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((struct dma_fence __force **)&chain->prev,
  66                               prev, replacement);
  67                 if (tmp == prev)
  68                         dma_fence_put(tmp);
  69                 else
  70                         dma_fence_put(replacement);
  71                 dma_fence_put(prev);
  72         }
  73
  74         dma_fence_put(fence);
  75         return prev;
  76 }
  77 EXPORT_SYMBOL(dma_fence_chain_walk);
  78
  79 /**
  80  * dma_fence_chain_find_seqno - find fence chain node by seqno
  81  * @pfence: pointer to the chain node where to start
  82  * @seqno: the sequence number to search for
  83  *
  84  * Advance the fence pointer to the chain node which will signal this sequence
  85  * number. If no sequence number is provided then this is a no-op.
  86  *
  87  * Returns EINVAL if the fence is not a chain node or the sequence number has
  88  * not yet advanced far enough.
  89  */
  90 int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno)
  91 {
  92         struct dma_fence_chain *chain;
  93
  94         if (!seqno)
  95                 return 0;
  96
  97         chain = to_dma_fence_chain(*pfence);
  98         if (!chain || chain->base.seqno < seqno)
  99                 return -EINVAL;
 100
 101         dma_fence_chain_for_each(*pfence, &chain->base) {
 102                 if ((*pfence)->context != chain->base.context ||
 103                     to_dma_fence_chain(*pfence)->prev_seqno < seqno)
 104                         break;
 105         }
 106         dma_fence_put(&chain->base);
 107
 108         return 0;
 109 }
 110 EXPORT_SYMBOL(dma_fence_chain_find_seqno);
 111
 112 static const char *dma_fence_chain_get_driver_name(struct dma_fence *fence)
 113 {
 114         return "dma_fence_chain";
 115 }
 116
 117 static const char *dma_fence_chain_get_timeline_name(struct dma_fence *fence)
 118 {
 119         return "unbound";
 120 }
 121
 122 static void dma_fence_chain_irq_work(struct irq_work *work)
 123 {
 124         struct dma_fence_chain *chain;
 125
 126         chain = container_of(work, typeof(*chain), work);
 127
 128         /* Try to rearm the callback */
 129         if (!dma_fence_chain_enable_signaling(&chain->base))
 130                 /* Ok, we are done. No more unsignaled fences left */
 131                 dma_fence_signal(&chain->base);
 132         dma_fence_put(&chain->base);
 133 }
 134
 135 static void dma_fence_chain_cb(struct dma_fence *f, struct dma_fence_cb *cb)
 136 {
 137         struct dma_fence_chain *chain;
 138
 139         chain = container_of(cb, typeof(*chain), cb);
 140         irq_work_queue(&chain->work);
 141         dma_fence_put(f);
 142 }
 143
 144 static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
 145 {
 146         struct dma_fence_chain *head = to_dma_fence_chain(fence);
 147
 148         dma_fence_get(&head->base);
 149         dma_fence_chain_for_each(fence, &head->base) {
 150                 struct dma_fence_chain *chain = to_dma_fence_chain(fence);
 151                 struct dma_fence *f = chain ? chain->fence : fence;
 152
 153                 dma_fence_get(f);
 154                 if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb)) {
 155                         dma_fence_put(fence);
 156                         return true;
 157                 }
 158                 dma_fence_put(f);
 159         }
 160         dma_fence_put(&head->base);
 161         return false;
 162 }
 163
 164 static bool dma_fence_chain_signaled(struct dma_fence *fence)
 165 {
 166         dma_fence_chain_for_each(fence, fence) {
 167                 struct dma_fence_chain *chain = to_dma_fence_chain(fence);
 168                 struct dma_fence *f = chain ? chain->fence : fence;
 169
 170                 if (!dma_fence_is_signaled(f)) {
 171                         dma_fence_put(fence);
 172                         return false;
 173                 }
 174         }
 175
 176         return true;
 177 }
 178
 179 static void dma_fence_chain_release(struct dma_fence *fence)
 180 {
 181         struct dma_fence_chain *chain = to_dma_fence_chain(fence);
 182         struct dma_fence *prev;
 183
 184         /* Manually unlink the chain as much as possible to avoid recursion
 185          * and potential stack overflow.
 186          */
 187         while ((prev = rcu_dereference_protected(chain->prev, true))) {
 188                 struct dma_fence_chain *prev_chain;
 189
 190                 if (kref_read(&prev->refcount) > 1)
 191                        break;
 192
 193                 prev_chain = to_dma_fence_chain(prev);
 194                 if (!prev_chain)
 195                         break;
 196
 197                 /* No need for atomic operations since we hold the last
 198                  * reference to prev_chain.
 199                  */
 200                 chain->prev = prev_chain->prev;
 201                 RCU_INIT_POINTER(prev_chain->prev, NULL);
 202                 dma_fence_put(prev);
 203         }
 204         dma_fence_put(prev);
 205
 206         dma_fence_put(chain->fence);
 207         dma_fence_free(fence);
 208 }
 209
 210 const struct dma_fence_ops dma_fence_chain_ops = {
 211         .use_64bit_seqno = true,
 212         .get_driver_name = dma_fence_chain_get_driver_name,
 213         .get_timeline_name = dma_fence_chain_get_timeline_name,
 214         .enable_signaling = dma_fence_chain_enable_signaling,
 215         .signaled = dma_fence_chain_signaled,
 216         .release = dma_fence_chain_release,
 217 };
 218 EXPORT_SYMBOL(dma_fence_chain_ops);
 219
 220 /**
 221  * dma_fence_chain_init - initialize a fence chain
 222  * @chain: the chain node to initialize
 223  * @prev: the previous fence
 224  * @fence: the current fence
 225  * @seqno: the sequence number to use for the fence chain
 226  *
 227  * Initialize a new chain node and either start a new chain or add the node to
 228  * the existing chain of the previous fence.
 229  */
 230 void dma_fence_chain_init(struct dma_fence_chain *chain,
 231                           struct dma_fence *prev,
 232                           struct dma_fence *fence,
 233                           uint64_t seqno)
 234 {
 235         struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
 236         uint64_t context;
 237
 238         spin_lock_init(&chain->lock);
 239         rcu_assign_pointer(chain->prev, prev);
 240         chain->fence = fence;
 241         chain->prev_seqno = 0;
 242         init_irq_work(&chain->work, dma_fence_chain_irq_work);
 243
 244         /* Try to reuse the context of the previous chain node. */
 245         if (prev_chain && __dma_fence_is_later(seqno, prev->seqno, prev->ops)) {
 246                 context = prev->context;
 247                 chain->prev_seqno = prev->seqno;
 248         } else {
 249                 context = dma_fence_context_alloc(1);
 250                 /* Make sure that we always have a valid sequence number. */
 251                 if (prev_chain)
 252                         seqno = max(prev->seqno, seqno);
 253         }
 254
 255         dma_fence_init(&chain->base, &dma_fence_chain_ops,
 256                        &chain->lock, context, seqno);
 257 }
 258 EXPORT_SYMBOL(dma_fence_chain_init);