1 /*
2  * SPDX-License-Identifier: MIT
3  *
4  * Copyright © 2014-2016 Intel Corporation
5  */
6 
7 #include <linux/dma-fence-array.h>
8 
9 #include "gt/intel_engine.h"
10 
11 #include "i915_gem_ioctls.h"
12 #include "i915_gem_object.h"
13 
14 static __always_inline u32 __busy_read_flag(u16 id)
15 {
16 	if (id == (u16)I915_ENGINE_CLASS_INVALID)
17 		return 0xffff0000u;
18 
19 	GEM_BUG_ON(id >= 16);
20 	return 0x10000u << id;
21 }
22 
23 static __always_inline u32 __busy_write_id(u16 id)
24 {
25 	/*
26 	 * The uABI guarantees an active writer is also amongst the read
27 	 * engines. This would be true if we accessed the activity tracking
28 	 * under the lock, but as we perform the lookup of the object and
29 	 * its activity locklessly we can not guarantee that the last_write
30 	 * being active implies that we have set the same engine flag from
31 	 * last_read - hence we always set both read and write busy for
32 	 * last_write.
33 	 */
34 	if (id == (u16)I915_ENGINE_CLASS_INVALID)
35 		return 0xffffffffu;
36 
37 	return (id + 1) | __busy_read_flag(id);
38 }
39 
40 static __always_inline unsigned int
41 __busy_set_if_active(struct dma_fence *fence, u32 (*flag)(u16 id))
42 {
43 	const struct i915_request *rq;
44 
45 	/*
46 	 * We have to check the current hw status of the fence as the uABI
47 	 * guarantees forward progress. We could rely on the idle worker
48 	 * to eventually flush us, but to minimise latency just ask the
49 	 * hardware.
50 	 *
51 	 * Note we only report on the status of native fences and we currently
52 	 * have two native fences:
53 	 *
54 	 * 1. A composite fence (dma_fence_array) constructed of i915 requests
55 	 * created during a parallel submission. In this case we deconstruct the
56 	 * composite fence into individual i915 requests and check the status of
57 	 * each request.
58 	 *
59 	 * 2. A single i915 request.
60 	 */
61 	if (dma_fence_is_array(fence)) {
62 		struct dma_fence_array *array = to_dma_fence_array(fence);
63 		struct dma_fence **child = array->fences;
64 		unsigned int nchild = array->num_fences;
65 
66 		do {
67 			struct dma_fence *current_fence = *child++;
68 
69 			/* Not an i915 fence, can't be busy per above */
70 			if (!dma_fence_is_i915(current_fence) ||
71 			    !test_bit(I915_FENCE_FLAG_COMPOSITE,
72 				      &current_fence->flags)) {
73 				return 0;
74 			}
75 
76 			rq = to_request(current_fence);
77 			if (!i915_request_completed(rq))
78 				return flag(rq->engine->uabi_class);
79 		} while (--nchild);
80 
81 		/* All requests in array complete, not busy */
82 		return 0;
83 	} else {
84 		if (!dma_fence_is_i915(fence))
85 			return 0;
86 
87 		rq = to_request(fence);
88 		if (i915_request_completed(rq))
89 			return 0;
90 
91 		/* Beware type-expansion follies! */
92 		BUILD_BUG_ON(!typecheck(u16, rq->engine->uabi_class));
93 		return flag(rq->engine->uabi_class);
94 	}
95 }
96 
97 static __always_inline unsigned int
98 busy_check_reader(struct dma_fence *fence)
99 {
100 	return __busy_set_if_active(fence, __busy_read_flag);
101 }
102 
103 static __always_inline unsigned int
104 busy_check_writer(struct dma_fence *fence)
105 {
106 	if (!fence)
107 		return 0;
108 
109 	return __busy_set_if_active(fence, __busy_write_id);
110 }
111 
112 int
113 i915_gem_busy_ioctl(struct drm_device *dev, void *data,
114 		    struct drm_file *file)
115 {
116 	struct drm_i915_gem_busy *args = data;
117 	struct drm_i915_gem_object *obj;
118 	struct dma_resv_list *list;
119 	unsigned int seq;
120 	int err;
121 
122 	err = -ENOENT;
123 	rcu_read_lock();
124 	obj = i915_gem_object_lookup_rcu(file, args->handle);
125 	if (!obj)
126 		goto out;
127 
128 	/*
129 	 * A discrepancy here is that we do not report the status of
130 	 * non-i915 fences, i.e. even though we may report the object as idle,
131 	 * a call to set-domain may still stall waiting for foreign rendering.
132 	 * This also means that wait-ioctl may report an object as busy,
133 	 * where busy-ioctl considers it idle.
134 	 *
135 	 * We trade the ability to warn of foreign fences to report on which
136 	 * i915 engines are active for the object.
137 	 *
138 	 * Alternatively, we can trade that extra information on read/write
139 	 * activity with
140 	 *	args->busy =
141 	 *		!dma_resv_test_signaled(obj->resv, true);
142 	 * to report the overall busyness. This is what the wait-ioctl does.
143 	 *
144 	 */
145 retry:
146 	seq = raw_read_seqcount(&obj->base.resv->seq);
147 
148 	/* Translate the exclusive fence to the READ *and* WRITE engine */
149 	args->busy = busy_check_writer(dma_resv_excl_fence(obj->base.resv));
150 
151 	/* Translate shared fences to READ set of engines */
152 	list = dma_resv_shared_list(obj->base.resv);
153 	if (list) {
154 		unsigned int shared_count = list->shared_count, i;
155 
156 		for (i = 0; i < shared_count; ++i) {
157 			struct dma_fence *fence =
158 				rcu_dereference(list->shared[i]);
159 
160 			args->busy |= busy_check_reader(fence);
161 		}
162 	}
163 
164 	if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq))
165 		goto retry;
166 
167 	err = 0;
168 out:
169 	rcu_read_unlock();
170 	return err;
171 }
172