drivers/dma-buf/dma-fence-chain.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * fence-chain: chain fences together in a timeline
   4  *
   5  * Copyright (C) 2018 Advanced Micro Devices, Inc.
   6  * Authors:
   7  *      Christian König <christian.koenig@amd.com>
   8  */
   9
  10 #include <linux/dma-fence-chain.h>
  11
  12 static bool dma_fence_chain_enable_signaling(struct dma_fence *fence);
  13
  14 /**
  15  * dma_fence_chain_get_prev - use RCU to get a reference to the previous fence
  16  * @chain: chain node to get the previous node from
  17  *
  18  * Use dma_fence_get_rcu_safe to get a reference to the previous fence of the
  19  * chain node.
  20  */
  21 static struct dma_fence *dma_fence_chain_get_prev(struct dma_fence_chain *chain)
  22 {
  23         struct dma_fence *prev;
  24
  25         rcu_read_lock();
  26         prev = dma_fence_get_rcu_safe(&chain->prev);
  27         rcu_read_unlock();
  28         return prev;
  29 }
  30
  31 /**
  32  * dma_fence_chain_walk - chain walking function
  33  * @fence: current chain node
  34  *
  35  * Walk the chain to the next node. Returns the next fence or NULL if we are at
  36  * the end of the chain. Garbage collects chain nodes which are already
  37  * signaled.
  38  */
  39 struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence)
  40 {
  41         struct dma_fence_chain *chain, *prev_chain;
  42         struct dma_fence *prev, *replacement, *tmp;
  43
  44         chain = to_dma_fence_chain(fence);
  45         if (!chain) {
  46                 dma_fence_put(fence);
  47                 return NULL;
  48         }
  49
  50         while ((prev = dma_fence_chain_get_prev(chain))) {
  51
  52                 prev_chain = to_dma_fence_chain(prev);
  53                 if (prev_chain) {
  54                         if (!dma_fence_is_signaled(prev_chain->fence))
  55                                 break;
  56
  57                         replacement = dma_fence_chain_get_prev(prev_chain);
  58                 } else {
  59                         if (!dma_fence_is_signaled(prev))
  60                                 break;
  61
  62                         replacement = NULL;
  63                 }
  64
  65                 tmp = cmpxchg((void **)&chain->prev, (void *)prev, (void *)replacement);
  66                 if (tmp == prev)
  67                         dma_fence_put(tmp);
  68                 else
  69                         dma_fence_put(replacement);
  70                 dma_fence_put(prev);
  71         }
  72
  73         dma_fence_put(fence);
  74         return prev;
  75 }
  76 EXPORT_SYMBOL(dma_fence_chain_walk);
  77
  78 /**
  79  * dma_fence_chain_find_seqno - find fence chain node by seqno
  80  * @pfence: pointer to the chain node where to start
  81  * @seqno: the sequence number to search for
  82  *
  83  * Advance the fence pointer to the chain node which will signal this sequence
  84  * number. If no sequence number is provided then this is a no-op.
  85  *
  86  * Returns EINVAL if the fence is not a chain node or the sequence number has
  87  * not yet advanced far enough.
  88  */
  89 int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno)
  90 {
  91         struct dma_fence_chain *chain;
  92
  93         if (!seqno)
  94                 return 0;
  95
  96         chain = to_dma_fence_chain(*pfence);
  97         if (!chain || chain->base.seqno < seqno)
  98                 return -EINVAL;
  99
 100         dma_fence_chain_for_each(*pfence, &chain->base) {
 101                 if ((*pfence)->context != chain->base.context ||
 102                     to_dma_fence_chain(*pfence)->prev_seqno < seqno)
 103                         break;
 104         }
 105         dma_fence_put(&chain->base);
 106
 107         return 0;
 108 }
 109 EXPORT_SYMBOL(dma_fence_chain_find_seqno);
 110
 111 static const char *dma_fence_chain_get_driver_name(struct dma_fence *fence)
 112 {
 113         return "dma_fence_chain";
 114 }
 115
 116 static const char *dma_fence_chain_get_timeline_name(struct dma_fence *fence)
 117 {
 118         return "unbound";
 119 }
 120
 121 static void dma_fence_chain_irq_work(struct irq_work *work)
 122 {
 123         struct dma_fence_chain *chain;
 124
 125         chain = container_of(work, typeof(*chain), work);
 126
 127         /* Try to rearm the callback */
 128         if (!dma_fence_chain_enable_signaling(&chain->base))
 129                 /* Ok, we are done. No more unsignaled fences left */
 130                 dma_fence_signal(&chain->base);
 131         dma_fence_put(&chain->base);
 132 }
 133
 134 static void dma_fence_chain_cb(struct dma_fence *f, struct dma_fence_cb *cb)
 135 {
 136         struct dma_fence_chain *chain;
 137
 138         chain = container_of(cb, typeof(*chain), cb);
 139         irq_work_queue(&chain->work);
 140         dma_fence_put(f);
 141 }
 142
 143 static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
 144 {
 145         struct dma_fence_chain *head = to_dma_fence_chain(fence);
 146
 147         dma_fence_get(&head->base);
 148         dma_fence_chain_for_each(fence, &head->base) {
 149                 struct dma_fence_chain *chain = to_dma_fence_chain(fence);
 150                 struct dma_fence *f = chain ? chain->fence : fence;
 151
 152                 dma_fence_get(f);
 153                 if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb)) {
 154                         dma_fence_put(fence);
 155                         return true;
 156                 }
 157                 dma_fence_put(f);
 158         }
 159         dma_fence_put(&head->base);
 160         return false;
 161 }
 162
 163 static bool dma_fence_chain_signaled(struct dma_fence *fence)
 164 {
 165         dma_fence_chain_for_each(fence, fence) {
 166                 struct dma_fence_chain *chain = to_dma_fence_chain(fence);
 167                 struct dma_fence *f = chain ? chain->fence : fence;
 168
 169                 if (!dma_fence_is_signaled(f)) {
 170                         dma_fence_put(fence);
 171                         return false;
 172                 }
 173         }
 174
 175         return true;
 176 }
 177
 178 static void dma_fence_chain_release(struct dma_fence *fence)
 179 {
 180         struct dma_fence_chain *chain = to_dma_fence_chain(fence);
 181         struct dma_fence *prev;
 182
 183         /* Manually unlink the chain as much as possible to avoid recursion
 184          * and potential stack overflow.
 185          */
 186         while ((prev = rcu_dereference_protected(chain->prev, true))) {
 187                 struct dma_fence_chain *prev_chain;
 188
 189                 if (kref_read(&prev->refcount) > 1)
 190                        break;
 191
 192                 prev_chain = to_dma_fence_chain(prev);
 193                 if (!prev_chain)
 194                         break;
 195
 196                 /* No need for atomic operations since we hold the last
 197                  * reference to prev_chain.
 198                  */
 199                 chain->prev = prev_chain->prev;
 200                 RCU_INIT_POINTER(prev_chain->prev, NULL);
 201                 dma_fence_put(prev);
 202         }
 203         dma_fence_put(prev);
 204
 205         dma_fence_put(chain->fence);
 206         dma_fence_free(fence);
 207 }
 208
 209 const struct dma_fence_ops dma_fence_chain_ops = {
 210         .use_64bit_seqno = true,
 211         .get_driver_name = dma_fence_chain_get_driver_name,
 212         .get_timeline_name = dma_fence_chain_get_timeline_name,
 213         .enable_signaling = dma_fence_chain_enable_signaling,
 214         .signaled = dma_fence_chain_signaled,
 215         .release = dma_fence_chain_release,
 216 };
 217 EXPORT_SYMBOL(dma_fence_chain_ops);
 218
 219 /**
 220  * dma_fence_chain_init - initialize a fence chain
 221  * @chain: the chain node to initialize
 222  * @prev: the previous fence
 223  * @fence: the current fence
 224  *
 225  * Initialize a new chain node and either start a new chain or add the node to
 226  * the existing chain of the previous fence.
 227  */
 228 void dma_fence_chain_init(struct dma_fence_chain *chain,
 229                           struct dma_fence *prev,
 230                           struct dma_fence *fence,
 231                           uint64_t seqno)
 232 {
 233         struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
 234         uint64_t context;
 235
 236         spin_lock_init(&chain->lock);
 237         rcu_assign_pointer(chain->prev, prev);
 238         chain->fence = fence;
 239         chain->prev_seqno = 0;
 240         init_irq_work(&chain->work, dma_fence_chain_irq_work);
 241
 242         /* Try to reuse the context of the previous chain node. */
 243         if (prev_chain && __dma_fence_is_later(seqno, prev->seqno, prev->ops)) {
 244                 context = prev->context;
 245                 chain->prev_seqno = prev->seqno;
 246         } else {
 247                 context = dma_fence_context_alloc(1);
 248                 /* Make sure that we always have a valid sequence number. */
 249                 if (prev_chain)
 250                         seqno = max(prev->seqno, seqno);
 251         }
 252
 253         dma_fence_init(&chain->base, &dma_fence_chain_ops,
 254                        &chain->lock, context, seqno);
 255 }
 256 EXPORT_SYMBOL(dma_fence_chain_init);