drm/i915/gt: Improve precision on defer_request assert

The kernel_context does not use initial-breadcrumbs, so when we ask if
its requests have started we do so by comparing against the completion
seqno of the previous request. This is very imprecise, not precise
enough for the defer_request assertion.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1847Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200508104220.9872-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1886,7 +1886,8 @@ static void defer_request(struct i915_request *rq, struct list_head * const pl)
 				continue;
 
 			/* No waiter should start before its signaler */
-			GEM_BUG_ON(i915_request_started(w) &&
+			GEM_BUG_ON(w->context->timeline->has_initial_breadcrumb &&
+				   i915_request_started(w) &&
 				   !i915_request_completed(rq));
 
 			GEM_BUG_ON(i915_request_is_active(w));