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 */
dma_fence_chain_get_prev(struct dma_fence_chain * chain)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 */
dma_fence_chain_walk(struct dma_fence * fence)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 */
dma_fence_chain_find_seqno(struct dma_fence ** pfence,uint64_t seqno)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
dma_fence_chain_get_driver_name(struct dma_fence * fence)112 static const char *dma_fence_chain_get_driver_name(struct dma_fence *fence)
113 {
114 return "dma_fence_chain";
115 }
116
dma_fence_chain_get_timeline_name(struct dma_fence * fence)117 static const char *dma_fence_chain_get_timeline_name(struct dma_fence *fence)
118 {
119 return "unbound";
120 }
121
dma_fence_chain_irq_work(struct irq_work * work)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
dma_fence_chain_cb(struct dma_fence * f,struct dma_fence_cb * cb)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
dma_fence_chain_enable_signaling(struct dma_fence * fence)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
dma_fence_chain_signaled(struct dma_fence * fence)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
dma_fence_chain_release(struct dma_fence * fence)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 */
dma_fence_chain_init(struct dma_fence_chain * chain,struct dma_fence * prev,struct dma_fence * fence,uint64_t seqno)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);
259