drm/i915: Only trigger missed-seqno checking next to boundary

If we have more interrupts pending (because we know there are more
breadcrumb signals before the completion), then we do not need to
trigger an irq_seqno_barrier or even wakeup the task on this interrupt
as there will be another. To allow some margin of error (we are trying
to work around incoherent seqno after all), we wakeup the breadcrumb
before the target as well as on the target.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180627201304.15817-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_irq.c

@@ -1191,7 +1191,8 @@ static void notify_ring(struct intel_engine_cs *engine)
 
 			tsk = wait->tsk;
 		} else {
-			if (engine->irq_seqno_barrier) {
+			if (engine->irq_seqno_barrier &&
+			    i915_seqno_passed(seqno, wait->seqno - 1)) {
 				set_bit(ENGINE_IRQ_BREADCRUMB,
 					&engine->irq_posted);
 				tsk = wait->tsk;