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
12static 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 */
21static 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 */
39struct 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}
77EXPORT_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 */
90int 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}
110EXPORT_SYMBOL(dma_fence_chain_find_seqno);
111
112static const char *dma_fence_chain_get_driver_name(struct dma_fence *fence)
113{
114        return "dma_fence_chain";
115}
116
117static const char *dma_fence_chain_get_timeline_name(struct dma_fence *fence)
118{
119        return "unbound";
120}
121
122static 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
135static 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
144static 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
164static 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
179static 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
210const 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};
218EXPORT_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 */
230void 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}
258EXPORT_SYMBOL(dma_fence_chain_init);
259