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 #ifdef CONFIG_SMP
  31 #define task_asleep(tsk) ((tsk)->state & TASK_NORMAL && !(tsk)->on_cpu)
  32 #else
  33 #define task_asleep(tsk) ((tsk)->state & TASK_NORMAL)
  34 #endif
  35
  36 static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b)
  37 {
  38         struct intel_wait *wait;
  39         unsigned int result = 0;
  40
  41         lockdep_assert_held(&b->irq_lock);
  42
  43         wait = b->irq_wait;
  44         if (wait) {
  45                 /*
  46                  * N.B. Since task_asleep() and ttwu are not atomic, the
  47                  * waiter may actually go to sleep after the check, causing
  48                  * us to suppress a valid wakeup. We prefer to reduce the
  49                  * number of false positive missed_breadcrumb() warnings
  50                  * at the expense of a few false negatives, as it it easy
  51                  * to trigger a false positive under heavy load. Enough
  52                  * signal should remain from genuine missed_breadcrumb()
  53                  * for us to detect in CI.
  54                  */
  55                 bool was_asleep = task_asleep(wait->tsk);
  56
  57                 result = ENGINE_WAKEUP_WAITER;
  58                 if (wake_up_process(wait->tsk) && was_asleep)
  59                         result |= ENGINE_WAKEUP_ASLEEP;
  60         }
  61
  62         return result;
  63 }
  64
  65 unsigned int intel_engine_wakeup(struct intel_engine_cs *engine)
  66 {
  67         struct intel_breadcrumbs *b = &engine->breadcrumbs;
  68         unsigned long flags;
  69         unsigned int result;
  70
  71         spin_lock_irqsave(&b->irq_lock, flags);
  72         result = __intel_breadcrumbs_wakeup(b);
  73         spin_unlock_irqrestore(&b->irq_lock, flags);
  74
  75         return result;
  76 }
  77
  78 static unsigned long wait_timeout(void)
  79 {
  80         return round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
  81 }
  82
  83 static noinline void missed_breadcrumb(struct intel_engine_cs *engine)
  84 {
  85         if (drm_debug & DRM_UT_DRIVER) {
  86                 struct drm_printer p = drm_debug_printer(__func__);
  87
  88                 intel_engine_dump(engine, &p,
  89                                   "%s missed breadcrumb at %pS\n",
  90                                   engine->name, __builtin_return_address(0));
  91         }
  92
  93         set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
  94 }
  95
  96 static void intel_breadcrumbs_hangcheck(struct timer_list *t)
  97 {
  98         struct intel_engine_cs *engine =
  99                 from_timer(engine, t, breadcrumbs.hangcheck);
 100         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 101
 102         if (!b->irq_armed)
 103                 return;
 104
 105         if (b->hangcheck_interrupts != atomic_read(&engine->irq_count)) {
 106                 b->hangcheck_interrupts = atomic_read(&engine->irq_count);
 107                 mod_timer(&b->hangcheck, wait_timeout());
 108                 return;
 109         }
 110
 111         /* We keep the hangcheck timer alive until we disarm the irq, even
 112          * if there are no waiters at present.
 113          *
 114          * If the waiter was currently running, assume it hasn't had a chance
 115          * to process the pending interrupt (e.g, low priority task on a loaded
 116          * system) and wait until it sleeps before declaring a missed interrupt.
 117          *
 118          * If the waiter was asleep (and not even pending a wakeup), then we
 119          * must have missed an interrupt as the GPU has stopped advancing
 120          * but we still have a waiter. Assuming all batches complete within
 121          * DRM_I915_HANGCHECK_JIFFIES [1.5s]!
 122          */
 123         if (intel_engine_wakeup(engine) & ENGINE_WAKEUP_ASLEEP) {
 124                 missed_breadcrumb(engine);
 125                 mod_timer(&b->fake_irq, jiffies + 1);
 126         } else {
 127                 mod_timer(&b->hangcheck, wait_timeout());
 128         }
 129 }
 130
 131 static void intel_breadcrumbs_fake_irq(struct timer_list *t)
 132 {
 133         struct intel_engine_cs *engine = from_timer(engine, t,
 134                                                     breadcrumbs.fake_irq);
 135         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 136
 137         /* The timer persists in case we cannot enable interrupts,
 138          * or if we have previously seen seqno/interrupt incoherency
 139          * ("missed interrupt" syndrome, better known as a "missed breadcrumb").
 140          * Here the worker will wake up every jiffie in order to kick the
 141          * oldest waiter to do the coherent seqno check.
 142          */
 143
 144         spin_lock_irq(&b->irq_lock);
 145         if (b->irq_armed && !__intel_breadcrumbs_wakeup(b))
 146                 __intel_engine_disarm_breadcrumbs(engine);
 147         spin_unlock_irq(&b->irq_lock);
 148         if (!b->irq_armed)
 149                 return;
 150
 151         mod_timer(&b->fake_irq, jiffies + 1);
 152
 153         /* Ensure that even if the GPU hangs, we get woken up.
 154          *
 155          * However, note that if no one is waiting, we never notice
 156          * a gpu hang. Eventually, we will have to wait for a resource
 157          * held by the GPU and so trigger a hangcheck. In the most
 158          * pathological case, this will be upon memory starvation! To
 159          * prevent this, we also queue the hangcheck from the retire
 160          * worker.
 161          */
 162         i915_queue_hangcheck(engine->i915);
 163 }
 164
 165 static void irq_enable(struct intel_engine_cs *engine)
 166 {
 167         /*
 168          * FIXME: Ideally we want this on the API boundary, but for the
 169          * sake of testing with mock breadcrumbs (no HW so unable to
 170          * enable irqs) we place it deep within the bowels, at the point
 171          * of no return.
 172          */
 173         GEM_BUG_ON(!intel_irqs_enabled(engine->i915));
 174
 175         /* Enabling the IRQ may miss the generation of the interrupt, but
 176          * we still need to force the barrier before reading the seqno,
 177          * just in case.
 178          */
 179         set_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 180
 181         /* Caller disables interrupts */
 182         spin_lock(&engine->i915->irq_lock);
 183         engine->irq_enable(engine);
 184         spin_unlock(&engine->i915->irq_lock);
 185 }
 186
 187 static void irq_disable(struct intel_engine_cs *engine)
 188 {
 189         /* Caller disables interrupts */
 190         spin_lock(&engine->i915->irq_lock);
 191         engine->irq_disable(engine);
 192         spin_unlock(&engine->i915->irq_lock);
 193 }
 194
 195 void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
 196 {
 197         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 198
 199         lockdep_assert_held(&b->irq_lock);
 200         GEM_BUG_ON(b->irq_wait);
 201         GEM_BUG_ON(!b->irq_armed);
 202
 203         GEM_BUG_ON(!b->irq_enabled);
 204         if (!--b->irq_enabled)
 205                 irq_disable(engine);
 206
 207         b->irq_armed = false;
 208 }
 209
 210 void intel_engine_pin_breadcrumbs_irq(struct intel_engine_cs *engine)
 211 {
 212         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 213
 214         spin_lock_irq(&b->irq_lock);
 215         if (!b->irq_enabled++)
 216                 irq_enable(engine);
 217         GEM_BUG_ON(!b->irq_enabled); /* no overflow! */
 218         spin_unlock_irq(&b->irq_lock);
 219 }
 220
 221 void intel_engine_unpin_breadcrumbs_irq(struct intel_engine_cs *engine)
 222 {
 223         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 224
 225         spin_lock_irq(&b->irq_lock);
 226         GEM_BUG_ON(!b->irq_enabled); /* no underflow! */
 227         if (!--b->irq_enabled)
 228                 irq_disable(engine);
 229         spin_unlock_irq(&b->irq_lock);
 230 }
 231
 232 void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
 233 {
 234         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 235         struct intel_wait *wait, *n;
 236
 237         if (!b->irq_armed)
 238                 goto wakeup_signaler;
 239
 240         /*
 241          * We only disarm the irq when we are idle (all requests completed),
 242          * so if the bottom-half remains asleep, it missed the request
 243          * completion.
 244          */
 245         if (intel_engine_wakeup(engine) & ENGINE_WAKEUP_ASLEEP)
 246                 missed_breadcrumb(engine);
 247
 248         spin_lock_irq(&b->rb_lock);
 249
 250         spin_lock(&b->irq_lock);
 251         b->irq_wait = NULL;
 252         if (b->irq_armed)
 253                 __intel_engine_disarm_breadcrumbs(engine);
 254         spin_unlock(&b->irq_lock);
 255
 256         rbtree_postorder_for_each_entry_safe(wait, n, &b->waiters, node) {
 257                 RB_CLEAR_NODE(&wait->node);
 258                 wake_up_process(wait->tsk);
 259         }
 260         b->waiters = RB_ROOT;
 261
 262         spin_unlock_irq(&b->rb_lock);
 263
 264         /*
 265          * The signaling thread may be asleep holding a reference to a request,
 266          * that had its signaling cancelled prior to being preempted. We need
 267          * to kick the signaler, just in case, to release any such reference.
 268          */
 269 wakeup_signaler:
 270         wake_up_process(b->signaler);
 271 }
 272
 273 static bool use_fake_irq(const struct intel_breadcrumbs *b)
 274 {
 275         const struct intel_engine_cs *engine =
 276                 container_of(b, struct intel_engine_cs, breadcrumbs);
 277
 278         if (!test_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings))
 279                 return false;
 280
 281         /* Only start with the heavy weight fake irq timer if we have not
 282          * seen any interrupts since enabling it the first time. If the
 283          * interrupts are still arriving, it means we made a mistake in our
 284          * engine->seqno_barrier(), a timing error that should be transient
 285          * and unlikely to reoccur.
 286          */
 287         return atomic_read(&engine->irq_count) == b->hangcheck_interrupts;
 288 }
 289
 290 static void enable_fake_irq(struct intel_breadcrumbs *b)
 291 {
 292         /* Ensure we never sleep indefinitely */
 293         if (!b->irq_enabled || use_fake_irq(b))
 294                 mod_timer(&b->fake_irq, jiffies + 1);
 295         else
 296                 mod_timer(&b->hangcheck, wait_timeout());
 297 }
 298
 299 static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
 300 {
 301         struct intel_engine_cs *engine =
 302                 container_of(b, struct intel_engine_cs, breadcrumbs);
 303         struct drm_i915_private *i915 = engine->i915;
 304         bool enabled;
 305
 306         lockdep_assert_held(&b->irq_lock);
 307         if (b->irq_armed)
 308                 return false;
 309
 310         /* The breadcrumb irq will be disarmed on the interrupt after the
 311          * waiters are signaled. This gives us a single interrupt window in
 312          * which we can add a new waiter and avoid the cost of re-enabling
 313          * the irq.
 314          */
 315         b->irq_armed = true;
 316
 317         if (I915_SELFTEST_ONLY(b->mock)) {
 318                 /* For our mock objects we want to avoid interaction
 319                  * with the real hardware (which is not set up). So
 320                  * we simply pretend we have enabled the powerwell
 321                  * and the irq, and leave it up to the mock
 322                  * implementation to call intel_engine_wakeup()
 323                  * itself when it wants to simulate a user interrupt,
 324                  */
 325                 return true;
 326         }
 327
 328         /* Since we are waiting on a request, the GPU should be busy
 329          * and should have its own rpm reference. This is tracked
 330          * by i915->gt.awake, we can forgo holding our own wakref
 331          * for the interrupt as before i915->gt.awake is released (when
 332          * the driver is idle) we disarm the breadcrumbs.
 333          */
 334
 335         /* No interrupts? Kick the waiter every jiffie! */
 336         enabled = false;
 337         if (!b->irq_enabled++ &&
 338             !test_bit(engine->id, &i915->gpu_error.test_irq_rings)) {
 339                 irq_enable(engine);
 340                 enabled = true;
 341         }
 342
 343         enable_fake_irq(b);
 344         return enabled;
 345 }
 346
 347 static inline struct intel_wait *to_wait(struct rb_node *node)
 348 {
 349         return rb_entry(node, struct intel_wait, node);
 350 }
 351
 352 static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
 353                                               struct intel_wait *wait)
 354 {
 355         lockdep_assert_held(&b->rb_lock);
 356         GEM_BUG_ON(b->irq_wait == wait);
 357
 358         /* This request is completed, so remove it from the tree, mark it as
 359          * complete, and *then* wake up the associated task. N.B. when the
 360          * task wakes up, it will find the empty rb_node, discern that it
 361          * has already been removed from the tree and skip the serialisation
 362          * of the b->rb_lock and b->irq_lock. This means that the destruction
 363          * of the intel_wait is not serialised with the interrupt handler
 364          * by the waiter - it must instead be serialised by the caller.
 365          */
 366         rb_erase(&wait->node, &b->waiters);
 367         RB_CLEAR_NODE(&wait->node);
 368
 369         wake_up_process(wait->tsk); /* implicit smp_wmb() */
 370 }
 371
 372 static inline void __intel_breadcrumbs_next(struct intel_engine_cs *engine,
 373                                             struct rb_node *next)
 374 {
 375         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 376
 377         spin_lock(&b->irq_lock);
 378         GEM_BUG_ON(!b->irq_armed);
 379         GEM_BUG_ON(!b->irq_wait);
 380         b->irq_wait = to_wait(next);
 381         spin_unlock(&b->irq_lock);
 382
 383         /* We always wake up the next waiter that takes over as the bottom-half
 384          * as we may delegate not only the irq-seqno barrier to the next waiter
 385          * but also the task of waking up concurrent waiters.
 386          */
 387         if (next)
 388                 wake_up_process(to_wait(next)->tsk);
 389 }
 390
 391 static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
 392                                     struct intel_wait *wait)
 393 {
 394         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 395         struct rb_node **p, *parent, *completed;
 396         bool first, armed;
 397         u32 seqno;
 398
 399         /* Insert the request into the retirement ordered list
 400          * of waiters by walking the rbtree. If we are the oldest
 401          * seqno in the tree (the first to be retired), then
 402          * set ourselves as the bottom-half.
 403          *
 404          * As we descend the tree, prune completed branches since we hold the
 405          * spinlock we know that the first_waiter must be delayed and can
 406          * reduce some of the sequential wake up latency if we take action
 407          * ourselves and wake up the completed tasks in parallel. Also, by
 408          * removing stale elements in the tree, we may be able to reduce the
 409          * ping-pong between the old bottom-half and ourselves as first-waiter.
 410          */
 411         armed = false;
 412         first = true;
 413         parent = NULL;
 414         completed = NULL;
 415         seqno = intel_engine_get_seqno(engine);
 416
 417          /* If the request completed before we managed to grab the spinlock,
 418           * return now before adding ourselves to the rbtree. We let the
 419           * current bottom-half handle any pending wakeups and instead
 420           * try and get out of the way quickly.
 421           */
 422         if (i915_seqno_passed(seqno, wait->seqno)) {
 423                 RB_CLEAR_NODE(&wait->node);
 424                 return first;
 425         }
 426
 427         p = &b->waiters.rb_node;
 428         while (*p) {
 429                 parent = *p;
 430                 if (wait->seqno == to_wait(parent)->seqno) {
 431                         /* We have multiple waiters on the same seqno, select
 432                          * the highest priority task (that with the smallest
 433                          * task->prio) to serve as the bottom-half for this
 434                          * group.
 435                          */
 436                         if (wait->tsk->prio > to_wait(parent)->tsk->prio) {
 437                                 p = &parent->rb_right;
 438                                 first = false;
 439                         } else {
 440                                 p = &parent->rb_left;
 441                         }
 442                 } else if (i915_seqno_passed(wait->seqno,
 443                                              to_wait(parent)->seqno)) {
 444                         p = &parent->rb_right;
 445                         if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
 446                                 completed = parent;
 447                         else
 448                                 first = false;
 449                 } else {
 450                         p = &parent->rb_left;
 451                 }
 452         }
 453         rb_link_node(&wait->node, parent, p);
 454         rb_insert_color(&wait->node, &b->waiters);
 455
 456         if (first) {
 457                 spin_lock(&b->irq_lock);
 458                 b->irq_wait = wait;
 459                 /* After assigning ourselves as the new bottom-half, we must
 460                  * perform a cursory check to prevent a missed interrupt.
 461                  * Either we miss the interrupt whilst programming the hardware,
 462                  * or if there was a previous waiter (for a later seqno) they
 463                  * may be woken instead of us (due to the inherent race
 464                  * in the unlocked read of b->irq_seqno_bh in the irq handler)
 465                  * and so we miss the wake up.
 466                  */
 467                 armed = __intel_breadcrumbs_enable_irq(b);
 468                 spin_unlock(&b->irq_lock);
 469         }
 470
 471         if (completed) {
 472                 /* Advance the bottom-half (b->irq_wait) before we wake up
 473                  * the waiters who may scribble over their intel_wait
 474                  * just as the interrupt handler is dereferencing it via
 475                  * b->irq_wait.
 476                  */
 477                 if (!first) {
 478                         struct rb_node *next = rb_next(completed);
 479                         GEM_BUG_ON(next == &wait->node);
 480                         __intel_breadcrumbs_next(engine, next);
 481                 }
 482
 483                 do {
 484                         struct intel_wait *crumb = to_wait(completed);
 485                         completed = rb_prev(completed);
 486                         __intel_breadcrumbs_finish(b, crumb);
 487                 } while (completed);
 488         }
 489
 490         GEM_BUG_ON(!b->irq_wait);
 491         GEM_BUG_ON(!b->irq_armed);
 492         GEM_BUG_ON(rb_first(&b->waiters) != &b->irq_wait->node);
 493
 494         return armed;
 495 }
 496
 497 bool intel_engine_add_wait(struct intel_engine_cs *engine,
 498                            struct intel_wait *wait)
 499 {
 500         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 501         bool armed;
 502
 503         spin_lock_irq(&b->rb_lock);
 504         armed = __intel_engine_add_wait(engine, wait);
 505         spin_unlock_irq(&b->rb_lock);
 506         if (armed)
 507                 return armed;
 508
 509         /* Make the caller recheck if its request has already started. */
 510         return i915_seqno_passed(intel_engine_get_seqno(engine),
 511                                  wait->seqno - 1);
 512 }
 513
 514 static inline bool chain_wakeup(struct rb_node *rb, int priority)
 515 {
 516         return rb && to_wait(rb)->tsk->prio <= priority;
 517 }
 518
 519 static inline int wakeup_priority(struct intel_breadcrumbs *b,
 520                                   struct task_struct *tsk)
 521 {
 522         if (tsk == b->signaler)
 523                 return INT_MIN;
 524         else
 525                 return tsk->prio;
 526 }
 527
 528 static void __intel_engine_remove_wait(struct intel_engine_cs *engine,
 529                                        struct intel_wait *wait)
 530 {
 531         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 532
 533         lockdep_assert_held(&b->rb_lock);
 534
 535         if (RB_EMPTY_NODE(&wait->node))
 536                 goto out;
 537
 538         if (b->irq_wait == wait) {
 539                 const int priority = wakeup_priority(b, wait->tsk);
 540                 struct rb_node *next;
 541
 542                 /* We are the current bottom-half. Find the next candidate,
 543                  * the first waiter in the queue on the remaining oldest
 544                  * request. As multiple seqnos may complete in the time it
 545                  * takes us to wake up and find the next waiter, we have to
 546                  * wake up that waiter for it to perform its own coherent
 547                  * completion check.
 548                  */
 549                 next = rb_next(&wait->node);
 550                 if (chain_wakeup(next, priority)) {
 551                         /* If the next waiter is already complete,
 552                          * wake it up and continue onto the next waiter. So
 553                          * if have a small herd, they will wake up in parallel
 554                          * rather than sequentially, which should reduce
 555                          * the overall latency in waking all the completed
 556                          * clients.
 557                          *
 558                          * However, waking up a chain adds extra latency to
 559                          * the first_waiter. This is undesirable if that
 560                          * waiter is a high priority task.
 561                          */
 562                         u32 seqno = intel_engine_get_seqno(engine);
 563
 564                         while (i915_seqno_passed(seqno, to_wait(next)->seqno)) {
 565                                 struct rb_node *n = rb_next(next);
 566
 567                                 __intel_breadcrumbs_finish(b, to_wait(next));
 568                                 next = n;
 569                                 if (!chain_wakeup(next, priority))
 570                                         break;
 571                         }
 572                 }
 573
 574                 __intel_breadcrumbs_next(engine, next);
 575         } else {
 576                 GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
 577         }
 578
 579         GEM_BUG_ON(RB_EMPTY_NODE(&wait->node));
 580         rb_erase(&wait->node, &b->waiters);
 581         RB_CLEAR_NODE(&wait->node);
 582
 583 out:
 584         GEM_BUG_ON(b->irq_wait == wait);
 585         GEM_BUG_ON(rb_first(&b->waiters) !=
 586                    (b->irq_wait ? &b->irq_wait->node : NULL));
 587 }
 588
 589 void intel_engine_remove_wait(struct intel_engine_cs *engine,
 590                               struct intel_wait *wait)
 591 {
 592         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 593
 594         /* Quick check to see if this waiter was already decoupled from
 595          * the tree by the bottom-half to avoid contention on the spinlock
 596          * by the herd.
 597          */
 598         if (RB_EMPTY_NODE(&wait->node)) {
 599                 GEM_BUG_ON(READ_ONCE(b->irq_wait) == wait);
 600                 return;
 601         }
 602
 603         spin_lock_irq(&b->rb_lock);
 604         __intel_engine_remove_wait(engine, wait);
 605         spin_unlock_irq(&b->rb_lock);
 606 }
 607
 608 static bool signal_valid(const struct drm_i915_gem_request *request)
 609 {
 610         return intel_wait_check_request(&request->signaling.wait, request);
 611 }
 612
 613 static bool signal_complete(const struct drm_i915_gem_request *request)
 614 {
 615         if (!request)
 616                 return false;
 617
 618         /* If another process served as the bottom-half it may have already
 619          * signalled that this wait is already completed.
 620          */
 621         if (intel_wait_complete(&request->signaling.wait))
 622                 return signal_valid(request);
 623
 624         /* Carefully check if the request is complete, giving time for the
 625          * seqno to be visible or if the GPU hung.
 626          */
 627         if (__i915_request_irq_complete(request))
 628                 return true;
 629
 630         return false;
 631 }
 632
 633 static struct drm_i915_gem_request *to_signaler(struct rb_node *rb)
 634 {
 635         return rb_entry(rb, struct drm_i915_gem_request, signaling.node);
 636 }
 637
 638 static void signaler_set_rtpriority(void)
 639 {
 640          struct sched_param param = { .sched_priority = 1 };
 641
 642          sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
 643 }
 644
 645 static int intel_breadcrumbs_signaler(void *arg)
 646 {
 647         struct intel_engine_cs *engine = arg;
 648         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 649         struct drm_i915_gem_request *request;
 650
 651         /* Install ourselves with high priority to reduce signalling latency */
 652         signaler_set_rtpriority();
 653
 654         do {
 655                 bool do_schedule = true;
 656
 657                 set_current_state(TASK_INTERRUPTIBLE);
 658
 659                 /* We are either woken up by the interrupt bottom-half,
 660                  * or by a client adding a new signaller. In both cases,
 661                  * the GPU seqno may have advanced beyond our oldest signal.
 662                  * If it has, propagate the signal, remove the waiter and
 663                  * check again with the next oldest signal. Otherwise we
 664                  * need to wait for a new interrupt from the GPU or for
 665                  * a new client.
 666                  */
 667                 rcu_read_lock();
 668                 request = rcu_dereference(b->first_signal);
 669                 if (request)
 670                         request = i915_gem_request_get_rcu(request);
 671                 rcu_read_unlock();
 672                 if (signal_complete(request)) {
 673                         local_bh_disable();
 674                         dma_fence_signal(&request->fence);
 675                         local_bh_enable(); /* kick start the tasklets */
 676
 677                         spin_lock_irq(&b->rb_lock);
 678
 679                         /* Wake up all other completed waiters and select the
 680                          * next bottom-half for the next user interrupt.
 681                          */
 682                         __intel_engine_remove_wait(engine,
 683                                                    &request->signaling.wait);
 684
 685                         /* Find the next oldest signal. Note that as we have
 686                          * not been holding the lock, another client may
 687                          * have installed an even older signal than the one
 688                          * we just completed - so double check we are still
 689                          * the oldest before picking the next one.
 690                          */
 691                         if (request == rcu_access_pointer(b->first_signal)) {
 692                                 struct rb_node *rb =
 693                                         rb_next(&request->signaling.node);
 694                                 rcu_assign_pointer(b->first_signal,
 695                                                    rb ? to_signaler(rb) : NULL);
 696                         }
 697                         rb_erase(&request->signaling.node, &b->signals);
 698                         RB_CLEAR_NODE(&request->signaling.node);
 699
 700                         spin_unlock_irq(&b->rb_lock);
 701
 702                         i915_gem_request_put(request);
 703
 704                         /* If the engine is saturated we may be continually
 705                          * processing completed requests. This angers the
 706                          * NMI watchdog if we never let anything else
 707                          * have access to the CPU. Let's pretend to be nice
 708                          * and relinquish the CPU if we burn through the
 709                          * entire RT timeslice!
 710                          */
 711                         do_schedule = need_resched();
 712                 }
 713
 714                 if (unlikely(do_schedule)) {
 715                         if (kthread_should_park())
 716                                 kthread_parkme();
 717
 718                         if (unlikely(kthread_should_stop())) {
 719                                 i915_gem_request_put(request);
 720                                 break;
 721                         }
 722
 723                         schedule();
 724                 }
 725                 i915_gem_request_put(request);
 726         } while (1);
 727         __set_current_state(TASK_RUNNING);
 728
 729         return 0;
 730 }
 731
 732 void intel_engine_enable_signaling(struct drm_i915_gem_request *request,
 733                                    bool wakeup)
 734 {
 735         struct intel_engine_cs *engine = request->engine;
 736         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 737         u32 seqno;
 738
 739         /* Note that we may be called from an interrupt handler on another
 740          * device (e.g. nouveau signaling a fence completion causing us
 741          * to submit a request, and so enable signaling). As such,
 742          * we need to make sure that all other users of b->rb_lock protect
 743          * against interrupts, i.e. use spin_lock_irqsave.
 744          */
 745
 746         /* locked by dma_fence_enable_sw_signaling() (irqsafe fence->lock) */
 747         GEM_BUG_ON(!irqs_disabled());
 748         lockdep_assert_held(&request->lock);
 749
 750         seqno = i915_gem_request_global_seqno(request);
 751         if (!seqno)
 752                 return;
 753
 754         request->signaling.wait.tsk = b->signaler;
 755         request->signaling.wait.request = request;
 756         request->signaling.wait.seqno = seqno;
 757         i915_gem_request_get(request);
 758
 759         spin_lock(&b->rb_lock);
 760
 761         /* First add ourselves into the list of waiters, but register our
 762          * bottom-half as the signaller thread. As per usual, only the oldest
 763          * waiter (not just signaller) is tasked as the bottom-half waking
 764          * up all completed waiters after the user interrupt.
 765          *
 766          * If we are the oldest waiter, enable the irq (after which we
 767          * must double check that the seqno did not complete).
 768          */
 769         wakeup &= __intel_engine_add_wait(engine, &request->signaling.wait);
 770
 771         if (!__i915_gem_request_completed(request, seqno)) {
 772                 struct rb_node *parent, **p;
 773                 bool first;
 774
 775                 /* Now insert ourselves into the retirement ordered list of
 776                  * signals on this engine. We track the oldest seqno as that
 777                  * will be the first signal to complete.
 778                  */
 779                 parent = NULL;
 780                 first = true;
 781                 p = &b->signals.rb_node;
 782                 while (*p) {
 783                         parent = *p;
 784                         if (i915_seqno_passed(seqno,
 785                                               to_signaler(parent)->signaling.wait.seqno)) {
 786                                 p = &parent->rb_right;
 787                                 first = false;
 788                         } else {
 789                                 p = &parent->rb_left;
 790                         }
 791                 }
 792                 rb_link_node(&request->signaling.node, parent, p);
 793                 rb_insert_color(&request->signaling.node, &b->signals);
 794                 if (first)
 795                         rcu_assign_pointer(b->first_signal, request);
 796         } else {
 797                 __intel_engine_remove_wait(engine, &request->signaling.wait);
 798                 i915_gem_request_put(request);
 799                 wakeup = false;
 800         }
 801
 802         spin_unlock(&b->rb_lock);
 803
 804         if (wakeup)
 805                 wake_up_process(b->signaler);
 806 }
 807
 808 void intel_engine_cancel_signaling(struct drm_i915_gem_request *request)
 809 {
 810         struct intel_engine_cs *engine = request->engine;
 811         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 812
 813         GEM_BUG_ON(!irqs_disabled());
 814         lockdep_assert_held(&request->lock);
 815         GEM_BUG_ON(!request->signaling.wait.seqno);
 816
 817         spin_lock(&b->rb_lock);
 818
 819         if (!RB_EMPTY_NODE(&request->signaling.node)) {
 820                 if (request == rcu_access_pointer(b->first_signal)) {
 821                         struct rb_node *rb =
 822                                 rb_next(&request->signaling.node);
 823                         rcu_assign_pointer(b->first_signal,
 824                                            rb ? to_signaler(rb) : NULL);
 825                 }
 826                 rb_erase(&request->signaling.node, &b->signals);
 827                 RB_CLEAR_NODE(&request->signaling.node);
 828                 i915_gem_request_put(request);
 829         }
 830
 831         __intel_engine_remove_wait(engine, &request->signaling.wait);
 832
 833         spin_unlock(&b->rb_lock);
 834
 835         request->signaling.wait.seqno = 0;
 836 }
 837
 838 int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
 839 {
 840         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 841         struct task_struct *tsk;
 842
 843         spin_lock_init(&b->rb_lock);
 844         spin_lock_init(&b->irq_lock);
 845
 846         timer_setup(&b->fake_irq, intel_breadcrumbs_fake_irq, 0);
 847         timer_setup(&b->hangcheck, intel_breadcrumbs_hangcheck, 0);
 848
 849         /* Spawn a thread to provide a common bottom-half for all signals.
 850          * As this is an asynchronous interface we cannot steal the current
 851          * task for handling the bottom-half to the user interrupt, therefore
 852          * we create a thread to do the coherent seqno dance after the
 853          * interrupt and then signal the waitqueue (via the dma-buf/fence).
 854          */
 855         tsk = kthread_run(intel_breadcrumbs_signaler, engine,
 856                           "i915/signal:%d", engine->id);
 857         if (IS_ERR(tsk))
 858                 return PTR_ERR(tsk);
 859
 860         b->signaler = tsk;
 861
 862         return 0;
 863 }
 864
 865 static void cancel_fake_irq(struct intel_engine_cs *engine)
 866 {
 867         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 868
 869         del_timer_sync(&b->hangcheck);
 870         del_timer_sync(&b->fake_irq);
 871         clear_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
 872 }
 873
 874 void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
 875 {
 876         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 877
 878         cancel_fake_irq(engine);
 879         spin_lock_irq(&b->irq_lock);
 880
 881         if (b->irq_enabled)
 882                 irq_enable(engine);
 883         else
 884                 irq_disable(engine);
 885
 886         /* We set the IRQ_BREADCRUMB bit when we enable the irq presuming the
 887          * GPU is active and may have already executed the MI_USER_INTERRUPT
 888          * before the CPU is ready to receive. However, the engine is currently
 889          * idle (we haven't started it yet), there is no possibility for a
 890          * missed interrupt as we enabled the irq and so we can clear the
 891          * immediate wakeup (until a real interrupt arrives for the waiter).
 892          */
 893         clear_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 894
 895         if (b->irq_armed)
 896                 enable_fake_irq(b);
 897
 898         spin_unlock_irq(&b->irq_lock);
 899 }
 900
 901 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 902 {
 903         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 904
 905         /* The engines should be idle and all requests accounted for! */
 906         WARN_ON(READ_ONCE(b->irq_wait));
 907         WARN_ON(!RB_EMPTY_ROOT(&b->waiters));
 908         WARN_ON(rcu_access_pointer(b->first_signal));
 909         WARN_ON(!RB_EMPTY_ROOT(&b->signals));
 910
 911         if (!IS_ERR_OR_NULL(b->signaler))
 912                 kthread_stop(b->signaler);
 913
 914         cancel_fake_irq(engine);
 915 }
 916
 917 bool intel_breadcrumbs_busy(struct intel_engine_cs *engine)
 918 {
 919         struct intel_breadcrumbs *b = &engine->breadcrumbs;
 920         bool busy = false;
 921
 922         spin_lock_irq(&b->rb_lock);
 923
 924         if (b->irq_wait) {
 925                 wake_up_process(b->irq_wait->tsk);
 926                 busy = true;
 927         }
 928
 929         if (rcu_access_pointer(b->first_signal)) {
 930                 wake_up_process(b->signaler);
 931                 busy = true;
 932         }
 933
 934         spin_unlock_irq(&b->rb_lock);
 935
 936         return busy;
 937 }
 938
 939 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 940 #include "selftests/intel_breadcrumbs.c"
 941 #endif