/*
 * Driver for the Cirrus Logic EP93xx DMA Controller
 *
 * Copyright (C) 2011 Mika Westerberg
 *
 * DMA M2P implementation is based on the original
 * arch/arm/mach-ep93xx/dma-m2p.c which has following copyrights:
 *
 *   Copyright (C) 2006 Lennert Buytenhek <buytenh@wantstofly.org>
 *   Copyright (C) 2006 Applied Data Systems
 *   Copyright (C) 2009 Ryan Mallon <rmallon@gmail.com>
 *
 * This driver is based on dw_dmac and amba-pl08x drivers.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

#include <linux/clk.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/dmaengine.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#include <linux/platform_data/dma-ep93xx.h>

#include "dmaengine.h"

/* M2P registers */
#define M2P_CONTROL                     0x0000
#define M2P_CONTROL_STALLINT            BIT(0)
#define M2P_CONTROL_NFBINT              BIT(1)
#define M2P_CONTROL_CH_ERROR_INT        BIT(3)
#define M2P_CONTROL_ENABLE              BIT(4)
#define M2P_CONTROL_ICE                 BIT(6)

#define M2P_INTERRUPT                   0x0004
#define M2P_INTERRUPT_STALL             BIT(0)
#define M2P_INTERRUPT_NFB               BIT(1)
#define M2P_INTERRUPT_ERROR             BIT(3)

#define M2P_PPALLOC                     0x0008
#define M2P_STATUS                      0x000c

#define M2P_MAXCNT0                     0x0020
#define M2P_BASE0                       0x0024
#define M2P_MAXCNT1                     0x0030
#define M2P_BASE1                       0x0034

#define M2P_STATE_IDLE                  0
#define M2P_STATE_STALL                 1
#define M2P_STATE_ON                    2
#define M2P_STATE_NEXT                  3

/* M2M registers */
#define M2M_CONTROL                     0x0000
#define M2M_CONTROL_DONEINT             BIT(2)
#define M2M_CONTROL_ENABLE              BIT(3)
#define M2M_CONTROL_START               BIT(4)
#define M2M_CONTROL_DAH                 BIT(11)
#define M2M_CONTROL_SAH                 BIT(12)
#define M2M_CONTROL_PW_SHIFT            9
#define M2M_CONTROL_PW_8                (0 << M2M_CONTROL_PW_SHIFT)
#define M2M_CONTROL_PW_16               (1 << M2M_CONTROL_PW_SHIFT)
#define M2M_CONTROL_PW_32               (2 << M2M_CONTROL_PW_SHIFT)
#define M2M_CONTROL_PW_MASK             (3 << M2M_CONTROL_PW_SHIFT)
#define M2M_CONTROL_TM_SHIFT            13
#define M2M_CONTROL_TM_TX               (1 << M2M_CONTROL_TM_SHIFT)
#define M2M_CONTROL_TM_RX               (2 << M2M_CONTROL_TM_SHIFT)
#define M2M_CONTROL_NFBINT              BIT(21)
#define M2M_CONTROL_RSS_SHIFT           22
#define M2M_CONTROL_RSS_SSPRX           (1 << M2M_CONTROL_RSS_SHIFT)
#define M2M_CONTROL_RSS_SSPTX           (2 << M2M_CONTROL_RSS_SHIFT)
#define M2M_CONTROL_RSS_IDE             (3 << M2M_CONTROL_RSS_SHIFT)
#define M2M_CONTROL_NO_HDSK             BIT(24)
#define M2M_CONTROL_PWSC_SHIFT          25

#define M2M_INTERRUPT                   0x0004
#define M2M_INTERRUPT_MASK              6

#define M2M_STATUS                      0x000c
#define M2M_STATUS_CTL_SHIFT            1
#define M2M_STATUS_CTL_IDLE             (0 << M2M_STATUS_CTL_SHIFT)
#define M2M_STATUS_CTL_STALL            (1 << M2M_STATUS_CTL_SHIFT)
#define M2M_STATUS_CTL_MEMRD            (2 << M2M_STATUS_CTL_SHIFT)
#define M2M_STATUS_CTL_MEMWR            (3 << M2M_STATUS_CTL_SHIFT)
#define M2M_STATUS_CTL_BWCWAIT          (4 << M2M_STATUS_CTL_SHIFT)
#define M2M_STATUS_CTL_MASK             (7 << M2M_STATUS_CTL_SHIFT)
#define M2M_STATUS_BUF_SHIFT            4
#define M2M_STATUS_BUF_NO               (0 << M2M_STATUS_BUF_SHIFT)
#define M2M_STATUS_BUF_ON               (1 << M2M_STATUS_BUF_SHIFT)
#define M2M_STATUS_BUF_NEXT             (2 << M2M_STATUS_BUF_SHIFT)
#define M2M_STATUS_BUF_MASK             (3 << M2M_STATUS_BUF_SHIFT)
#define M2M_STATUS_DONE                 BIT(6)

#define M2M_BCR0                        0x0010
#define M2M_BCR1                        0x0014
#define M2M_SAR_BASE0                   0x0018
#define M2M_SAR_BASE1                   0x001c
#define M2M_DAR_BASE0                   0x002c
#define M2M_DAR_BASE1                   0x0030

#define DMA_MAX_CHAN_BYTES              0xffff
#define DMA_MAX_CHAN_DESCRIPTORS        32

struct ep93xx_dma_engine;

/**
 * struct ep93xx_dma_desc - EP93xx specific transaction descriptor
 * @src_addr: source address of the transaction
 * @dst_addr: destination address of the transaction
 * @size: size of the transaction (in bytes)
 * @complete: this descriptor is completed
 * @txd: dmaengine API descriptor
 * @tx_list: list of linked descriptors
 * @node: link used for putting this into a channel queue
 */
struct ep93xx_dma_desc {
        u32                             src_addr;
        u32                             dst_addr;
        size_t                          size;
        bool                            complete;
        struct dma_async_tx_descriptor  txd;
        struct list_head                tx_list;
        struct list_head                node;
};

/**
 * struct ep93xx_dma_chan - an EP93xx DMA M2P/M2M channel
 * @chan: dmaengine API channel
 * @edma: pointer to to the engine device
 * @regs: memory mapped registers
 * @irq: interrupt number of the channel
 * @clk: clock used by this channel
 * @tasklet: channel specific tasklet used for callbacks
 * @lock: lock protecting the fields following
 * @flags: flags for the channel
 * @buffer: which buffer to use next (0/1)
 * @active: flattened chain of descriptors currently being processed
 * @queue: pending descriptors which are handled next
 * @free_list: list of free descriptors which can be used
 * @runtime_addr: physical address currently used as dest/src (M2M only). This
 *                is set via .device_config before slave operation is
 *                prepared
 * @runtime_ctrl: M2M runtime values for the control register.
 *
 * As EP93xx DMA controller doesn't support real chained DMA descriptors we
 * will have slightly different scheme here: @active points to a head of
 * flattened DMA descriptor chain.
 *
 * @queue holds pending transactions. These are linked through the first
 * descriptor in the chain. When a descriptor is moved to the @active queue,
 * the first and chained descriptors are flattened into a single list.
 *
 * @chan.private holds pointer to &struct ep93xx_dma_data which contains
 * necessary channel configuration information. For memcpy channels this must
 * be %NULL.
 */
struct ep93xx_dma_chan {
        struct dma_chan                 chan;
        const struct ep93xx_dma_engine  *edma;
        void __iomem                    *regs;
        int                             irq;
        struct clk                      *clk;
        struct tasklet_struct           tasklet;
        /* protects the fields following */
        spinlock_t                      lock;
        unsigned long                   flags;
/* Channel is configured for cyclic transfers */
#define EP93XX_DMA_IS_CYCLIC            0

        int                             buffer;
        struct list_head                active;
        struct list_head                queue;
        struct list_head                free_list;
        u32                             runtime_addr;
        u32                             runtime_ctrl;
};

/**
 * struct ep93xx_dma_engine - the EP93xx DMA engine instance
 * @dma_dev: holds the dmaengine device
 * @m2m: is this an M2M or M2P device
 * @hw_setup: method which sets the channel up for operation
 * @hw_shutdown: shuts the channel down and flushes whatever is left
 * @hw_submit: pushes active descriptor(s) to the hardware
 * @hw_interrupt: handle the interrupt
 * @num_channels: number of channels for this instance
 * @channels: array of channels
 *
 * There is one instance of this struct for the M2P channels and one for the
 * M2M channels. hw_xxx() methods are used to perform operations which are
 * different on M2M and M2P channels. These methods are called with channel
 * lock held and interrupts disabled so they cannot sleep.
 */
struct ep93xx_dma_engine {
        struct dma_device       dma_dev;
        bool                    m2m;
        int                     (*hw_setup)(struct ep93xx_dma_chan *);
        void                    (*hw_shutdown)(struct ep93xx_dma_chan *);
        void                    (*hw_submit)(struct ep93xx_dma_chan *);
        int                     (*hw_interrupt)(struct ep93xx_dma_chan *);
#define INTERRUPT_UNKNOWN       0
#define INTERRUPT_DONE          1
#define INTERRUPT_NEXT_BUFFER   2

        size_t                  num_channels;
        struct ep93xx_dma_chan  channels[];
};

static inline struct device *chan2dev(struct ep93xx_dma_chan *edmac)
{
        return &edmac->chan.dev->device;
}

static struct ep93xx_dma_chan *to_ep93xx_dma_chan(struct dma_chan *chan)
{
        return container_of(chan, struct ep93xx_dma_chan, chan);
}

/**
 * ep93xx_dma_set_active - set new active descriptor chain
 * @edmac: channel
 * @desc: head of the new active descriptor chain
 *
 * Sets @desc to be the head of the new active descriptor chain. This is the
 * chain which is processed next. The active list must be empty before calling
 * this function.
 *
 * Called with @edmac->lock held and interrupts disabled.
 */
static void ep93xx_dma_set_active(struct ep93xx_dma_chan *edmac,
                                  struct ep93xx_dma_desc *desc)
{
        BUG_ON(!list_empty(&edmac->active));

        list_add_tail(&desc->node, &edmac->active);

        /* Flatten the @desc->tx_list chain into @edmac->active list */
        while (!list_empty(&desc->tx_list)) {
                struct ep93xx_dma_desc *d = list_first_entry(&desc->tx_list,
                        struct ep93xx_dma_desc, node);

                /*
                 * We copy the callback parameters from the first descriptor
                 * to all the chained descriptors. This way we can call the
                 * callback without having to find out the first descriptor in
                 * the chain. Useful for cyclic transfers.
                 */
                d->txd.callback = desc->txd.callback;
                d->txd.callback_param = desc->txd.callback_param;

                list_move_tail(&d->node, &edmac->active);
        }
}

/* Called with @edmac->lock held and interrupts disabled */
static struct ep93xx_dma_desc *
ep93xx_dma_get_active(struct ep93xx_dma_chan *edmac)
{
        if (list_empty(&edmac->active))
                return NULL;

        return list_first_entry(&edmac->active, struct ep93xx_dma_desc, node);
}

/**
 * ep93xx_dma_advance_active - advances to the next active descriptor
 * @edmac: channel
 *
 * Function advances active descriptor to the next in the @edmac->active and
 * returns %true if we still have descriptors in the chain to process.
 * Otherwise returns %false.
 *
 * When the channel is in cyclic mode always returns %true.
 *
 * Called with @edmac->lock held and interrupts disabled.
 */
static bool ep93xx_dma_advance_active(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_desc *desc;

        list_rotate_left(&edmac->active);

        if (test_bit(EP93XX_DMA_IS_CYCLIC, &edmac->flags))
                return true;

        desc = ep93xx_dma_get_active(edmac);
        if (!desc)
                return false;

        /*
         * If txd.cookie is set it means that we are back in the first
         * descriptor in the chain and hence done with it.
         */
        return !desc->txd.cookie;
}

/*
 * M2P DMA implementation
 */

static void m2p_set_control(struct ep93xx_dma_chan *edmac, u32 control)
{
        writel(control, edmac->regs + M2P_CONTROL);
        /*
         * EP93xx User's Guide states that we must perform a dummy read after
         * write to the control register.
         */
        readl(edmac->regs + M2P_CONTROL);
}

static int m2p_hw_setup(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_data *data = edmac->chan.private;
        u32 control;

        writel(data->port & 0xf, edmac->regs + M2P_PPALLOC);

        control = M2P_CONTROL_CH_ERROR_INT | M2P_CONTROL_ICE
                | M2P_CONTROL_ENABLE;
        m2p_set_control(edmac, control);

        return 0;
}

static inline u32 m2p_channel_state(struct ep93xx_dma_chan *edmac)
{
        return (readl(edmac->regs + M2P_STATUS) >> 4) & 0x3;
}

static void m2p_hw_shutdown(struct ep93xx_dma_chan *edmac)
{
        u32 control;

        control = readl(edmac->regs + M2P_CONTROL);
        control &= ~(M2P_CONTROL_STALLINT | M2P_CONTROL_NFBINT);
        m2p_set_control(edmac, control);

        while (m2p_channel_state(edmac) >= M2P_STATE_ON)
                cpu_relax();

        m2p_set_control(edmac, 0);

        while (m2p_channel_state(edmac) == M2P_STATE_STALL)
                cpu_relax();
}

static void m2p_fill_desc(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_desc *desc;
        u32 bus_addr;

        desc = ep93xx_dma_get_active(edmac);
        if (!desc) {
                dev_warn(chan2dev(edmac), "M2P: empty descriptor list\n");
                return;
        }

        if (ep93xx_dma_chan_direction(&edmac->chan) == DMA_MEM_TO_DEV)
                bus_addr = desc->src_addr;
        else
                bus_addr = desc->dst_addr;

        if (edmac->buffer == 0) {
                writel(desc->size, edmac->regs + M2P_MAXCNT0);
                writel(bus_addr, edmac->regs + M2P_BASE0);
        } else {
                writel(desc->size, edmac->regs + M2P_MAXCNT1);
                writel(bus_addr, edmac->regs + M2P_BASE1);
        }

        edmac->buffer ^= 1;
}

static void m2p_hw_submit(struct ep93xx_dma_chan *edmac)
{
        u32 control = readl(edmac->regs + M2P_CONTROL);

        m2p_fill_desc(edmac);
        control |= M2P_CONTROL_STALLINT;

        if (ep93xx_dma_advance_active(edmac)) {
                m2p_fill_desc(edmac);
                control |= M2P_CONTROL_NFBINT;
        }

        m2p_set_control(edmac, control);
}

static int m2p_hw_interrupt(struct ep93xx_dma_chan *edmac)
{
        u32 irq_status = readl(edmac->regs + M2P_INTERRUPT);
        u32 control;

        if (irq_status & M2P_INTERRUPT_ERROR) {
                struct ep93xx_dma_desc *desc = ep93xx_dma_get_active(edmac);

                /* Clear the error interrupt */
                writel(1, edmac->regs + M2P_INTERRUPT);

                /*
                 * It seems that there is no easy way of reporting errors back
                 * to client so we just report the error here and continue as
                 * usual.
                 *
                 * Revisit this when there is a mechanism to report back the
                 * errors.
                 */
                dev_err(chan2dev(edmac),
                        "DMA transfer failed! Details:\n"
                        "\tcookie       : %d\n"
                        "\tsrc_addr     : 0x%08x\n"
                        "\tdst_addr     : 0x%08x\n"
                        "\tsize         : %zu\n",
                        desc->txd.cookie, desc->src_addr, desc->dst_addr,
                        desc->size);
        }

        /*
         * Even latest E2 silicon revision sometimes assert STALL interrupt
         * instead of NFB. Therefore we treat them equally, basing on the
         * amount of data we still have to transfer.
         */
        if (!(irq_status & (M2P_INTERRUPT_STALL | M2P_INTERRUPT_NFB)))
                return INTERRUPT_UNKNOWN;

        if (ep93xx_dma_advance_active(edmac)) {
                m2p_fill_desc(edmac);
                return INTERRUPT_NEXT_BUFFER;
        }

        /* Disable interrupts */
        control = readl(edmac->regs + M2P_CONTROL);
        control &= ~(M2P_CONTROL_STALLINT | M2P_CONTROL_NFBINT);
        m2p_set_control(edmac, control);

        return INTERRUPT_DONE;
}

/*
 * M2M DMA implementation
 */

static int m2m_hw_setup(struct ep93xx_dma_chan *edmac)
{
        const struct ep93xx_dma_data *data = edmac->chan.private;
        u32 control = 0;

        if (!data) {
                /* This is memcpy channel, nothing to configure */
                writel(control, edmac->regs + M2M_CONTROL);
                return 0;
        }

        switch (data->port) {
        case EP93XX_DMA_SSP:
                /*
                 * This was found via experimenting - anything less than 5
                 * causes the channel to perform only a partial transfer which
                 * leads to problems since we don't get DONE interrupt then.
                 */
                control = (5 << M2M_CONTROL_PWSC_SHIFT);
                control |= M2M_CONTROL_NO_HDSK;

                if (data->direction == DMA_MEM_TO_DEV) {
                        control |= M2M_CONTROL_DAH;
                        control |= M2M_CONTROL_TM_TX;
                        control |= M2M_CONTROL_RSS_SSPTX;
                } else {
                        control |= M2M_CONTROL_SAH;
                        control |= M2M_CONTROL_TM_RX;
                        control |= M2M_CONTROL_RSS_SSPRX;
                }
                break;

        case EP93XX_DMA_IDE:
                /*
                 * This IDE part is totally untested. Values below are taken
                 * from the EP93xx Users's Guide and might not be correct.
                 */
                if (data->direction == DMA_MEM_TO_DEV) {
                        /* Worst case from the UG */
                        control = (3 << M2M_CONTROL_PWSC_SHIFT);
                        control |= M2M_CONTROL_DAH;
                        control |= M2M_CONTROL_TM_TX;
                } else {
                        control = (2 << M2M_CONTROL_PWSC_SHIFT);
                        control |= M2M_CONTROL_SAH;
                        control |= M2M_CONTROL_TM_RX;
                }

                control |= M2M_CONTROL_NO_HDSK;
                control |= M2M_CONTROL_RSS_IDE;
                control |= M2M_CONTROL_PW_16;
                break;

        default:
                return -EINVAL;
        }

        writel(control, edmac->regs + M2M_CONTROL);
        return 0;
}

static void m2m_hw_shutdown(struct ep93xx_dma_chan *edmac)
{
        /* Just disable the channel */
        writel(0, edmac->regs + M2M_CONTROL);
}

static void m2m_fill_desc(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_desc *desc;

        desc = ep93xx_dma_get_active(edmac);
        if (!desc) {
                dev_warn(chan2dev(edmac), "M2M: empty descriptor list\n");
                return;
        }

        if (edmac->buffer == 0) {
                writel(desc->src_addr, edmac->regs + M2M_SAR_BASE0);
                writel(desc->dst_addr, edmac->regs + M2M_DAR_BASE0);
                writel(desc->size, edmac->regs + M2M_BCR0);
        } else {
                writel(desc->src_addr, edmac->regs + M2M_SAR_BASE1);
                writel(desc->dst_addr, edmac->regs + M2M_DAR_BASE1);
                writel(desc->size, edmac->regs + M2M_BCR1);
        }

        edmac->buffer ^= 1;
}

static void m2m_hw_submit(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_data *data = edmac->chan.private;
        u32 control = readl(edmac->regs + M2M_CONTROL);

        /*
         * Since we allow clients to configure PW (peripheral width) we always
         * clear PW bits here and then set them according what is given in
         * the runtime configuration.
         */
        control &= ~M2M_CONTROL_PW_MASK;
        control |= edmac->runtime_ctrl;

        m2m_fill_desc(edmac);
        control |= M2M_CONTROL_DONEINT;

        if (ep93xx_dma_advance_active(edmac)) {
                m2m_fill_desc(edmac);
                control |= M2M_CONTROL_NFBINT;
        }

        /*
         * Now we can finally enable the channel. For M2M channel this must be
         * done _after_ the BCRx registers are programmed.
         */
        control |= M2M_CONTROL_ENABLE;
        writel(control, edmac->regs + M2M_CONTROL);

        if (!data) {
                /*
                 * For memcpy channels the software trigger must be asserted
                 * in order to start the memcpy operation.
                 */
                control |= M2M_CONTROL_START;
                writel(control, edmac->regs + M2M_CONTROL);
        }
}

/*
 * According to EP93xx User's Guide, we should receive DONE interrupt when all
 * M2M DMA controller transactions complete normally. This is not always the
 * case - sometimes EP93xx M2M DMA asserts DONE interrupt when the DMA channel
 * is still running (channel Buffer FSM in DMA_BUF_ON state, and channel
 * Control FSM in DMA_MEM_RD state, observed at least in IDE-DMA operation).
 * In effect, disabling the channel when only DONE bit is set could stop
 * currently running DMA transfer. To avoid this, we use Buffer FSM and
 * Control FSM to check current state of DMA channel.
 */
static int m2m_hw_interrupt(struct ep93xx_dma_chan *edmac)
{
        u32 status = readl(edmac->regs + M2M_STATUS);
        u32 ctl_fsm = status & M2M_STATUS_CTL_MASK;
        u32 buf_fsm = status & M2M_STATUS_BUF_MASK;
        bool done = status & M2M_STATUS_DONE;
        bool last_done;
        u32 control;
        struct ep93xx_dma_desc *desc;

        /* Accept only DONE and NFB interrupts */
        if (!(readl(edmac->regs + M2M_INTERRUPT) & M2M_INTERRUPT_MASK))
                return INTERRUPT_UNKNOWN;

        if (done) {
                /* Clear the DONE bit */
                writel(0, edmac->regs + M2M_INTERRUPT);
        }

        /*
         * Check whether we are done with descriptors or not. This, together
         * with DMA channel state, determines action to take in interrupt.
         */
        desc = ep93xx_dma_get_active(edmac);
        last_done = !desc || desc->txd.cookie;

        /*
         * Use M2M DMA Buffer FSM and Control FSM to check current state of
         * DMA channel. Using DONE and NFB bits from channel status register
         * or bits from channel interrupt register is not reliable.
         */
        if (!last_done &&
            (buf_fsm == M2M_STATUS_BUF_NO ||
             buf_fsm == M2M_STATUS_BUF_ON)) {
                /*
                 * Two buffers are ready for update when Buffer FSM is in
                 * DMA_NO_BUF state. Only one buffer can be prepared without
                 * disabling the channel or polling the DONE bit.
                 * To simplify things, always prepare only one buffer.
                 */
                if (ep93xx_dma_advance_active(edmac)) {
                        m2m_fill_desc(edmac);
                        if (done && !edmac->chan.private) {
                                /* Software trigger for memcpy channel */
                                control = readl(edmac->regs + M2M_CONTROL);
                                control |= M2M_CONTROL_START;
                                writel(control, edmac->regs + M2M_CONTROL);
                        }
                        return INTERRUPT_NEXT_BUFFER;
                } else {
                        last_done = true;
                }
        }

        /*
         * Disable the channel only when Buffer FSM is in DMA_NO_BUF state
         * and Control FSM is in DMA_STALL state.
         */
        if (last_done &&
            buf_fsm == M2M_STATUS_BUF_NO &&
            ctl_fsm == M2M_STATUS_CTL_STALL) {
                /* Disable interrupts and the channel */
                control = readl(edmac->regs + M2M_CONTROL);
                control &= ~(M2M_CONTROL_DONEINT | M2M_CONTROL_NFBINT
                            | M2M_CONTROL_ENABLE);
                writel(control, edmac->regs + M2M_CONTROL);
                return INTERRUPT_DONE;
        }

        /*
         * Nothing to do this time.
         */
        return INTERRUPT_NEXT_BUFFER;
}

/*
 * DMA engine API implementation
 */

static struct ep93xx_dma_desc *
ep93xx_dma_desc_get(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_desc *desc, *_desc;
        struct ep93xx_dma_desc *ret = NULL;
        unsigned long flags;

        spin_lock_irqsave(&edmac->lock, flags);
        list_for_each_entry_safe(desc, _desc, &edmac->free_list, node) {
                if (async_tx_test_ack(&desc->txd)) {
                        list_del_init(&desc->node);

                        /* Re-initialize the descriptor */
                        desc->src_addr = 0;
                        desc->dst_addr = 0;
                        desc->size = 0;
                        desc->complete = false;
                        desc->txd.cookie = 0;
                        desc->txd.callback = NULL;
                        desc->txd.callback_param = NULL;

                        ret = desc;
                        break;
                }
        }
        spin_unlock_irqrestore(&edmac->lock, flags);
        return ret;
}

static void ep93xx_dma_desc_put(struct ep93xx_dma_chan *edmac,
                                struct ep93xx_dma_desc *desc)
{
        if (desc) {
                unsigned long flags;

                spin_lock_irqsave(&edmac->lock, flags);
                list_splice_init(&desc->tx_list, &edmac->free_list);
                list_add(&desc->node, &edmac->free_list);
                spin_unlock_irqrestore(&edmac->lock, flags);
        }
}

/**
 * ep93xx_dma_advance_work - start processing the next pending transaction
 * @edmac: channel
 *
 * If we have pending transactions queued and we are currently idling, this
 * function takes the next queued transaction from the @edmac->queue and
 * pushes it to the hardware for execution.
 */
static void ep93xx_dma_advance_work(struct ep93xx_dma_chan *edmac)
{
        struct ep93xx_dma_desc *new;
        unsigned long flags;

        spin_lock_irqsave(&edmac->lock, flags);
        if (!list_empty(&edmac->active) || list_empty(&edmac->queue)) {
                spin_unlock_irqrestore(&edmac->lock, flags);
                return;
        }

        /* Take the next descriptor from the pending queue */
        new = list_first_entry(&edmac->queue, struct ep93xx_dma_desc, node);
        list_del_init(&new->node);

        ep93xx_dma_set_active(edmac, new);

        /* Push it to the hardware */
        edmac->edma->hw_submit(edmac);
        spin_unlock_irqrestore(&edmac->lock, flags);
}

static void ep93xx_dma_tasklet(unsigned long data)
{
        struct ep93xx_dma_chan *edmac = (struct ep93xx_dma_chan *)data;
        struct ep93xx_dma_desc *desc, *d;
        dma_async_tx_callback callback = NULL;
        void *callback_param = NULL;
        LIST_HEAD(list);

        spin_lock_irq(&edmac->lock);
        /*
         * If dma_terminate_all() was called before we get to run, the active
         * list has become empty. If that happens we aren't supposed to do
         * anything more than call ep93xx_dma_advance_work().
         */
        desc = ep93xx_dma_get_active(edmac);
        if (desc) {
                if (desc->complete) {
                        /* mark descriptor complete for non cyclic case only */
                        if (!test_bit(EP93XX_DMA_IS_CYCLIC, &edmac->flags))
                                dma_cookie_complete(&desc->txd);
                        list_splice_init(&edmac->active, &list);
                }
                callback = desc->txd.callback;
                callback_param = desc->txd.callback_param;
        }
        spin_unlock_irq(&edmac->lock);

        /* Pick up the next descriptor from the queue */
        ep93xx_dma_advance_work(edmac);

        /* Now we can release all the chained descriptors */
        list_for_each_entry_safe(desc, d, &list, node) {
                dma_descriptor_unmap(&desc->txd);
                ep93xx_dma_desc_put(edmac, desc);
        }

        if (callback)
                callback(callback_param);
}

static irqreturn_t ep93xx_dma_interrupt(int irq, void *dev_id)
{
        struct ep93xx_dma_chan *edmac = dev_id;
        struct ep93xx_dma_desc *desc;
        irqreturn_t ret = IRQ_HANDLED;

        spin_lock(&edmac->lock);

        desc = ep93xx_dma_get_active(edmac);
        if (!desc) {
                dev_warn(chan2dev(edmac),
                         "got interrupt while active list is empty\n");
                spin_unlock(&edmac->lock);
                return IRQ_NONE;
        }

        switch (edmac->edma->hw_interrupt(edmac)) {
        case INTERRUPT_DONE:
                desc->complete = true;
                tasklet_schedule(&edmac->tasklet);
                break;

        case INTERRUPT_NEXT_BUFFER:
                if (test_bit(EP93XX_DMA_IS_CYCLIC, &edmac->flags))
                        tasklet_schedule(&edmac->tasklet);
                break;

        default:
                dev_warn(chan2dev(edmac), "unknown interrupt!\n");
                ret = IRQ_NONE;
                break;
        }

        spin_unlock(&edmac->lock);
        return ret;
}

/**
 * ep93xx_dma_tx_submit - set the prepared descriptor(s) to be executed
 * @tx: descriptor to be executed
 *
 * Function will execute given descriptor on the hardware or if the hardware
 * is busy, queue the descriptor to be executed later on. Returns cookie which
 * can be used to poll the status of the descriptor.
 */
static dma_cookie_t ep93xx_dma_tx_submit(struct dma_async_tx_descriptor *tx)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(tx->chan);
        struct ep93xx_dma_desc *desc;
        dma_cookie_t cookie;
        unsigned long flags;

        spin_lock_irqsave(&edmac->lock, flags);
        cookie = dma_cookie_assign(tx);

        desc = container_of(tx, struct ep93xx_dma_desc, txd);

        /*
         * If nothing is currently prosessed, we push this descriptor
         * directly to the hardware. Otherwise we put the descriptor
         * to the pending queue.
         */
        if (list_empty(&edmac->active)) {
                ep93xx_dma_set_active(edmac, desc);
                edmac->edma->hw_submit(edmac);
        } else {
                list_add_tail(&desc->node, &edmac->queue);
        }

        spin_unlock_irqrestore(&edmac->lock, flags);
        return cookie;
}

/**
 * ep93xx_dma_alloc_chan_resources - allocate resources for the channel
 * @chan: channel to allocate resources
 *
 * Function allocates necessary resources for the given DMA channel and
 * returns number of allocated descriptors for the channel. Negative errno
 * is returned in case of failure.
 */
static int ep93xx_dma_alloc_chan_resources(struct dma_chan *chan)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        struct ep93xx_dma_data *data = chan->private;
        const char *name = dma_chan_name(chan);
        int ret, i;

        /* Sanity check the channel parameters */
        if (!edmac->edma->m2m) {
                if (!data)
                        return -EINVAL;
                if (data->port < EP93XX_DMA_I2S1 ||
                    data->port > EP93XX_DMA_IRDA)
                        return -EINVAL;
                if (data->direction != ep93xx_dma_chan_direction(chan))
                        return -EINVAL;
        } else {
                if (data) {
                        switch (data->port) {
                        case EP93XX_DMA_SSP:
                        case EP93XX_DMA_IDE:
                                if (!is_slave_direction(data->direction))
                                        return -EINVAL;
                                break;
                        default:
                                return -EINVAL;
                        }
                }
        }

        if (data && data->name)
                name = data->name;

        ret = clk_enable(edmac->clk);
        if (ret)
                return ret;

        ret = request_irq(edmac->irq, ep93xx_dma_interrupt, 0, name, edmac);
        if (ret)
                goto fail_clk_disable;

        spin_lock_irq(&edmac->lock);
        dma_cookie_init(&edmac->chan);
        ret = edmac->edma->hw_setup(edmac);
        spin_unlock_irq(&edmac->lock);

        if (ret)
                goto fail_free_irq;

        for (i = 0; i < DMA_MAX_CHAN_DESCRIPTORS; i++) {
                struct ep93xx_dma_desc *desc;

                desc = kzalloc(sizeof(*desc), GFP_KERNEL);
                if (!desc) {
                        dev_warn(chan2dev(edmac), "not enough descriptors\n");
                        break;
                }

                INIT_LIST_HEAD(&desc->tx_list);

                dma_async_tx_descriptor_init(&desc->txd, chan);
                desc->txd.flags = DMA_CTRL_ACK;
                desc->txd.tx_submit = ep93xx_dma_tx_submit;

                ep93xx_dma_desc_put(edmac, desc);
        }

        return i;

fail_free_irq:
        free_irq(edmac->irq, edmac);
fail_clk_disable:
        clk_disable(edmac->clk);

        return ret;
}

/**
 * ep93xx_dma_free_chan_resources - release resources for the channel
 * @chan: channel
 *
 * Function releases all the resources allocated for the given channel.
 * The channel must be idle when this is called.
 */
static void ep93xx_dma_free_chan_resources(struct dma_chan *chan)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        struct ep93xx_dma_desc *desc, *d;
        unsigned long flags;
        LIST_HEAD(list);

        BUG_ON(!list_empty(&edmac->active));
        BUG_ON(!list_empty(&edmac->queue));

        spin_lock_irqsave(&edmac->lock, flags);
        edmac->edma->hw_shutdown(edmac);
        edmac->runtime_addr = 0;
        edmac->runtime_ctrl = 0;
        edmac->buffer = 0;
        list_splice_init(&edmac->free_list, &list);
        spin_unlock_irqrestore(&edmac->lock, flags);

        list_for_each_entry_safe(desc, d, &list, node)
                kfree(desc);

        clk_disable(edmac->clk);
        free_irq(edmac->irq, edmac);
}

/**
 * ep93xx_dma_prep_dma_memcpy - prepare a memcpy DMA operation
 * @chan: channel
 * @dest: destination bus address
 * @src: source bus address
 * @len: size of the transaction
 * @flags: flags for the descriptor
 *
 * Returns a valid DMA descriptor or %NULL in case of failure.
 */
static struct dma_async_tx_descriptor *
ep93xx_dma_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest,
                           dma_addr_t src, size_t len, unsigned long flags)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        struct ep93xx_dma_desc *desc, *first;
        size_t bytes, offset;

        first = NULL;
        for (offset = 0; offset < len; offset += bytes) {
                desc = ep93xx_dma_desc_get(edmac);
                if (!desc) {
                        dev_warn(chan2dev(edmac), "couln't get descriptor\n");
                        goto fail;
                }

                bytes = min_t(size_t, len - offset, DMA_MAX_CHAN_BYTES);

                desc->src_addr = src + offset;
                desc->dst_addr = dest + offset;
                desc->size = bytes;

                if (!first)

                        first = desc;
                else
                        list_add_tail(&desc->node, &first->tx_list);
        }

        first->txd.cookie = -EBUSY;
        first->txd.flags = flags;

        return &first->txd;
fail:
        ep93xx_dma_desc_put(edmac, first);
        return NULL;
}

/**
 * ep93xx_dma_prep_slave_sg - prepare a slave DMA operation
 * @chan: channel
 * @sgl: list of buffers to transfer
 * @sg_len: number of entries in @sgl
 * @dir: direction of tha DMA transfer
 * @flags: flags for the descriptor
 * @context: operation context (ignored)
 *
 * Returns a valid DMA descriptor or %NULL in case of failure.
 */
static struct dma_async_tx_descriptor *
ep93xx_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 ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        struct ep93xx_dma_desc *desc, *first;
        struct scatterlist *sg;
        int i;

        if (!edmac->edma->m2m && dir != ep93xx_dma_chan_direction(chan)) {
                dev_warn(chan2dev(edmac),
                         "channel was configured with different direction\n");
                return NULL;
        }

        if (test_bit(EP93XX_DMA_IS_CYCLIC, &edmac->flags)) {
                dev_warn(chan2dev(edmac),
                         "channel is already used for cyclic transfers\n");
                return NULL;
        }

        first = NULL;
        for_each_sg(sgl, sg, sg_len, i) {
                size_t sg_len = sg_dma_len(sg);

                if (sg_len > DMA_MAX_CHAN_BYTES) {
                        dev_warn(chan2dev(edmac), "too big transfer size %d\n",
                                 sg_len);
                        goto fail;
                }

                desc = ep93xx_dma_desc_get(edmac);
                if (!desc) {
                        dev_warn(chan2dev(edmac), "couln't get descriptor\n");
                        goto fail;
                }

                if (dir == DMA_MEM_TO_DEV) {
                        desc->src_addr = sg_dma_address(sg);
                        desc->dst_addr = edmac->runtime_addr;
                } else {
                        desc->src_addr = edmac->runtime_addr;
                        desc->dst_addr = sg_dma_address(sg);
                }
                desc->size = sg_len;

                if (!first)
                        first = desc;
                else
                        list_add_tail(&desc->node, &first->tx_list);
        }

        first->txd.cookie = -EBUSY;
        first->txd.flags = flags;

        return &first->txd;

fail:
        ep93xx_dma_desc_put(edmac, first);
        return NULL;
}

/**
 * ep93xx_dma_prep_dma_cyclic - prepare a cyclic DMA operation
 * @chan: channel
 * @dma_addr: DMA mapped address of the buffer
 * @buf_len: length of the buffer (in bytes)
 * @period_len: length of a single period
 * @dir: direction of the operation
 * @flags: tx descriptor status flags
 *
 * Prepares a descriptor for cyclic DMA operation. This means that once the
 * descriptor is submitted, we will be submitting in a @period_len sized
 * buffers and calling callback once the period has been elapsed. Transfer
 * terminates only when client calls dmaengine_terminate_all() for this
 * channel.
 *
 * Returns a valid DMA descriptor or %NULL in case of failure.
 */
static struct dma_async_tx_descriptor *
ep93xx_dma_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t dma_addr,
                           size_t buf_len, size_t period_len,
                           enum dma_transfer_direction dir, unsigned long flags)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        struct ep93xx_dma_desc *desc, *first;
        size_t offset = 0;

        if (!edmac->edma->m2m && dir != ep93xx_dma_chan_direction(chan)) {
                dev_warn(chan2dev(edmac),
                         "channel was configured with different direction\n");
                return NULL;
        }

        if (test_and_set_bit(EP93XX_DMA_IS_CYCLIC, &edmac->flags)) {
                dev_warn(chan2dev(edmac),
                         "channel is already used for cyclic transfers\n");
                return NULL;
        }

        if (period_len > DMA_MAX_CHAN_BYTES) {
                dev_warn(chan2dev(edmac), "too big period length %d\n",
                         period_len);
                return NULL;
        }

        /* Split the buffer into period size chunks */
        first = NULL;
        for (offset = 0; offset < buf_len; offset += period_len) {
                desc = ep93xx_dma_desc_get(edmac);
                if (!desc) {
                        dev_warn(chan2dev(edmac), "couln't get descriptor\n");
                        goto fail;
                }

                if (dir == DMA_MEM_TO_DEV) {
                        desc->src_addr = dma_addr + offset;
                        desc->dst_addr = edmac->runtime_addr;
                } else {
                        desc->src_addr = edmac->runtime_addr;
                        desc->dst_addr = dma_addr + offset;
                }

                desc->size = period_len;

                if (!first)
                        first = desc;
                else
                        list_add_tail(&desc->node, &first->tx_list);
        }

        first->txd.cookie = -EBUSY;

        return &first->txd;

fail:
        ep93xx_dma_desc_put(edmac, first);
        return NULL;
}

/**
 * ep93xx_dma_terminate_all - terminate all transactions
 * @chan: channel
 *
 * Stops all DMA transactions. All descriptors are put back to the
 * @edmac->free_list and callbacks are _not_ called.
 */
static int ep93xx_dma_terminate_all(struct dma_chan *chan)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        struct ep93xx_dma_desc *desc, *_d;
        unsigned long flags;
        LIST_HEAD(list);

        spin_lock_irqsave(&edmac->lock, flags);
        /* First we disable and flush the DMA channel */
        edmac->edma->hw_shutdown(edmac);
        clear_bit(EP93XX_DMA_IS_CYCLIC, &edmac->flags);
        list_splice_init(&edmac->active, &list);
        list_splice_init(&edmac->queue, &list);
        /*
         * We then re-enable the channel. This way we can continue submitting
         * the descriptors by just calling ->hw_submit() again.
         */
        edmac->edma->hw_setup(edmac);
        spin_unlock_irqrestore(&edmac->lock, flags);

        list_for_each_entry_safe(desc, _d, &list, node)
                ep93xx_dma_desc_put(edmac, desc);

        return 0;
}

static int ep93xx_dma_slave_config(struct dma_chan *chan,
                                   struct dma_slave_config *config)
{
        struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
        enum dma_slave_buswidth width;
        unsigned long flags;
        u32 addr, ctrl;

        if (!edmac->edma->m2m)
                return -EINVAL;

        switch (config->direction) {
        case DMA_DEV_TO_MEM:
                width = config->src_addr_width;
                addr = config->src_addr;
                break;

        case DMA_MEM_TO_DEV:
                width = config->dst_addr_width;
                addr = config->dst_addr;
                break;

        default:
                return -EINVAL;
        }

        switch (width) {
        case DMA_SLAVE_BUSWIDTH_1_BYTE:
                ctrl = 0;
                break;
        case DMA_SLAVE_BUSWIDTH_2_BYTES:
                ctrl = M2M_CONTROL_PW_16;
                break;
        case DMA_SLAVE_BUSWIDTH_4_BYTES:
                ctrl = M2M_CONTROL_PW_32;
                break;
        default:
                return -EINVAL;
        }

        spin_lock_irqsave(&edmac->lock, flags);
        edmac->runtime_addr = addr;
        edmac->runtime_ctrl = ctrl;
        spin_unlock_irqrestore(&edmac->lock, flags);

        return 0;
}

/**
 * ep93xx_dma_tx_status - check if a transaction is completed
 * @chan: channel
 * @cookie: transaction specific cookie
 * @state: state of the transaction is stored here if given
 *
 * This function can be used to query state of a given transaction.
 */
static enum dma_status ep93xx_dma_tx_status(struct dma_chan *chan,
                                            dma_cookie_t cookie,
                                            struct dma_tx_state *state)
{
        return dma_cookie_status(chan, cookie, state);
}

/**
 * ep93xx_dma_issue_pending - push pending transactions to the hardware
 * @chan: channel
 *
 * When this function is called, all pending transactions are pushed to the
 * hardware and executed.
 */
static void ep93xx_dma_issue_pending(struct dma_chan *chan)
{
        ep93xx_dma_advance_work(to_ep93xx_dma_chan(chan));
}

static int __init ep93xx_dma_probe(struct platform_device *pdev)
{
        struct ep93xx_dma_platform_data *pdata = dev_get_platdata(&pdev->dev);
        struct ep93xx_dma_engine *edma;
        struct dma_device *dma_dev;
        size_t edma_size;
        int ret, i;

        edma_size = pdata->num_channels * sizeof(struct ep93xx_dma_chan);
        edma = kzalloc(sizeof(*edma) + edma_size, GFP_KERNEL);
        if (!edma)
                return -ENOMEM;

        dma_dev = &edma->dma_dev;
        edma->m2m = platform_get_device_id(pdev)->driver_data;
        edma->num_channels = pdata->num_channels;

        INIT_LIST_HEAD(&dma_dev->channels);
        for (i = 0; i < pdata->num_channels; i++) {
                const struct ep93xx_dma_chan_data *cdata = &pdata->channels[i];
                struct ep93xx_dma_chan *edmac = &edma->channels[i];

                edmac->chan.device = dma_dev;
                edmac->regs = cdata->base;
                edmac->irq = cdata->irq;
                edmac->edma = edma;

                edmac->clk = clk_get(NULL, cdata->name);
                if (IS_ERR(edmac->clk)) {
                        dev_warn(&pdev->dev, "failed to get clock for %s\n",
                                 cdata->name);
                        continue;
                }

                spin_lock_init(&edmac->lock);
                INIT_LIST_HEAD(&edmac->active);
                INIT_LIST_HEAD(&edmac->queue);
                INIT_LIST_HEAD(&edmac->free_list);
                tasklet_init(&edmac->tasklet, ep93xx_dma_tasklet,
                             (unsigned long)edmac);

                list_add_tail(&edmac->chan.device_node,
                              &dma_dev->channels);
        }

        dma_cap_zero(dma_dev->cap_mask);
        dma_cap_set(DMA_SLAVE, dma_dev->cap_mask);
        dma_cap_set(DMA_CYCLIC, dma_dev->cap_mask);

        dma_dev->dev = &pdev->dev;
        dma_dev->device_alloc_chan_resources = ep93xx_dma_alloc_chan_resources;
        dma_dev->device_free_chan_resources = ep93xx_dma_free_chan_resources;
        dma_dev->device_prep_slave_sg = ep93xx_dma_prep_slave_sg;
        dma_dev->device_prep_dma_cyclic = ep93xx_dma_prep_dma_cyclic;
        dma_dev->device_config = ep93xx_dma_slave_config;
        dma_dev->device_terminate_all = ep93xx_dma_terminate_all;
        dma_dev->device_issue_pending = ep93xx_dma_issue_pending;
        dma_dev->device_tx_status = ep93xx_dma_tx_status;

        dma_set_max_seg_size(dma_dev->dev, DMA_MAX_CHAN_BYTES);

        if (edma->m2m) {
                dma_cap_set(DMA_MEMCPY, dma_dev->cap_mask);
                dma_dev->device_prep_dma_memcpy = ep93xx_dma_prep_dma_memcpy;

                edma->hw_setup = m2m_hw_setup;
                edma->hw_shutdown = m2m_hw_shutdown;
                edma->hw_submit = m2m_hw_submit;
                edma->hw_interrupt = m2m_hw_interrupt;
        } else {
                dma_cap_set(DMA_PRIVATE, dma_dev->cap_mask);

                edma->hw_setup = m2p_hw_setup;
                edma->hw_shutdown = m2p_hw_shutdown;
                edma->hw_submit = m2p_hw_submit;
                edma->hw_interrupt = m2p_hw_interrupt;
        }

        ret = dma_async_device_register(dma_dev);
        if (unlikely(ret)) {
                for (i = 0; i < edma->num_channels; i++) {
                        struct ep93xx_dma_chan *edmac = &edma->channels[i];
                        if (!IS_ERR_OR_NULL(edmac->clk))
                                clk_put(edmac->clk);
                }
                kfree(edma);
        } else {
                dev_info(dma_dev->dev, "EP93xx M2%s DMA ready\n",
                         edma->m2m ? "M" : "P");
        }

        return ret;
}

static const struct platform_device_id ep93xx_dma_driver_ids[] = {
        { "ep93xx-dma-m2p", 0 },
        { "ep93xx-dma-m2m", 1 },
        { },
};

static struct platform_driver ep93xx_dma_driver = {
        .driver         = {
                .name   = "ep93xx-dma",
        },
        .id_table       = ep93xx_dma_driver_ids,
};

static int __init ep93xx_dma_module_init(void)
{
        return platform_driver_probe(&ep93xx_dma_driver, ep93xx_dma_probe);
}
subsys_initcall(ep93xx_dma_module_init);

MODULE_AUTHOR("Mika Westerberg <mika.westerberg@iki.fi>");
MODULE_DESCRIPTION("EP93xx DMA driver");
MODULE_LICENSE("GPL");