drivers/gpu/drm/i915/intel_breadcrumbs.c

   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 <linux/kthread.h>
  26 #include <uapi/linux/sched/types.h>
  27
  28 #include "i915_drv.h"
  29
  30 static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b)
  31 {
  32         struct intel_wait *wait;
  33         unsigned int result = 0;
  34
  35         lockdep_assert_held(&b->irq_lock);
  36
  37         wait = b->irq_wait;
  38         if (wait) {
  39                 result = ENGINE_WAKEUP_WAITER;
  40                 if (wake_up_process(wait->tsk))
  41                         result |= ENGINE_WAKEUP_ASLEEP;
  42         }
  43
  44         return result;
  45 }
  46
  47 unsigned int intel_engine_wakeup(struct intel_engine_cs *engine)
  48 {
  49         struct intel_breadcrumbs *b = &engine->breadcrumbs;
  50         unsigned long flags;
  51         unsigned int result;
  52
  53         spin_lock_irqsave(&b->irq_lock, flags);
  54         result = __intel_breadcrumbs_wakeup(b);
  55         spin_unlock_irqrestore(&b->irq_lock, flags);
  56
  57         return result;
  58 }
  59
  60 static unsigned long wait_timeout(void)
  61 {
  62         return round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
  63 }
  64
  65 static noinline void missed_breadcrumb(struct intel_engine_cs *engine)
  66 {
  67         DRM_DEBUG_DRIVER("%s missed breadcrumb at %pS, irq posted? %s, current seqno=%x, last=%x\n",
  68                          engine->name, __builtin_return_address(0),
  69                          yesno(test_bit(ENGINE_IRQ_BREADCRUMB,
  70                                         &engine->irq_posted)),
  71                          intel_engine_get_seqno(engine),
  72                          intel_engine_last_submit(engine));
  73
  74         set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
  75 }
  76
  77 static void intel_breadcrumbs_hangcheck(struct timer_list *t)
  78 {
  79         struct intel_engine_cs *engine = from_timer(engine, t,
  80                                                     breadcrumbs.hangcheck);
  81         struct intel_breadcrumbs *b = &engine->breadcrumbs;
  82
  83         if (!b->irq_armed)
  84                 return;
  85
  86         if (b->hangcheck_interrupts != atomic_read(&engine->irq_count)) {
  87                 b->hangcheck_interrupts = atomic_read(&engine->irq_count);
  88                 mod_timer(&b->hangcheck, wait_timeout());
  89                 return;
  90         }
  91
  92         /* We keep the hangcheck timer alive until we disarm the irq, even
  93          * if there are no waiters at present.
  94          *
  95          * If the waiter was currently running, assume it hasn't had a chance
  96          * to process the pending interrupt (e.g, low priority task on a loaded
  97          * system) and wait until it sleeps before declaring a missed interrupt.
  98          *
  99          * If the waiter was asleep (and not even pending a wakeup), then we
 100          * must have missed an interrupt as the GPU has stopped advancing
 101          * but we still have a waiter. Assuming all batches complete within
 102          * DRM_I915_HANGCHECK_JIFFIES [1.5s]!
 103          */
 104         if (intel_engine_wakeup(engine) & ENGINE_WAKEUP_ASLEEP) {
 105                 missed_breadcrumb(engine);
 106                 mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
 107         } else {
 108                 mod_timer(&b->hangcheck, wait_timeout());
 109         }
 110 }
 111
 112 static void intel_breadcrumbs_fake_irq(struct timer_list *t)
 113 {
 114         struct intel_engine_cs *engine = from_timer(engine, t,
 115                                                     breadcrumbs.fake_irq);
 116         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 117
 118         /* The timer persists in case we cannot enable interrupts,
 119          * or if we have previously seen seqno/interrupt incoherency
 120          * ("missed interrupt" syndrome, better known as a "missed breadcrumb").
 121          * Here the worker will wake up every jiffie in order to kick the
 122          * oldest waiter to do the coherent seqno check.
 123          */
 124
 125         spin_lock_irq(&b->irq_lock);
 126         if (!__intel_breadcrumbs_wakeup(b))
 127                 __intel_engine_disarm_breadcrumbs(engine);
 128         spin_unlock_irq(&b->irq_lock);
 129         if (!b->irq_armed)
 130                 return;
 131
 132         mod_timer(&b->fake_irq, jiffies + 1);
 133
 134         /* Ensure that even if the GPU hangs, we get woken up.
 135          *
 136          * However, note that if no one is waiting, we never notice
 137          * a gpu hang. Eventually, we will have to wait for a resource
 138          * held by the GPU and so trigger a hangcheck. In the most
 139          * pathological case, this will be upon memory starvation! To
 140          * prevent this, we also queue the hangcheck from the retire
 141          * worker.
 142          */
 143         i915_queue_hangcheck(engine->i915);
 144 }
 145
 146 static void irq_enable(struct intel_engine_cs *engine)
 147 {
 148         /* Enabling the IRQ may miss the generation of the interrupt, but
 149          * we still need to force the barrier before reading the seqno,
 150          * just in case.
 151          */
 152         set_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 153
 154         /* Caller disables interrupts */
 155         spin_lock(&engine->i915->irq_lock);
 156         engine->irq_enable(engine);
 157         spin_unlock(&engine->i915->irq_lock);
 158 }
 159
 160 static void irq_disable(struct intel_engine_cs *engine)
 161 {
 162         /* Caller disables interrupts */
 163         spin_lock(&engine->i915->irq_lock);
 164         engine->irq_disable(engine);
 165         spin_unlock(&engine->i915->irq_lock);
 166 }
 167
 168 void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
 169 {
 170         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 171
 172         lockdep_assert_held(&b->irq_lock);
 173         GEM_BUG_ON(b->irq_wait);
 174
 175         if (b->irq_enabled) {
 176                 irq_disable(engine);
 177                 b->irq_enabled = false;
 178         }
 179
 180         b->irq_armed = false;
 181 }
 182
 183 void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
 184 {
 185         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 186         struct intel_wait *wait, *n, *first;
 187
 188         if (!b->irq_armed)
 189                 goto wakeup_signaler;
 190
 191         /* We only disarm the irq when we are idle (all requests completed),
 192          * so if the bottom-half remains asleep, it missed the request
 193          * completion.
 194          */
 195
 196         spin_lock_irq(&b->rb_lock);
 197
 198         spin_lock(&b->irq_lock);
 199         first = fetch_and_zero(&b->irq_wait);
 200         __intel_engine_disarm_breadcrumbs(engine);
 201         spin_unlock(&b->irq_lock);
 202
 203         rbtree_postorder_for_each_entry_safe(wait, n, &b->waiters, node) {
 204                 RB_CLEAR_NODE(&wait->node);
 205                 if (wake_up_process(wait->tsk) && wait == first)
 206                         missed_breadcrumb(engine);
 207         }
 208         b->waiters = RB_ROOT;
 209
 210         spin_unlock_irq(&b->rb_lock);
 211
 212         /*
 213          * The signaling thread may be asleep holding a reference to a request,
 214          * that had its signaling cancelled prior to being preempted. We need
 215          * to kick the signaler, just in case, to release any such reference.
 216          */
 217 wakeup_signaler:
 218         wake_up_process(b->signaler);
 219 }
 220
 221 static bool use_fake_irq(const struct intel_breadcrumbs *b)
 222 {
 223         const struct intel_engine_cs *engine =
 224                 container_of(b, struct intel_engine_cs, breadcrumbs);
 225
 226         if (!test_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings))
 227                 return false;
 228
 229         /* Only start with the heavy weight fake irq timer if we have not
 230          * seen any interrupts since enabling it the first time. If the
 231          * interrupts are still arriving, it means we made a mistake in our
 232          * engine->seqno_barrier(), a timing error that should be transient
 233          * and unlikely to reoccur.
 234          */
 235         return atomic_read(&engine->irq_count) == b->hangcheck_interrupts;
 236 }
 237
 238 static void enable_fake_irq(struct intel_breadcrumbs *b)
 239 {
 240         /* Ensure we never sleep indefinitely */
 241         if (!b->irq_enabled || use_fake_irq(b))
 242                 mod_timer(&b->fake_irq, jiffies + 1);
 243         else
 244                 mod_timer(&b->hangcheck, wait_timeout());
 245 }
 246
 247 static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
 248 {
 249         struct intel_engine_cs *engine =
 250                 container_of(b, struct intel_engine_cs, breadcrumbs);
 251         struct drm_i915_private *i915 = engine->i915;
 252
 253         lockdep_assert_held(&b->irq_lock);
 254         if (b->irq_armed)
 255                 return false;
 256
 257         /* The breadcrumb irq will be disarmed on the interrupt after the
 258          * waiters are signaled. This gives us a single interrupt window in
 259          * which we can add a new waiter and avoid the cost of re-enabling
 260          * the irq.
 261          */
 262         b->irq_armed = true;
 263         GEM_BUG_ON(b->irq_enabled);
 264
 265         if (I915_SELFTEST_ONLY(b->mock)) {
 266                 /* For our mock objects we want to avoid interaction
 267                  * with the real hardware (which is not set up). So
 268                  * we simply pretend we have enabled the powerwell
 269                  * and the irq, and leave it up to the mock
 270                  * implementation to call intel_engine_wakeup()
 271                  * itself when it wants to simulate a user interrupt,
 272                  */
 273                 return true;
 274         }
 275
 276         /* Since we are waiting on a request, the GPU should be busy
 277          * and should have its own rpm reference. This is tracked
 278          * by i915->gt.awake, we can forgo holding our own wakref
 279          * for the interrupt as before i915->gt.awake is released (when
 280          * the driver is idle) we disarm the breadcrumbs.
 281          */
 282
 283         /* No interrupts? Kick the waiter every jiffie! */
 284         if (intel_irqs_enabled(i915)) {
 285                 if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings))
 286                         irq_enable(engine);
 287                 b->irq_enabled = true;
 288         }
 289
 290         enable_fake_irq(b);
 291         return true;
 292 }
 293
 294 static inline struct intel_wait *to_wait(struct rb_node *node)
 295 {
 296         return rb_entry(node, struct intel_wait, node);
 297 }
 298
 299 static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
 300                                               struct intel_wait *wait)
 301 {
 302         lockdep_assert_held(&b->rb_lock);
 303         GEM_BUG_ON(b->irq_wait == wait);
 304
 305         /* This request is completed, so remove it from the tree, mark it as
 306          * complete, and *then* wake up the associated task. N.B. when the
 307          * task wakes up, it will find the empty rb_node, discern that it
 308          * has already been removed from the tree and skip the serialisation
 309          * of the b->rb_lock and b->irq_lock. This means that the destruction
 310          * of the intel_wait is not serialised with the interrupt handler
 311          * by the waiter - it must instead be serialised by the caller.
 312          */
 313         rb_erase(&wait->node, &b->waiters);
 314         RB_CLEAR_NODE(&wait->node);
 315
 316         wake_up_process(wait->tsk); /* implicit smp_wmb() */
 317 }
 318
 319 static inline void __intel_breadcrumbs_next(struct intel_engine_cs *engine,
 320                                             struct rb_node *next)
 321 {
 322         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 323
 324         spin_lock(&b->irq_lock);
 325         GEM_BUG_ON(!b->irq_armed);
 326         GEM_BUG_ON(!b->irq_wait);
 327         b->irq_wait = to_wait(next);
 328         spin_unlock(&b->irq_lock);
 329
 330         /* We always wake up the next waiter that takes over as the bottom-half
 331          * as we may delegate not only the irq-seqno barrier to the next waiter
 332          * but also the task of waking up concurrent waiters.
 333          */
 334         if (next)
 335                 wake_up_process(to_wait(next)->tsk);
 336 }
 337
 338 static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
 339                                     struct intel_wait *wait)
 340 {
 341         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 342         struct rb_node **p, *parent, *completed;
 343         bool first, armed;
 344         u32 seqno;
 345
 346         /* Insert the request into the retirement ordered list
 347          * of waiters by walking the rbtree. If we are the oldest
 348          * seqno in the tree (the first to be retired), then
 349          * set ourselves as the bottom-half.
 350          *
 351          * As we descend the tree, prune completed branches since we hold the
 352          * spinlock we know that the first_waiter must be delayed and can
 353          * reduce some of the sequential wake up latency if we take action
 354          * ourselves and wake up the completed tasks in parallel. Also, by
 355          * removing stale elements in the tree, we may be able to reduce the
 356          * ping-pong between the old bottom-half and ourselves as first-waiter.
 357          */
 358         armed = false;
 359         first = true;
 360         parent = NULL;
 361         completed = NULL;
 362         seqno = intel_engine_get_seqno(engine);
 363
 364          /* If the request completed before we managed to grab the spinlock,
 365           * return now before adding ourselves to the rbtree. We let the
 366           * current bottom-half handle any pending wakeups and instead
 367           * try and get out of the way quickly.
 368           */
 369         if (i915_seqno_passed(seqno, wait->seqno)) {
 370                 RB_CLEAR_NODE(&wait->node);
 371                 return first;
 372         }
 373
 374         p = &b->waiters.rb_node;
 375         while (*p) {
 376                 parent = *p;
 377                 if (wait->seqno == to_wait(parent)->seqno) {
 378                         /* We have multiple waiters on the same seqno, select
 379                          * the highest priority task (that with the smallest
 380                          * task->prio) to serve as the bottom-half for this
 381                          * group.
 382                          */
 383                         if (wait->tsk->prio > to_wait(parent)->tsk->prio) {
 384                                 p = &parent->rb_right;
 385                                 first = false;
 386                         } else {
 387                                 p = &parent->rb_left;
 388                         }
 389                 } else if (i915_seqno_passed(wait->seqno,
 390                                              to_wait(parent)->seqno)) {
 391                         p = &parent->rb_right;
 392                         if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
 393                                 completed = parent;
 394                         else
 395                                 first = false;
 396                 } else {
 397                         p = &parent->rb_left;
 398                 }
 399         }
 400         rb_link_node(&wait->node, parent, p);
 401         rb_insert_color(&wait->node, &b->waiters);
 402
 403         if (first) {
 404                 spin_lock(&b->irq_lock);
 405                 b->irq_wait = wait;
 406                 /* After assigning ourselves as the new bottom-half, we must
 407                  * perform a cursory check to prevent a missed interrupt.
 408                  * Either we miss the interrupt whilst programming the hardware,
 409                  * or if there was a previous waiter (for a later seqno) they
 410                  * may be woken instead of us (due to the inherent race
 411                  * in the unlocked read of b->irq_seqno_bh in the irq handler)
 412                  * and so we miss the wake up.
 413                  */
 414                 armed = __intel_breadcrumbs_enable_irq(b);
 415                 spin_unlock(&b->irq_lock);
 416         }
 417
 418         if (completed) {
 419                 /* Advance the bottom-half (b->irq_wait) before we wake up
 420                  * the waiters who may scribble over their intel_wait
 421                  * just as the interrupt handler is dereferencing it via
 422                  * b->irq_wait.
 423                  */
 424                 if (!first) {
 425                         struct rb_node *next = rb_next(completed);
 426                         GEM_BUG_ON(next == &wait->node);
 427                         __intel_breadcrumbs_next(engine, next);
 428                 }
 429
 430                 do {
 431                         struct intel_wait *crumb = to_wait(completed);
 432                         completed = rb_prev(completed);
 433                         __intel_breadcrumbs_finish(b, crumb);
 434                 } while (completed);
 435         }
 436
 437         GEM_BUG_ON(!b->irq_wait);
 438         GEM_BUG_ON(!b->irq_armed);
 439         GEM_BUG_ON(rb_first(&b->waiters) != &b->irq_wait->node);
 440
 441         return armed;
 442 }
 443
 444 bool intel_engine_add_wait(struct intel_engine_cs *engine,
 445                            struct intel_wait *wait)
 446 {
 447         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 448         bool armed;
 449
 450         spin_lock_irq(&b->rb_lock);
 451         armed = __intel_engine_add_wait(engine, wait);
 452         spin_unlock_irq(&b->rb_lock);
 453         if (armed)
 454                 return armed;
 455
 456         /* Make the caller recheck if its request has already started. */
 457         return i915_seqno_passed(intel_engine_get_seqno(engine),
 458                                  wait->seqno - 1);
 459 }
 460
 461 static inline bool chain_wakeup(struct rb_node *rb, int priority)
 462 {
 463         return rb && to_wait(rb)->tsk->prio <= priority;
 464 }
 465
 466 static inline int wakeup_priority(struct intel_breadcrumbs *b,
 467                                   struct task_struct *tsk)
 468 {
 469         if (tsk == b->signaler)
 470                 return INT_MIN;
 471         else
 472                 return tsk->prio;
 473 }
 474
 475 static void __intel_engine_remove_wait(struct intel_engine_cs *engine,
 476                                        struct intel_wait *wait)
 477 {
 478         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 479
 480         lockdep_assert_held(&b->rb_lock);
 481
 482         if (RB_EMPTY_NODE(&wait->node))
 483                 goto out;
 484
 485         if (b->irq_wait == wait) {
 486                 const int priority = wakeup_priority(b, wait->tsk);
 487                 struct rb_node *next;
 488
 489                 /* We are the current bottom-half. Find the next candidate,
 490                  * the first waiter in the queue on the remaining oldest
 491                  * request. As multiple seqnos may complete in the time it
 492                  * takes us to wake up and find the next waiter, we have to
 493                  * wake up that waiter for it to perform its own coherent
 494                  * completion check.
 495                  */
 496                 next = rb_next(&wait->node);
 497                 if (chain_wakeup(next, priority)) {
 498                         /* If the next waiter is already complete,
 499                          * wake it up and continue onto the next waiter. So
 500                          * if have a small herd, they will wake up in parallel
 501                          * rather than sequentially, which should reduce
 502                          * the overall latency in waking all the completed
 503                          * clients.
 504                          *
 505                          * However, waking up a chain adds extra latency to
 506                          * the first_waiter. This is undesirable if that
 507                          * waiter is a high priority task.
 508                          */
 509                         u32 seqno = intel_engine_get_seqno(engine);
 510
 511                         while (i915_seqno_passed(seqno, to_wait(next)->seqno)) {
 512                                 struct rb_node *n = rb_next(next);
 513
 514                                 __intel_breadcrumbs_finish(b, to_wait(next));
 515                                 next = n;
 516                                 if (!chain_wakeup(next, priority))
 517                                         break;
 518                         }
 519                 }
 520
 521                 __intel_breadcrumbs_next(engine, next);
 522         } else {
 523                 GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
 524         }
 525
 526         GEM_BUG_ON(RB_EMPTY_NODE(&wait->node));
 527         rb_erase(&wait->node, &b->waiters);
 528         RB_CLEAR_NODE(&wait->node);
 529
 530 out:
 531         GEM_BUG_ON(b->irq_wait == wait);
 532         GEM_BUG_ON(rb_first(&b->waiters) !=
 533                    (b->irq_wait ? &b->irq_wait->node : NULL));
 534 }
 535
 536 void intel_engine_remove_wait(struct intel_engine_cs *engine,
 537                               struct intel_wait *wait)
 538 {
 539         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 540
 541         /* Quick check to see if this waiter was already decoupled from
 542          * the tree by the bottom-half to avoid contention on the spinlock
 543          * by the herd.
 544          */
 545         if (RB_EMPTY_NODE(&wait->node)) {
 546                 GEM_BUG_ON(READ_ONCE(b->irq_wait) == wait);
 547                 return;
 548         }
 549
 550         spin_lock_irq(&b->rb_lock);
 551         __intel_engine_remove_wait(engine, wait);
 552         spin_unlock_irq(&b->rb_lock);
 553 }
 554
 555 static bool signal_valid(const struct drm_i915_gem_request *request)
 556 {
 557         return intel_wait_check_request(&request->signaling.wait, request);
 558 }
 559
 560 static bool signal_complete(const struct drm_i915_gem_request *request)
 561 {
 562         if (!request)
 563                 return false;
 564
 565         /* If another process served as the bottom-half it may have already
 566          * signalled that this wait is already completed.
 567          */
 568         if (intel_wait_complete(&request->signaling.wait))
 569                 return signal_valid(request);
 570
 571         /* Carefully check if the request is complete, giving time for the
 572          * seqno to be visible or if the GPU hung.
 573          */
 574         if (__i915_request_irq_complete(request))
 575                 return true;
 576
 577         return false;
 578 }
 579
 580 static struct drm_i915_gem_request *to_signaler(struct rb_node *rb)
 581 {
 582         return rb_entry(rb, struct drm_i915_gem_request, signaling.node);
 583 }
 584
 585 static void signaler_set_rtpriority(void)
 586 {
 587          struct sched_param param = { .sched_priority = 1 };
 588
 589          sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
 590 }
 591
 592 static int intel_breadcrumbs_signaler(void *arg)
 593 {
 594         struct intel_engine_cs *engine = arg;
 595         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 596         struct drm_i915_gem_request *request;
 597
 598         /* Install ourselves with high priority to reduce signalling latency */
 599         signaler_set_rtpriority();
 600
 601         do {
 602                 bool do_schedule = true;
 603
 604                 set_current_state(TASK_INTERRUPTIBLE);
 605
 606                 /* We are either woken up by the interrupt bottom-half,
 607                  * or by a client adding a new signaller. In both cases,
 608                  * the GPU seqno may have advanced beyond our oldest signal.
 609                  * If it has, propagate the signal, remove the waiter and
 610                  * check again with the next oldest signal. Otherwise we
 611                  * need to wait for a new interrupt from the GPU or for
 612                  * a new client.
 613                  */
 614                 rcu_read_lock();
 615                 request = rcu_dereference(b->first_signal);
 616                 if (request)
 617                         request = i915_gem_request_get_rcu(request);
 618                 rcu_read_unlock();
 619                 if (signal_complete(request)) {
 620                         local_bh_disable();
 621                         dma_fence_signal(&request->fence);
 622                         local_bh_enable(); /* kick start the tasklets */
 623
 624                         spin_lock_irq(&b->rb_lock);
 625
 626                         /* Wake up all other completed waiters and select the
 627                          * next bottom-half for the next user interrupt.
 628                          */
 629                         __intel_engine_remove_wait(engine,
 630                                                    &request->signaling.wait);
 631
 632                         /* Find the next oldest signal. Note that as we have
 633                          * not been holding the lock, another client may
 634                          * have installed an even older signal than the one
 635                          * we just completed - so double check we are still
 636                          * the oldest before picking the next one.
 637                          */
 638                         if (request == rcu_access_pointer(b->first_signal)) {
 639                                 struct rb_node *rb =
 640                                         rb_next(&request->signaling.node);
 641                                 rcu_assign_pointer(b->first_signal,
 642                                                    rb ? to_signaler(rb) : NULL);
 643                         }
 644                         rb_erase(&request->signaling.node, &b->signals);
 645                         RB_CLEAR_NODE(&request->signaling.node);
 646
 647                         spin_unlock_irq(&b->rb_lock);
 648
 649                         i915_gem_request_put(request);
 650
 651                         /* If the engine is saturated we may be continually
 652                          * processing completed requests. This angers the
 653                          * NMI watchdog if we never let anything else
 654                          * have access to the CPU. Let's pretend to be nice
 655                          * and relinquish the CPU if we burn through the
 656                          * entire RT timeslice!
 657                          */
 658                         do_schedule = need_resched();
 659                 }
 660
 661                 if (unlikely(do_schedule)) {
 662                         if (kthread_should_park())
 663                                 kthread_parkme();
 664
 665                         if (unlikely(kthread_should_stop())) {
 666                                 i915_gem_request_put(request);
 667                                 break;
 668                         }
 669
 670                         schedule();
 671                 }
 672                 i915_gem_request_put(request);
 673         } while (1);
 674         __set_current_state(TASK_RUNNING);
 675
 676         return 0;
 677 }
 678
 679 void intel_engine_enable_signaling(struct drm_i915_gem_request *request,
 680                                    bool wakeup)
 681 {
 682         struct intel_engine_cs *engine = request->engine;
 683         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 684         u32 seqno;
 685
 686         /* Note that we may be called from an interrupt handler on another
 687          * device (e.g. nouveau signaling a fence completion causing us
 688          * to submit a request, and so enable signaling). As such,
 689          * we need to make sure that all other users of b->rb_lock protect
 690          * against interrupts, i.e. use spin_lock_irqsave.
 691          */
 692
 693         /* locked by dma_fence_enable_sw_signaling() (irqsafe fence->lock) */
 694         GEM_BUG_ON(!irqs_disabled());
 695         lockdep_assert_held(&request->lock);
 696
 697         seqno = i915_gem_request_global_seqno(request);
 698         if (!seqno)
 699                 return;
 700
 701         request->signaling.wait.tsk = b->signaler;
 702         request->signaling.wait.request = request;
 703         request->signaling.wait.seqno = seqno;
 704         i915_gem_request_get(request);
 705
 706         spin_lock(&b->rb_lock);
 707
 708         /* First add ourselves into the list of waiters, but register our
 709          * bottom-half as the signaller thread. As per usual, only the oldest
 710          * waiter (not just signaller) is tasked as the bottom-half waking
 711          * up all completed waiters after the user interrupt.
 712          *
 713          * If we are the oldest waiter, enable the irq (after which we
 714          * must double check that the seqno did not complete).
 715          */
 716         wakeup &= __intel_engine_add_wait(engine, &request->signaling.wait);
 717
 718         if (!__i915_gem_request_completed(request, seqno)) {
 719                 struct rb_node *parent, **p;
 720                 bool first;
 721
 722                 /* Now insert ourselves into the retirement ordered list of
 723                  * signals on this engine. We track the oldest seqno as that
 724                  * will be the first signal to complete.
 725                  */
 726                 parent = NULL;
 727                 first = true;
 728                 p = &b->signals.rb_node;
 729                 while (*p) {
 730                         parent = *p;
 731                         if (i915_seqno_passed(seqno,
 732                                               to_signaler(parent)->signaling.wait.seqno)) {
 733                                 p = &parent->rb_right;
 734                                 first = false;
 735                         } else {
 736                                 p = &parent->rb_left;
 737                         }
 738                 }
 739                 rb_link_node(&request->signaling.node, parent, p);
 740                 rb_insert_color(&request->signaling.node, &b->signals);
 741                 if (first)
 742                         rcu_assign_pointer(b->first_signal, request);
 743         } else {
 744                 __intel_engine_remove_wait(engine, &request->signaling.wait);
 745                 i915_gem_request_put(request);
 746                 wakeup = false;
 747         }
 748
 749         spin_unlock(&b->rb_lock);
 750
 751         if (wakeup)
 752                 wake_up_process(b->signaler);
 753 }
 754
 755 void intel_engine_cancel_signaling(struct drm_i915_gem_request *request)
 756 {
 757         struct intel_engine_cs *engine = request->engine;
 758         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 759
 760         GEM_BUG_ON(!irqs_disabled());
 761         lockdep_assert_held(&request->lock);
 762         GEM_BUG_ON(!request->signaling.wait.seqno);
 763
 764         spin_lock(&b->rb_lock);
 765
 766         if (!RB_EMPTY_NODE(&request->signaling.node)) {
 767                 if (request == rcu_access_pointer(b->first_signal)) {
 768                         struct rb_node *rb =
 769                                 rb_next(&request->signaling.node);
 770                         rcu_assign_pointer(b->first_signal,
 771                                            rb ? to_signaler(rb) : NULL);
 772                 }
 773                 rb_erase(&request->signaling.node, &b->signals);
 774                 RB_CLEAR_NODE(&request->signaling.node);
 775                 i915_gem_request_put(request);
 776         }
 777
 778         __intel_engine_remove_wait(engine, &request->signaling.wait);
 779
 780         spin_unlock(&b->rb_lock);
 781
 782         request->signaling.wait.seqno = 0;
 783 }
 784
 785 int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
 786 {
 787         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 788         struct task_struct *tsk;
 789
 790         spin_lock_init(&b->rb_lock);
 791         spin_lock_init(&b->irq_lock);
 792
 793         timer_setup(&b->fake_irq, intel_breadcrumbs_fake_irq, 0);
 794         timer_setup(&b->hangcheck, intel_breadcrumbs_hangcheck, 0);
 795
 796         /* Spawn a thread to provide a common bottom-half for all signals.
 797          * As this is an asynchronous interface we cannot steal the current
 798          * task for handling the bottom-half to the user interrupt, therefore
 799          * we create a thread to do the coherent seqno dance after the
 800          * interrupt and then signal the waitqueue (via the dma-buf/fence).
 801          */
 802         tsk = kthread_run(intel_breadcrumbs_signaler, engine,
 803                           "i915/signal:%d", engine->id);
 804         if (IS_ERR(tsk))
 805                 return PTR_ERR(tsk);
 806
 807         b->signaler = tsk;
 808
 809         return 0;
 810 }
 811
 812 static void cancel_fake_irq(struct intel_engine_cs *engine)
 813 {
 814         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 815
 816         del_timer_sync(&b->hangcheck);
 817         del_timer_sync(&b->fake_irq);
 818         clear_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
 819 }
 820
 821 void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
 822 {
 823         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 824
 825         cancel_fake_irq(engine);
 826         spin_lock_irq(&b->irq_lock);
 827
 828         if (b->irq_enabled)
 829                 irq_enable(engine);
 830         else
 831                 irq_disable(engine);
 832
 833         /* We set the IRQ_BREADCRUMB bit when we enable the irq presuming the
 834          * GPU is active and may have already executed the MI_USER_INTERRUPT
 835          * before the CPU is ready to receive. However, the engine is currently
 836          * idle (we haven't started it yet), there is no possibility for a
 837          * missed interrupt as we enabled the irq and so we can clear the
 838          * immediate wakeup (until a real interrupt arrives for the waiter).
 839          */
 840         clear_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 841
 842         if (b->irq_armed)
 843                 enable_fake_irq(b);
 844
 845         spin_unlock_irq(&b->irq_lock);
 846 }
 847
 848 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 849 {
 850         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 851
 852         /* The engines should be idle and all requests accounted for! */
 853         WARN_ON(READ_ONCE(b->irq_wait));
 854         WARN_ON(!RB_EMPTY_ROOT(&b->waiters));
 855         WARN_ON(rcu_access_pointer(b->first_signal));
 856         WARN_ON(!RB_EMPTY_ROOT(&b->signals));
 857
 858         if (!IS_ERR_OR_NULL(b->signaler))
 859                 kthread_stop(b->signaler);
 860
 861         cancel_fake_irq(engine);
 862 }
 863
 864 bool intel_breadcrumbs_busy(struct intel_engine_cs *engine)
 865 {
 866         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 867         bool busy = false;
 868
 869         spin_lock_irq(&b->rb_lock);
 870
 871         if (b->irq_wait) {
 872                 wake_up_process(b->irq_wait->tsk);
 873                 busy = true;
 874         }
 875
 876         if (rcu_access_pointer(b->first_signal)) {
 877                 wake_up_process(b->signaler);
 878                 busy = true;
 879         }
 880
 881         spin_unlock_irq(&b->rb_lock);
 882
 883         return busy;
 884 }
 885
 886 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 887 #include "selftests/intel_breadcrumbs.c"
 888 #endif