drm/i915: Assert that we always complete a submission to guc/execlists

The continual resubmission model for execlists (and emulated over guc)
requires that we keep feeding requests into the HW in order to generate
more CS interrupts to drain the rest of the queue. Add a couple of
asserts to ensure that we don't skip a cycle and come to a grinding
halt.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180215162553.23348-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_guc_submission.c

@@ -747,6 +747,12 @@ done:
 		execlists_set_active(execlists, EXECLISTS_ACTIVE_USER);
 		guc_submit(engine);
 	}
+
+	/* We must always keep the beast fed if we have work piled up */
+	GEM_BUG_ON(port_isset(execlists->port) &&
+		   !execlists_is_active(execlists, EXECLISTS_ACTIVE_USER));
+	GEM_BUG_ON(execlists->first && !port_isset(execlists->port));
+
 unlock:
 	spin_unlock_irq(&engine->timeline->lock);
 }

drivers/gpu/drm/i915/intel_lrc.c

@@ -642,6 +642,12 @@ done:
 	execlists->first = rb;
 	if (submit)
 		port_assign(port, last);
+
+	/* We must always keep the beast fed if we have work piled up */
+	GEM_BUG_ON(port_isset(execlists->port) &&
+		   !execlists_is_active(execlists, EXECLISTS_ACTIVE_USER));
+	GEM_BUG_ON(execlists->first && !port_isset(execlists->port));
+
 unlock:
 	spin_unlock_irq(&engine->timeline->lock);