Quelle  dma-fence-chain.c   Sprache: C

// 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 = unrcu_pointer(cmpxchg(&chain->prev, RCU_INITIALIZER(prev),
          RCU_INITIALIZER(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 *f = dma_fence_chain_contained(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 *f = dma_fence_chain_contained(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);
}


static void dma_fence_chain_set_deadline(struct dma_fence *fence,
      ktime_t deadline)
{
 dma_fence_chain_for_each(fence, fence) {
  struct dma_fence *f = dma_fence_chain_contained(fence);

  dma_fence_set_deadline(f, deadline);
 }
}

const struct dma_fence_ops dma_fence_chain_ops = {
 .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,
 .set_deadline = dma_fence_chain_set_deadline,
};
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(prev, seqno, prev->seqno)) {
  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_init64(&chain->base, &dma_fence_chain_ops, &chain->lock,
    context, seqno);

 /*
 * Chaining dma_fence_chain container together is only allowed through
 * the prev fence and not through the contained fence.
 *
 * The correct way of handling this is to flatten out the fence
 * structure into a dma_fence_array by the caller instead.
 */
 WARN_ON(dma_fence_is_chain(fence));
}
EXPORT_SYMBOL(dma_fence_chain_init);