/*
 * Copyright (c) 2015, Sony Mobile Communications AB.
 * Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/mfd/syscon.h>
#include <linux/module.h>
#include <linux/of_irq.h>
#include <linux/of_platform.h>
#include <linux/platform_device.h>
#include <linux/regmap.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/soc/qcom/smem.h>
#include <linux/wait.h>
#include <linux/rpmsg.h>
#include <linux/rpmsg/qcom_smd.h>

#include "rpmsg_internal.h"

/*
 * The Qualcomm Shared Memory communication solution provides point-to-point
 * channels for clients to send and receive streaming or packet based data.
 *
 * Each channel consists of a control item (channel info) and a ring buffer
 * pair. The channel info carry information related to channel state, flow
 * control and the offsets within the ring buffer.
 *
 * All allocated channels are listed in an allocation table, identifying the
 * pair of items by name, type and remote processor.
 *
 * Upon creating a new channel the remote processor allocates channel info and
 * ring buffer items from the smem heap and populate the allocation table. An
 * interrupt is sent to the other end of the channel and a scan for new
 * channels should be done. A channel never goes away, it will only change
 * state.
 *
 * The remote processor signals it intent for bring up the communication
 * channel by setting the state of its end of the channel to "opening" and
 * sends out an interrupt. We detect this change and register a smd device to
 * consume the channel. Upon finding a consumer we finish the handshake and the
 * channel is up.
 *
 * Upon closing a channel, the remote processor will update the state of its
 * end of the channel and signal us, we will then unregister any attached
 * device and close our end of the channel.
 *
 * Devices attached to a channel can use the qcom_smd_send function to push
 * data to the channel, this is done by copying the data into the tx ring
 * buffer, updating the pointers in the channel info and signaling the remote
 * processor.
 *
 * The remote processor does the equivalent when it transfer data and upon
 * receiving the interrupt we check the channel info for new data and delivers
 * this to the attached device. If the device is not ready to receive the data
 * we leave it in the ring buffer for now.
 */

struct smd_channel_info;
struct smd_channel_info_pair;
struct smd_channel_info_word;
struct smd_channel_info_word_pair;

static const struct rpmsg_endpoint_ops qcom_smd_endpoint_ops;

#define SMD_ALLOC_TBL_COUNT     2
#define SMD_ALLOC_TBL_SIZE      64

/*
 * This lists the various smem heap items relevant for the allocation table and
 * smd channel entries.
 */
static const struct {
        unsigned alloc_tbl_id;
        unsigned info_base_id;
        unsigned fifo_base_id;
} smem_items[SMD_ALLOC_TBL_COUNT] = {
        {
                .alloc_tbl_id = 13,
                .info_base_id = 14,
                .fifo_base_id = 338
        },
        {
                .alloc_tbl_id = 266,
                .info_base_id = 138,
                .fifo_base_id = 202,
        },
};

/**
 * struct qcom_smd_edge - representing a remote processor
 * @of_node:            of_node handle for information related to this edge
 * @edge_id:            identifier of this edge
 * @remote_pid:         identifier of remote processor
 * @irq:                interrupt for signals on this edge
 * @ipc_regmap:         regmap handle holding the outgoing ipc register
 * @ipc_offset:         offset within @ipc_regmap of the register for ipc
 * @ipc_bit:            bit in the register at @ipc_offset of @ipc_regmap
 * @channels:           list of all channels detected on this edge
 * @channels_lock:      guard for modifications of @channels
 * @allocated:          array of bitmaps representing already allocated channels
 * @smem_available:     last available amount of smem triggering a channel scan
 * @scan_work:          work item for discovering new channels
 * @state_work:         work item for edge state changes
 */
struct qcom_smd_edge {
        struct device dev;

        const char *name;

        struct device_node *of_node;
        unsigned edge_id;
        unsigned remote_pid;

        int irq;

        struct regmap *ipc_regmap;
        int ipc_offset;
        int ipc_bit;

        struct list_head channels;
        spinlock_t channels_lock;

        DECLARE_BITMAP(allocated[SMD_ALLOC_TBL_COUNT], SMD_ALLOC_TBL_SIZE);

        unsigned smem_available;

        wait_queue_head_t new_channel_event;

        struct work_struct scan_work;
        struct work_struct state_work;
};

/*
 * SMD channel states.
 */
enum smd_channel_state {
        SMD_CHANNEL_CLOSED,
        SMD_CHANNEL_OPENING,
        SMD_CHANNEL_OPENED,
        SMD_CHANNEL_FLUSHING,
        SMD_CHANNEL_CLOSING,
        SMD_CHANNEL_RESET,
        SMD_CHANNEL_RESET_OPENING
};

struct qcom_smd_device {
        struct rpmsg_device rpdev;

        struct qcom_smd_edge *edge;
};

struct qcom_smd_endpoint {
        struct rpmsg_endpoint ept;

        struct qcom_smd_channel *qsch;
};

#define to_smd_device(r)        container_of(r, struct qcom_smd_device, rpdev)
#define to_smd_edge(d)          container_of(d, struct qcom_smd_edge, dev)
#define to_smd_endpoint(e)      container_of(e, struct qcom_smd_endpoint, ept)

/**
 * struct qcom_smd_channel - smd channel struct
 * @edge:               qcom_smd_edge this channel is living on
 * @qsdev:              reference to a associated smd client device
 * @name:               name of the channel
 * @state:              local state of the channel
 * @remote_state:       remote state of the channel
 * @info:               byte aligned outgoing/incoming channel info
 * @info_word:          word aligned outgoing/incoming channel info
 * @tx_lock:            lock to make writes to the channel mutually exclusive
 * @fblockread_event:   wakeup event tied to tx fBLOCKREADINTR
 * @tx_fifo:            pointer to the outgoing ring buffer
 * @rx_fifo:            pointer to the incoming ring buffer
 * @fifo_size:          size of each ring buffer
 * @bounce_buffer:      bounce buffer for reading wrapped packets
 * @cb:                 callback function registered for this channel
 * @recv_lock:          guard for rx info modifications and cb pointer
 * @pkt_size:           size of the currently handled packet
 * @list:               lite entry for @channels in qcom_smd_edge
 */
struct qcom_smd_channel {
        struct qcom_smd_edge *edge;

        struct qcom_smd_endpoint *qsept;
        bool registered;

        char *name;
        enum smd_channel_state state;
        enum smd_channel_state remote_state;
        wait_queue_head_t state_change_event;

        struct smd_channel_info_pair *info;
        struct smd_channel_info_word_pair *info_word;

        spinlock_t tx_lock;
        wait_queue_head_t fblockread_event;

        void *tx_fifo;
        void *rx_fifo;
        int fifo_size;

        void *bounce_buffer;

        spinlock_t recv_lock;

        int pkt_size;

        void *drvdata;

        struct list_head list;
};

/*
 * Format of the smd_info smem items, for byte aligned channels.
 */
struct smd_channel_info {
        __le32 state;
        u8  fDSR;
        u8  fCTS;
        u8  fCD;
        u8  fRI;
        u8  fHEAD;
        u8  fTAIL;
        u8  fSTATE;
        u8  fBLOCKREADINTR;
        __le32 tail;
        __le32 head;
};

struct smd_channel_info_pair {
        struct smd_channel_info tx;
        struct smd_channel_info rx;
};

/*
 * Format of the smd_info smem items, for word aligned channels.
 */
struct smd_channel_info_word {
        __le32 state;
        __le32 fDSR;
        __le32 fCTS;
        __le32 fCD;
        __le32 fRI;
        __le32 fHEAD;
        __le32 fTAIL;
        __le32 fSTATE;
        __le32 fBLOCKREADINTR;
        __le32 tail;
        __le32 head;
};

struct smd_channel_info_word_pair {
        struct smd_channel_info_word tx;
        struct smd_channel_info_word rx;
};

#define GET_RX_CHANNEL_FLAG(channel, param)                                  \
        ({                                                                   \
                BUILD_BUG_ON(sizeof(channel->info->rx.param) != sizeof(u8)); \
                channel->info_word ?                                         \
                        le32_to_cpu(channel->info_word->rx.param) :          \
                        channel->info->rx.param;                             \
        })

#define GET_RX_CHANNEL_INFO(channel, param)                                   \
        ({                                                                    \
                BUILD_BUG_ON(sizeof(channel->info->rx.param) != sizeof(u32)); \
                le32_to_cpu(channel->info_word ?                              \
                        channel->info_word->rx.param :                        \
                        channel->info->rx.param);                             \
        })

#define SET_RX_CHANNEL_FLAG(channel, param, value)                           \
        ({                                                                   \
                BUILD_BUG_ON(sizeof(channel->info->rx.param) != sizeof(u8)); \
                if (channel->info_word)                                      \
                        channel->info_word->rx.param = cpu_to_le32(value);   \
                else                                                         \
                        channel->info->rx.param = value;                     \
        })

#define SET_RX_CHANNEL_INFO(channel, param, value)                            \
        ({                                                                    \
                BUILD_BUG_ON(sizeof(channel->info->rx.param) != sizeof(u32)); \
                if (channel->info_word)                                       \
                        channel->info_word->rx.param = cpu_to_le32(value);    \
                else                                                          \
                        channel->info->rx.param = cpu_to_le32(value);         \
        })

#define GET_TX_CHANNEL_FLAG(channel, param)                                  \
        ({                                                                   \
                BUILD_BUG_ON(sizeof(channel->info->tx.param) != sizeof(u8)); \
                channel->info_word ?                                         \
                        le32_to_cpu(channel->info_word->tx.param) :          \
                        channel->info->tx.param;                             \
        })

#define GET_TX_CHANNEL_INFO(channel, param)                                   \
        ({                                                                    \
                BUILD_BUG_ON(sizeof(channel->info->tx.param) != sizeof(u32)); \
                le32_to_cpu(channel->info_word ?                              \
                        channel->info_word->tx.param :                        \
                        channel->info->tx.param);                             \
        })

#define SET_TX_CHANNEL_FLAG(channel, param, value)                           \
        ({                                                                   \
                BUILD_BUG_ON(sizeof(channel->info->tx.param) != sizeof(u8)); \
                if (channel->info_word)                                      \
                        channel->info_word->tx.param = cpu_to_le32(value);   \
                else                                                         \
                        channel->info->tx.param = value;                     \
        })

#define SET_TX_CHANNEL_INFO(channel, param, value)                            \
        ({                                                                    \
                BUILD_BUG_ON(sizeof(channel->info->tx.param) != sizeof(u32)); \
                if (channel->info_word)                                       \
                        channel->info_word->tx.param = cpu_to_le32(value);   \
                else                                                          \
                        channel->info->tx.param = cpu_to_le32(value);         \
        })

/**
 * struct qcom_smd_alloc_entry - channel allocation entry
 * @name:       channel name
 * @cid:        channel index
 * @flags:      channel flags and edge id
 * @ref_count:  reference count of the channel
 */
struct qcom_smd_alloc_entry {
        u8 name[20];
        __le32 cid;
        __le32 flags;
        __le32 ref_count;
} __packed;

#define SMD_CHANNEL_FLAGS_EDGE_MASK     0xff
#define SMD_CHANNEL_FLAGS_STREAM        BIT(8)
#define SMD_CHANNEL_FLAGS_PACKET        BIT(9)

/*
 * Each smd packet contains a 20 byte header, with the first 4 being the length
 * of the packet.
 */
#define SMD_PACKET_HEADER_LEN   20

/*
 * Signal the remote processor associated with 'channel'.
 */
static void qcom_smd_signal_channel(struct qcom_smd_channel *channel)
{
        struct qcom_smd_edge *edge = channel->edge;

        regmap_write(edge->ipc_regmap, edge->ipc_offset, BIT(edge->ipc_bit));
}

/*
 * Initialize the tx channel info
 */
static void qcom_smd_channel_reset(struct qcom_smd_channel *channel)
{
        SET_TX_CHANNEL_INFO(channel, state, SMD_CHANNEL_CLOSED);
        SET_TX_CHANNEL_FLAG(channel, fDSR, 0);
        SET_TX_CHANNEL_FLAG(channel, fCTS, 0);
        SET_TX_CHANNEL_FLAG(channel, fCD, 0);
        SET_TX_CHANNEL_FLAG(channel, fRI, 0);
        SET_TX_CHANNEL_FLAG(channel, fHEAD, 0);
        SET_TX_CHANNEL_FLAG(channel, fTAIL, 0);
        SET_TX_CHANNEL_FLAG(channel, fSTATE, 1);
        SET_TX_CHANNEL_FLAG(channel, fBLOCKREADINTR, 1);
        SET_TX_CHANNEL_INFO(channel, head, 0);
        SET_RX_CHANNEL_INFO(channel, tail, 0);

        qcom_smd_signal_channel(channel);

        channel->state = SMD_CHANNEL_CLOSED;
        channel->pkt_size = 0;
}

/*
 * Set the callback for a channel, with appropriate locking
 */
static void qcom_smd_channel_set_callback(struct qcom_smd_channel *channel,
                                          rpmsg_rx_cb_t cb)
{
        struct rpmsg_endpoint *ept = &channel->qsept->ept;
        unsigned long flags;

        spin_lock_irqsave(&channel->recv_lock, flags);
        ept->cb = cb;
        spin_unlock_irqrestore(&channel->recv_lock, flags);
};

/*
 * Calculate the amount of data available in the rx fifo
 */
static size_t qcom_smd_channel_get_rx_avail(struct qcom_smd_channel *channel)
{
        unsigned head;
        unsigned tail;

        head = GET_RX_CHANNEL_INFO(channel, head);
        tail = GET_RX_CHANNEL_INFO(channel, tail);

        return (head - tail) & (channel->fifo_size - 1);
}

/*
 * Set tx channel state and inform the remote processor
 */
static void qcom_smd_channel_set_state(struct qcom_smd_channel *channel,
                                       int state)
{
        struct qcom_smd_edge *edge = channel->edge;
        bool is_open = state == SMD_CHANNEL_OPENED;

        if (channel->state == state)
                return;

        dev_dbg(&edge->dev, "set_state(%s, %d)\n", channel->name, state);

        SET_TX_CHANNEL_FLAG(channel, fDSR, is_open);
        SET_TX_CHANNEL_FLAG(channel, fCTS, is_open);
        SET_TX_CHANNEL_FLAG(channel, fCD, is_open);

        SET_TX_CHANNEL_INFO(channel, state, state);
        SET_TX_CHANNEL_FLAG(channel, fSTATE, 1);

        channel->state = state;
        qcom_smd_signal_channel(channel);
}

/*
 * Copy count bytes of data using 32bit accesses, if that's required.
 */
static void smd_copy_to_fifo(void __iomem *dst,
                             const void *src,
                             size_t count,
                             bool word_aligned)
{
        if (word_aligned) {
                __iowrite32_copy(dst, src, count / sizeof(u32));
        } else {
                memcpy_toio(dst, src, count);
        }
}

/*
 * Copy count bytes of data using 32bit accesses, if that is required.
 */
static void smd_copy_from_fifo(void *dst,
                               const void __iomem *src,
                               size_t count,
                               bool word_aligned)
{
        if (word_aligned) {
                __ioread32_copy(dst, src, count / sizeof(u32));
        } else {
                memcpy_fromio(dst, src, count);
        }
}

/*
 * Read count bytes of data from the rx fifo into buf, but don't advance the
 * tail.
 */
static size_t qcom_smd_channel_peek(struct qcom_smd_channel *channel,
                                    void *buf, size_t count)
{
        bool word_aligned;
        unsigned tail;
        size_t len;

        word_aligned = channel->info_word;
        tail = GET_RX_CHANNEL_INFO(channel, tail);

        len = min_t(size_t, count, channel->fifo_size - tail);
        if (len) {
                smd_copy_from_fifo(buf,
                                   channel->rx_fifo + tail,
                                   len,
                                   word_aligned);
        }

        if (len != count) {
                smd_copy_from_fifo(buf + len,
                                   channel->rx_fifo,
                                   count - len,
                                   word_aligned);
        }

        return count;
}

/*
 * Advance the rx tail by count bytes.
 */
static void qcom_smd_channel_advance(struct qcom_smd_channel *channel,
                                     size_t count)
{
        unsigned tail;

        tail = GET_RX_CHANNEL_INFO(channel, tail);
        tail += count;
        tail &= (channel->fifo_size - 1);
        SET_RX_CHANNEL_INFO(channel, tail, tail);
}

/*
 * Read out a single packet from the rx fifo and deliver it to the device
 */
static int qcom_smd_channel_recv_single(struct qcom_smd_channel *channel)
{
        struct rpmsg_endpoint *ept = &channel->qsept->ept;
        unsigned tail;
        size_t len;
        void *ptr;
        int ret;

        tail = GET_RX_CHANNEL_INFO(channel, tail);

        /* Use bounce buffer if the data wraps */
        if (tail + channel->pkt_size >= channel->fifo_size) {
                ptr = channel->bounce_buffer;
                len = qcom_smd_channel_peek(channel, ptr, channel->pkt_size);
        } else {
                ptr = channel->rx_fifo + tail;
                len = channel->pkt_size;
        }

        ret = ept->cb(ept->rpdev, ptr, len, ept->priv, RPMSG_ADDR_ANY);
        if (ret < 0)
                return ret;

        /* Only forward the tail if the client consumed the data */
        qcom_smd_channel_advance(channel, len);

        channel->pkt_size = 0;

        return 0;
}

/*
 * Per channel interrupt handling
 */
static bool qcom_smd_channel_intr(struct qcom_smd_channel *channel)
{
        bool need_state_scan = false;
        int remote_state;
        __le32 pktlen;
        int avail;
        int ret;

        /* Handle state changes */
        remote_state = GET_RX_CHANNEL_INFO(channel, state);
        if (remote_state != channel->remote_state) {
                channel->remote_state = remote_state;
                need_state_scan = true;

                wake_up_interruptible_all(&channel->state_change_event);
        }
        /* Indicate that we have seen any state change */
        SET_RX_CHANNEL_FLAG(channel, fSTATE, 0);

        /* Signal waiting qcom_smd_send() about the interrupt */
        if (!GET_TX_CHANNEL_FLAG(channel, fBLOCKREADINTR))
                wake_up_interruptible_all(&channel->fblockread_event);

        /* Don't consume any data until we've opened the channel */
        if (channel->state != SMD_CHANNEL_OPENED)
                goto out;

        /* Indicate that we've seen the new data */
        SET_RX_CHANNEL_FLAG(channel, fHEAD, 0);

        /* Consume data */
        for (;;) {
                avail = qcom_smd_channel_get_rx_avail(channel);

                if (!channel->pkt_size && avail >= SMD_PACKET_HEADER_LEN) {
                        qcom_smd_channel_peek(channel, &pktlen, sizeof(pktlen));
                        qcom_smd_channel_advance(channel, SMD_PACKET_HEADER_LEN);
                        channel->pkt_size = le32_to_cpu(pktlen);
                } else if (channel->pkt_size && avail >= channel->pkt_size) {
                        ret = qcom_smd_channel_recv_single(channel);
                        if (ret)
                                break;
                } else {
                        break;
                }
        }

        /* Indicate that we have seen and updated tail */
        SET_RX_CHANNEL_FLAG(channel, fTAIL, 1);

        /* Signal the remote that we've consumed the data (if requested) */
        if (!GET_RX_CHANNEL_FLAG(channel, fBLOCKREADINTR)) {
                /* Ensure ordering of channel info updates */
                wmb();

                qcom_smd_signal_channel(channel);
        }

out:
        return need_state_scan;
}

/*
 * The edge interrupts are triggered by the remote processor on state changes,
 * channel info updates or when new channels are created.
 */
static irqreturn_t qcom_smd_edge_intr(int irq, void *data)
{
        struct qcom_smd_edge *edge = data;
        struct qcom_smd_channel *channel;
        unsigned available;
        bool kick_scanner = false;
        bool kick_state = false;

        /*
         * Handle state changes or data on each of the channels on this edge
         */
        spin_lock(&edge->channels_lock);
        list_for_each_entry(channel, &edge->channels, list) {
                spin_lock(&channel->recv_lock);
                kick_state |= qcom_smd_channel_intr(channel);
                spin_unlock(&channel->recv_lock);
        }
        spin_unlock(&edge->channels_lock);

        /*
         * Creating a new channel requires allocating an smem entry, so we only
         * have to scan if the amount of available space in smem have changed
         * since last scan.
         */
        available = qcom_smem_get_free_space(edge->remote_pid);
        if (available != edge->smem_available) {
                edge->smem_available = available;
                kick_scanner = true;
        }

        if (kick_scanner)
                schedule_work(&edge->scan_work);
        if (kick_state)
                schedule_work(&edge->state_work);

        return IRQ_HANDLED;
}

/*
 * Calculate how much space is available in the tx fifo.
 */
static size_t qcom_smd_get_tx_avail(struct qcom_smd_channel *channel)
{
        unsigned head;
        unsigned tail;
        unsigned mask = channel->fifo_size - 1;

        head = GET_TX_CHANNEL_INFO(channel, head);
        tail = GET_TX_CHANNEL_INFO(channel, tail);

        return mask - ((head - tail) & mask);
}

/*
 * Write count bytes of data into channel, possibly wrapping in the ring buffer
 */
static int qcom_smd_write_fifo(struct qcom_smd_channel *channel,
                               const void *data,
                               size_t count)
{
        bool word_aligned;
        unsigned head;
        size_t len;

        word_aligned = channel->info_word;
        head = GET_TX_CHANNEL_INFO(channel, head);

        len = min_t(size_t, count, channel->fifo_size - head);
        if (len) {
                smd_copy_to_fifo(channel->tx_fifo + head,
                                 data,
                                 len,
                                 word_aligned);
        }

        if (len != count) {
                smd_copy_to_fifo(channel->tx_fifo,
                                 data + len,
                                 count - len,
                                 word_aligned);
        }

        head += count;
        head &= (channel->fifo_size - 1);
        SET_TX_CHANNEL_INFO(channel, head, head);

        return count;
}

/**
 * qcom_smd_send - write data to smd channel
 * @channel:    channel handle
 * @data:       buffer of data to write
 * @len:        number of bytes to write
 *
 * This is a blocking write of len bytes into the channel's tx ring buffer and
 * signal the remote end. It will sleep until there is enough space available
 * in the tx buffer, utilizing the fBLOCKREADINTR signaling mechanism to avoid
 * polling.
 */
static int __qcom_smd_send(struct qcom_smd_channel *channel, const void *data,
                           int len, bool wait)
{
        __le32 hdr[5] = { cpu_to_le32(len), };
        int tlen = sizeof(hdr) + len;
        unsigned long flags;
        int ret;

        /* Word aligned channels only accept word size aligned data */
        if (channel->info_word && len % 4)
                return -EINVAL;

        /* Reject packets that are too big */
        if (tlen >= channel->fifo_size)
                return -EINVAL;

        /* Highlight the fact that if we enter the loop below we might sleep */
        if (wait)
                might_sleep();

        spin_lock_irqsave(&channel->tx_lock, flags);

        while (qcom_smd_get_tx_avail(channel) < tlen &&
               channel->state == SMD_CHANNEL_OPENED) {
                if (!wait) {
                        ret = -EAGAIN;
                        goto out_unlock;
                }

                SET_TX_CHANNEL_FLAG(channel, fBLOCKREADINTR, 0);

                /* Wait without holding the tx_lock */
                spin_unlock_irqrestore(&channel->tx_lock, flags);

                ret = wait_event_interruptible(channel->fblockread_event,
                                       qcom_smd_get_tx_avail(channel) >= tlen ||
                                       channel->state != SMD_CHANNEL_OPENED);
                if (ret)
                        return ret;

                spin_lock_irqsave(&channel->tx_lock, flags);

                SET_TX_CHANNEL_FLAG(channel, fBLOCKREADINTR, 1);
        }

        /* Fail if the channel was closed */
        if (channel->state != SMD_CHANNEL_OPENED) {
                ret = -EPIPE;
                goto out_unlock;
        }

        SET_TX_CHANNEL_FLAG(channel, fTAIL, 0);

        qcom_smd_write_fifo(channel, hdr, sizeof(hdr));
        qcom_smd_write_fifo(channel, data, len);

        SET_TX_CHANNEL_FLAG(channel, fHEAD, 1);

        /* Ensure ordering of channel info updates */
        wmb();

        qcom_smd_signal_channel(channel);

out_unlock:
        spin_unlock_irqrestore(&channel->tx_lock, flags);

        return ret;
}

/*
 * Helper for opening a channel
 */
static int qcom_smd_channel_open(struct qcom_smd_channel *channel,
                                 rpmsg_rx_cb_t cb)
{
        struct qcom_smd_edge *edge = channel->edge;
        size_t bb_size;
        int ret;

        /*
         * Packets are maximum 4k, but reduce if the fifo is smaller
         */
        bb_size = min(channel->fifo_size, SZ_4K);
        channel->bounce_buffer = kmalloc(bb_size, GFP_KERNEL);
        if (!channel->bounce_buffer)
                return -ENOMEM;

        qcom_smd_channel_set_callback(channel, cb);
        qcom_smd_channel_set_state(channel, SMD_CHANNEL_OPENING);

        /* Wait for remote to enter opening or opened */
        ret = wait_event_interruptible_timeout(channel->state_change_event,
                        channel->remote_state == SMD_CHANNEL_OPENING ||
                        channel->remote_state == SMD_CHANNEL_OPENED,
                        HZ);
        if (!ret) {
                dev_err(&edge->dev, "remote side did not enter opening state\n");
                goto out_close_timeout;
        }

        qcom_smd_channel_set_state(channel, SMD_CHANNEL_OPENED);

        /* Wait for remote to enter opened */
        ret = wait_event_interruptible_timeout(channel->state_change_event,
                        channel->remote_state == SMD_CHANNEL_OPENED,
                        HZ);
        if (!ret) {
                dev_err(&edge->dev, "remote side did not enter open state\n");
                goto out_close_timeout;
        }

        return 0;

out_close_timeout:
        qcom_smd_channel_set_state(channel, SMD_CHANNEL_CLOSED);
        return -ETIMEDOUT;
}

/*
 * Helper for closing and resetting a channel
 */
static void qcom_smd_channel_close(struct qcom_smd_channel *channel)
{
        qcom_smd_channel_set_callback(channel, NULL);

        kfree(channel->bounce_buffer);
        channel->bounce_buffer = NULL;

        qcom_smd_channel_set_state(channel, SMD_CHANNEL_CLOSED);
        qcom_smd_channel_reset(channel);
}

static struct qcom_smd_channel *
qcom_smd_find_channel(struct qcom_smd_edge *edge, const char *name)
{
        struct qcom_smd_channel *channel;
        struct qcom_smd_channel *ret = NULL;
        unsigned long flags;

        spin_lock_irqsave(&edge->channels_lock, flags);
        list_for_each_entry(channel, &edge->channels, list) {
                if (!strcmp(channel->name, name)) {
                        ret = channel;
                        break;
                }
        }
        spin_unlock_irqrestore(&edge->channels_lock, flags);

        return ret;
}

static void __ept_release(struct kref *kref)
{
        struct rpmsg_endpoint *ept = container_of(kref, struct rpmsg_endpoint,
                                                  refcount);
        kfree(to_smd_endpoint(ept));
}

static struct rpmsg_endpoint *qcom_smd_create_ept(struct rpmsg_device *rpdev,
                                                  rpmsg_rx_cb_t cb, void *priv,
                                                  struct rpmsg_channel_info chinfo)
{
        struct qcom_smd_endpoint *qsept;
        struct qcom_smd_channel *channel;
        struct qcom_smd_device *qsdev = to_smd_device(rpdev);
        struct qcom_smd_edge *edge = qsdev->edge;
        struct rpmsg_endpoint *ept;
        const char *name = chinfo.name;
        int ret;

        /* Wait up to HZ for the channel to appear */
        ret = wait_event_interruptible_timeout(edge->new_channel_event,
                        (channel = qcom_smd_find_channel(edge, name)) != NULL,
                        HZ);
        if (!ret)
                return NULL;

        if (channel->state != SMD_CHANNEL_CLOSED) {
                dev_err(&rpdev->dev, "channel %s is busy\n", channel->name);
                return NULL;
        }

        qsept = kzalloc(sizeof(*qsept), GFP_KERNEL);
        if (!qsept)
                return NULL;

        ept = &qsept->ept;

        kref_init(&ept->refcount);

        ept->rpdev = rpdev;
        ept->cb = cb;
        ept->priv = priv;
        ept->ops = &qcom_smd_endpoint_ops;

        channel->qsept = qsept;
        qsept->qsch = channel;

        ret = qcom_smd_channel_open(channel, cb);
        if (ret)
                goto free_ept;

        return ept;

free_ept:
        channel->qsept = NULL;
        kref_put(&ept->refcount, __ept_release);
        return NULL;
}

static void qcom_smd_destroy_ept(struct rpmsg_endpoint *ept)
{
        struct qcom_smd_endpoint *qsept = to_smd_endpoint(ept);
        struct qcom_smd_channel *ch = qsept->qsch;

        qcom_smd_channel_close(ch);
        ch->qsept = NULL;
        kref_put(&ept->refcount, __ept_release);
}

static int qcom_smd_send(struct rpmsg_endpoint *ept, void *data, int len)
{
        struct qcom_smd_endpoint *qsept = to_smd_endpoint(ept);

        return __qcom_smd_send(qsept->qsch, data, len, true);
}

static int qcom_smd_trysend(struct rpmsg_endpoint *ept, void *data, int len)
{
        struct qcom_smd_endpoint *qsept = to_smd_endpoint(ept);

        return __qcom_smd_send(qsept->qsch, data, len, false);
}

static __poll_t qcom_smd_poll(struct rpmsg_endpoint *ept,
                                  struct file *filp, poll_table *wait)
{
        struct qcom_smd_endpoint *qsept = to_smd_endpoint(ept);
        struct qcom_smd_channel *channel = qsept->qsch;
        __poll_t mask = 0;

        poll_wait(filp, &channel->fblockread_event, wait);

        if (qcom_smd_get_tx_avail(channel) > 20)
                mask |= EPOLLOUT | EPOLLWRNORM;

        return mask;
}

/*
 * Finds the device_node for the smd child interested in this channel.
 */
static struct device_node *qcom_smd_match_channel(struct device_node *edge_node,
                                                  const char *channel)
{
        struct device_node *child;
        const char *name;
        const char *key;
        int ret;

        for_each_available_child_of_node(edge_node, child) {
                key = "qcom,smd-channels";
                ret = of_property_read_string(child, key, &name);
                if (ret)
                        continue;

                if (strcmp(name, channel) == 0)
                        return child;
        }

        return NULL;
}

static int qcom_smd_announce_create(struct rpmsg_device *rpdev)

{
        struct qcom_smd_endpoint *qept = to_smd_endpoint(rpdev->ept);
        struct qcom_smd_channel *channel = qept->qsch;
        unsigned long flags;
        bool kick_state;

        spin_lock_irqsave(&channel->recv_lock, flags);
        kick_state = qcom_smd_channel_intr(channel);
        spin_unlock_irqrestore(&channel->recv_lock, flags);

        if (kick_state)
                schedule_work(&channel->edge->state_work);

        return 0;
}

static const struct rpmsg_device_ops qcom_smd_device_ops = {
        .create_ept = qcom_smd_create_ept,
        .announce_create = qcom_smd_announce_create,
};

static const struct rpmsg_endpoint_ops qcom_smd_endpoint_ops = {
        .destroy_ept = qcom_smd_destroy_ept,
        .send = qcom_smd_send,
        .trysend = qcom_smd_trysend,
        .poll = qcom_smd_poll,
};

static void qcom_smd_release_device(struct device *dev)
{
        struct rpmsg_device *rpdev = to_rpmsg_device(dev);
        struct qcom_smd_device *qsdev = to_smd_device(rpdev);

        kfree(qsdev);
}

/*
 * Create a smd client device for channel that is being opened.
 */
static int qcom_smd_create_device(struct qcom_smd_channel *channel)
{
        struct qcom_smd_device *qsdev;
        struct rpmsg_device *rpdev;
        struct qcom_smd_edge *edge = channel->edge;

        dev_dbg(&edge->dev, "registering '%s'\n", channel->name);

        qsdev = kzalloc(sizeof(*qsdev), GFP_KERNEL);
        if (!qsdev)
                return -ENOMEM;

        /* Link qsdev to our SMD edge */
        qsdev->edge = edge;

        /* Assign callbacks for rpmsg_device */
        qsdev->rpdev.ops = &qcom_smd_device_ops;

        /* Assign public information to the rpmsg_device */
        rpdev = &qsdev->rpdev;
        strncpy(rpdev->id.name, channel->name, RPMSG_NAME_SIZE);
        rpdev->src = RPMSG_ADDR_ANY;
        rpdev->dst = RPMSG_ADDR_ANY;

        rpdev->dev.of_node = qcom_smd_match_channel(edge->of_node, channel->name);
        rpdev->dev.parent = &edge->dev;
        rpdev->dev.release = qcom_smd_release_device;

        return rpmsg_register_device(rpdev);
}

static int qcom_smd_create_chrdev(struct qcom_smd_edge *edge)
{
        struct qcom_smd_device *qsdev;

        qsdev = kzalloc(sizeof(*qsdev), GFP_KERNEL);
        if (!qsdev)
                return -ENOMEM;

        qsdev->edge = edge;
        qsdev->rpdev.ops = &qcom_smd_device_ops;
        qsdev->rpdev.dev.parent = &edge->dev;
        qsdev->rpdev.dev.release = qcom_smd_release_device;

        return rpmsg_chrdev_register_device(&qsdev->rpdev);
}

/*
 * Allocate the qcom_smd_channel object for a newly found smd channel,
 * retrieving and validating the smem items involved.
 */
static struct qcom_smd_channel *qcom_smd_create_channel(struct qcom_smd_edge *edge,
                                                        unsigned smem_info_item,
                                                        unsigned smem_fifo_item,
                                                        char *name)
{
        struct qcom_smd_channel *channel;
        size_t fifo_size;
        size_t info_size;
        void *fifo_base;
        void *info;
        int ret;

        channel = devm_kzalloc(&edge->dev, sizeof(*channel), GFP_KERNEL);
        if (!channel)
                return ERR_PTR(-ENOMEM);

        channel->edge = edge;
        channel->name = devm_kstrdup(&edge->dev, name, GFP_KERNEL);
        if (!channel->name)
                return ERR_PTR(-ENOMEM);

        spin_lock_init(&channel->tx_lock);
        spin_lock_init(&channel->recv_lock);
        init_waitqueue_head(&channel->fblockread_event);
        init_waitqueue_head(&channel->state_change_event);

        info = qcom_smem_get(edge->remote_pid, smem_info_item, &info_size);
        if (IS_ERR(info)) {
                ret = PTR_ERR(info);
                goto free_name_and_channel;
        }

        /*
         * Use the size of the item to figure out which channel info struct to
         * use.
         */
        if (info_size == 2 * sizeof(struct smd_channel_info_word)) {
                channel->info_word = info;
        } else if (info_size == 2 * sizeof(struct smd_channel_info)) {
                channel->info = info;
        } else {
                dev_err(&edge->dev,
                        "channel info of size %zu not supported\n", info_size);
                ret = -EINVAL;
                goto free_name_and_channel;
        }

        fifo_base = qcom_smem_get(edge->remote_pid, smem_fifo_item, &fifo_size);
        if (IS_ERR(fifo_base)) {
                ret =  PTR_ERR(fifo_base);
                goto free_name_and_channel;
        }

        /* The channel consist of a rx and tx fifo of equal size */
        fifo_size /= 2;

        dev_dbg(&edge->dev, "new channel '%s' info-size: %zu fifo-size: %zu\n",
                          name, info_size, fifo_size);

        channel->tx_fifo = fifo_base;
        channel->rx_fifo = fifo_base + fifo_size;
        channel->fifo_size = fifo_size;

        qcom_smd_channel_reset(channel);

        return channel;

free_name_and_channel:
        devm_kfree(&edge->dev, channel->name);
        devm_kfree(&edge->dev, channel);

        return ERR_PTR(ret);
}

/*
 * Scans the allocation table for any newly allocated channels, calls
 * qcom_smd_create_channel() to create representations of these and add
 * them to the edge's list of channels.
 */
static void qcom_channel_scan_worker(struct work_struct *work)
{
        struct qcom_smd_edge *edge = container_of(work, struct qcom_smd_edge, scan_work);
        struct qcom_smd_alloc_entry *alloc_tbl;
        struct qcom_smd_alloc_entry *entry;
        struct qcom_smd_channel *channel;
        unsigned long flags;
        unsigned fifo_id;
        unsigned info_id;
        int tbl;
        int i;
        u32 eflags, cid;

        for (tbl = 0; tbl < SMD_ALLOC_TBL_COUNT; tbl++) {
                alloc_tbl = qcom_smem_get(edge->remote_pid,
                                    smem_items[tbl].alloc_tbl_id, NULL);
                if (IS_ERR(alloc_tbl))
                        continue;

                for (i = 0; i < SMD_ALLOC_TBL_SIZE; i++) {
                        entry = &alloc_tbl[i];
                        eflags = le32_to_cpu(entry->flags);
                        if (test_bit(i, edge->allocated[tbl]))
                                continue;

                        if (entry->ref_count == 0)
                                continue;

                        if (!entry->name[0])
                                continue;

                        if (!(eflags & SMD_CHANNEL_FLAGS_PACKET))
                                continue;

                        if ((eflags & SMD_CHANNEL_FLAGS_EDGE_MASK) != edge->edge_id)
                                continue;

                        cid = le32_to_cpu(entry->cid);
                        info_id = smem_items[tbl].info_base_id + cid;
                        fifo_id = smem_items[tbl].fifo_base_id + cid;

                        channel = qcom_smd_create_channel(edge, info_id, fifo_id, entry->name);
                        if (IS_ERR(channel))
                                continue;

                        spin_lock_irqsave(&edge->channels_lock, flags);
                        list_add(&channel->list, &edge->channels);
                        spin_unlock_irqrestore(&edge->channels_lock, flags);

                        dev_dbg(&edge->dev, "new channel found: '%s'\n", channel->name);
                        set_bit(i, edge->allocated[tbl]);

                        wake_up_interruptible_all(&edge->new_channel_event);
                }
        }

        schedule_work(&edge->state_work);
}

/*
 * This per edge worker scans smem for any new channels and register these. It
 * then scans all registered channels for state changes that should be handled
 * by creating or destroying smd client devices for the registered channels.
 *
 * LOCKING: edge->channels_lock only needs to cover the list operations, as the
 * worker is killed before any channels are deallocated
 */
static void qcom_channel_state_worker(struct work_struct *work)
{
        struct qcom_smd_channel *channel;
        struct qcom_smd_edge *edge = container_of(work,
                                                  struct qcom_smd_edge,
                                                  state_work);
        struct rpmsg_channel_info chinfo;
        unsigned remote_state;
        unsigned long flags;

        /*
         * Register a device for any closed channel where the remote processor
         * is showing interest in opening the channel.
         */
        spin_lock_irqsave(&edge->channels_lock, flags);
        list_for_each_entry(channel, &edge->channels, list) {
                if (channel->state != SMD_CHANNEL_CLOSED)
                        continue;

                remote_state = GET_RX_CHANNEL_INFO(channel, state);
                if (remote_state != SMD_CHANNEL_OPENING &&
                    remote_state != SMD_CHANNEL_OPENED)
                        continue;

                if (channel->registered)
                        continue;

                spin_unlock_irqrestore(&edge->channels_lock, flags);
                qcom_smd_create_device(channel);
                channel->registered = true;
                spin_lock_irqsave(&edge->channels_lock, flags);

                channel->registered = true;
        }

        /*
         * Unregister the device for any channel that is opened where the
         * remote processor is closing the channel.
         */
        list_for_each_entry(channel, &edge->channels, list) {
                if (channel->state != SMD_CHANNEL_OPENING &&
                    channel->state != SMD_CHANNEL_OPENED)
                        continue;

                remote_state = GET_RX_CHANNEL_INFO(channel, state);
                if (remote_state == SMD_CHANNEL_OPENING ||
                    remote_state == SMD_CHANNEL_OPENED)
                        continue;

                spin_unlock_irqrestore(&edge->channels_lock, flags);

                strncpy(chinfo.name, channel->name, sizeof(chinfo.name));
                chinfo.src = RPMSG_ADDR_ANY;
                chinfo.dst = RPMSG_ADDR_ANY;
                rpmsg_unregister_device(&edge->dev, &chinfo);
                channel->registered = false;
                spin_lock_irqsave(&edge->channels_lock, flags);
        }
        spin_unlock_irqrestore(&edge->channels_lock, flags);
}

/*
 * Parses an of_node describing an edge.
 */
static int qcom_smd_parse_edge(struct device *dev,
                               struct device_node *node,
                               struct qcom_smd_edge *edge)
{
        struct device_node *syscon_np;
        const char *key;
        int irq;
        int ret;

        INIT_LIST_HEAD(&edge->channels);
        spin_lock_init(&edge->channels_lock);

        INIT_WORK(&edge->scan_work, qcom_channel_scan_worker);
        INIT_WORK(&edge->state_work, qcom_channel_state_worker);

        edge->of_node = of_node_get(node);

        key = "qcom,smd-edge";
        ret = of_property_read_u32(node, key, &edge->edge_id);
        if (ret) {
                dev_err(dev, "edge missing %s property\n", key);
                return -EINVAL;
        }

        edge->remote_pid = QCOM_SMEM_HOST_ANY;
        key = "qcom,remote-pid";
        of_property_read_u32(node, key, &edge->remote_pid);

        syscon_np = of_parse_phandle(node, "qcom,ipc", 0);
        if (!syscon_np) {
                dev_err(dev, "no qcom,ipc node\n");
                return -ENODEV;
        }

        edge->ipc_regmap = syscon_node_to_regmap(syscon_np);
        if (IS_ERR(edge->ipc_regmap))
                return PTR_ERR(edge->ipc_regmap);

        key = "qcom,ipc";
        ret = of_property_read_u32_index(node, key, 1, &edge->ipc_offset);
        if (ret < 0) {
                dev_err(dev, "no offset in %s\n", key);
                return -EINVAL;
        }

        ret = of_property_read_u32_index(node, key, 2, &edge->ipc_bit);
        if (ret < 0) {
                dev_err(dev, "no bit in %s\n", key);
                return -EINVAL;
        }

        ret = of_property_read_string(node, "label", &edge->name);
        if (ret < 0)
                edge->name = node->name;

        irq = irq_of_parse_and_map(node, 0);
        if (irq < 0) {
                dev_err(dev, "required smd interrupt missing\n");
                return -EINVAL;
        }

        ret = devm_request_irq(dev, irq,
                               qcom_smd_edge_intr, IRQF_TRIGGER_RISING,
                               node->name, edge);
        if (ret) {
                dev_err(dev, "failed to request smd irq\n");
                return ret;
        }

        edge->irq = irq;

        return 0;
}

/*
 * Release function for an edge.
  * Reset the state of each associated channel and free the edge context.
 */
static void qcom_smd_edge_release(struct device *dev)
{
        struct qcom_smd_channel *channel;
        struct qcom_smd_edge *edge = to_smd_edge(dev);

        list_for_each_entry(channel, &edge->channels, list) {
                SET_RX_CHANNEL_INFO(channel, state, SMD_CHANNEL_CLOSED);
                SET_RX_CHANNEL_INFO(channel, head, 0);
                SET_RX_CHANNEL_INFO(channel, tail, 0);
        }

        kfree(edge);
}

static ssize_t rpmsg_name_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct qcom_smd_edge *edge = to_smd_edge(dev);

        return sprintf(buf, "%s\n", edge->name);
}
static DEVICE_ATTR_RO(rpmsg_name);

static struct attribute *qcom_smd_edge_attrs[] = {
        &dev_attr_rpmsg_name.attr,
        NULL
};
ATTRIBUTE_GROUPS(qcom_smd_edge);

/**
 * qcom_smd_register_edge() - register an edge based on an device_node
 * @parent:    parent device for the edge
 * @node:      device_node describing the edge
 *
 * Returns an edge reference, or negative ERR_PTR() on failure.
 */
struct qcom_smd_edge *qcom_smd_register_edge(struct device *parent,
                                             struct device_node *node)
{
        struct qcom_smd_edge *edge;
        int ret;

        edge = kzalloc(sizeof(*edge), GFP_KERNEL);
        if (!edge)
                return ERR_PTR(-ENOMEM);

        init_waitqueue_head(&edge->new_channel_event);

        edge->dev.parent = parent;
        edge->dev.release = qcom_smd_edge_release;
        edge->dev.of_node = node;
        edge->dev.groups = qcom_smd_edge_groups;
        dev_set_name(&edge->dev, "%s:%s", dev_name(parent), node->name);
        ret = device_register(&edge->dev);
        if (ret) {
                pr_err("failed to register smd edge\n");
                put_device(&edge->dev);
                return ERR_PTR(ret);
        }

        ret = qcom_smd_parse_edge(&edge->dev, node, edge);
        if (ret) {
                dev_err(&edge->dev, "failed to parse smd edge\n");
                goto unregister_dev;
        }

        ret = qcom_smd_create_chrdev(edge);
        if (ret) {
                dev_err(&edge->dev, "failed to register chrdev for edge\n");
                goto unregister_dev;
        }

        schedule_work(&edge->scan_work);

        return edge;

unregister_dev:
        device_unregister(&edge->dev);
        return ERR_PTR(ret);
}
EXPORT_SYMBOL(qcom_smd_register_edge);

static int qcom_smd_remove_device(struct device *dev, void *data)
{
        device_unregister(dev);

        return 0;
}

/**
 * qcom_smd_unregister_edge() - release an edge and its children
 * @edge:      edge reference acquired from qcom_smd_register_edge
 */
int qcom_smd_unregister_edge(struct qcom_smd_edge *edge)
{
        int ret;

        disable_irq(edge->irq);
        cancel_work_sync(&edge->scan_work);
        cancel_work_sync(&edge->state_work);

        ret = device_for_each_child(&edge->dev, NULL, qcom_smd_remove_device);
        if (ret)
                dev_warn(&edge->dev, "can't remove smd device: %d\n", ret);

        device_unregister(&edge->dev);

        return 0;
}
EXPORT_SYMBOL(qcom_smd_unregister_edge);

static int qcom_smd_probe(struct platform_device *pdev)
{
        struct device_node *node;
        void *p;

        /* Wait for smem */
        p = qcom_smem_get(QCOM_SMEM_HOST_ANY, smem_items[0].alloc_tbl_id, NULL);
        if (PTR_ERR(p) == -EPROBE_DEFER)
                return PTR_ERR(p);

        for_each_available_child_of_node(pdev->dev.of_node, node)
                qcom_smd_register_edge(&pdev->dev, node);

        return 0;
}

static int qcom_smd_remove_edge(struct device *dev, void *data)
{
        struct qcom_smd_edge *edge = to_smd_edge(dev);

        return qcom_smd_unregister_edge(edge);
}

/*
 * Shut down all smd clients by making sure that each edge stops processing
 * events and scanning for new channels, then call destroy on the devices.
 */
static int qcom_smd_remove(struct platform_device *pdev)
{
        int ret;

        ret = device_for_each_child(&pdev->dev, NULL, qcom_smd_remove_edge);
        if (ret)
                dev_warn(&pdev->dev, "can't remove smd device: %d\n", ret);

        return ret;
}

static const struct of_device_id qcom_smd_of_match[] = {
        { .compatible = "qcom,smd" },
        {}
};
MODULE_DEVICE_TABLE(of, qcom_smd_of_match);

static struct platform_driver qcom_smd_driver = {
        .probe = qcom_smd_probe,
        .remove = qcom_smd_remove,
        .driver = {
                .name = "qcom-smd",
                .of_match_table = qcom_smd_of_match,
        },
};

static int __init qcom_smd_init(void)
{
        return platform_driver_register(&qcom_smd_driver);
}
subsys_initcall(qcom_smd_init);

static void __exit qcom_smd_exit(void)
{
        platform_driver_unregister(&qcom_smd_driver);
}
module_exit(qcom_smd_exit);

MODULE_AUTHOR("Bjorn Andersson <bjorn.andersson@sonymobile.com>");
MODULE_DESCRIPTION("Qualcomm Shared Memory Driver");
MODULE_LICENSE("GPL v2");