summaryrefslogtreecommitdiff
path: root/drivers/gpu/drm/i915/i915_active.c
blob: d960d0be5bd2fb62cae1261f35b51c8174cc76ef (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright © 2019 Intel Corporation
 */

#include <linux/debugobjects.h>

#include "gt/intel_context.h"
#include "gt/intel_engine_heartbeat.h"
#include "gt/intel_engine_pm.h"
#include "gt/intel_ring.h"

#include "i915_drv.h"
#include "i915_active.h"
#include "i915_globals.h"

/*
 * Active refs memory management
 *
 * To be more economical with memory, we reap all the i915_active trees as
 * they idle (when we know the active requests are inactive) and allocate the
 * nodes from a local slab cache to hopefully reduce the fragmentation.
 */
static struct i915_global_active {
	struct i915_global base;
	struct kmem_cache *slab_cache;
} global;

struct active_node {
	struct i915_active_fence base;
	struct i915_active *ref;
	struct rb_node node;
	u64 timeline;
};

static inline struct active_node *
node_from_active(struct i915_active_fence *active)
{
	return container_of(active, struct active_node, base);
}

#define take_preallocated_barriers(x) llist_del_all(&(x)->preallocated_barriers)

static inline bool is_barrier(const struct i915_active_fence *active)
{
	return IS_ERR(rcu_access_pointer(active->fence));
}

static inline struct llist_node *barrier_to_ll(struct active_node *node)
{
	GEM_BUG_ON(!is_barrier(&node->base));
	return (struct llist_node *)&node->base.cb.node;
}

static inline struct intel_engine_cs *
__barrier_to_engine(struct active_node *node)
{
	return (struct intel_engine_cs *)READ_ONCE(node->base.cb.node.prev);
}

static inline struct intel_engine_cs *
barrier_to_engine(struct active_node *node)
{
	GEM_BUG_ON(!is_barrier(&node->base));
	return __barrier_to_engine(node);
}

static inline struct active_node *barrier_from_ll(struct llist_node *x)
{
	return container_of((struct list_head *)x,
			    struct active_node, base.cb.node);
}

#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && IS_ENABLED(CONFIG_DEBUG_OBJECTS)

static void *active_debug_hint(void *addr)
{
	struct i915_active *ref = addr;

	return (void *)ref->active ?: (void *)ref->retire ?: (void *)ref;
}

static struct debug_obj_descr active_debug_desc = {
	.name = "i915_active",
	.debug_hint = active_debug_hint,
};

static void debug_active_init(struct i915_active *ref)
{
	debug_object_init(ref, &active_debug_desc);
}

static void debug_active_activate(struct i915_active *ref)
{
	lockdep_assert_held(&ref->tree_lock);
	if (!atomic_read(&ref->count)) /* before the first inc */
		debug_object_activate(ref, &active_debug_desc);
}

static void debug_active_deactivate(struct i915_active *ref)
{
	lockdep_assert_held(&ref->tree_lock);
	if (!atomic_read(&ref->count)) /* after the last dec */
		debug_object_deactivate(ref, &active_debug_desc);
}

static void debug_active_fini(struct i915_active *ref)
{
	debug_object_free(ref, &active_debug_desc);
}

static void debug_active_assert(struct i915_active *ref)
{
	debug_object_assert_init(ref, &active_debug_desc);
}

#else

static inline void debug_active_init(struct i915_active *ref) { }
static inline void debug_active_activate(struct i915_active *ref) { }
static inline void debug_active_deactivate(struct i915_active *ref) { }
static inline void debug_active_fini(struct i915_active *ref) { }
static inline void debug_active_assert(struct i915_active *ref) { }

#endif

static void
__active_retire(struct i915_active *ref)
{
	struct active_node *it, *n;
	struct rb_root root;
	unsigned long flags;

	GEM_BUG_ON(i915_active_is_idle(ref));

	/* return the unused nodes to our slabcache -- flushing the allocator */
	if (!atomic_dec_and_lock_irqsave(&ref->count, &ref->tree_lock, flags))
		return;

	GEM_BUG_ON(rcu_access_pointer(ref->excl.fence));
	debug_active_deactivate(ref);

	root = ref->tree;
	ref->tree = RB_ROOT;
	ref->cache = NULL;

	spin_unlock_irqrestore(&ref->tree_lock, flags);

	/* After the final retire, the entire struct may be freed */
	if (ref->retire)
		ref->retire(ref);

	/* ... except if you wait on it, you must manage your own references! */
	wake_up_var(ref);

	rbtree_postorder_for_each_entry_safe(it, n, &root, node) {
		GEM_BUG_ON(i915_active_fence_isset(&it->base));
		kmem_cache_free(global.slab_cache, it);
	}
}

static void
active_work(struct work_struct *wrk)
{
	struct i915_active *ref = container_of(wrk, typeof(*ref), work);

	GEM_BUG_ON(!atomic_read(&ref->count));
	if (atomic_add_unless(&ref->count, -1, 1))
		return;

	__active_retire(ref);
}

static void
active_retire(struct i915_active *ref)
{
	GEM_BUG_ON(!atomic_read(&ref->count));
	if (atomic_add_unless(&ref->count, -1, 1))
		return;

	if (ref->flags & I915_ACTIVE_RETIRE_SLEEPS) {
		queue_work(system_unbound_wq, &ref->work);
		return;
	}

	__active_retire(ref);
}

static inline struct dma_fence **
__active_fence_slot(struct i915_active_fence *active)
{
	return (struct dma_fence ** __force)&active->fence;
}

static inline bool
active_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
{
	struct i915_active_fence *active =
		container_of(cb, typeof(*active), cb);

	return cmpxchg(__active_fence_slot(active), fence, NULL) == fence;
}

static void
node_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
{
	if (active_fence_cb(fence, cb))
		active_retire(container_of(cb, struct active_node, base.cb)->ref);
}

static void
excl_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
{
	if (active_fence_cb(fence, cb))
		active_retire(container_of(cb, struct i915_active, excl.cb));
}

static struct i915_active_fence *
active_instance(struct i915_active *ref, struct intel_timeline *tl)
{
	struct active_node *node, *prealloc;
	struct rb_node **p, *parent;
	u64 idx = tl->fence_context;

	/*
	 * We track the most recently used timeline to skip a rbtree search
	 * for the common case, under typical loads we never need the rbtree
	 * at all. We can reuse the last slot if it is empty, that is
	 * after the previous activity has been retired, or if it matches the
	 * current timeline.
	 */
	node = READ_ONCE(ref->cache);
	if (node && node->timeline == idx)
		return &node->base;

	/* Preallocate a replacement, just in case */
	prealloc = kmem_cache_alloc(global.slab_cache, GFP_KERNEL);
	if (!prealloc)
		return NULL;

	spin_lock_irq(&ref->tree_lock);
	GEM_BUG_ON(i915_active_is_idle(ref));

	parent = NULL;
	p = &ref->tree.rb_node;
	while (*p) {
		parent = *p;

		node = rb_entry(parent, struct active_node, node);
		if (node->timeline == idx) {
			kmem_cache_free(global.slab_cache, prealloc);
			goto out;
		}

		if (node->timeline < idx)
			p = &parent->rb_right;
		else
			p = &parent->rb_left;
	}

	node = prealloc;
	__i915_active_fence_init(&node->base, NULL, node_retire);
	node->ref = ref;
	node->timeline = idx;

	rb_link_node(&node->node, parent, p);
	rb_insert_color(&node->node, &ref->tree);

out:
	ref->cache = node;
	spin_unlock_irq(&ref->tree_lock);

	BUILD_BUG_ON(offsetof(typeof(*node), base));
	return &node->base;
}

void __i915_active_init(struct i915_active *ref,
			int (*active)(struct i915_active *ref),
			void (*retire)(struct i915_active *ref),
			struct lock_class_key *mkey,
			struct lock_class_key *wkey)
{
	unsigned long bits;

	debug_active_init(ref);

	ref->flags = 0;
	ref->active = active;
	ref->retire = ptr_unpack_bits(retire, &bits, 2);
	if (bits & I915_ACTIVE_MAY_SLEEP)
		ref->flags |= I915_ACTIVE_RETIRE_SLEEPS;

	spin_lock_init(&ref->tree_lock);
	ref->tree = RB_ROOT;
	ref->cache = NULL;

	init_llist_head(&ref->preallocated_barriers);
	atomic_set(&ref->count, 0);
	__mutex_init(&ref->mutex, "i915_active", mkey);
	__i915_active_fence_init(&ref->excl, NULL, excl_retire);
	INIT_WORK(&ref->work, active_work);
#if IS_ENABLED(CONFIG_LOCKDEP)
	lockdep_init_map(&ref->work.lockdep_map, "i915_active.work", wkey, 0);
#endif
}

static bool ____active_del_barrier(struct i915_active *ref,
				   struct active_node *node,
				   struct intel_engine_cs *engine)

{
	struct llist_node *head = NULL, *tail = NULL;
	struct llist_node *pos, *next;

	GEM_BUG_ON(node->timeline != engine->kernel_context->timeline->fence_context);

	/*
	 * Rebuild the llist excluding our node. We may perform this
	 * outside of the kernel_context timeline mutex and so someone
	 * else may be manipulating the engine->barrier_tasks, in
	 * which case either we or they will be upset :)
	 *
	 * A second __active_del_barrier() will report failure to claim
	 * the active_node and the caller will just shrug and know not to
	 * claim ownership of its node.
	 *
	 * A concurrent i915_request_add_active_barriers() will miss adding
	 * any of the tasks, but we will try again on the next -- and since
	 * we are actively using the barrier, we know that there will be
	 * at least another opportunity when we idle.
	 */
	llist_for_each_safe(pos, next, llist_del_all(&engine->barrier_tasks)) {
		if (node == barrier_from_ll(pos)) {
			node = NULL;
			continue;
		}

		pos->next = head;
		head = pos;
		if (!tail)
			tail = pos;
	}
	if (head)
		llist_add_batch(head, tail, &engine->barrier_tasks);

	return !node;
}

static bool
__active_del_barrier(struct i915_active *ref, struct active_node *node)
{
	return ____active_del_barrier(ref, node, barrier_to_engine(node));
}

int i915_active_ref(struct i915_active *ref,
		    struct intel_timeline *tl,
		    struct dma_fence *fence)
{
	struct i915_active_fence *active;
	int err;

	lockdep_assert_held(&tl->mutex);

	/* Prevent reaping in case we malloc/wait while building the tree */
	err = i915_active_acquire(ref);
	if (err)
		return err;

	active = active_instance(ref, tl);
	if (!active) {
		err = -ENOMEM;
		goto out;
	}

	if (is_barrier(active)) { /* proto-node used by our idle barrier */
		/*
		 * This request is on the kernel_context timeline, and so
		 * we can use it to substitute for the pending idle-barrer
		 * request that we want to emit on the kernel_context.
		 */
		__active_del_barrier(ref, node_from_active(active));
		RCU_INIT_POINTER(active->fence, NULL);
		atomic_dec(&ref->count);
	}
	if (!__i915_active_fence_set(active, fence))
		atomic_inc(&ref->count);

out:
	i915_active_release(ref);
	return err;
}

struct dma_fence *
i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
{
	struct dma_fence *prev;

	/* We expect the caller to manage the exclusive timeline ordering */
	GEM_BUG_ON(i915_active_is_idle(ref));

	rcu_read_lock();
	prev = __i915_active_fence_set(&ref->excl, f);
	if (prev)
		prev = dma_fence_get_rcu(prev);
	else
		atomic_inc(&ref->count);
	rcu_read_unlock();

	return prev;
}

bool i915_active_acquire_if_busy(struct i915_active *ref)
{
	debug_active_assert(ref);
	return atomic_add_unless(&ref->count, 1, 0);
}

int i915_active_acquire(struct i915_active *ref)
{
	int err;

	if (i915_active_acquire_if_busy(ref))
		return 0;

	err = mutex_lock_interruptible(&ref->mutex);
	if (err)
		return err;

	if (likely(!i915_active_acquire_if_busy(ref))) {
		if (ref->active)
			err = ref->active(ref);
		if (!err) {
			spin_lock_irq(&ref->tree_lock); /* __active_retire() */
			debug_active_activate(ref);
			atomic_inc(&ref->count);
			spin_unlock_irq(&ref->tree_lock);
		}
	}

	mutex_unlock(&ref->mutex);

	return err;
}

void i915_active_release(struct i915_active *ref)
{
	debug_active_assert(ref);
	active_retire(ref);
}

static void enable_signaling(struct i915_active_fence *active)
{
	struct dma_fence *fence;

	if (unlikely(is_barrier(active)))
		return;

	fence = i915_active_fence_get(active);
	if (!fence)
		return;

	dma_fence_enable_sw_signaling(fence);
	dma_fence_put(fence);
}

static int flush_barrier(struct active_node *it)
{
	struct intel_engine_cs *engine;

	if (likely(!is_barrier(&it->base)))
		return 0;

	engine = __barrier_to_engine(it);
	smp_rmb(); /* serialise with add_active_barriers */
	if (!is_barrier(&it->base))
		return 0;

	return intel_engine_flush_barriers(engine);
}

static int flush_lazy_signals(struct i915_active *ref)
{
	struct active_node *it, *n;
	int err = 0;

	enable_signaling(&ref->excl);
	rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
		err = flush_barrier(it); /* unconnected idle barrier? */
		if (err)
			break;

		enable_signaling(&it->base);
	}

	return err;
}

int __i915_active_wait(struct i915_active *ref, int state)
{
	int err;

	might_sleep();

	if (!i915_active_acquire_if_busy(ref))
		return 0;

	/* Any fence added after the wait begins will not be auto-signaled */
	err = flush_lazy_signals(ref);
	i915_active_release(ref);
	if (err)
		return err;

	if (!i915_active_is_idle(ref) &&
	    ___wait_var_event(ref, i915_active_is_idle(ref),
			      state, 0, 0, schedule()))
		return -EINTR;

	flush_work(&ref->work);
	return 0;
}

static int __await_active(struct i915_active_fence *active,
			  int (*fn)(void *arg, struct dma_fence *fence),
			  void *arg)
{
	struct dma_fence *fence;

	if (is_barrier(active)) /* XXX flush the barrier? */
		return 0;

	fence = i915_active_fence_get(active);
	if (fence) {
		int err;

		err = fn(arg, fence);
		dma_fence_put(fence);
		if (err < 0)
			return err;
	}

	return 0;
}

struct wait_barrier {
	struct wait_queue_entry base;
	struct i915_active *ref;
};

static int
barrier_wake(wait_queue_entry_t *wq, unsigned int mode, int flags, void *key)
{
	struct wait_barrier *wb = container_of(wq, typeof(*wb), base);

	if (i915_active_is_idle(wb->ref)) {
		list_del(&wq->entry);
		i915_sw_fence_complete(wq->private);
		kfree(wq);
	}

	return 0;
}

static int __await_barrier(struct i915_active *ref, struct i915_sw_fence *fence)
{
	struct wait_barrier *wb;

	wb = kmalloc(sizeof(*wb), GFP_KERNEL);
	if (unlikely(!wb))
		return -ENOMEM;

	GEM_BUG_ON(i915_active_is_idle(ref));
	if (!i915_sw_fence_await(fence)) {
		kfree(wb);
		return -EINVAL;
	}

	wb->base.flags = 0;
	wb->base.func = barrier_wake;
	wb->base.private = fence;
	wb->ref = ref;

	add_wait_queue(__var_waitqueue(ref), &wb->base);
	return 0;
}

static int await_active(struct i915_active *ref,
			unsigned int flags,
			int (*fn)(void *arg, struct dma_fence *fence),
			void *arg, struct i915_sw_fence *barrier)
{
	int err = 0;

	if (!i915_active_acquire_if_busy(ref))
		return 0;

	if (flags & I915_ACTIVE_AWAIT_EXCL &&
	    rcu_access_pointer(ref->excl.fence)) {
		err = __await_active(&ref->excl, fn, arg);
		if (err)
			goto out;
	}

	if (flags & I915_ACTIVE_AWAIT_ACTIVE) {
		struct active_node *it, *n;

		rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
			err = __await_active(&it->base, fn, arg);
			if (err)
				goto out;
		}
	}

	if (flags & I915_ACTIVE_AWAIT_BARRIER) {
		err = flush_lazy_signals(ref);
		if (err)
			goto out;

		err = __await_barrier(ref, barrier);
		if (err)
			goto out;
	}

out:
	i915_active_release(ref);
	return err;
}

static int rq_await_fence(void *arg, struct dma_fence *fence)
{
	return i915_request_await_dma_fence(arg, fence);
}

int i915_request_await_active(struct i915_request *rq,
			      struct i915_active *ref,
			      unsigned int flags)
{
	return await_active(ref, flags, rq_await_fence, rq, &rq->submit);
}

static int sw_await_fence(void *arg, struct dma_fence *fence)
{
	return i915_sw_fence_await_dma_fence(arg, fence, 0,
					     GFP_NOWAIT | __GFP_NOWARN);
}

int i915_sw_fence_await_active(struct i915_sw_fence *fence,
			       struct i915_active *ref,
			       unsigned int flags)
{
	return await_active(ref, flags, sw_await_fence, fence, fence);
}

#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
void i915_active_fini(struct i915_active *ref)
{
	debug_active_fini(ref);
	GEM_BUG_ON(atomic_read(&ref->count));
	GEM_BUG_ON(work_pending(&ref->work));
	GEM_BUG_ON(!RB_EMPTY_ROOT(&ref->tree));
	mutex_destroy(&ref->mutex);
}
#endif

static inline bool is_idle_barrier(struct active_node *node, u64 idx)
{
	return node->timeline == idx && !i915_active_fence_isset(&node->base);
}

static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
{
	struct rb_node *prev, *p;

	if (RB_EMPTY_ROOT(&ref->tree))
		return NULL;

	spin_lock_irq(&ref->tree_lock);
	GEM_BUG_ON(i915_active_is_idle(ref));

	/*
	 * Try to reuse any existing barrier nodes already allocated for this
	 * i915_active, due to overlapping active phases there is likely a
	 * node kept alive (as we reuse before parking). We prefer to reuse
	 * completely idle barriers (less hassle in manipulating the llists),
	 * but otherwise any will do.
	 */
	if (ref->cache && is_idle_barrier(ref->cache, idx)) {
		p = &ref->cache->node;
		goto match;
	}

	prev = NULL;
	p = ref->tree.rb_node;
	while (p) {
		struct active_node *node =
			rb_entry(p, struct active_node, node);

		if (is_idle_barrier(node, idx))
			goto match;

		prev = p;
		if (node->timeline < idx)
			p = p->rb_right;
		else
			p = p->rb_left;
	}

	/*
	 * No quick match, but we did find the leftmost rb_node for the
	 * kernel_context. Walk the rb_tree in-order to see if there were
	 * any idle-barriers on this timeline that we missed, or just use
	 * the first pending barrier.
	 */
	for (p = prev; p; p = rb_next(p)) {
		struct active_node *node =
			rb_entry(p, struct active_node, node);
		struct intel_engine_cs *engine;

		if (node->timeline > idx)
			break;

		if (node->timeline < idx)
			continue;

		if (is_idle_barrier(node, idx))
			goto match;

		/*
		 * The list of pending barriers is protected by the
		 * kernel_context timeline, which notably we do not hold
		 * here. i915_request_add_active_barriers() may consume
		 * the barrier before we claim it, so we have to check
		 * for success.
		 */
		engine = __barrier_to_engine(node);
		smp_rmb(); /* serialise with add_active_barriers */
		if (is_barrier(&node->base) &&
		    ____active_del_barrier(ref, node, engine))
			goto match;
	}

	spin_unlock_irq(&ref->tree_lock);

	return NULL;

match:
	rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */
	if (p == &ref->cache->node)
		ref->cache = NULL;
	spin_unlock_irq(&ref->tree_lock);

	return rb_entry(p, struct active_node, node);
}

int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
					    struct intel_engine_cs *engine)
{
	intel_engine_mask_t tmp, mask = engine->mask;
	struct llist_node *first = NULL, *last = NULL;
	struct intel_gt *gt = engine->gt;
	int err;

	GEM_BUG_ON(i915_active_is_idle(ref));

	/* Wait until the previous preallocation is completed */
	while (!llist_empty(&ref->preallocated_barriers))
		cond_resched();

	/*
	 * Preallocate a node for each physical engine supporting the target
	 * engine (remember virtual engines have more than one sibling).
	 * We can then use the preallocated nodes in
	 * i915_active_acquire_barrier()
	 */
	GEM_BUG_ON(!mask);
	for_each_engine_masked(engine, gt, mask, tmp) {
		u64 idx = engine->kernel_context->timeline->fence_context;
		struct llist_node *prev = first;
		struct active_node *node;

		node = reuse_idle_barrier(ref, idx);
		if (!node) {
			node = kmem_cache_alloc(global.slab_cache, GFP_KERNEL);
			if (!node) {
				err = ENOMEM;
				goto unwind;
			}

			RCU_INIT_POINTER(node->base.fence, NULL);
			node->base.cb.func = node_retire;
			node->timeline = idx;
			node->ref = ref;
		}

		if (!i915_active_fence_isset(&node->base)) {
			/*
			 * Mark this as being *our* unconnected proto-node.
			 *
			 * Since this node is not in any list, and we have
			 * decoupled it from the rbtree, we can reuse the
			 * request to indicate this is an idle-barrier node
			 * and then we can use the rb_node and list pointers
			 * for our tracking of the pending barrier.
			 */
			RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN));
			node->base.cb.node.prev = (void *)engine;
			atomic_inc(&ref->count);
		}
		GEM_BUG_ON(rcu_access_pointer(node->base.fence) != ERR_PTR(-EAGAIN));

		GEM_BUG_ON(barrier_to_engine(node) != engine);
		first = barrier_to_ll(node);
		first->next = prev;
		if (!last)
			last = first;
		intel_engine_pm_get(engine);
	}

	GEM_BUG_ON(!llist_empty(&ref->preallocated_barriers));
	llist_add_batch(first, last, &ref->preallocated_barriers);

	return 0;

unwind:
	while (first) {
		struct active_node *node = barrier_from_ll(first);

		first = first->next;

		atomic_dec(&ref->count);
		intel_engine_pm_put(barrier_to_engine(node));

		kmem_cache_free(global.slab_cache, node);
	}
	return err;
}

void i915_active_acquire_barrier(struct i915_active *ref)
{
	struct llist_node *pos, *next;
	unsigned long flags;

	GEM_BUG_ON(i915_active_is_idle(ref));

	/*
	 * Transfer the list of preallocated barriers into the
	 * i915_active rbtree, but only as proto-nodes. They will be
	 * populated by i915_request_add_active_barriers() to point to the
	 * request that will eventually release them.
	 */
	llist_for_each_safe(pos, next, take_preallocated_barriers(ref)) {
		struct active_node *node = barrier_from_ll(pos);
		struct intel_engine_cs *engine = barrier_to_engine(node);
		struct rb_node **p, *parent;

		spin_lock_irqsave_nested(&ref->tree_lock, flags,
					 SINGLE_DEPTH_NESTING);
		parent = NULL;
		p = &ref->tree.rb_node;
		while (*p) {
			struct active_node *it;

			parent = *p;

			it = rb_entry(parent, struct active_node, node);
			if (it->timeline < node->timeline)
				p = &parent->rb_right;
			else
				p = &parent->rb_left;
		}
		rb_link_node(&node->node, parent, p);
		rb_insert_color(&node->node, &ref->tree);
		spin_unlock_irqrestore(&ref->tree_lock, flags);

		GEM_BUG_ON(!intel_engine_pm_is_awake(engine));
		llist_add(barrier_to_ll(node), &engine->barrier_tasks);
		intel_engine_pm_put_delay(engine, 1);
	}
}

static struct dma_fence **ll_to_fence_slot(struct llist_node *node)
{
	return __active_fence_slot(&barrier_from_ll(node)->base);
}

void i915_request_add_active_barriers(struct i915_request *rq)
{
	struct intel_engine_cs *engine = rq->engine;
	struct llist_node *node, *next;
	unsigned long flags;

	GEM_BUG_ON(!intel_context_is_barrier(rq->context));
	GEM_BUG_ON(intel_engine_is_virtual(engine));
	GEM_BUG_ON(i915_request_timeline(rq) != engine->kernel_context->timeline);

	node = llist_del_all(&engine->barrier_tasks);
	if (!node)
		return;
	/*
	 * Attach the list of proto-fences to the in-flight request such
	 * that the parent i915_active will be released when this request
	 * is retired.
	 */
	spin_lock_irqsave(&rq->lock, flags);
	llist_for_each_safe(node, next, node) {
		/* serialise with reuse_idle_barrier */
		smp_store_mb(*ll_to_fence_slot(node), &rq->fence);
		list_add_tail((struct list_head *)node, &rq->fence.cb_list);
	}
	spin_unlock_irqrestore(&rq->lock, flags);
}

/*
 * __i915_active_fence_set: Update the last active fence along its timeline
 * @active: the active tracker
 * @fence: the new fence (under construction)
 *
 * Records the new @fence as the last active fence along its timeline in
 * this active tracker, moving the tracking callbacks from the previous
 * fence onto this one. Returns the previous fence (if not already completed),
 * which the caller must ensure is executed before the new fence. To ensure
 * that the order of fences within the timeline of the i915_active_fence is
 * understood, it should be locked by the caller.
 */
struct dma_fence *
__i915_active_fence_set(struct i915_active_fence *active,
			struct dma_fence *fence)
{
	struct dma_fence *prev;
	unsigned long flags;

	if (fence == rcu_access_pointer(active->fence))
		return fence;

	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));

	/*
	 * Consider that we have two threads arriving (A and B), with
	 * C already resident as the active->fence.
	 *
	 * A does the xchg first, and so it sees C or NULL depending
	 * on the timing of the interrupt handler. If it is NULL, the
	 * previous fence must have been signaled and we know that
	 * we are first on the timeline. If it is still present,
	 * we acquire the lock on that fence and serialise with the interrupt
	 * handler, in the process removing it from any future interrupt
	 * callback. A will then wait on C before executing (if present).
	 *
	 * As B is second, it sees A as the previous fence and so waits for
	 * it to complete its transition and takes over the occupancy for
	 * itself -- remembering that it needs to wait on A before executing.
	 *
	 * Note the strong ordering of the timeline also provides consistent
	 * nesting rules for the fence->lock; the inner lock is always the
	 * older lock.
	 */
	spin_lock_irqsave(fence->lock, flags);
	prev = xchg(__active_fence_slot(active), fence);
	if (prev) {
		GEM_BUG_ON(prev == fence);
		spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
		__list_del_entry(&active->cb.node);
		spin_unlock(prev->lock); /* serialise with prev->cb_list */
	}
	list_add_tail(&active->cb.node, &fence->cb_list);
	spin_unlock_irqrestore(fence->lock, flags);

	return prev;
}

int i915_active_fence_set(struct i915_active_fence *active,
			  struct i915_request *rq)
{
	struct dma_fence *fence;
	int err = 0;

	/* Must maintain timeline ordering wrt previous active requests */
	rcu_read_lock();
	fence = __i915_active_fence_set(active, &rq->fence);
	if (fence) /* but the previous fence may not belong to that timeline! */
		fence = dma_fence_get_rcu(fence);
	rcu_read_unlock();
	if (fence) {
		err = i915_request_await_dma_fence(rq, fence);
		dma_fence_put(fence);
	}

	return err;
}

void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb)
{
	active_fence_cb(fence, cb);
}

struct auto_active {
	struct i915_active base;
	struct kref ref;
};

struct i915_active *i915_active_get(struct i915_active *ref)
{
	struct auto_active *aa = container_of(ref, typeof(*aa), base);

	kref_get(&aa->ref);
	return &aa->base;
}

static void auto_release(struct kref *ref)
{
	struct auto_active *aa = container_of(ref, typeof(*aa), ref);

	i915_active_fini(&aa->base);
	kfree(aa);
}

void i915_active_put(struct i915_active *ref)
{
	struct auto_active *aa = container_of(ref, typeof(*aa), base);

	kref_put(&aa->ref, auto_release);
}

static int auto_active(struct i915_active *ref)
{
	i915_active_get(ref);
	return 0;
}

static void auto_retire(struct i915_active *ref)
{
	i915_active_put(ref);
}

struct i915_active *i915_active_create(void)
{
	struct auto_active *aa;

	aa = kmalloc(sizeof(*aa), GFP_KERNEL);
	if (!aa)
		return NULL;

	kref_init(&aa->ref);
	i915_active_init(&aa->base, auto_active, auto_retire);

	return &aa->base;
}

#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftests/i915_active.c"
#endif

static void i915_global_active_shrink(void)
{
	kmem_cache_shrink(global.slab_cache);
}

static void i915_global_active_exit(void)
{
	kmem_cache_destroy(global.slab_cache);
}

static struct i915_global_active global = { {
	.shrink = i915_global_active_shrink,
	.exit = i915_global_active_exit,
} };

int __init i915_global_active_init(void)
{
	global.slab_cache = KMEM_CACHE(active_node, SLAB_HWCACHE_ALIGN);
	if (!global.slab_cache)
		return -ENOMEM;

	i915_global_register(&global.base);
	return 0;
}