// SPDX-License-Identifier: GPL-2.0+
/*
 * BCM2835 DMA engine support
 *
 * Author:      Florian Meier <florian.meier@koalo.de>
 *              Copyright 2013
 *
 * Based on
 *      OMAP DMAengine support by Russell King
 *
 *      BCM2708 DMA Driver
 *      Copyright (C) 2010 Broadcom
 *
 *      Raspberry Pi PCM I2S ALSA Driver
 *      Copyright (c) by Phil Poole 2013
 *
 *      MARVELL MMP Peripheral DMA Driver
 *      Copyright 2012 Marvell International Ltd.
 */
#include <linux/dmaengine.h>
#include <linux/dma-mapping.h>
#include <linux/dmapool.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/spinlock.h>
#include <linux/of.h>
#include <linux/of_dma.h>

#include "virt-dma.h"

#define BCM2835_DMA_MAX_DMA_CHAN_SUPPORTED 14
#define BCM2835_DMA_CHAN_NAME_SIZE 8

/**
 * struct bcm2835_dmadev - BCM2835 DMA controller
 * @ddev: DMA device
 * @base: base address of register map
 * @zero_page: bus address of zero page (to detect transactions copying from
 *      zero page and avoid accessing memory if so)
 */
struct bcm2835_dmadev {
        struct dma_device ddev;
        void __iomem *base;
        dma_addr_t zero_page;
};

struct bcm2835_dma_cb {
        uint32_t info;
        uint32_t src;
        uint32_t dst;
        uint32_t length;
        uint32_t stride;
        uint32_t next;
        uint32_t pad[2];
};

struct bcm2835_cb_entry {
        struct bcm2835_dma_cb *cb;
        dma_addr_t paddr;
};

struct bcm2835_chan {
        struct virt_dma_chan vc;

        struct dma_slave_config cfg;
        unsigned int dreq;

        int ch;
        struct bcm2835_desc *desc;
        struct dma_pool *cb_pool;

        void __iomem *chan_base;
        int irq_number;
        unsigned int irq_flags;

        bool is_lite_channel;
};

struct bcm2835_desc {
        struct bcm2835_chan *c;
        struct virt_dma_desc vd;
        enum dma_transfer_direction dir;

        unsigned int frames;
        size_t size;

        bool cyclic;

        struct bcm2835_cb_entry cb_list[];
};

#define BCM2835_DMA_CS          0x00
#define BCM2835_DMA_ADDR        0x04
#define BCM2835_DMA_TI          0x08
#define BCM2835_DMA_SOURCE_AD   0x0c
#define BCM2835_DMA_DEST_AD     0x10
#define BCM2835_DMA_LEN         0x14
#define BCM2835_DMA_STRIDE      0x18
#define BCM2835_DMA_NEXTCB      0x1c
#define BCM2835_DMA_DEBUG       0x20

/* DMA CS Control and Status bits */
#define BCM2835_DMA_ACTIVE      BIT(0)  /* activate the DMA */
#define BCM2835_DMA_END         BIT(1)  /* current CB has ended */
#define BCM2835_DMA_INT         BIT(2)  /* interrupt status */
#define BCM2835_DMA_DREQ        BIT(3)  /* DREQ state */
#define BCM2835_DMA_ISPAUSED    BIT(4)  /* Pause requested or not active */
#define BCM2835_DMA_ISHELD      BIT(5)  /* Is held by DREQ flow control */
#define BCM2835_DMA_WAITING_FOR_WRITES BIT(6) /* waiting for last
                                               * AXI-write to ack
                                               */
#define BCM2835_DMA_ERR         BIT(8)
#define BCM2835_DMA_PRIORITY(x) ((x & 15) << 16) /* AXI priority */
#define BCM2835_DMA_PANIC_PRIORITY(x) ((x & 15) << 20) /* panic priority */
/* current value of TI.BCM2835_DMA_WAIT_RESP */
#define BCM2835_DMA_WAIT_FOR_WRITES BIT(28)
#define BCM2835_DMA_DIS_DEBUG   BIT(29) /* disable debug pause signal */
#define BCM2835_DMA_ABORT       BIT(30) /* Stop current CB, go to next, WO */
#define BCM2835_DMA_RESET       BIT(31) /* WO, self clearing */

/* Transfer information bits - also bcm2835_cb.info field */
#define BCM2835_DMA_INT_EN      BIT(0)
#define BCM2835_DMA_TDMODE      BIT(1) /* 2D-Mode */
#define BCM2835_DMA_WAIT_RESP   BIT(3) /* wait for AXI-write to be acked */
#define BCM2835_DMA_D_INC       BIT(4)
#define BCM2835_DMA_D_WIDTH     BIT(5) /* 128bit writes if set */
#define BCM2835_DMA_D_DREQ      BIT(6) /* enable DREQ for destination */
#define BCM2835_DMA_D_IGNORE    BIT(7) /* ignore destination writes */
#define BCM2835_DMA_S_INC       BIT(8)
#define BCM2835_DMA_S_WIDTH     BIT(9) /* 128bit writes if set */
#define BCM2835_DMA_S_DREQ      BIT(10) /* enable SREQ for source */
#define BCM2835_DMA_S_IGNORE    BIT(11) /* ignore source reads - read 0 */
#define BCM2835_DMA_BURST_LENGTH(x) ((x & 15) << 12)
#define BCM2835_DMA_PER_MAP(x)  ((x & 31) << 16) /* REQ source */
#define BCM2835_DMA_WAIT(x)     ((x & 31) << 21) /* add DMA-wait cycles */
#define BCM2835_DMA_NO_WIDE_BURSTS BIT(26) /* no 2 beat write bursts */

/* debug register bits */
#define BCM2835_DMA_DEBUG_LAST_NOT_SET_ERR      BIT(0)
#define BCM2835_DMA_DEBUG_FIFO_ERR              BIT(1)
#define BCM2835_DMA_DEBUG_READ_ERR              BIT(2)
#define BCM2835_DMA_DEBUG_OUTSTANDING_WRITES_SHIFT 4
#define BCM2835_DMA_DEBUG_OUTSTANDING_WRITES_BITS 4
#define BCM2835_DMA_DEBUG_ID_SHIFT              16
#define BCM2835_DMA_DEBUG_ID_BITS               9
#define BCM2835_DMA_DEBUG_STATE_SHIFT           16
#define BCM2835_DMA_DEBUG_STATE_BITS            9
#define BCM2835_DMA_DEBUG_VERSION_SHIFT         25
#define BCM2835_DMA_DEBUG_VERSION_BITS          3
#define BCM2835_DMA_DEBUG_LITE                  BIT(28)

/* shared registers for all dma channels */
#define BCM2835_DMA_INT_STATUS         0xfe0
#define BCM2835_DMA_ENABLE             0xff0

#define BCM2835_DMA_DATA_TYPE_S8        1
#define BCM2835_DMA_DATA_TYPE_S16       2
#define BCM2835_DMA_DATA_TYPE_S32       4
#define BCM2835_DMA_DATA_TYPE_S128      16

/* Valid only for channels 0 - 14, 15 has its own base address */
#define BCM2835_DMA_CHAN(n)     ((n) << 8) /* Base address */
#define BCM2835_DMA_CHANIO(base, n) ((base) + BCM2835_DMA_CHAN(n))

/* the max dma length for different channels */
#define MAX_DMA_LEN SZ_1G
#define MAX_LITE_DMA_LEN (SZ_64K - 4)

static inline size_t bcm2835_dma_max_frame_length(struct bcm2835_chan *c)
{
        /* lite and normal channels have different max frame length */
        return c->is_lite_channel ? MAX_LITE_DMA_LEN : MAX_DMA_LEN;
}

/* how many frames of max_len size do we need to transfer len bytes */
static inline size_t bcm2835_dma_frames_for_length(size_t len,
                                                   size_t max_len)
{
        return DIV_ROUND_UP(len, max_len);
}

static inline struct bcm2835_dmadev *to_bcm2835_dma_dev(struct dma_device *d)
{
        return container_of(d, struct bcm2835_dmadev, ddev);
}

static inline struct bcm2835_chan *to_bcm2835_dma_chan(struct dma_chan *c)
{
        return container_of(c, struct bcm2835_chan, vc.chan);
}

static inline struct bcm2835_desc *to_bcm2835_dma_desc(
                struct dma_async_tx_descriptor *t)
{
        return container_of(t, struct bcm2835_desc, vd.tx);
}

static void bcm2835_dma_free_cb_chain(struct bcm2835_desc *desc)
{
        size_t i;

        for (i = 0; i < desc->frames; i++)
                dma_pool_free(desc->c->cb_pool, desc->cb_list[i].cb,
                              desc->cb_list[i].paddr);

        kfree(desc);
}

static void bcm2835_dma_desc_free(struct virt_dma_desc *vd)
{
        bcm2835_dma_free_cb_chain(
                container_of(vd, struct bcm2835_desc, vd));
}

static void bcm2835_dma_create_cb_set_length(
        struct bcm2835_chan *chan,
        struct bcm2835_dma_cb *control_block,
        size_t len,
        size_t period_len,
        size_t *total_len,
        u32 finalextrainfo)
{
        size_t max_len = bcm2835_dma_max_frame_length(chan);

        /* set the length taking lite-channel limitations into account */
        control_block->length = min_t(u32, len, max_len);

        /* finished if we have no period_length */
        if (!period_len)
                return;

        /*
         * period_len means: that we need to generate
         * transfers that are terminating at every
         * multiple of period_len - this is typically
         * used to set the interrupt flag in info
         * which is required during cyclic transfers
         */

        /* have we filled in period_length yet? */
        if (*total_len + control_block->length < period_len) {
                /* update number of bytes in this period so far */
                *total_len += control_block->length;
                return;
        }

        /* calculate the length that remains to reach period_length */
        control_block->length = period_len - *total_len;

        /* reset total_length for next period */
        *total_len = 0;

        /* add extrainfo bits in info */
        control_block->info |= finalextrainfo;
}

/**
 * bcm2835_dma_create_cb_chain - create a control block and fills data in
 *
 * @chan:           the @dma_chan for which we run this
 * @direction:      the direction in which we transfer
 * @cyclic:         it is a cyclic transfer
 * @info:           the default info bits to apply per controlblock
 * @frames:         number of controlblocks to allocate
 * @src:            the src address to assign (if the S_INC bit is set
 *                  in @info, then it gets incremented)
 * @dst:            the dst address to assign (if the D_INC bit is set
 *                  in @info, then it gets incremented)
 * @buf_len:        the full buffer length (may also be 0)
 * @period_len:     the period length when to apply @finalextrainfo
 *                  in addition to the last transfer
 *                  this will also break some control-blocks early
 * @finalextrainfo: additional bits in last controlblock
 *                  (or when period_len is reached in case of cyclic)
 * @gfp:            the GFP flag to use for allocation
 */
static struct bcm2835_desc *bcm2835_dma_create_cb_chain(
        struct dma_chan *chan, enum dma_transfer_direction direction,
        bool cyclic, u32 info, u32 finalextrainfo, size_t frames,
        dma_addr_t src, dma_addr_t dst, size_t buf_len,
        size_t period_len, gfp_t gfp)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        size_t len = buf_len, total_len;
        size_t frame;
        struct bcm2835_desc *d;
        struct bcm2835_cb_entry *cb_entry;
        struct bcm2835_dma_cb *control_block;

        if (!frames)
                return NULL;

        /* allocate and setup the descriptor. */
        d = kzalloc_flex(*d, cb_list, frames, gfp);
        if (!d)
                return NULL;

        d->c = c;
        d->dir = direction;
        d->cyclic = cyclic;

        /*
         * Iterate over all frames, create a control block
         * for each frame and link them together.
         */
        for (frame = 0, total_len = 0; frame < frames; d->frames++, frame++) {
                cb_entry = &d->cb_list[frame];
                cb_entry->cb = dma_pool_alloc(c->cb_pool, gfp,
                                              &cb_entry->paddr);
                if (!cb_entry->cb)
                        goto error_cb;

                /* fill in the control block */
                control_block = cb_entry->cb;
                control_block->info = info;
                control_block->src = src;
                control_block->dst = dst;
                control_block->stride = 0;
                control_block->next = 0;
                /* set up length in control_block if requested */
                if (buf_len) {
                        /* calculate length honoring period_length */
                        bcm2835_dma_create_cb_set_length(
                                c, control_block,
                                len, period_len, &total_len,
                                cyclic ? finalextrainfo : 0);

                        /* calculate new remaining length */
                        len -= control_block->length;
                }

                /* link this the last controlblock */
                if (frame)
                        d->cb_list[frame - 1].cb->next = cb_entry->paddr;

                /* update src and dst and length */
                if (src && (info & BCM2835_DMA_S_INC))
                        src += control_block->length;
                if (dst && (info & BCM2835_DMA_D_INC))
                        dst += control_block->length;

                /* Length of total transfer */
                d->size += control_block->length;
        }

        /* the last frame requires extra flags */
        d->cb_list[d->frames - 1].cb->info |= finalextrainfo;

        /* detect a size mismatch */
        if (buf_len && (d->size != buf_len))
                goto error_cb;

        return d;
error_cb:
        bcm2835_dma_free_cb_chain(d);

        return NULL;
}

static void bcm2835_dma_fill_cb_chain_with_sg(
        struct dma_chan *chan,
        enum dma_transfer_direction direction,
        struct bcm2835_cb_entry *cb,
        struct scatterlist *sgl,
        unsigned int sg_len)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        size_t len, max_len;
        unsigned int i;
        dma_addr_t addr;
        struct scatterlist *sgent;

        max_len = bcm2835_dma_max_frame_length(c);
        for_each_sg(sgl, sgent, sg_len, i) {
                for (addr = sg_dma_address(sgent), len = sg_dma_len(sgent);
                     len > 0;
                     addr += cb->cb->length, len -= cb->cb->length, cb++) {
                        if (direction == DMA_DEV_TO_MEM)
                                cb->cb->dst = addr;
                        else
                                cb->cb->src = addr;
                        cb->cb->length = min(len, max_len);
                }
        }
}

static void bcm2835_dma_abort(struct bcm2835_chan *c)
{
        void __iomem *chan_base = c->chan_base;
        long int timeout = 10000;

        /*
         * A zero control block address means the channel is idle.
         * (The ACTIVE flag in the CS register is not a reliable indicator.)
         */
        if (!readl(chan_base + BCM2835_DMA_ADDR))
                return;

        /* Write 0 to the active bit - Pause the DMA */
        writel(0, chan_base + BCM2835_DMA_CS);

        /* Wait for any current AXI transfer to complete */
        while ((readl(chan_base + BCM2835_DMA_CS) &
                BCM2835_DMA_WAITING_FOR_WRITES) && --timeout)
                cpu_relax();

        /* Peripheral might be stuck and fail to signal AXI write responses */
        if (!timeout)
                dev_err(c->vc.chan.device->dev,
                        "failed to complete outstanding writes\n");

        writel(BCM2835_DMA_RESET, chan_base + BCM2835_DMA_CS);
}

static void bcm2835_dma_start_desc(struct bcm2835_chan *c)
{
        struct virt_dma_desc *vd = vchan_next_desc(&c->vc);
        struct bcm2835_desc *d;

        if (!vd) {
                c->desc = NULL;
                return;
        }

        list_del(&vd->node);

        c->desc = d = to_bcm2835_dma_desc(&vd->tx);

        writel(d->cb_list[0].paddr, c->chan_base + BCM2835_DMA_ADDR);
        writel(BCM2835_DMA_ACTIVE, c->chan_base + BCM2835_DMA_CS);
}

static irqreturn_t bcm2835_dma_callback(int irq, void *data)
{
        struct bcm2835_chan *c = data;
        struct bcm2835_desc *d;
        unsigned long flags;

        /* check the shared interrupt */
        if (c->irq_flags & IRQF_SHARED) {
                /* check if the interrupt is enabled */
                flags = readl(c->chan_base + BCM2835_DMA_CS);
                /* if not set then we are not the reason for the irq */
                if (!(flags & BCM2835_DMA_INT))
                        return IRQ_NONE;
        }

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

        /*
         * Clear the INT flag to receive further interrupts. Keep the channel
         * active in case the descriptor is cyclic or in case the client has
         * already terminated the descriptor and issued a new one. (May happen
         * if this IRQ handler is threaded.) If the channel is finished, it
         * will remain idle despite the ACTIVE flag being set.
         */
        writel(BCM2835_DMA_INT | BCM2835_DMA_ACTIVE,
               c->chan_base + BCM2835_DMA_CS);

        d = c->desc;

        if (d) {
                if (d->cyclic) {
                        /* call the cyclic callback */
                        vchan_cyclic_callback(&d->vd);
                } else if (!readl(c->chan_base + BCM2835_DMA_ADDR)) {
                        vchan_cookie_complete(&c->desc->vd);
                        bcm2835_dma_start_desc(c);
                }
        }

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

        return IRQ_HANDLED;
}

static int bcm2835_dma_alloc_chan_resources(struct dma_chan *chan)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        struct device *dev = c->vc.chan.device->dev;

        dev_dbg(dev, "Allocating DMA channel %d\n", c->ch);

        /*
         * Control blocks are 256 bit in length and must start at a 256 bit
         * (32 byte) aligned address (BCM2835 ARM Peripherals, sec. 4.2.1.1).
         */
        c->cb_pool = dma_pool_create(dev_name(dev), dev,
                                     sizeof(struct bcm2835_dma_cb), 32, 0);
        if (!c->cb_pool) {
                dev_err(dev, "unable to allocate descriptor pool\n");
                return -ENOMEM;
        }

        return request_irq(c->irq_number, bcm2835_dma_callback,
                           c->irq_flags, "DMA IRQ", c);
}

static void bcm2835_dma_free_chan_resources(struct dma_chan *chan)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);

        vchan_free_chan_resources(&c->vc);
        free_irq(c->irq_number, c);
        dma_pool_destroy(c->cb_pool);

        dev_dbg(c->vc.chan.device->dev, "Freeing DMA channel %u\n", c->ch);
}

static size_t bcm2835_dma_desc_size(struct bcm2835_desc *d)
{
        return d->size;
}

static size_t bcm2835_dma_desc_size_pos(struct bcm2835_desc *d, dma_addr_t addr)
{
        unsigned int i;
        size_t size;

        for (size = i = 0; i < d->frames; i++) {
                struct bcm2835_dma_cb *control_block = d->cb_list[i].cb;
                size_t this_size = control_block->length;
                dma_addr_t dma;

                if (d->dir == DMA_DEV_TO_MEM)
                        dma = control_block->dst;
                else
                        dma = control_block->src;

                if (size)
                        size += this_size;
                else if (addr >= dma && addr < dma + this_size)
                        size += dma + this_size - addr;
        }

        return size;
}

static enum dma_status bcm2835_dma_tx_status(struct dma_chan *chan,
        dma_cookie_t cookie, struct dma_tx_state *txstate)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        struct virt_dma_desc *vd;
        enum dma_status ret;
        unsigned long flags;

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

        spin_lock_irqsave(&c->vc.lock, flags);
        vd = vchan_find_desc(&c->vc, cookie);
        if (vd) {
                txstate->residue =
                        bcm2835_dma_desc_size(to_bcm2835_dma_desc(&vd->tx));
        } else if (c->desc && c->desc->vd.tx.cookie == cookie) {
                struct bcm2835_desc *d = c->desc;
                dma_addr_t pos;

                if (d->dir == DMA_MEM_TO_DEV)
                        pos = readl(c->chan_base + BCM2835_DMA_SOURCE_AD);
                else if (d->dir == DMA_DEV_TO_MEM)
                        pos = readl(c->chan_base + BCM2835_DMA_DEST_AD);
                else
                        pos = 0;

                txstate->residue = bcm2835_dma_desc_size_pos(d, pos);
        } else {
                txstate->residue = 0;
        }

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

        return ret;
}

static void bcm2835_dma_issue_pending(struct dma_chan *chan)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        unsigned long flags;

        spin_lock_irqsave(&c->vc.lock, flags);
        if (vchan_issue_pending(&c->vc) && !c->desc)
                bcm2835_dma_start_desc(c);

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

static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_memcpy(
        struct dma_chan *chan, dma_addr_t dst, dma_addr_t src,
        size_t len, unsigned long flags)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        struct bcm2835_desc *d;
        u32 info = BCM2835_DMA_D_INC | BCM2835_DMA_S_INC;
        u32 extra = BCM2835_DMA_INT_EN | BCM2835_DMA_WAIT_RESP;
        size_t max_len = bcm2835_dma_max_frame_length(c);
        size_t frames;

        /* if src, dst or len is not given return with an error */
        if (!src || !dst || !len)
                return NULL;

        /* calculate number of frames */
        frames = bcm2835_dma_frames_for_length(len, max_len);

        /* allocate the CB chain - this also fills in the pointers */
        d = bcm2835_dma_create_cb_chain(chan, DMA_MEM_TO_MEM, false,
                                        info, extra, frames,
                                        src, dst, len, 0, GFP_KERNEL);
        if (!d)
                return NULL;

        return vchan_tx_prep(&c->vc, &d->vd, flags);
}

static struct dma_async_tx_descriptor *bcm2835_dma_prep_slave_sg(
        struct dma_chan *chan,
        struct scatterlist *sgl, unsigned int sg_len,
        enum dma_transfer_direction direction,
        unsigned long flags, void *context)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        struct bcm2835_desc *d;
        dma_addr_t src = 0, dst = 0;
        u32 info = BCM2835_DMA_WAIT_RESP;
        u32 extra = BCM2835_DMA_INT_EN;
        size_t frames;

        if (!is_slave_direction(direction)) {
                dev_err(chan->device->dev,
                        "%s: bad direction?\n", __func__);
                return NULL;
        }

        if (c->dreq != 0)
                info |= BCM2835_DMA_PER_MAP(c->dreq);

        if (direction == DMA_DEV_TO_MEM) {
                if (c->cfg.src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
                        return NULL;
                src = c->cfg.src_addr;
                info |= BCM2835_DMA_S_DREQ | BCM2835_DMA_D_INC;
        } else {
                if (c->cfg.dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
                        return NULL;
                dst = c->cfg.dst_addr;
                info |= BCM2835_DMA_D_DREQ | BCM2835_DMA_S_INC;
        }

        /* count frames in sg list */
        frames = sg_nents_for_dma(sgl, sg_len, bcm2835_dma_max_frame_length(c));

        /* allocate the CB chain */
        d = bcm2835_dma_create_cb_chain(chan, direction, false,
                                        info, extra,
                                        frames, src, dst, 0, 0,
                                        GFP_NOWAIT);
        if (!d)
                return NULL;

        /* fill in frames with scatterlist pointers */
        bcm2835_dma_fill_cb_chain_with_sg(chan, direction, d->cb_list,
                                          sgl, sg_len);

        return vchan_tx_prep(&c->vc, &d->vd, flags);
}

static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
        struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
        size_t period_len, enum dma_transfer_direction direction,
        unsigned long flags)
{
        struct bcm2835_dmadev *od = to_bcm2835_dma_dev(chan->device);
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        struct bcm2835_desc *d;
        dma_addr_t src, dst;
        u32 info = BCM2835_DMA_WAIT_RESP;
        u32 extra = 0;
        size_t max_len = bcm2835_dma_max_frame_length(c);
        size_t frames;

        /* Grab configuration */
        if (!is_slave_direction(direction)) {
                dev_err(chan->device->dev, "%s: bad direction?\n", __func__);
                return NULL;
        }

        if (!buf_len) {
                dev_err(chan->device->dev,
                        "%s: bad buffer length (= 0)\n", __func__);
                return NULL;
        }

        if (flags & DMA_PREP_INTERRUPT)
                extra |= BCM2835_DMA_INT_EN;
        else
                period_len = buf_len;

        /*
         * warn if buf_len is not a multiple of period_len - this may leed
         * to unexpected latencies for interrupts and thus audiable clicks
         */
        if (buf_len % period_len)
                dev_warn_once(chan->device->dev,
                              "%s: buffer_length (%zd) is not a multiple of period_len (%zd)\n",
                              __func__, buf_len, period_len);

        /* Setup DREQ channel */
        if (c->dreq != 0)
                info |= BCM2835_DMA_PER_MAP(c->dreq);

        if (direction == DMA_DEV_TO_MEM) {
                if (c->cfg.src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
                        return NULL;
                src = c->cfg.src_addr;
                dst = buf_addr;
                info |= BCM2835_DMA_S_DREQ | BCM2835_DMA_D_INC;
        } else {
                if (c->cfg.dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
                        return NULL;
                dst = c->cfg.dst_addr;
                src = buf_addr;
                info |= BCM2835_DMA_D_DREQ | BCM2835_DMA_S_INC;

                /* non-lite channels can write zeroes w/o accessing memory */
                if (buf_addr == od->zero_page && !c->is_lite_channel)
                        info |= BCM2835_DMA_S_IGNORE;
        }

        /* calculate number of frames */
        frames = /* number of periods */
                 DIV_ROUND_UP(buf_len, period_len) *
                 /* number of frames per period */
                 bcm2835_dma_frames_for_length(period_len, max_len);

        /*
         * allocate the CB chain
         * note that we need to use GFP_NOWAIT, as the ALSA i2s dmaengine
         * implementation calls prep_dma_cyclic with interrupts disabled.
         */
        d = bcm2835_dma_create_cb_chain(chan, direction, true,
                                        info, extra,
                                        frames, src, dst, buf_len,
                                        period_len, GFP_NOWAIT);
        if (!d)
                return NULL;

        /* wrap around into a loop */
        d->cb_list[d->frames - 1].cb->next = d->cb_list[0].paddr;

        return vchan_tx_prep(&c->vc, &d->vd, flags);
}

static int bcm2835_dma_slave_config(struct dma_chan *chan,
                                    struct dma_slave_config *cfg)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);

        c->cfg = *cfg;

        return 0;
}

static int bcm2835_dma_terminate_all(struct dma_chan *chan)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
        unsigned long flags;
        LIST_HEAD(head);

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

        /* stop DMA activity */
        if (c->desc) {
                vchan_terminate_vdesc(&c->desc->vd);
                c->desc = NULL;
                bcm2835_dma_abort(c);
        }

        vchan_get_all_descriptors(&c->vc, &head);
        spin_unlock_irqrestore(&c->vc.lock, flags);
        vchan_dma_desc_free_list(&c->vc, &head);

        return 0;
}

static void bcm2835_dma_synchronize(struct dma_chan *chan)
{
        struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);

        vchan_synchronize(&c->vc);
}

static int bcm2835_dma_chan_init(struct bcm2835_dmadev *d, int chan_id,
                                 int irq, unsigned int irq_flags)
{
        struct bcm2835_chan *c;

        c = devm_kzalloc(d->ddev.dev, sizeof(*c), GFP_KERNEL);
        if (!c)
                return -ENOMEM;

        c->vc.desc_free = bcm2835_dma_desc_free;
        vchan_init(&c->vc, &d->ddev);

        c->chan_base = BCM2835_DMA_CHANIO(d->base, chan_id);
        c->ch = chan_id;
        c->irq_number = irq;
        c->irq_flags = irq_flags;

        /* check in DEBUG register if this is a LITE channel */
        if (readl(c->chan_base + BCM2835_DMA_DEBUG) &
                BCM2835_DMA_DEBUG_LITE)
                c->is_lite_channel = true;

        return 0;
}

static void bcm2835_dma_free(struct bcm2835_dmadev *od)
{
        struct bcm2835_chan *c, *next;

        list_for_each_entry_safe(c, next, &od->ddev.channels,
                                 vc.chan.device_node) {
                list_del(&c->vc.chan.device_node);
                tasklet_kill(&c->vc.task);
        }

        dma_unmap_page_attrs(od->ddev.dev, od->zero_page, PAGE_SIZE,
                             DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
}

static const struct of_device_id bcm2835_dma_of_match[] = {
        { .compatible = "brcm,bcm2835-dma", },
        {},
};
MODULE_DEVICE_TABLE(of, bcm2835_dma_of_match);

static struct dma_chan *bcm2835_dma_xlate(struct of_phandle_args *spec,
                                           struct of_dma *ofdma)
{
        struct bcm2835_dmadev *d = ofdma->of_dma_data;
        struct dma_chan *chan;

        chan = dma_get_any_slave_channel(&d->ddev);
        if (!chan)
                return NULL;

        /* Set DREQ from param */
        to_bcm2835_dma_chan(chan)->dreq = spec->args[0];

        return chan;
}

static int bcm2835_dma_suspend_late(struct device *dev)
{
        struct bcm2835_dmadev *od = dev_get_drvdata(dev);
        struct bcm2835_chan *c, *next;

        list_for_each_entry_safe(c, next, &od->ddev.channels,
                                 vc.chan.device_node) {
                void __iomem *chan_base = c->chan_base;

                /* Check if DMA channel is busy */
                if (readl(chan_base + BCM2835_DMA_ADDR))
                        return -EBUSY;
        }

        return 0;
}

static const struct dev_pm_ops bcm2835_dma_pm_ops = {
        LATE_SYSTEM_SLEEP_PM_OPS(bcm2835_dma_suspend_late, NULL)
};

static int bcm2835_dma_probe(struct platform_device *pdev)
{
        struct bcm2835_dmadev *od;
        void __iomem *base;
        int rc;
        int i, j;
        int irq[BCM2835_DMA_MAX_DMA_CHAN_SUPPORTED + 1];
        int irq_flags;
        uint32_t chans_available;
        char chan_name[BCM2835_DMA_CHAN_NAME_SIZE];

        if (!pdev->dev.dma_mask)
                pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;

        rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
        if (rc) {
                dev_err(&pdev->dev, "Unable to set DMA mask\n");
                return rc;
        }

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

        dma_set_max_seg_size(&pdev->dev, 0x3FFFFFFF);

        base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(base))
                return PTR_ERR(base);

        od->base = base;

        dma_cap_set(DMA_SLAVE, od->ddev.cap_mask);
        dma_cap_set(DMA_PRIVATE, od->ddev.cap_mask);
        dma_cap_set(DMA_CYCLIC, od->ddev.cap_mask);
        dma_cap_set(DMA_MEMCPY, od->ddev.cap_mask);
        od->ddev.device_alloc_chan_resources = bcm2835_dma_alloc_chan_resources;
        od->ddev.device_free_chan_resources = bcm2835_dma_free_chan_resources;
        od->ddev.device_tx_status = bcm2835_dma_tx_status;
        od->ddev.device_issue_pending = bcm2835_dma_issue_pending;
        od->ddev.device_prep_dma_cyclic = bcm2835_dma_prep_dma_cyclic;
        od->ddev.device_prep_slave_sg = bcm2835_dma_prep_slave_sg;
        od->ddev.device_prep_dma_memcpy = bcm2835_dma_prep_dma_memcpy;
        od->ddev.device_config = bcm2835_dma_slave_config;
        od->ddev.device_terminate_all = bcm2835_dma_terminate_all;
        od->ddev.device_synchronize = bcm2835_dma_synchronize;
        od->ddev.src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
        od->ddev.dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
        od->ddev.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV) |
                              BIT(DMA_MEM_TO_MEM);
        od->ddev.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
        od->ddev.descriptor_reuse = true;
        od->ddev.dev = &pdev->dev;
        INIT_LIST_HEAD(&od->ddev.channels);

        platform_set_drvdata(pdev, od);

        od->zero_page = dma_map_page_attrs(od->ddev.dev, ZERO_PAGE(0), 0,
                                           PAGE_SIZE, DMA_TO_DEVICE,
                                           DMA_ATTR_SKIP_CPU_SYNC);
        if (dma_mapping_error(od->ddev.dev, od->zero_page)) {
                dev_err(&pdev->dev, "Failed to map zero page\n");
                return -ENOMEM;
        }

        /* Request DMA channel mask from device tree */
        if (of_property_read_u32(pdev->dev.of_node,
                        "brcm,dma-channel-mask",
                        &chans_available)) {
                dev_err(&pdev->dev, "Failed to get channel mask\n");
                rc = -EINVAL;
                goto err_no_dma;
        }

        /* get irqs for each channel that we support */
        for (i = 0; i <= BCM2835_DMA_MAX_DMA_CHAN_SUPPORTED; i++) {
                /* skip masked out channels */
                if (!(chans_available & (1 << i))) {
                        irq[i] = -1;
                        continue;
                }

                /* get the named irq */
                snprintf(chan_name, sizeof(chan_name), "dma%i", i);
                irq[i] = platform_get_irq_byname(pdev, chan_name);
                if (irq[i] >= 0)
                        continue;

                /* legacy device tree case handling */
                dev_warn_once(&pdev->dev,
                              "missing interrupt-names property in device tree - legacy interpretation is used\n");
                /*
                 * in case of channel >= 11
                 * use the 11th interrupt and that is shared
                 */
                irq[i] = platform_get_irq(pdev, i < 11 ? i : 11);
        }

        /* get irqs for each channel */
        for (i = 0; i <= BCM2835_DMA_MAX_DMA_CHAN_SUPPORTED; i++) {
                /* skip channels without irq */
                if (irq[i] < 0)
                        continue;

                /* check if there are other channels that also use this irq */
                irq_flags = 0;
                for (j = 0; j <= BCM2835_DMA_MAX_DMA_CHAN_SUPPORTED; j++)
                        if ((i != j) && (irq[j] == irq[i])) {
                                irq_flags = IRQF_SHARED;
                                break;
                        }

                /* initialize the channel */
                rc = bcm2835_dma_chan_init(od, i, irq[i], irq_flags);
                if (rc)
                        goto err_no_dma;
        }

        dev_dbg(&pdev->dev, "Initialized %i DMA channels\n", i);

        /* Device-tree DMA controller registration */
        rc = of_dma_controller_register(pdev->dev.of_node,
                        bcm2835_dma_xlate, od);
        if (rc) {
                dev_err(&pdev->dev, "Failed to register DMA controller\n");
                goto err_no_dma;
        }

        rc = dma_async_device_register(&od->ddev);
        if (rc) {
                dev_err(&pdev->dev,
                        "Failed to register slave DMA engine device: %d\n", rc);
                goto err_no_dma;
        }

        dev_dbg(&pdev->dev, "Load BCM2835 DMA engine driver\n");

        return 0;

err_no_dma:
        bcm2835_dma_free(od);
        return rc;
}

static void bcm2835_dma_remove(struct platform_device *pdev)
{
        struct bcm2835_dmadev *od = platform_get_drvdata(pdev);

        dma_async_device_unregister(&od->ddev);
        bcm2835_dma_free(od);
}

static struct platform_driver bcm2835_dma_driver = {
        .probe  = bcm2835_dma_probe,
        .remove = bcm2835_dma_remove,
        .driver = {
                .name = "bcm2835-dma",
                .of_match_table = of_match_ptr(bcm2835_dma_of_match),
                .pm = pm_ptr(&bcm2835_dma_pm_ops),
        },
};

module_platform_driver(bcm2835_dma_driver);

MODULE_DESCRIPTION("BCM2835 DMA engine driver");
MODULE_AUTHOR("Florian Meier <florian.meier@koalo.de>");
MODULE_LICENSE("GPL");