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
 12static __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
 21static __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
 38static __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
 64static __always_inline unsigned int
 65busy_check_reader(const struct dma_fence *fence)
 66{
 67	return __busy_set_if_active(fence, __busy_read_flag);
 68}
 69
 70static __always_inline unsigned int
 71busy_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
 79int
 80i915_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	 */
112retry:
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;
136out:
137	rcu_read_unlock();
138	return err;
139}