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
 14static __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
 23static __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
 40static __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
 97static __always_inline unsigned int
 98busy_check_reader(struct dma_fence *fence)
 99{
100	return __busy_set_if_active(fence, __busy_read_flag);
101}
102
103static __always_inline unsigned int
104busy_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
112int
113i915_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_iter cursor;
119	struct dma_fence *fence;
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, DMA_RESV_USAGE_READ);
142	 * to report the overall busyness. This is what the wait-ioctl does.
143	 *
144	 */
145	args->busy = 0;
146	dma_resv_iter_begin(&cursor, obj->base.resv, DMA_RESV_USAGE_READ);
147	dma_resv_for_each_fence_unlocked(&cursor, fence) {
148		if (dma_resv_iter_is_restarted(&cursor))
149			args->busy = 0;
150
151		if (dma_resv_iter_usage(&cursor) <= DMA_RESV_USAGE_WRITE)
152			/* Translate the write fences to the READ *and* WRITE engine */
153			args->busy |= busy_check_writer(fence);
154		else
155			/* Translate read fences to READ set of engines */
156			args->busy |= busy_check_reader(fence);
157	}
158	dma_resv_iter_end(&cursor);
159
160	err = 0;
161out:
162	rcu_read_unlock();
163	return err;
164}