drm/i915: Flush waiters on seqno wraparound

Previously, we would spin waiting for all waiters to wake up and notice
their request had completed before we would reset the seqno upon
wraparound.  However, we can mark their waits as complete and wake them
up directly using the existing machinery for handling the flushing of
missed wakeups when idling.

Suggested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180306130143.13312-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_request.c

@@ -217,10 +217,8 @@ static int reset_all_global_seqno(struct drm_i915_private *i915, u32 seqno)
 		struct intel_timeline *tl = engine->timeline;
 
 		if (!i915_seqno_passed(seqno, tl->seqno)) {
-			/* spin until threads are complete */
-			while (intel_breadcrumbs_busy(engine))
-				cond_resched();
-
+			/* Flush any waiters before we reuse the seqno */
+			intel_engine_disarm_breadcrumbs(engine);
 			GEM_BUG_ON(!list_empty(&engine->breadcrumbs.signals));
 		}
 

drivers/gpu/drm/i915/intel_breadcrumbs.c

@@ -873,25 +873,6 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 	cancel_fake_irq(engine);
 }
 
-bool intel_breadcrumbs_busy(struct intel_engine_cs *engine)
-{
-	struct intel_breadcrumbs *b = &engine->breadcrumbs;
-	bool busy = false;
-
-	if (b->irq_wait) {
-		spin_lock_irq(&b->irq_lock);
-
-		if (b->irq_wait) {
-			wake_up_process(b->irq_wait->tsk);
-			busy = true;
-		}
-
-		spin_unlock_irq(&b->irq_lock);
-	}
-
-	return busy;
-}
-
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/intel_breadcrumbs.c"
 #endif

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -951,7 +951,6 @@ void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine);
 
 void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine);
 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
-bool intel_breadcrumbs_busy(struct intel_engine_cs *engine);
 
 static inline u32 *gen8_emit_pipe_control(u32 *batch, u32 flags, u32 offset)
 {