/*
 * Copyright (c) 2014-2016, NVIDIA CORPORATION.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope 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 <soc/tegra/ivc.h>

#define TEGRA_IVC_ALIGN 64

/*
 * IVC channel reset protocol.
 *
 * Each end uses its tx_channel.state to indicate its synchronization state.
 */
enum tegra_ivc_state {
        /*
         * This value is zero for backwards compatibility with services that
         * assume channels to be initially zeroed. Such channels are in an
         * initially valid state, but cannot be asynchronously reset, and must
         * maintain a valid state at all times.
         *
         * The transmitting end can enter the established state from the sync or
         * ack state when it observes the receiving endpoint in the ack or
         * established state, indicating that has cleared the counters in our
         * rx_channel.
         */
        TEGRA_IVC_STATE_ESTABLISHED = 0,

        /*
         * If an endpoint is observed in the sync state, the remote endpoint is
         * allowed to clear the counters it owns asynchronously with respect to
         * the current endpoint. Therefore, the current endpoint is no longer
         * allowed to communicate.
         */
        TEGRA_IVC_STATE_SYNC,

        /*
         * When the transmitting end observes the receiving end in the sync
         * state, it can clear the w_count and r_count and transition to the ack
         * state. If the remote endpoint observes us in the ack state, it can
         * return to the established state once it has cleared its counters.
         */
        TEGRA_IVC_STATE_ACK
};

/*
 * This structure is divided into two-cache aligned parts, the first is only
 * written through the tx.channel pointer, while the second is only written
 * through the rx.channel pointer. This delineates ownership of the cache
 * lines, which is critical to performance and necessary in non-cache coherent
 * implementations.
 */
struct tegra_ivc_header {
        union {
                struct {
                        /* fields owned by the transmitting end */
                        u32 count;
                        u32 state;
                };

                u8 pad[TEGRA_IVC_ALIGN];
        } tx;

        union {
                /* fields owned by the receiving end */
                u32 count;
                u8 pad[TEGRA_IVC_ALIGN];
        } rx;
};

static inline void tegra_ivc_invalidate(struct tegra_ivc *ivc, dma_addr_t phys)
{
        if (!ivc->peer)
                return;

        dma_sync_single_for_cpu(ivc->peer, phys, TEGRA_IVC_ALIGN,
                                DMA_FROM_DEVICE);
}

static inline void tegra_ivc_flush(struct tegra_ivc *ivc, dma_addr_t phys)
{
        if (!ivc->peer)
                return;

        dma_sync_single_for_device(ivc->peer, phys, TEGRA_IVC_ALIGN,
                                   DMA_TO_DEVICE);
}

static inline bool tegra_ivc_empty(struct tegra_ivc *ivc,
                                   struct tegra_ivc_header *header)
{
        /*
         * This function performs multiple checks on the same values with
         * security implications, so create snapshots with READ_ONCE() to
         * ensure that these checks use the same values.
         */
        u32 tx = READ_ONCE(header->tx.count);
        u32 rx = READ_ONCE(header->rx.count);

        /*
         * Perform an over-full check to prevent denial of service attacks
         * where a server could be easily fooled into believing that there's
         * an extremely large number of frames ready, since receivers are not
         * expected to check for full or over-full conditions.
         *
         * Although the channel isn't empty, this is an invalid case caused by
         * a potentially malicious peer, so returning empty is safer, because
         * it gives the impression that the channel has gone silent.
         */
        if (tx - rx > ivc->num_frames)
                return true;

        return tx == rx;
}

static inline bool tegra_ivc_full(struct tegra_ivc *ivc,
                                  struct tegra_ivc_header *header)
{
        u32 tx = READ_ONCE(header->tx.count);
        u32 rx = READ_ONCE(header->rx.count);

        /*
         * Invalid cases where the counters indicate that the queue is over
         * capacity also appear full.
         */
        return tx - rx >= ivc->num_frames;
}

static inline u32 tegra_ivc_available(struct tegra_ivc *ivc,
                                      struct tegra_ivc_header *header)
{
        u32 tx = READ_ONCE(header->tx.count);
        u32 rx = READ_ONCE(header->rx.count);

        /*
         * This function isn't expected to be used in scenarios where an
         * over-full situation can lead to denial of service attacks. See the
         * comment in tegra_ivc_empty() for an explanation about special
         * over-full considerations.
         */
        return tx - rx;
}

static inline void tegra_ivc_advance_tx(struct tegra_ivc *ivc)
{
        WRITE_ONCE(ivc->tx.channel->tx.count,
                   READ_ONCE(ivc->tx.channel->tx.count) + 1);

        if (ivc->tx.position == ivc->num_frames - 1)
                ivc->tx.position = 0;
        else
                ivc->tx.position++;
}

static inline void tegra_ivc_advance_rx(struct tegra_ivc *ivc)
{
        WRITE_ONCE(ivc->rx.channel->rx.count,
                   READ_ONCE(ivc->rx.channel->rx.count) + 1);

        if (ivc->rx.position == ivc->num_frames - 1)
                ivc->rx.position = 0;
        else
                ivc->rx.position++;
}

static inline int tegra_ivc_check_read(struct tegra_ivc *ivc)
{
        unsigned int offset = offsetof(struct tegra_ivc_header, tx.count);

        /*
         * tx.channel->state is set locally, so it is not synchronized with
         * state from the remote peer. The remote peer cannot reset its
         * transmit counters until we've acknowledged its synchronization
         * request, so no additional synchronization is required because an
         * asynchronous transition of rx.channel->state to
         * TEGRA_IVC_STATE_ACK is not allowed.
         */
        if (ivc->tx.channel->tx.state != TEGRA_IVC_STATE_ESTABLISHED)
                return -ECONNRESET;

        /*
         * Avoid unnecessary invalidations when performing repeated accesses
         * to an IVC channel by checking the old queue pointers first.
         *
         * Synchronization is only necessary when these pointers indicate
         * empty or full.
         */
        if (!tegra_ivc_empty(ivc, ivc->rx.channel))
                return 0;

        tegra_ivc_invalidate(ivc, ivc->rx.phys + offset);

        if (tegra_ivc_empty(ivc, ivc->rx.channel))
                return -ENOSPC;

        return 0;
}

static inline int tegra_ivc_check_write(struct tegra_ivc *ivc)
{
        unsigned int offset = offsetof(struct tegra_ivc_header, rx.count);

        if (ivc->tx.channel->tx.state != TEGRA_IVC_STATE_ESTABLISHED)
                return -ECONNRESET;

        if (!tegra_ivc_full(ivc, ivc->tx.channel))
                return 0;

        tegra_ivc_invalidate(ivc, ivc->tx.phys + offset);

        if (tegra_ivc_full(ivc, ivc->tx.channel))
                return -ENOSPC;

        return 0;
}

static void *tegra_ivc_frame_virt(struct tegra_ivc *ivc,
                                  struct tegra_ivc_header *header,
                                  unsigned int frame)
{
        if (WARN_ON(frame >= ivc->num_frames))
                return ERR_PTR(-EINVAL);

        return (void *)(header + 1) + ivc->frame_size * frame;
}

static inline dma_addr_t tegra_ivc_frame_phys(struct tegra_ivc *ivc,
                                              dma_addr_t phys,
                                              unsigned int frame)
{
        unsigned long offset;

        offset = sizeof(struct tegra_ivc_header) + ivc->frame_size * frame;

        return phys + offset;
}

static inline void tegra_ivc_invalidate_frame(struct tegra_ivc *ivc,
                                              dma_addr_t phys,
                                              unsigned int frame,
                                              unsigned int offset,
                                              size_t size)
{
        if (!ivc->peer || WARN_ON(frame >= ivc->num_frames))
                return;

        phys = tegra_ivc_frame_phys(ivc, phys, frame) + offset;

        dma_sync_single_for_cpu(ivc->peer, phys, size, DMA_FROM_DEVICE);
}

static inline void tegra_ivc_flush_frame(struct tegra_ivc *ivc,
                                         dma_addr_t phys,
                                         unsigned int frame,
                                         unsigned int offset,
                                         size_t size)
{
        if (!ivc->peer || WARN_ON(frame >= ivc->num_frames))
                return;

        phys = tegra_ivc_frame_phys(ivc, phys, frame) + offset;

        dma_sync_single_for_device(ivc->peer, phys, size, DMA_TO_DEVICE);
}

/* directly peek at the next frame rx'ed */
void *tegra_ivc_read_get_next_frame(struct tegra_ivc *ivc)
{
        int err;

        if (WARN_ON(ivc == NULL))
                return ERR_PTR(-EINVAL);

        err = tegra_ivc_check_read(ivc);
        if (err < 0)
                return ERR_PTR(err);

        /*
         * Order observation of ivc->rx.position potentially indicating new
         * data before data read.
         */
        smp_rmb();

        tegra_ivc_invalidate_frame(ivc, ivc->rx.phys, ivc->rx.position, 0,
                                   ivc->frame_size);

        return tegra_ivc_frame_virt(ivc, ivc->rx.channel, ivc->rx.position);
}
EXPORT_SYMBOL(tegra_ivc_read_get_next_frame);

int tegra_ivc_read_advance(struct tegra_ivc *ivc)
{
        unsigned int rx = offsetof(struct tegra_ivc_header, rx.count);
        unsigned int tx = offsetof(struct tegra_ivc_header, tx.count);
        int err;

        /*
         * No read barriers or synchronization here: the caller is expected to
         * have already observed the channel non-empty. This check is just to
         * catch programming errors.
         */
        err = tegra_ivc_check_read(ivc);
        if (err < 0)
                return err;

        tegra_ivc_advance_rx(ivc);

        tegra_ivc_flush(ivc, ivc->rx.phys + rx);

        /*
         * Ensure our write to ivc->rx.position occurs before our read from
         * ivc->tx.position.
         */
        smp_mb();

        /*
         * Notify only upon transition from full to non-full. The available
         * count can only asynchronously increase, so the worst possible
         * side-effect will be a spurious notification.
         */
        tegra_ivc_invalidate(ivc, ivc->rx.phys + tx);

        if (tegra_ivc_available(ivc, ivc->rx.channel) == ivc->num_frames - 1)
                ivc->notify(ivc, ivc->notify_data);

        return 0;
}
EXPORT_SYMBOL(tegra_ivc_read_advance);

/* directly poke at the next frame to be tx'ed */
void *tegra_ivc_write_get_next_frame(struct tegra_ivc *ivc)
{
        int err;

        err = tegra_ivc_check_write(ivc);
        if (err < 0)
                return ERR_PTR(err);

        return tegra_ivc_frame_virt(ivc, ivc->tx.channel, ivc->tx.position);
}
EXPORT_SYMBOL(tegra_ivc_write_get_next_frame);

/* advance the tx buffer */
int tegra_ivc_write_advance(struct tegra_ivc *ivc)
{
        unsigned int tx = offsetof(struct tegra_ivc_header, tx.count);
        unsigned int rx = offsetof(struct tegra_ivc_header, rx.count);
        int err;

        err = tegra_ivc_check_write(ivc);
        if (err < 0)
                return err;

        tegra_ivc_flush_frame(ivc, ivc->tx.phys, ivc->tx.position, 0,
                              ivc->frame_size);

        /*
         * Order any possible stores to the frame before update of
         * ivc->tx.position.
         */
        smp_wmb();

        tegra_ivc_advance_tx(ivc);
        tegra_ivc_flush(ivc, ivc->tx.phys + tx);

        /*
         * Ensure our write to ivc->tx.position occurs before our read from
         * ivc->rx.position.
         */
        smp_mb();

        /*
         * Notify only upon transition from empty to non-empty. The available
         * count can only asynchronously decrease, so the worst possible
         * side-effect will be a spurious notification.
         */
        tegra_ivc_invalidate(ivc, ivc->tx.phys + rx);

        if (tegra_ivc_available(ivc, ivc->tx.channel) == 1)
                ivc->notify(ivc, ivc->notify_data);

        return 0;
}
EXPORT_SYMBOL(tegra_ivc_write_advance);

void tegra_ivc_reset(struct tegra_ivc *ivc)
{
        unsigned int offset = offsetof(struct tegra_ivc_header, tx.count);

        ivc->tx.channel->tx.state = TEGRA_IVC_STATE_SYNC;
        tegra_ivc_flush(ivc, ivc->tx.phys + offset);
        ivc->notify(ivc, ivc->notify_data);
}
EXPORT_SYMBOL(tegra_ivc_reset);

/*
 * =======================================================
 *  IVC State Transition Table - see tegra_ivc_notified()
 * =======================================================
 *
 *      local   remote  action
 *      -----   ------  -----------------------------------
 *      SYNC    EST     <none>
 *      SYNC    ACK     reset counters; move to EST; notify
 *      SYNC    SYNC    reset counters; move to ACK; notify
 *      ACK     EST     move to EST; notify
 *      ACK     ACK     move to EST; notify
 *      ACK     SYNC    reset counters; move to ACK; notify
 *      EST     EST     <none>
 *      EST     ACK     <none>
 *      EST     SYNC    reset counters; move to ACK; notify
 *
 * ===============================================================
 */

int tegra_ivc_notified(struct tegra_ivc *ivc)
{
        unsigned int offset = offsetof(struct tegra_ivc_header, tx.count);
        enum tegra_ivc_state state;

        /* Copy the receiver's state out of shared memory. */
        tegra_ivc_invalidate(ivc, ivc->rx.phys + offset);
        state = READ_ONCE(ivc->rx.channel->tx.state);

        if (state == TEGRA_IVC_STATE_SYNC) {
                offset = offsetof(struct tegra_ivc_header, tx.count);

                /*
                 * Order observation of TEGRA_IVC_STATE_SYNC before stores
                 * clearing tx.channel.
                 */
                smp_rmb();

                /*
                 * Reset tx.channel counters. The remote end is in the SYNC
                 * state and won't make progress until we change our state,
                 * so the counters are not in use at this time.
                 */
                ivc->tx.channel->tx.count = 0;
                ivc->rx.channel->rx.count = 0;

                ivc->tx.position = 0;
                ivc->rx.position = 0;

                /*
                 * Ensure that counters appear cleared before new state can be
                 * observed.
                 */
                smp_wmb();

                /*
                 * Move to ACK state. We have just cleared our counters, so it
                 * is now safe for the remote end to start using these values.
                 */
                ivc->tx.channel->tx.state = TEGRA_IVC_STATE_ACK;
                tegra_ivc_flush(ivc, ivc->tx.phys + offset);

                /*
                 * Notify remote end to observe state transition.
                 */
                ivc->notify(ivc, ivc->notify_data);

        } else if (ivc->tx.channel->tx.state == TEGRA_IVC_STATE_SYNC &&
                   state == TEGRA_IVC_STATE_ACK) {
                offset = offsetof(struct tegra_ivc_header, tx.count);

                /*
                 * Order observation of ivc_state_sync before stores clearing
                 * tx_channel.
                 */
                smp_rmb();

                /*
                 * Reset tx.channel counters. The remote end is in the ACK
                 * state and won't make progress until we change our state,
                 * so the counters are not in use at this time.
                 */
                ivc->tx.channel->tx.count = 0;
                ivc->rx.channel->rx.count = 0;

                ivc->tx.position = 0;
                ivc->rx.position = 0;

                /*
                 * Ensure that counters appear cleared before new state can be
                 * observed.
                 */
                smp_wmb();

                /*
                 * Move to ESTABLISHED state. We know that the remote end has
                 * already cleared its counters, so it is safe to start
                 * writing/reading on this channel.
                 */
                ivc->tx.channel->tx.state = TEGRA_IVC_STATE_ESTABLISHED;
                tegra_ivc_flush(ivc, ivc->tx.phys + offset);

                /*
                 * Notify remote end to observe state transition.
                 */
                ivc->notify(ivc, ivc->notify_data);

        } else if (ivc->tx.channel->tx.state == TEGRA_IVC_STATE_ACK) {
                offset = offsetof(struct tegra_ivc_header, tx.count);

                /*
                 * At this point, we have observed the peer to be in either
                 * the ACK or ESTABLISHED state. Next, order observation of
                 * peer state before storing to tx.channel.
                 */
                smp_rmb();

                /*
                 * Move to ESTABLISHED state. We know that we have previously
                 * cleared our counters, and we know that the remote end has
                 * cleared its counters, so it is safe to start writing/reading
                 * on this channel.
                 */
                ivc->tx.channel->tx.state = TEGRA_IVC_STATE_ESTABLISHED;
                tegra_ivc_flush(ivc, ivc->tx.phys + offset);

                /*
                 * Notify remote end to observe state transition.
                 */
                ivc->notify(ivc, ivc->notify_data);

        } else {
                /*
                 * There is no need to handle any further action. Either the
                 * channel is already fully established, or we are waiting for
                 * the remote end to catch up with our current state. Refer
                 * to the diagram in "IVC State Transition Table" above.
                 */
        }

        if (ivc->tx.channel->tx.state != TEGRA_IVC_STATE_ESTABLISHED)
                return -EAGAIN;

        return 0;
}
EXPORT_SYMBOL(tegra_ivc_notified);

size_t tegra_ivc_align(size_t size)
{
        return ALIGN(size, TEGRA_IVC_ALIGN);
}
EXPORT_SYMBOL(tegra_ivc_align);

unsigned tegra_ivc_total_queue_size(unsigned queue_size)
{
        if (!IS_ALIGNED(queue_size, TEGRA_IVC_ALIGN)) {
                pr_err("%s: queue_size (%u) must be %u-byte aligned\n",
                       __func__, queue_size, TEGRA_IVC_ALIGN);
                return 0;
        }

        return queue_size + sizeof(struct tegra_ivc_header);
}
EXPORT_SYMBOL(tegra_ivc_total_queue_size);

static int tegra_ivc_check_params(unsigned long rx, unsigned long tx,
                                  unsigned int num_frames, size_t frame_size)
{
        BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct tegra_ivc_header, tx.count),
                                 TEGRA_IVC_ALIGN));
        BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct tegra_ivc_header, rx.count),
                                 TEGRA_IVC_ALIGN));
        BUILD_BUG_ON(!IS_ALIGNED(sizeof(struct tegra_ivc_header),
                                 TEGRA_IVC_ALIGN));

        if ((uint64_t)num_frames * (uint64_t)frame_size >= 0x100000000UL) {
                pr_err("num_frames * frame_size overflows\n");
                return -EINVAL;
        }

        if (!IS_ALIGNED(frame_size, TEGRA_IVC_ALIGN)) {
                pr_err("frame size not adequately aligned: %zu\n", frame_size);
                return -EINVAL;
        }

        /*
         * The headers must at least be aligned enough for counters
         * to be accessed atomically.
         */
        if (!IS_ALIGNED(rx, TEGRA_IVC_ALIGN)) {
                pr_err("IVC channel start not aligned: %#lx\n", rx);
                return -EINVAL;
        }

        if (!IS_ALIGNED(tx, TEGRA_IVC_ALIGN)) {
                pr_err("IVC channel start not aligned: %#lx\n", tx);
                return -EINVAL;
        }

        if (rx < tx) {
                if (rx + frame_size * num_frames > tx) {
                        pr_err("queue regions overlap: %#lx + %zx > %#lx\n",
                               rx, frame_size * num_frames, tx);
                        return -EINVAL;
                }
        } else {
                if (tx + frame_size * num_frames > rx) {
                        pr_err("queue regions overlap: %#lx + %zx > %#lx\n",
                               tx, frame_size * num_frames, rx);
                        return -EINVAL;
                }
        }

        return 0;
}

int tegra_ivc_init(struct tegra_ivc *ivc, struct device *peer, void *rx,
                   dma_addr_t rx_phys, void *tx, dma_addr_t tx_phys,
                   unsigned int num_frames, size_t frame_size,
                   void (*notify)(struct tegra_ivc *ivc, void *data),
                   void *data)
{
        size_t queue_size;
        int err;

        if (WARN_ON(!ivc || !notify))
                return -EINVAL;

        /*
         * All sizes that can be returned by communication functions should
         * fit in an int.
         */
        if (frame_size > INT_MAX)
                return -E2BIG;

        err = tegra_ivc_check_params((unsigned long)rx, (unsigned long)tx,
                                     num_frames, frame_size);
        if (err < 0)
                return err;

        queue_size = tegra_ivc_total_queue_size(num_frames * frame_size);

        if (peer) {
                ivc->rx.phys = dma_map_single(peer, rx, queue_size,
                                              DMA_BIDIRECTIONAL);
                if (dma_mapping_error(peer, ivc->rx.phys))
                        return -ENOMEM;

                ivc->tx.phys = dma_map_single(peer, tx, queue_size,
                                              DMA_BIDIRECTIONAL);
                if (dma_mapping_error(peer, ivc->tx.phys)) {
                        dma_unmap_single(peer, ivc->rx.phys, queue_size,
                                         DMA_BIDIRECTIONAL);
                        return -ENOMEM;
                }
        } else {
                ivc->rx.phys = rx_phys;
                ivc->tx.phys = tx_phys;
        }

        ivc->rx.channel = rx;
        ivc->tx.channel = tx;
        ivc->peer = peer;
        ivc->notify = notify;
        ivc->notify_data = data;
        ivc->frame_size = frame_size;
        ivc->num_frames = num_frames;

        /*
         * These values aren't necessarily correct until the channel has been
         * reset.
         */
        ivc->tx.position = 0;
        ivc->rx.position = 0;

        return 0;
}
EXPORT_SYMBOL(tegra_ivc_init);

void tegra_ivc_cleanup(struct tegra_ivc *ivc)
{
        if (ivc->peer) {
                size_t size = tegra_ivc_total_queue_size(ivc->num_frames *
                                                         ivc->frame_size);

                dma_unmap_single(ivc->peer, ivc->rx.phys, size,
                                 DMA_BIDIRECTIONAL);
                dma_unmap_single(ivc->peer, ivc->tx.phys, size,
                                 DMA_BIDIRECTIONAL);
        }
}
EXPORT_SYMBOL(tegra_ivc_cleanup);