// SPDX-License-Identifier: GPL-2.0-only
/*
 * fence-chain: chain fences together in a timeline
 *
 * Copyright (C) 2018 Advanced Micro Devices, Inc.
 * Authors:
 *      Christian König <christian.koenig@amd.com>
 */

#include <linux/dma-fence-chain.h>

static bool dma_fence_chain_enable_signaling(struct dma_fence *fence);

/**
 * dma_fence_chain_get_prev - use RCU to get a reference to the previous fence
 * @chain: chain node to get the previous node from
 *
 * Use dma_fence_get_rcu_safe to get a reference to the previous fence of the
 * chain node.
 */
static struct dma_fence *dma_fence_chain_get_prev(struct dma_fence_chain *chain)
{
        struct dma_fence *prev;

        rcu_read_lock();
        prev = dma_fence_get_rcu_safe(&chain->prev);
        rcu_read_unlock();
        return prev;
}

/**
 * dma_fence_chain_walk - chain walking function
 * @fence: current chain node
 *
 * Walk the chain to the next node. Returns the next fence or NULL if we are at
 * the end of the chain. Garbage collects chain nodes which are already
 * signaled.
 */
struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence)
{
        struct dma_fence_chain *chain, *prev_chain;
        struct dma_fence *prev, *replacement, *tmp;

        chain = to_dma_fence_chain(fence);
        if (!chain) {
                dma_fence_put(fence);
                return NULL;
        }

        while ((prev = dma_fence_chain_get_prev(chain))) {

                prev_chain = to_dma_fence_chain(prev);
                if (prev_chain) {
                        if (!dma_fence_is_signaled(prev_chain->fence))
                                break;

                        replacement = dma_fence_chain_get_prev(prev_chain);
                } else {
                        if (!dma_fence_is_signaled(prev))
                                break;

                        replacement = NULL;
                }

                tmp = cmpxchg((struct dma_fence __force **)&chain->prev,
                              prev, replacement);
                if (tmp == prev)
                        dma_fence_put(tmp);
                else
                        dma_fence_put(replacement);
                dma_fence_put(prev);
        }

        dma_fence_put(fence);
        return prev;
}
EXPORT_SYMBOL(dma_fence_chain_walk);

/**
 * dma_fence_chain_find_seqno - find fence chain node by seqno
 * @pfence: pointer to the chain node where to start
 * @seqno: the sequence number to search for
 *
 * Advance the fence pointer to the chain node which will signal this sequence
 * number. If no sequence number is provided then this is a no-op.
 *
 * Returns EINVAL if the fence is not a chain node or the sequence number has
 * not yet advanced far enough.
 */
int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno)
{
        struct dma_fence_chain *chain;

        if (!seqno)
                return 0;

        chain = to_dma_fence_chain(*pfence);
        if (!chain || chain->base.seqno < seqno)
                return -EINVAL;

        dma_fence_chain_for_each(*pfence, &chain->base) {
                if ((*pfence)->context != chain->base.context ||
                    to_dma_fence_chain(*pfence)->prev_seqno < seqno)
                        break;
        }
        dma_fence_put(&chain->base);

        return 0;
}
EXPORT_SYMBOL(dma_fence_chain_find_seqno);

static const char *dma_fence_chain_get_driver_name(struct dma_fence *fence)
{
        return "dma_fence_chain";
}

static const char *dma_fence_chain_get_timeline_name(struct dma_fence *fence)
{
        return "unbound";
}

static void dma_fence_chain_irq_work(struct irq_work *work)
{
        struct dma_fence_chain *chain;

        chain = container_of(work, typeof(*chain), work);

        /* Try to rearm the callback */
        if (!dma_fence_chain_enable_signaling(&chain->base))
                /* Ok, we are done. No more unsignaled fences left */
                dma_fence_signal(&chain->base);
        dma_fence_put(&chain->base);
}

static void dma_fence_chain_cb(struct dma_fence *f, struct dma_fence_cb *cb)
{
        struct dma_fence_chain *chain;

        chain = container_of(cb, typeof(*chain), cb);
        init_irq_work(&chain->work, dma_fence_chain_irq_work);
        irq_work_queue(&chain->work);
        dma_fence_put(f);
}

static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
{
        struct dma_fence_chain *head = to_dma_fence_chain(fence);

        dma_fence_get(&head->base);
        dma_fence_chain_for_each(fence, &head->base) {
                struct dma_fence_chain *chain = to_dma_fence_chain(fence);
                struct dma_fence *f = chain ? chain->fence : fence;

                dma_fence_get(f);
                if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb)) {
                        dma_fence_put(fence);
                        return true;
                }
                dma_fence_put(f);
        }
        dma_fence_put(&head->base);
        return false;
}

static bool dma_fence_chain_signaled(struct dma_fence *fence)
{
        dma_fence_chain_for_each(fence, fence) {
                struct dma_fence_chain *chain = to_dma_fence_chain(fence);
                struct dma_fence *f = chain ? chain->fence : fence;

                if (!dma_fence_is_signaled(f)) {
                        dma_fence_put(fence);
                        return false;
                }
        }

        return true;
}

static void dma_fence_chain_release(struct dma_fence *fence)
{
        struct dma_fence_chain *chain = to_dma_fence_chain(fence);
        struct dma_fence *prev;

        /* Manually unlink the chain as much as possible to avoid recursion
         * and potential stack overflow.
         */
        while ((prev = rcu_dereference_protected(chain->prev, true))) {
                struct dma_fence_chain *prev_chain;

                if (kref_read(&prev->refcount) > 1)
                       break;

                prev_chain = to_dma_fence_chain(prev);
                if (!prev_chain)
                        break;

                /* No need for atomic operations since we hold the last
                 * reference to prev_chain.
                 */
                chain->prev = prev_chain->prev;
                RCU_INIT_POINTER(prev_chain->prev, NULL);
                dma_fence_put(prev);
        }
        dma_fence_put(prev);

        dma_fence_put(chain->fence);
        dma_fence_free(fence);
}

const struct dma_fence_ops dma_fence_chain_ops = {
        .use_64bit_seqno = true,
        .get_driver_name = dma_fence_chain_get_driver_name,
        .get_timeline_name = dma_fence_chain_get_timeline_name,
        .enable_signaling = dma_fence_chain_enable_signaling,
        .signaled = dma_fence_chain_signaled,
        .release = dma_fence_chain_release,
};
EXPORT_SYMBOL(dma_fence_chain_ops);

/**
 * dma_fence_chain_init - initialize a fence chain
 * @chain: the chain node to initialize
 * @prev: the previous fence
 * @fence: the current fence
 * @seqno: the sequence number to use for the fence chain
 *
 * Initialize a new chain node and either start a new chain or add the node to
 * the existing chain of the previous fence.
 */
void dma_fence_chain_init(struct dma_fence_chain *chain,
                          struct dma_fence *prev,
                          struct dma_fence *fence,
                          uint64_t seqno)
{
        struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
        uint64_t context;

        spin_lock_init(&chain->lock);
        rcu_assign_pointer(chain->prev, prev);
        chain->fence = fence;
        chain->prev_seqno = 0;

        /* Try to reuse the context of the previous chain node. */
        if (prev_chain && __dma_fence_is_later(seqno, prev->seqno, prev->ops)) {
                context = prev->context;
                chain->prev_seqno = prev->seqno;
        } else {
                context = dma_fence_context_alloc(1);
                /* Make sure that we always have a valid sequence number. */
                if (prev_chain)
                        seqno = max(prev->seqno, seqno);
        }

        dma_fence_init(&chain->base, &dma_fence_chain_ops,
                       &chain->lock, context, seqno);
}
EXPORT_SYMBOL(dma_fence_chain_init);