1 /*
2  * SPDX-License-Identifier: MIT
3  *
4  * Copyright © 2014-2016 Intel Corporation
5  */
6 
7 #include "gt/intel_engine.h"
8 
9 #include "i915_gem_ioctls.h"
10 #include "i915_gem_object.h"
11 
12 static __always_inline u32 __busy_read_flag(u8 id)
13 {
14 	if (id == (u8)I915_ENGINE_CLASS_INVALID)
15 		return 0xffff0000u;
16 
17 	GEM_BUG_ON(id >= 16);
18 	return 0x10000u << id;
19 }
20 
21 static __always_inline u32 __busy_write_id(u8 id)
22 {
23 	/*
24 	 * The uABI guarantees an active writer is also amongst the read
25 	 * engines. This would be true if we accessed the activity tracking
26 	 * under the lock, but as we perform the lookup of the object and
27 	 * its activity locklessly we can not guarantee that the last_write
28 	 * being active implies that we have set the same engine flag from
29 	 * last_read - hence we always set both read and write busy for
30 	 * last_write.
31 	 */
32 	if (id == (u8)I915_ENGINE_CLASS_INVALID)
33 		return 0xffffffffu;
34 
35 	return (id + 1) | __busy_read_flag(id);
36 }
37 
38 static __always_inline unsigned int
39 __busy_set_if_active(const struct dma_fence *fence, u32 (*flag)(u8 id))
40 {
41 	const struct i915_request *rq;
42 
43 	/*
44 	 * We have to check the current hw status of the fence as the uABI
45 	 * guarantees forward progress. We could rely on the idle worker
46 	 * to eventually flush us, but to minimise latency just ask the
47 	 * hardware.
48 	 *
49 	 * Note we only report on the status of native fences.
50 	 */
51 	if (!dma_fence_is_i915(fence))
52 		return 0;
53 
54 	/* opencode to_request() in order to avoid const warnings */
55 	rq = container_of(fence, const struct i915_request, fence);
56 	if (i915_request_completed(rq))
57 		return 0;
58 
59 	/* Beware type-expansion follies! */
60 	BUILD_BUG_ON(!typecheck(u8, rq->engine->uabi_class));
61 	return flag(rq->engine->uabi_class);
62 }
63 
64 static __always_inline unsigned int
65 busy_check_reader(const struct dma_fence *fence)
66 {
67 	return __busy_set_if_active(fence, __busy_read_flag);
68 }
69 
70 static __always_inline unsigned int
71 busy_check_writer(const struct dma_fence *fence)
72 {
73 	if (!fence)
74 		return 0;
75 
76 	return __busy_set_if_active(fence, __busy_write_id);
77 }
78 
79 int
80 i915_gem_busy_ioctl(struct drm_device *dev, void *data,
81 		    struct drm_file *file)
82 {
83 	struct drm_i915_gem_busy *args = data;
84 	struct drm_i915_gem_object *obj;
85 	struct dma_resv_list *list;
86 	unsigned int seq;
87 	int err;
88 
89 	err = -ENOENT;
90 	rcu_read_lock();
91 	obj = i915_gem_object_lookup_rcu(file, args->handle);
92 	if (!obj)
93 		goto out;
94 
95 	/*
96 	 * A discrepancy here is that we do not report the status of
97 	 * non-i915 fences, i.e. even though we may report the object as idle,
98 	 * a call to set-domain may still stall waiting for foreign rendering.
99 	 * This also means that wait-ioctl may report an object as busy,
100 	 * where busy-ioctl considers it idle.
101 	 *
102 	 * We trade the ability to warn of foreign fences to report on which
103 	 * i915 engines are active for the object.
104 	 *
105 	 * Alternatively, we can trade that extra information on read/write
106 	 * activity with
107 	 *	args->busy =
108 	 *		!dma_resv_test_signaled_rcu(obj->resv, true);
109 	 * to report the overall busyness. This is what the wait-ioctl does.
110 	 *
111 	 */
112 retry:
113 	seq = raw_read_seqcount(&obj->base.resv->seq);
114 
115 	/* Translate the exclusive fence to the READ *and* WRITE engine */
116 	args->busy =
117 		busy_check_writer(rcu_dereference(obj->base.resv->fence_excl));
118 
119 	/* Translate shared fences to READ set of engines */
120 	list = rcu_dereference(obj->base.resv->fence);
121 	if (list) {
122 		unsigned int shared_count = list->shared_count, i;
123 
124 		for (i = 0; i < shared_count; ++i) {
125 			struct dma_fence *fence =
126 				rcu_dereference(list->shared[i]);
127 
128 			args->busy |= busy_check_reader(fence);
129 		}
130 	}
131 
132 	if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq))
133 		goto retry;
134 
135 	err = 0;
136 out:
137 	rcu_read_unlock();
138 	return err;
139 }
140