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 	init_irq_work(&chain->work, dma_fence_chain_irq_work);
141 	irq_work_queue(&chain->work);
142 	dma_fence_put(f);
143 }
144 
145 static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
146 {
147 	struct dma_fence_chain *head = to_dma_fence_chain(fence);
148 
149 	dma_fence_get(&head->base);
150 	dma_fence_chain_for_each(fence, &head->base) {
151 		struct dma_fence *f = dma_fence_chain_contained(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 *f = dma_fence_chain_contained(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  * @seqno: the sequence number to use for the fence chain
225  *
226  * Initialize a new chain node and either start a new chain or add the node to
227  * the existing chain of the previous fence.
228  */
229 void dma_fence_chain_init(struct dma_fence_chain *chain,
230 			  struct dma_fence *prev,
231 			  struct dma_fence *fence,
232 			  uint64_t seqno)
233 {
234 	struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
235 	uint64_t context;
236 
237 	spin_lock_init(&chain->lock);
238 	rcu_assign_pointer(chain->prev, prev);
239 	chain->fence = fence;
240 	chain->prev_seqno = 0;
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 	/*
257 	 * Chaining dma_fence_chain container together is only allowed through
258 	 * the prev fence and not through the contained fence.
259 	 *
260 	 * The correct way of handling this is to flatten out the fence
261 	 * structure into a dma_fence_array by the caller instead.
262 	 */
263 	WARN_ON(dma_fence_is_chain(fence));
264 }
265 EXPORT_SYMBOL(dma_fence_chain_init);
266