxed(d->src, pchan->base + SUN4I_NDMA_SRC_ADDR_REG);
                writel_relaxed(d->dst, pchan->base + SUN4I_NDMA_DST_ADDR_REG);
                writel_relaxed(d->len, pchan->base + SUN4I_NDMA_BYTE_COUNT_REG);
                writel_relaxed(d->cfg, pchan->base + SUN4I_NDMA_CFG_REG);
        }
}

static void set_pchan_interrupt(struct sun4i_dma_dev *priv,
                                struct sun4i_dma_pchan *pchan,
                                int half, int end)
{
        u32 reg;
        int pchan_number = pchan - priv->pchans;
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);

        reg = readl_relaxed(priv->base + SUN4I_DMA_IRQ_ENABLE_REG);

        if (half)
                reg |= BIT(pchan_number * 2);
        else
                reg &= ~BIT(pchan_number * 2);

        if (end)
                reg |= BIT(pchan_number * 2 + 1);
        else
                reg &= ~BIT(pchan_number * 2 + 1);

        writel_relaxed(reg, priv->base + SUN4I_DMA_IRQ_ENABLE_REG);

        spin_unlock_irqrestore(&priv->lock, flags);
}

/*
 * Execute pending operations on a vchan
 *
 * When given a vchan, this function will try to acquire a suitable
 * pchan and, if successful, will configure it to fulfill a promise
 * from the next pending contract.
 *
 * This function must be called with &vchan->vc.lock held.
 */
static int __execute_vchan_pending(struct sun4i_dma_dev *priv,
                                   struct sun4i_dma_vchan *vchan)
{
        struct sun4i_dma_promise *promise = NULL;
        struct sun4i_dma_contract *contract = NULL;
        struct sun4i_dma_pchan *pchan;
        struct virt_dma_desc *vd;
        int ret;

        lockdep_assert_held(&vchan->vc.lock);

        /* We need a pchan to do anything, so secure one if available */
        pchan = find_and_use_pchan(priv, vchan);
        if (!pchan)
                return -EBUSY;

        /*
         * Channel endpoints must not be repeated, so if this vchan
         * has already submitted some work, we can't do anything else
         */
        if (vchan->processing) {
                dev_dbg(chan2dev(&vchan->vc.chan),
                        "processing something to this endpoint already\n");
                ret = -EBUSY;
                goto release_pchan;
        }

        do {
                /* Figure out which contract we're working with today */
                vd = vchan_next_desc(&vchan->vc);
                if (!vd) {
                        dev_dbg(chan2dev(&vchan->vc.chan),
                                "No pending contract found");
                        ret = 0;
                        goto release_pchan;
                }

                contract = to_sun4i_dma_contract(vd);
                if (list_empty(&contract->demands)) {
                        /* The contract has been completed so mark it as such */
                        list_del(&contract->vd.node);
                        vchan_cookie_complete(&contract->vd);
                        dev_dbg(chan2dev(&vchan->vc.chan),
                                "Empty contract found and marked complete");
                }
        } while (list_empty(&contract->demands));

        /* Now find out what we need to do */
        promise = list_first_entry(&contract->demands,
                                   struct sun4i_dma_promise, list);
        vchan->processing = promise;

        /* ... and make it reality */
        if (promise) {
                vchan->contract = contract;
                vchan->pchan = pchan;
                set_pchan_interrupt(priv, pchan, contract->is_cyclic, 1);
                configure_pchan(pchan, promise);
        }

        return 0;

release_pchan:
        release_pchan(priv, pchan);
        return ret;
}

static int sanitize_config(struct dma_slave_config *sconfig,
                           enum dma_transfer_direction direction)
{
        switch (direction) {
        case DMA_MEM_TO_DEV:
                if ((sconfig->dst_addr_width == DMA_SLAVE_BUSWIDTH_UNDEFINED) ||
                    !sconfig->dst_maxburst)
                        return -EINVAL;

                if (sconfig->src_addr_width == DMA_SLAVE_BUSWIDTH_UNDEFINED)
                        sconfig->src_addr_width = sconfig->dst_addr_width;

                if (!sconfig->src_maxburst)
                        sconfig->src_maxburst = sconfig->dst_maxburst;

                break;

        case DMA_DEV_TO_MEM:
                if ((sconfig->src_addr_width == DMA_SLAVE_BUSWIDTH_UNDEFINED) ||
                    !sconfig->src_maxburst)
                        return -EINVAL;

                if (sconfig->dst_addr_width == DMA_SLAVE_BUSWIDTH_UNDEFINED)
                        sconfig->dst_addr_width = sconfig->src_addr_width;

                if (!sconfig->dst_maxburst)
                        sconfig->dst_maxburst = sconfig->src_maxburst;

                break;
        default:
                return 0;
        }

        return 0;
}

/*
 * Generate a promise, to be used in a normal DMA contract.
 *
 * A NDMA promise contains all the information required to program the
 * normal part of the DMA Engine and get data copied. A non-executed
 * promise will live in the demands list on a contract. Once it has been
 * completed, it will be moved to the completed demands list for later freeing.
 * All linked promises will be freed when the corresponding contract is freed
 */
static struct sun4i_dma_promise *
generate_ndma_promise(struct dma_chan *chan, dma_addr_t src, dma_addr_t dest,
                      size_t len, struct dma_slave_config *sconfig,
                      enum dma_transfer_direction direction)
{
        struct sun4i_dma_promise *promise;
        int ret;

        ret = sanitize_config(sconfig, direction);
        if (ret)
                return NULL;

        promise = kzalloc(sizeof(*promise), GFP_NOWAIT);
        if (!promise)
                return NULL;

        promise->src = src;
        promise->dst = dest;
        promise->len = len;
        promise->cfg = SUN4I_DMA_CFG_LOADING |
                SUN4I_NDMA_CFG_BYTE_COUNT_MODE_REMAIN;

        dev_dbg(chan2dev(chan),
                "src burst %d, dst burst %d, src buswidth %d, dst buswidth %d",
                sconfig->src_maxburst, sconfig->dst_maxburst,
                sconfig->src_addr_width, sconfig->dst_addr_width);

        /* Source burst */
        ret = convert_burst(sconfig->src_maxburst);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_SRC_BURST_LENGTH(ret);

        /* Destination burst */
        ret = convert_burst(sconfig->dst_maxburst);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_DST_BURST_LENGTH(ret);

        /* Source bus width */
        ret = convert_buswidth(sconfig->src_addr_width);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_SRC_DATA_WIDTH(ret);

        /* Destination bus width */
        ret = convert_buswidth(sconfig->dst_addr_width);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_DST_DATA_WIDTH(ret);

        return promise;

fail:
        kfree(promise);
        return NULL;
}

/*
 * Generate a promise, to be used in a dedicated DMA contract.
 *
 * A DDMA promise contains all the information required to program the
 * Dedicated part of the DMA Engine and get data copied. A non-executed
 * promise will live in the demands list on a contract. Once it has been
 * completed, it will be moved to the completed demands list for later freeing.
 * All linked promises will be freed when the corresponding contract is freed
 */
static struct sun4i_dma_promise *
generate_ddma_promise(struct dma_chan *chan, dma_addr_t src, dma_addr_t dest,
                      size_t len, struct dma_slave_config *sconfig)
{
        struct sun4i_dma_promise *promise;
        int ret;

        promise = kzalloc(sizeof(*promise), GFP_NOWAIT);
        if (!promise)
                return NULL;

        promise->src = src;
        promise->dst = dest;
        promise->len = len;
        promise->cfg = SUN4I_DMA_CFG_LOADING |
                SUN4I_DDMA_CFG_BYTE_COUNT_MODE_REMAIN;

        /* Source burst */
        ret = convert_burst(sconfig->src_maxburst);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_SRC_BURST_LENGTH(ret);

        /* Destination burst */
        ret = convert_burst(sconfig->dst_maxburst);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_DST_BURST_LENGTH(ret);

        /* Source bus width */
        ret = convert_buswidth(sconfig->src_addr_width);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_SRC_DATA_WIDTH(ret);

        /* Destination bus width */
        ret = convert_buswidth(sconfig->dst_addr_width);
        if (ret < 0)
                goto fail;
        promise->cfg |= SUN4I_DMA_CFG_DST_DATA_WIDTH(ret);

        return promise;

fail:
        kfree(promise);
        return NULL;
}

/*
 * Generate a contract
 *
 * Contracts function as DMA descriptors. As our hardware does not support
 * linked lists, we need to implement SG via software. We use a contract
 * to hold all the pieces of the request and process them serially one
 * after another. Each piece is represented as a promise.
 */
static struct sun4i_dma_contract *generate_dma_contract(void)
{
        struct sun4i_dma_contract *contract;

        contract = kzalloc(sizeof(*contract), GFP_NOWAIT);
        if (!contract)
                return NULL;

        INIT_LIST_HEAD(&contract->demands);
        INIT_LIST_HEAD(&contract->completed_demands);

        return contract;
}

/*
 * Get next promise on a cyclic transfer
 *
 * Cyclic contracts contain a series of promises which are executed on a
 * loop. This function returns the next promise from a cyclic contract,
 * so it can be programmed into the hardware.
 */
static struct sun4i_dma_promise *
get_next_cyclic_promise(struct sun4i_dma_contract *contract)
{
        struct sun4i_dma_promise *promise;

        promise = list_first_entry_or_null(&contract->demands,
                                           struct sun4i_dma_promise, list);
        if (!promise) {
                list_splice_init(&contract->completed_demands,
                                 &contract->demands);
                promise = list_first_entry(&contract->demands,
                                           struct sun4i_dma_promise, list);
        }

        return promise;
}

/*
 * Free a contract and all its associated promises
 */
static void sun4i_dma_free_contract(struct virt_dma_desc *vd)
{
        struct sun4i_dma_contract *contract = to_sun4i_dma_contract(vd);
        struct sun4i_dma_promise *promise, *tmp;

        /* Free all the demands and completed demands */
        list_for_each_entry_safe(promise, tmp, &contract->demands, list)
                kfree(promise);

        list_for_each_entry_safe(promise, tmp, &contract->completed_demands, list)
                kfree(promise);

        kfree(contract);
}

static struct dma_async_tx_descriptor *
sun4i_dma_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest,
                          dma_addr_t src, size_t len, unsigned long flags)
{
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);
        struct dma_slave_config *sconfig = &vchan->cfg;
        struct sun4i_dma_promise *promise;
        struct sun4i_dma_contract *contract;

        contract = generate_dma_contract();
        if (!contract)
                return NULL;

        /*
         * We can only do the copy to bus aligned addresses, so
         * choose the best one so we get decent performance. We also
         * maximize the burst size for this same reason.
         */
        sconfig->src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
        sconfig->dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
        sconfig->src_maxburst = 8;
        sconfig->dst_maxburst = 8;

        if (vchan->is_dedicated)
                promise = generate_ddma_promise(chan, src, dest, len, sconfig);
        else
                promise = generate_ndma_promise(chan, src, dest, len, sconfig,
                                                DMA_MEM_TO_MEM);

        if (!promise) {
                kfree(contract);
                return NULL;
        }

        /* Configure memcpy mode */
        if (vchan->is_dedicated) {
                promise->cfg |= SUN4I_DMA_CFG_SRC_DRQ_TYPE(SUN4I_DDMA_DRQ_TYPE_SDRAM) |
                                SUN4I_DMA_CFG_DST_DRQ_TYPE(SUN4I_DDMA_DRQ_TYPE_SDRAM);
        } else {
                promise->cfg |= SUN4I_DMA_CFG_SRC_DRQ_TYPE(SUN4I_NDMA_DRQ_TYPE_SDRAM) |
                                SUN4I_DMA_CFG_DST_DRQ_TYPE(SUN4I_NDMA_DRQ_TYPE_SDRAM);
        }

        /* Fill the contract with our only promise */
        list_add_tail(&promise->list, &contract->demands);

        /* And add it to the vchan */
        return vchan_tx_prep(&vchan->vc, &contract->vd, flags);
}

static struct dma_async_tx_descriptor *
sun4i_dma_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf, size_t len,
                          size_t period_len, enum dma_transfer_direction dir,
                          unsigned long flags)
{
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);
        struct dma_slave_config *sconfig = &vchan->cfg;
        struct sun4i_dma_promise *promise;
        struct sun4i_dma_contract *contract;
        dma_addr_t src, dest;
        u32 endpoints;
        int nr_periods, offset, plength, i;
        u8 ram_type, io_mode, linear_mode;

        if (!is_slave_direction(dir)) {
                dev_err(chan2dev(chan), "Invalid DMA direction\n");
                return NULL;
        }

        contract = generate_dma_contract();
        if (!contract)
                return NULL;

        contract->is_cyclic = 1;

        if (vchan->is_dedicated) {
                io_mode = SUN4I_DDMA_ADDR_MODE_IO;
                linear_mode = SUN4I_DDMA_ADDR_MODE_LINEAR;
                ram_type = SUN4I_DDMA_DRQ_TYPE_SDRAM;
        } else {
                io_mode = SUN4I_NDMA_ADDR_MODE_IO;
                linear_mode = SUN4I_NDMA_ADDR_MODE_LINEAR;
                ram_type = SUN4I_NDMA_DRQ_TYPE_SDRAM;
        }

        if (dir == DMA_MEM_TO_DEV) {
                src = buf;
                dest = sconfig->dst_addr;
                endpoints = SUN4I_DMA_CFG_DST_DRQ_TYPE(vchan->endpoint) |
                            SUN4I_DMA_CFG_DST_ADDR_MODE(io_mode) |
                            SUN4I_DMA_CFG_SRC_DRQ_TYPE(ram_type) |
                            SUN4I_DMA_CFG_SRC_ADDR_MODE(linear_mode);
        } else {
                src = sconfig->src_addr;
                dest = buf;
                endpoints = SUN4I_DMA_CFG_DST_DRQ_TYPE(ram_type) |
                            SUN4I_DMA_CFG_DST_ADDR_MODE(linear_mode) |
                            SUN4I_DMA_CFG_SRC_DRQ_TYPE(vchan->endpoint) |
                            SUN4I_DMA_CFG_SRC_ADDR_MODE(io_mode);
        }

        /*
         * We will be using half done interrupts to make two periods
         * out of a promise, so we need to program the DMA engine less
         * often
         */

        /*
         * The engine can interrupt on half-transfer, so we can use
         * this feature to program the engine half as often as if we
         * didn't use it (keep in mind the hardware doesn't support
         * linked lists).
         *
         * Say you have a set of periods (| marks the start/end, I for
         * interrupt, P for programming the engine to do a new
         * transfer), the easy but slow way would be to do
         *
         *  |---|---|---|---| (periods / promises)
         *  P  I,P I,P I,P  I
         *
         * Using half transfer interrupts you can do
         *
         *  |-------|-------| (promises as configured on hw)
         *  |---|---|---|---| (periods)
         *  P   I  I,P  I   I
         *
         * Which requires half the engine programming for the same
         * functionality.
         */
        nr_periods = DIV_ROUND_UP(len / period_len, 2);
        for (i = 0; i < nr_periods; i++) {
                /* Calculate the offset in the buffer and the length needed */
                offset = i * period_len * 2;
                plength = min((len - offset), (period_len * 2));
                if (dir == DMA_MEM_TO_DEV)
                        src = buf + offset;
                else
                        dest = buf + offset;

                /* Make the promise */
                if (vchan->is_dedicated)
                        promise = generate_ddma_promise(chan, src, dest,
                                                        plength, sconfig);
                else
                        promise = generate_ndma_promise(chan, src, dest,
                                                        plength, sconfig, dir);

                if (!promise) {
                        /* TODO: should we free everything? */
                        return NULL;
                }
                promise->cfg |= endpoints;

                /* Then add it to the contract */
                list_add_tail(&promise->list, &contract->demands);
        }

        /* And add it to the vchan */
        return vchan_tx_prep(&vchan->vc, &contract->vd, flags);
}

static struct dma_async_tx_descriptor *
sun4i_dma_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 sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);
        struct dma_slave_config *sconfig = &vchan->cfg;
        struct sun4i_dma_promise *promise;
        struct sun4i_dma_contract *contract;
        u8 ram_type, io_mode, linear_mode;
        struct scatterlist *sg;
        dma_addr_t srcaddr, dstaddr;
        u32 endpoints, para;
        int i;

        if (!sgl)
                return NULL;

        if (!is_slave_direction(dir)) {
                dev_err(chan2dev(chan), "Invalid DMA direction\n");
                return NULL;
        }

        contract = generate_dma_contract();
        if (!contract)
                return NULL;

        if (vchan->is_dedicated) {
                io_mode = SUN4I_DDMA_ADDR_MODE_IO;
                linear_mode = SUN4I_DDMA_ADDR_MODE_LINEAR;
                ram_type = SUN4I_DDMA_DRQ_TYPE_SDRAM;
        } else {
                io_mode = SUN4I_NDMA_ADDR_MODE_IO;
                linear_mode = SUN4I_NDMA_ADDR_MODE_LINEAR;
                ram_type = SUN4I_NDMA_DRQ_TYPE_SDRAM;
        }

        if (dir == DMA_MEM_TO_DEV)
                endpoints = SUN4I_DMA_CFG_DST_DRQ_TYPE(vchan->endpoint) |
                            SUN4I_DMA_CFG_DST_ADDR_MODE(io_mode) |
                            SUN4I_DMA_CFG_SRC_DRQ_TYPE(ram_type) |
                            SUN4I_DMA_CFG_SRC_ADDR_MODE(linear_mode);
        else
                endpoints = SUN4I_DMA_CFG_DST_DRQ_TYPE(ram_type) |
                            SUN4I_DMA_CFG_DST_ADDR_MODE(linear_mode) |
                            SUN4I_DMA_CFG_SRC_DRQ_TYPE(vchan->endpoint) |
                            SUN4I_DMA_CFG_SRC_ADDR_MODE(io_mode);

        for_each_sg(sgl, sg, sg_len, i) {
                /* Figure out addresses */
                if (dir == DMA_MEM_TO_DEV) {
                        srcaddr = sg_dma_address(sg);
                        dstaddr = sconfig->dst_addr;
                } else {
                        srcaddr = sconfig->src_addr;
                        dstaddr = sg_dma_address(sg);
                }

                /*
                 * These are the magic DMA engine timings that keep SPI going.
                 * I haven't seen any interface on DMAEngine to configure
                 * timings, and so far they seem to work for everything we
                 * support, so I've kept them here. I don't know if other
                 * devices need different timings because, as usual, we only
                 * have the "para" bitfield meanings, but no comment on what
                 * the values should be when doing a certain operation :|
                 */
                para = SUN4I_DDMA_MAGIC_SPI_PARAMETERS;

                /* And make a suitable promise */
                if (vchan->is_dedicated)
                        promise = generate_ddma_promise(chan, srcaddr, dstaddr,
                                                        sg_dma_len(sg),
                                                        sconfig);
                else
                        promise = generate_ndma_promise(chan, srcaddr, dstaddr,
                                                        sg_dma_len(sg),
                                                        sconfig, dir);

                if (!promise)
                        return NULL; /* TODO: should we free everything? */

                promise->cfg |= endpoints;
                promise->para = para;

                /* Then add it to the contract */
                list_add_tail(&promise->list, &contract->demands);
        }

        /*
         * Once we've got all the promises ready, add the contract
         * to the pending list on the vchan
         */
        return vchan_tx_prep(&vchan->vc, &contract->vd, flags);
}

static int sun4i_dma_terminate_all(struct dma_chan *chan)
{
        struct sun4i_dma_dev *priv = to_sun4i_dma_dev(chan->device);
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);
        struct sun4i_dma_pchan *pchan = vchan->pchan;
        LIST_HEAD(head);
        unsigned long flags;

        spin_lock_irqsave(&vchan->vc.lock, flags);
        vchan_get_all_descriptors(&vchan->vc, &head);
        spin_unlock_irqrestore(&vchan->vc.lock, flags);

        /*
         * Clearing the configuration register will halt the pchan. Interrupts
         * may still trigger, so don't forget to disable them.
         */
        if (pchan) {
                if (pchan->is_dedicated)
                        writel(0, pchan->base + SUN4I_DDMA_CFG_REG);
                else
                        writel(0, pchan->base + SUN4I_NDMA_CFG_REG);
                set_pchan_interrupt(priv, pchan, 0, 0);
                release_pchan(priv, pchan);
        }

        spin_lock_irqsave(&vchan->vc.lock, flags);
        /* Clear these so the vchan is usable again */
        vchan->processing = NULL;
        vchan->pchan = NULL;
        spin_unlock_irqrestore(&vchan->vc.lock, flags);

        vchan_dma_desc_free_list(&vchan->vc, &head);

        return 0;
}

static int sun4i_dma_config(struct dma_chan *chan,
                            struct dma_slave_config *config)
{
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);

        memcpy(&vchan->cfg, config, sizeof(*config));

        return 0;
}

static struct dma_chan *sun4i_dma_of_xlate(struct of_phandle_args *dma_spec,
                                           struct of_dma *ofdma)
{
        struct sun4i_dma_dev *priv = ofdma->of_dma_data;
        struct sun4i_dma_vchan *vchan;
        struct dma_chan *chan;
        u8 is_dedicated = dma_spec->args[0];
        u8 endpoint = dma_spec->args[1];

        /* Check if type is Normal or Dedicated */
        if (is_dedicated != 0 && is_dedicated != 1)
                return NULL;

        /* Make sure the endpoint looks sane */
        if ((is_dedicated && endpoint >= SUN4I_DDMA_DRQ_TYPE_LIMIT) ||
            (!is_dedicated && endpoint >= SUN4I_NDMA_DRQ_TYPE_LIMIT))
                return NULL;

        chan = dma_get_any_slave_channel(&priv->slave);
        if (!chan)
                return NULL;

        /* Assign the endpoint to the vchan */
        vchan = to_sun4i_dma_vchan(chan);
        vchan->is_dedicated = is_dedicated;
        vchan->endpoint = endpoint;

        return chan;
}

static enum dma_status sun4i_dma_tx_status(struct dma_chan *chan,
                                           dma_cookie_t cookie,
                                           struct dma_tx_state *state)
{
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);
        struct sun4i_dma_pchan *pchan = vchan->pchan;
        struct sun4i_dma_contract *contract;
        struct sun4i_dma_promise *promise;
        struct virt_dma_desc *vd;
        unsigned long flags;
        enum dma_status ret;
        size_t bytes = 0;

        ret = dma_cookie_status(chan, cookie, state);
        if (!state || (ret == DMA_COMPLETE))
                return ret;

        spin_lock_irqsave(&vchan->vc.lock, flags);
        vd = vchan_find_desc(&vchan->vc, cookie);
        if (!vd)
                goto exit;
        contract = to_sun4i_dma_contract(vd);

        list_for_each_entry(promise, &contract->demands, list)
                bytes += promise->len;

        /*
         * The hardware is configured to return the remaining byte
         * quantity. If possible, replace the first listed element's
         * full size with the actual remaining amount
         */
        promise = list_first_entry_or_null(&contract->demands,
                                           struct sun4i_dma_promise, list);
        if (promise && pchan) {
                bytes -= promise->len;
                if (pchan->is_dedicated)
                        bytes += readl(pchan->base + SUN4I_DDMA_BYTE_COUNT_REG);
                else
                        bytes += readl(pchan->base + SUN4I_NDMA_BYTE_COUNT_REG);
        }

exit:

        dma_set_residue(state, bytes);
        spin_unlock_irqrestore(&vchan->vc.lock, flags);

        return ret;
}

static void sun4i_dma_issue_pending(struct dma_chan *chan)
{
        struct sun4i_dma_dev *priv = to_sun4i_dma_dev(chan->device);
        struct sun4i_dma_vchan *vchan = to_sun4i_dma_vchan(chan);
        unsigned long flags;

        spin_lock_irqsave(&vchan->vc.lock, flags);

        /*

         * If there are pending transactions for this vchan, push one of
         * them into the engine to get the ball rolling.
         */
        if (vchan_issue_pending(&vchan->vc))
                __execute_vchan_pending(priv, vchan);

        spin_unlock_irqrestore(&vchan->vc.lock, flags);
}

static irqreturn_t sun4i_dma_interrupt(int irq, void *dev_id)
{
        struct sun4i_dma_dev *priv = dev_id;
        struct sun4i_dma_pchan *pchans = priv->pchans, *pchan;
        struct sun4i_dma_vchan *vchan;
        struct sun4i_dma_contract *contract;
        struct sun4i_dma_promise *promise;
        unsigned long pendirq, irqs, disableirqs;
        int bit, i, free_room, allow_mitigation = 1;

        pendirq = readl_relaxed(priv->base + SUN4I_DMA_IRQ_PENDING_STATUS_REG);

handle_pending:

        disableirqs = 0;
        free_room = 0;

        for_each_set_bit(bit, &pendirq, 32) {
                pchan = &pchans[bit >> 1];
                vchan = pchan->vchan;
                if (!vchan) /* a terminated channel may still interrupt */
                        continue;
                contract = vchan->contract;

                /*
                 * Disable the IRQ and free the pchan if it's an end
                 * interrupt (odd bit)
                 */
                if (bit & 1) {
                        spin_lock(&vchan->vc.lock);

                        /*
                         * Move the promise into the completed list now that
                         * we're done with it
                         */
                        list_move_tail(&vchan->processing->list,
                                       &contract->completed_demands);

                        /*
                         * Cyclic DMA transfers are special:
                         * - There's always something we can dispatch
                         * - We need to run the callback
                         * - Latency is very important, as this is used by audio
                         * We therefore just cycle through the list and dispatch
                         * whatever we have here, reusing the pchan. There's
                         * no need to run the thread after this.
                         *
                         * For non-cyclic transfers we need to look around,
                         * so we can program some more work, or notify the
                         * client that their transfers have been completed.
                         */
                        if (contract->is_cyclic) {
                                promise = get_next_cyclic_promise(contract);
                                vchan->processing = promise;
                                configure_pchan(pchan, promise);
                                vchan_cyclic_callback(&contract->vd);
                        } else {
                                vchan->processing = NULL;
                                vchan->pchan = NULL;

                                free_room = 1;
                                disableirqs |= BIT(bit);
                                release_pchan(priv, pchan);
                        }

                        spin_unlock(&vchan->vc.lock);
                } else {
                        /* Half done interrupt */
                        if (contract->is_cyclic)
                                vchan_cyclic_callback(&contract->vd);
                        else
                                disableirqs |= BIT(bit);
                }
        }

        /* Disable the IRQs for events we handled */
        spin_lock(&priv->lock);
        irqs = readl_relaxed(priv->base + SUN4I_DMA_IRQ_ENABLE_REG);
        writel_relaxed(irqs & ~disableirqs,
                       priv->base + SUN4I_DMA_IRQ_ENABLE_REG);
        spin_unlock(&priv->lock);

        /* Writing 1 to the pending field will clear the pending interrupt */
        writel_relaxed(pendirq, priv->base + SUN4I_DMA_IRQ_PENDING_STATUS_REG);

        /*
         * If a pchan was freed, we may be able to schedule something else,
         * so have a look around
         */
        if (free_room) {
                for (i = 0; i < SUN4I_DMA_NR_MAX_VCHANS; i++) {
                        vchan = &priv->vchans[i];
                        spin_lock(&vchan->vc.lock);
                        __execute_vchan_pending(priv, vchan);
                        spin_unlock(&vchan->vc.lock);
                }
        }

        /*
         * Handle newer interrupts if some showed up, but only do it once
         * to avoid a too long a loop
         */
        if (allow_mitigation) {
                pendirq = readl_relaxed(priv->base +
                                        SUN4I_DMA_IRQ_PENDING_STATUS_REG);
                if (pendirq) {
                        allow_mitigation = 0;
                        goto handle_pending;
                }
        }

        return IRQ_HANDLED;
}

static int sun4i_dma_probe(struct platform_device *pdev)
{
        struct sun4i_dma_dev *priv;
        struct resource *res;
        int i, j, ret;

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

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        priv->base = devm_ioremap_resource(&pdev->dev, res);
        if (IS_ERR(priv->base))
                return PTR_ERR(priv->base);

        priv->irq = platform_get_irq(pdev, 0);
        if (priv->irq < 0)
                return priv->irq;

        priv->clk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(priv->clk)) {
                dev_err(&pdev->dev, "No clock specified\n");
                return PTR_ERR(priv->clk);
        }

        platform_set_drvdata(pdev, priv);
        spin_lock_init(&priv->lock);

        dma_cap_zero(priv->slave.cap_mask);
        dma_cap_set(DMA_PRIVATE, priv->slave.cap_mask);
        dma_cap_set(DMA_MEMCPY, priv->slave.cap_mask);
        dma_cap_set(DMA_CYCLIC, priv->slave.cap_mask);
        dma_cap_set(DMA_SLAVE, priv->slave.cap_mask);

        INIT_LIST_HEAD(&priv->slave.channels);
        priv->slave.device_free_chan_resources  = sun4i_dma_free_chan_resources;
        priv->slave.device_tx_status            = sun4i_dma_tx_status;
        priv->slave.device_issue_pending        = sun4i_dma_issue_pending;
        priv->slave.device_prep_slave_sg        = sun4i_dma_prep_slave_sg;
        priv->slave.device_prep_dma_memcpy      = sun4i_dma_prep_dma_memcpy;
        priv->slave.device_prep_dma_cyclic      = sun4i_dma_prep_dma_cyclic;
        priv->slave.device_config               = sun4i_dma_config;
        priv->slave.device_terminate_all        = sun4i_dma_terminate_all;
        priv->slave.copy_align                  = 2;
        priv->slave.src_addr_widths             = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
                                                  BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
                                                  BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
        priv->slave.dst_addr_widths             = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
                                                  BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
                                                  BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
        priv->slave.directions                  = BIT(DMA_DEV_TO_MEM) |
                                                  BIT(DMA_MEM_TO_DEV);
        priv->slave.residue_granularity         = DMA_RESIDUE_GRANULARITY_BURST;

        priv->slave.dev = &pdev->dev;

        priv->pchans = devm_kcalloc(&pdev->dev, SUN4I_DMA_NR_MAX_CHANNELS,
                                    sizeof(struct sun4i_dma_pchan), GFP_KERNEL);
        priv->vchans = devm_kcalloc(&pdev->dev, SUN4I_DMA_NR_MAX_VCHANS,
                                    sizeof(struct sun4i_dma_vchan), GFP_KERNEL);
        if (!priv->vchans || !priv->pchans)
                return -ENOMEM;

        /*
         * [0..SUN4I_NDMA_NR_MAX_CHANNELS) are normal pchans, and
         * [SUN4I_NDMA_NR_MAX_CHANNELS..SUN4I_DMA_NR_MAX_CHANNELS) are
         * dedicated ones
         */
        for (i = 0; i < SUN4I_NDMA_NR_MAX_CHANNELS; i++)
                priv->pchans[i].base = priv->base +
                        SUN4I_NDMA_CHANNEL_REG_BASE(i);

        for (j = 0; i < SUN4I_DMA_NR_MAX_CHANNELS; i++, j++) {
                priv->pchans[i].base = priv->base +
                        SUN4I_DDMA_CHANNEL_REG_BASE(j);
                priv->pchans[i].is_dedicated = 1;
        }

        for (i = 0; i < SUN4I_DMA_NR_MAX_VCHANS; i++) {
                struct sun4i_dma_vchan *vchan = &priv->vchans[i];

                spin_lock_init(&vchan->vc.lock);
                vchan->vc.desc_free = sun4i_dma_free_contract;
                vchan_init(&vchan->vc, &priv->slave);
        }

        ret = clk_prepare_enable(priv->clk);
        if (ret) {
                dev_err(&pdev->dev, "Couldn't enable the clock\n");
                return ret;
        }

        /*
         * Make sure the IRQs are all disabled and accounted for. The bootloader
         * likes to leave these dirty
         */
        writel(0, priv->base + SUN4I_DMA_IRQ_ENABLE_REG);
        writel(0xFFFFFFFF, priv->base + SUN4I_DMA_IRQ_PENDING_STATUS_REG);

        ret = devm_request_irq(&pdev->dev, priv->irq, sun4i_dma_interrupt,
                               0, dev_name(&pdev->dev), priv);
        if (ret) {
                dev_err(&pdev->dev, "Cannot request IRQ\n");
                goto err_clk_disable;
        }

        ret = dma_async_device_register(&priv->slave);
        if (ret) {
                dev_warn(&pdev->dev, "Failed to register DMA engine device\n");
                goto err_clk_disable;
        }

        ret = of_dma_controller_register(pdev->dev.of_node, sun4i_dma_of_xlate,
                                         priv);
        if (ret) {
                dev_err(&pdev->dev, "of_dma_controller_register failed\n");
                goto err_dma_unregister;
        }

        dev_dbg(&pdev->dev, "Successfully probed SUN4I_DMA\n");

        return 0;

err_dma_unregister:
        dma_async_device_unregister(&priv->slave);
err_clk_disable:
        clk_disable_unprepare(priv->clk);
        return ret;
}

static int sun4i_dma_remove(struct platform_device *pdev)
{
        struct sun4i_dma_dev *priv = platform_get_drvdata(pdev);

        /* Disable IRQ so no more work is scheduled */
        disable_irq(priv->irq);

        of_dma_controller_free(pdev->dev.of_node);
        dma_async_device_unregister(&priv->slave);

        clk_disable_unprepare(priv->clk);

        return 0;
}

static const struct of_device_id sun4i_dma_match[] = {
        { .compatible = "allwinner,sun4i-a10-dma" },
        { /* sentinel */ },
};
MODULE_DEVICE_TABLE(of, sun4i_dma_match);

static struct platform_driver sun4i_dma_driver = {
        .probe  = sun4i_dma_probe,
        .remove = sun4i_dma_remove,
        .driver = {
                .name           = "sun4i-dma",
                .of_match_table = sun4i_dma_match,
        },
};

module_platform_driver(sun4i_dma_driver);

MODULE_DESCRIPTION("Allwinner A10 Dedicated DMA Controller Driver");
MODULE_AUTHOR("Emilio López <emilio@elopez.com.ar>");
MODULE_LICENSE("GPL");