[deliverable/linux.git] / drivers / gpu / drm / i915 / intel_breadcrumbs.c

/*
 * Copyright © 2015 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 */

#include "i915_drv.h"

static void intel_breadcrumbs_fake_irq(unsigned long data)
{
	struct intel_engine_cs *engine = (struct intel_engine_cs *)data;

	/*
	 * The timer persists in case we cannot enable interrupts,
	 * or if we have previously seen seqno/interrupt incoherency
	 * ("missed interrupt" syndrome). Here the worker will wake up
	 * every jiffie in order to kick the oldest waiter to do the
	 * coherent seqno check.
	 */
	rcu_read_lock();
	if (intel_engine_wakeup(engine))
		mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
	rcu_read_unlock();
}

static void irq_enable(struct intel_engine_cs *engine)
{
	/* Enabling the IRQ may miss the generation of the interrupt, but
	 * we still need to force the barrier before reading the seqno,
	 * just in case.
	 */
	engine->irq_posted = true;
	WARN_ON(!engine->irq_get(engine));
}

static void irq_disable(struct intel_engine_cs *engine)
{
	engine->irq_put(engine);
	engine->irq_posted = false;
}

static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
{
	struct intel_engine_cs *engine =
		container_of(b, struct intel_engine_cs, breadcrumbs);
	struct drm_i915_private *i915 = engine->i915;

	assert_spin_locked(&b->lock);
	if (b->rpm_wakelock)
		return false;

	/* Since we are waiting on a request, the GPU should be busy
	 * and should have its own rpm reference. For completeness,
	 * record an rpm reference for ourselves to cover the
	 * interrupt we unmask.
	 */
	intel_runtime_pm_get_noresume(i915);
	b->rpm_wakelock = true;

	/* No interrupts? Kick the waiter every jiffie! */
	if (intel_irqs_enabled(i915)) {
		if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings))
			irq_enable(engine);
		b->irq_enabled = true;
	}

	if (!b->irq_enabled ||
	    test_bit(engine->id, &i915->gpu_error.missed_irq_rings))
		mod_timer(&b->fake_irq, jiffies + 1);

	return engine->irq_posted;
}

static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
{
	struct intel_engine_cs *engine =
		container_of(b, struct intel_engine_cs, breadcrumbs);

	assert_spin_locked(&b->lock);
	if (!b->rpm_wakelock)
		return;

	if (b->irq_enabled) {
		irq_disable(engine);
		b->irq_enabled = false;
	}

	intel_runtime_pm_put(engine->i915);
	b->rpm_wakelock = false;
}

static inline struct intel_wait *to_wait(struct rb_node *node)
{
	return container_of(node, struct intel_wait, node);
}

static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
					      struct intel_wait *wait)
{
	assert_spin_locked(&b->lock);

	/* This request is completed, so remove it from the tree, mark it as
	 * complete, and *then* wake up the associated task.
	 */
	rb_erase(&wait->node, &b->waiters);
	RB_CLEAR_NODE(&wait->node);

	wake_up_process(wait->tsk); /* implicit smp_wmb() */
}

static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
				    struct intel_wait *wait)
{
	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	struct rb_node **p, *parent, *completed;
	bool first;
	u32 seqno;

	/* Insert the request into the retirement ordered list
	 * of waiters by walking the rbtree. If we are the oldest
	 * seqno in the tree (the first to be retired), then
	 * set ourselves as the bottom-half.
	 *
	 * As we descend the tree, prune completed branches since we hold the
	 * spinlock we know that the first_waiter must be delayed and can
	 * reduce some of the sequential wake up latency if we take action
	 * ourselves and wake up the completed tasks in parallel. Also, by
	 * removing stale elements in the tree, we may be able to reduce the
	 * ping-pong between the old bottom-half and ourselves as first-waiter.
	 */
	first = true;
	parent = NULL;
	completed = NULL;
	seqno = intel_engine_get_seqno(engine);

	 /* If the request completed before we managed to grab the spinlock,
	  * return now before adding ourselves to the rbtree. We let the
	  * current bottom-half handle any pending wakeups and instead
	  * try and get out of the way quickly.
	  */
	if (i915_seqno_passed(seqno, wait->seqno)) {
		RB_CLEAR_NODE(&wait->node);
		return first;
	}

	p = &b->waiters.rb_node;
	while (*p) {
		parent = *p;
		if (wait->seqno == to_wait(parent)->seqno) {
			/* We have multiple waiters on the same seqno, select
			 * the highest priority task (that with the smallest
			 * task->prio) to serve as the bottom-half for this
			 * group.
			 */
			if (wait->tsk->prio > to_wait(parent)->tsk->prio) {
				p = &parent->rb_right;
				first = false;
			} else {
				p = &parent->rb_left;
			}
		} else if (i915_seqno_passed(wait->seqno,
					     to_wait(parent)->seqno)) {
			p = &parent->rb_right;
			if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
				completed = parent;
			else
				first = false;
		} else {
			p = &parent->rb_left;
		}
	}
	rb_link_node(&wait->node, parent, p);
	rb_insert_color(&wait->node, &b->waiters);
	GEM_BUG_ON(!first && !b->tasklet);

	if (completed) {
		struct rb_node *next = rb_next(completed);

		GEM_BUG_ON(!next && !first);
		if (next && next != &wait->node) {
			GEM_BUG_ON(first);
			b->first_wait = to_wait(next);
			smp_store_mb(b->tasklet, b->first_wait->tsk);
			/* As there is a delay between reading the current
			 * seqno, processing the completed tasks and selecting
			 * the next waiter, we may have missed the interrupt
			 * and so need for the next bottom-half to wakeup.
			 *
			 * Also as we enable the IRQ, we may miss the
			 * interrupt for that seqno, so we have to wake up
			 * the next bottom-half in order to do a coherent check
			 * in case the seqno passed.
			 */
			__intel_breadcrumbs_enable_irq(b);
			if (READ_ONCE(engine->irq_posted))
				wake_up_process(to_wait(next)->tsk);
		}

		do {
			struct intel_wait *crumb = to_wait(completed);
			completed = rb_prev(completed);
			__intel_breadcrumbs_finish(b, crumb);
		} while (completed);
	}

	if (first) {
		GEM_BUG_ON(rb_first(&b->waiters) != &wait->node);
		b->first_wait = wait;
		smp_store_mb(b->tasklet, wait->tsk);
		first = __intel_breadcrumbs_enable_irq(b);
	}
	GEM_BUG_ON(!b->tasklet);
	GEM_BUG_ON(!b->first_wait);
	GEM_BUG_ON(rb_first(&b->waiters) != &b->first_wait->node);

	return first;
}

bool intel_engine_add_wait(struct intel_engine_cs *engine,
			   struct intel_wait *wait)
{
	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	bool first;

	spin_lock(&b->lock);
	first = __intel_engine_add_wait(engine, wait);
	spin_unlock(&b->lock);

	return first;
}

void intel_engine_enable_fake_irq(struct intel_engine_cs *engine)
{
	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
}

static inline bool chain_wakeup(struct rb_node *rb, int priority)
{
	return rb && to_wait(rb)->tsk->prio <= priority;
}

void intel_engine_remove_wait(struct intel_engine_cs *engine,
			      struct intel_wait *wait)
{
	struct intel_breadcrumbs *b = &engine->breadcrumbs;

	/* Quick check to see if this waiter was already decoupled from
	 * the tree by the bottom-half to avoid contention on the spinlock
	 * by the herd.
	 */
	if (RB_EMPTY_NODE(&wait->node))
		return;

	spin_lock(&b->lock);

	if (RB_EMPTY_NODE(&wait->node))
		goto out_unlock;

	if (b->first_wait == wait) {
		struct rb_node *next;
		const int priority = wait->tsk->prio;

		GEM_BUG_ON(b->tasklet != wait->tsk);

		/* We are the current bottom-half. Find the next candidate,
		 * the first waiter in the queue on the remaining oldest
		 * request. As multiple seqnos may complete in the time it
		 * takes us to wake up and find the next waiter, we have to
		 * wake up that waiter for it to perform its own coherent
		 * completion check.
		 */
		next = rb_next(&wait->node);
		if (chain_wakeup(next, priority)) {
			/* If the next waiter is already complete,
			 * wake it up and continue onto the next waiter. So
			 * if have a small herd, they will wake up in parallel
			 * rather than sequentially, which should reduce
			 * the overall latency in waking all the completed
			 * clients.
			 *
			 * However, waking up a chain adds extra latency to
			 * the first_waiter. This is undesirable if that
			 * waiter is a high priority task.
			 */
			u32 seqno = intel_engine_get_seqno(engine);

			while (i915_seqno_passed(seqno, to_wait(next)->seqno)) {
				struct rb_node *n = rb_next(next);

				__intel_breadcrumbs_finish(b, to_wait(next));
				next = n;
				if (!chain_wakeup(next, priority))
					break;
			}
		}

		if (next) {
			/* In our haste, we may have completed the first waiter
			 * before we enabled the interrupt. Do so now as we
			 * have a second waiter for a future seqno. Afterwards,
			 * we have to wake up that waiter in case we missed
			 * the interrupt, or if we have to handle an
			 * exception rather than a seqno completion.
			 */
			b->first_wait = to_wait(next);
			smp_store_mb(b->tasklet, b->first_wait->tsk);
			if (b->first_wait->seqno != wait->seqno)
				__intel_breadcrumbs_enable_irq(b);
			wake_up_process(b->tasklet);
		} else {
			b->first_wait = NULL;
			WRITE_ONCE(b->tasklet, NULL);
			__intel_breadcrumbs_disable_irq(b);
		}
	} else {
		GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
	}

	GEM_BUG_ON(RB_EMPTY_NODE(&wait->node));
	rb_erase(&wait->node, &b->waiters);

out_unlock:
	GEM_BUG_ON(b->first_wait == wait);
	GEM_BUG_ON(rb_first(&b->waiters) !=
		   (b->first_wait ? &b->first_wait->node : NULL));
	GEM_BUG_ON(!b->tasklet ^ RB_EMPTY_ROOT(&b->waiters));
	spin_unlock(&b->lock);
}

int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
{
	struct intel_breadcrumbs *b = &engine->breadcrumbs;

	spin_lock_init(&b->lock);
	setup_timer(&b->fake_irq,
		    intel_breadcrumbs_fake_irq,
		    (unsigned long)engine);

	return 0;
}

void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
{
	struct intel_breadcrumbs *b = &engine->breadcrumbs;

	del_timer_sync(&b->fake_irq);
}

unsigned int intel_kick_waiters(struct drm_i915_private *i915)
{
	struct intel_engine_cs *engine;
	unsigned int mask = 0;

	/* To avoid the task_struct disappearing beneath us as we wake up
	 * the process, we must first inspect the task_struct->state under the
	 * RCU lock, i.e. as we call wake_up_process() we must be holding the
	 * rcu_read_lock().
	 */
	rcu_read_lock();
	for_each_engine(engine, i915)
		if (unlikely(intel_engine_wakeup(engine)))
			mask |= intel_engine_flag(engine);
	rcu_read_unlock();

	return mask;
}
Commit	Line	Data
688e6c72 CW	1	/*
	2	* Copyright © 2015 Intel Corporation
	3	*
	4	* Permission is hereby granted, free of charge, to any person obtaining a
	5	* copy of this software and associated documentation files (the "Software"),
	6	* to deal in the Software without restriction, including without limitation
	7	* the rights to use, copy, modify, merge, publish, distribute, sublicense,
	8	* and/or sell copies of the Software, and to permit persons to whom the
	9	* Software is furnished to do so, subject to the following conditions:
	10	*
	11	* The above copyright notice and this permission notice (including the next
	12	* paragraph) shall be included in all copies or substantial portions of the
	13	* Software.
	14	*
	15	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	16	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	17	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	18	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	19	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	20	* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
	21	* IN THE SOFTWARE.
	22	*
	23	*/
	24
	25	#include "i915_drv.h"
	26
	27	static void intel_breadcrumbs_fake_irq(unsigned long data)
	28	{
	29	struct intel_engine_cs engine = (struct intel_engine_cs )data;
	30
	31	/*
	32	* The timer persists in case we cannot enable interrupts,
	33	* or if we have previously seen seqno/interrupt incoherency
	34	* ("missed interrupt" syndrome). Here the worker will wake up
	35	* every jiffie in order to kick the oldest waiter to do the
	36	* coherent seqno check.
	37	*/
	38	rcu_read_lock();
	39	if (intel_engine_wakeup(engine))
	40	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
	41	rcu_read_unlock();
	42	}
	43
	44	static void irq_enable(struct intel_engine_cs *engine)
	45	{
3d5564e9 CW	46	/* Enabling the IRQ may miss the generation of the interrupt, but
	47	* we still need to force the barrier before reading the seqno,
	48	* just in case.
	49	*/
	50	engine->irq_posted = true;
688e6c72 CW	51	WARN_ON(!engine->irq_get(engine));
	52	}
	53
	54	static void irq_disable(struct intel_engine_cs *engine)
	55	{
	56	engine->irq_put(engine);
3d5564e9	57	engine->irq_posted = false;
688e6c72 CW	58	}
	59
	60	static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
	61	{
	62	struct intel_engine_cs *engine =
	63	container_of(b, struct intel_engine_cs, breadcrumbs);
	64	struct drm_i915_private *i915 = engine->i915;
688e6c72 CW	65
	66	assert_spin_locked(&b->lock);
	67	if (b->rpm_wakelock)
	68	return false;
	69
	70	/* Since we are waiting on a request, the GPU should be busy
	71	* and should have its own rpm reference. For completeness,
	72	* record an rpm reference for ourselves to cover the
	73	* interrupt we unmask.
	74	*/
	75	intel_runtime_pm_get_noresume(i915);
	76	b->rpm_wakelock = true;
	77
	78	/* No interrupts? Kick the waiter every jiffie! */
	79	if (intel_irqs_enabled(i915)) {
3d5564e9	80	if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings))
688e6c72	81	irq_enable(engine);
688e6c72 CW	82	b->irq_enabled = true;
	83	}
	84
	85	if (!b->irq_enabled \|\|
	86	test_bit(engine->id, &i915->gpu_error.missed_irq_rings))
	87	mod_timer(&b->fake_irq, jiffies + 1);
	88
3d5564e9	89	return engine->irq_posted;
688e6c72 CW	90	}
	91
	92	static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
	93	{
	94	struct intel_engine_cs *engine =
	95	container_of(b, struct intel_engine_cs, breadcrumbs);
	96
	97	assert_spin_locked(&b->lock);
	98	if (!b->rpm_wakelock)
	99	return;
	100
	101	if (b->irq_enabled) {
	102	irq_disable(engine);
	103	b->irq_enabled = false;
	104	}
	105
	106	intel_runtime_pm_put(engine->i915);
	107	b->rpm_wakelock = false;
	108	}
	109
	110	static inline struct intel_wait to_wait(struct rb_node node)
	111	{
	112	return container_of(node, struct intel_wait, node);
	113	}
	114
	115	static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
	116	struct intel_wait *wait)
	117	{
	118	assert_spin_locked(&b->lock);
	119
	120	/* This request is completed, so remove it from the tree, mark it as
	121	* complete, and then wake up the associated task.
	122	*/
	123	rb_erase(&wait->node, &b->waiters);
	124	RB_CLEAR_NODE(&wait->node);
	125
	126	wake_up_process(wait->tsk); /* implicit smp_wmb() */
	127	}
	128
	129	static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
	130	struct intel_wait *wait)
	131	{
	132	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	133	struct rb_node *p, parent, *completed;
	134	bool first;
	135	u32 seqno;
	136
	137	/* Insert the request into the retirement ordered list
	138	* of waiters by walking the rbtree. If we are the oldest
	139	* seqno in the tree (the first to be retired), then
	140	* set ourselves as the bottom-half.
	141	*
	142	* As we descend the tree, prune completed branches since we hold the
	143	* spinlock we know that the first_waiter must be delayed and can
	144	* reduce some of the sequential wake up latency if we take action
	145	* ourselves and wake up the completed tasks in parallel. Also, by
	146	* removing stale elements in the tree, we may be able to reduce the
	147	* ping-pong between the old bottom-half and ourselves as first-waiter.
	148	*/
	149	first = true;
	150	parent = NULL;
	151	completed = NULL;
1b7744e7	152	seqno = intel_engine_get_seqno(engine);
688e6c72 CW	153
	154	/* If the request completed before we managed to grab the spinlock,
	155	* return now before adding ourselves to the rbtree. We let the
	156	* current bottom-half handle any pending wakeups and instead
	157	* try and get out of the way quickly.
	158	*/
	159	if (i915_seqno_passed(seqno, wait->seqno)) {
	160	RB_CLEAR_NODE(&wait->node);
	161	return first;
	162	}
	163
	164	p = &b->waiters.rb_node;
	165	while (*p) {
	166	parent = *p;
	167	if (wait->seqno == to_wait(parent)->seqno) {
	168	/* We have multiple waiters on the same seqno, select
	169	* the highest priority task (that with the smallest
	170	* task->prio) to serve as the bottom-half for this
	171	* group.
	172	*/
	173	if (wait->tsk->prio > to_wait(parent)->tsk->prio) {
	174	p = &parent->rb_right;
	175	first = false;
	176	} else {
	177	p = &parent->rb_left;
	178	}
	179	} else if (i915_seqno_passed(wait->seqno,
	180	to_wait(parent)->seqno)) {
	181	p = &parent->rb_right;
	182	if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
	183	completed = parent;
	184	else
	185	first = false;
	186	} else {
	187	p = &parent->rb_left;
	188	}
	189	}
	190	rb_link_node(&wait->node, parent, p);
	191	rb_insert_color(&wait->node, &b->waiters);
	192	GEM_BUG_ON(!first && !b->tasklet);
	193
	194	if (completed) {
	195	struct rb_node *next = rb_next(completed);
	196
	197	GEM_BUG_ON(!next && !first);
	198	if (next && next != &wait->node) {
	199	GEM_BUG_ON(first);
	200	b->first_wait = to_wait(next);
	201	smp_store_mb(b->tasklet, b->first_wait->tsk);
	202	/* As there is a delay between reading the current
	203	* seqno, processing the completed tasks and selecting
	204	* the next waiter, we may have missed the interrupt
	205	* and so need for the next bottom-half to wakeup.
	206	*
	207	* Also as we enable the IRQ, we may miss the
	208	* interrupt for that seqno, so we have to wake up
	209	* the next bottom-half in order to do a coherent check
	210	* in case the seqno passed.
	211	*/
	212	__intel_breadcrumbs_enable_irq(b);
3d5564e9 CW	213	if (READ_ONCE(engine->irq_posted))
3d5564e9 CW	214	wake_up_process(to_wait(next)->tsk);
688e6c72 CW	215	}
	216
	217	do {
	218	struct intel_wait *crumb = to_wait(completed);
	219	completed = rb_prev(completed);
	220	__intel_breadcrumbs_finish(b, crumb);
	221	} while (completed);
	222	}
	223
	224	if (first) {
	225	GEM_BUG_ON(rb_first(&b->waiters) != &wait->node);
	226	b->first_wait = wait;
	227	smp_store_mb(b->tasklet, wait->tsk);
	228	first = __intel_breadcrumbs_enable_irq(b);
	229	}
	230	GEM_BUG_ON(!b->tasklet);
	231	GEM_BUG_ON(!b->first_wait);
	232	GEM_BUG_ON(rb_first(&b->waiters) != &b->first_wait->node);
	233
	234	return first;
	235	}
	236
	237	bool intel_engine_add_wait(struct intel_engine_cs *engine,
	238	struct intel_wait *wait)
	239	{
	240	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	241	bool first;
	242
	243	spin_lock(&b->lock);
	244	first = __intel_engine_add_wait(engine, wait);
	245	spin_unlock(&b->lock);
	246
	247	return first;
	248	}
	249
	250	void intel_engine_enable_fake_irq(struct intel_engine_cs *engine)
	251	{
	252	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
	253	}
	254
	255	static inline bool chain_wakeup(struct rb_node *rb, int priority)
	256	{
	257	return rb && to_wait(rb)->tsk->prio <= priority;
	258	}
	259
	260	void intel_engine_remove_wait(struct intel_engine_cs *engine,
	261	struct intel_wait *wait)
	262	{
	263	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	264
	265	/* Quick check to see if this waiter was already decoupled from
	266	* the tree by the bottom-half to avoid contention on the spinlock
	267	* by the herd.
	268	*/
	269	if (RB_EMPTY_NODE(&wait->node))
	270	return;
	271
	272	spin_lock(&b->lock);
	273
	274	if (RB_EMPTY_NODE(&wait->node))
	275	goto out_unlock;
	276
	277	if (b->first_wait == wait) {
	278	struct rb_node *next;
279	const int priority = wait->tsk->prio;
280
281	GEM_BUG_ON(b->tasklet != wait->tsk);
282
283	/* We are the current bottom-half. Find the next candidate,
284	* the first waiter in the queue on the remaining oldest
285	* request. As multiple seqnos may complete in the time it
286	* takes us to wake up and find the next waiter, we have to
287	* wake up that waiter for it to perform its own coherent
288	* completion check.
289	*/
290	next = rb_next(&wait->node);
291	if (chain_wakeup(next, priority)) {
292	/* If the next waiter is already complete,
293	* wake it up and continue onto the next waiter. So
294	* if have a small herd, they will wake up in parallel
295	* rather than sequentially, which should reduce
296	* the overall latency in waking all the completed
297	* clients.
298	*
299	* However, waking up a chain adds extra latency to
300	* the first_waiter. This is undesirable if that
301	* waiter is a high priority task.
302	*/
1b7744e7	303	u32 seqno = intel_engine_get_seqno(engine);
688e6c72 CW	304
	305	while (i915_seqno_passed(seqno, to_wait(next)->seqno)) {
	306	struct rb_node *n = rb_next(next);
	307
	308	__intel_breadcrumbs_finish(b, to_wait(next));
	309	next = n;
	310	if (!chain_wakeup(next, priority))
	311	break;
	312	}
	313	}
	314
	315	if (next) {
	316	/* In our haste, we may have completed the first waiter
	317	* before we enabled the interrupt. Do so now as we
	318	* have a second waiter for a future seqno. Afterwards,
	319	* we have to wake up that waiter in case we missed
	320	* the interrupt, or if we have to handle an
	321	* exception rather than a seqno completion.
	322	*/
	323	b->first_wait = to_wait(next);
	324	smp_store_mb(b->tasklet, b->first_wait->tsk);
	325	if (b->first_wait->seqno != wait->seqno)
	326	__intel_breadcrumbs_enable_irq(b);
	327	wake_up_process(b->tasklet);
	328	} else {
	329	b->first_wait = NULL;
	330	WRITE_ONCE(b->tasklet, NULL);
	331	__intel_breadcrumbs_disable_irq(b);
	332	}
	333	} else {
	334	GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
	335	}
	336
	337	GEM_BUG_ON(RB_EMPTY_NODE(&wait->node));
	338	rb_erase(&wait->node, &b->waiters);
	339
	340	out_unlock:
	341	GEM_BUG_ON(b->first_wait == wait);
	342	GEM_BUG_ON(rb_first(&b->waiters) !=
	343	(b->first_wait ? &b->first_wait->node : NULL));
	344	GEM_BUG_ON(!b->tasklet ^ RB_EMPTY_ROOT(&b->waiters));
	345	spin_unlock(&b->lock);
	346	}
	347
	348	int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
	349	{
	350	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	351
	352	spin_lock_init(&b->lock);
	353	setup_timer(&b->fake_irq,
	354	intel_breadcrumbs_fake_irq,
	355	(unsigned long)engine);
	356
	357	return 0;
	358	}
	359
	360	void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
	361	{
	362	struct intel_breadcrumbs *b = &engine->breadcrumbs;
	363
	364	del_timer_sync(&b->fake_irq);
	365	}
	366
	367	unsigned int intel_kick_waiters(struct drm_i915_private *i915)
368	{
369	struct intel_engine_cs *engine;
370	unsigned int mask = 0;
371
372	/* To avoid the task_struct disappearing beneath us as we wake up
373	* the process, we must first inspect the task_struct->state under the
374	* RCU lock, i.e. as we call wake_up_process() we must be holding the
375	* rcu_read_lock().
376	*/
377	rcu_read_lock();
378	for_each_engine(engine, i915)
379	if (unlikely(intel_engine_wakeup(engine)))
380	mask \|= intel_engine_flag(engine);
381	rcu_read_unlock();
382
383	return mask;
384	}