drm/i915: Do not record a successful syncpoint for a dma-await

As we may unwind the requests, even though the request we are awaiting
has a global_seqno that seqno may be revoked during the await and so we
can not reliably use it as a barrier for all future awaits on the same
timeline.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170503093924.5320-6-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_request.c

@@ -708,33 +708,34 @@ i915_gem_request_await_request(struct drm_i915_gem_request *to,
 	}
 
 	seqno = i915_gem_request_global_seqno(from);
-	if (!seqno) {
-		ret = i915_sw_fence_await_dma_fence(&to->submit,
-						    &from->fence, 0,
-						    GFP_KERNEL);
-		return ret < 0 ? ret : 0;
-	}
+	if (!seqno)
+		goto await_dma_fence;
+
+	if (!i915.semaphores) {
+		if (!__i915_gem_request_started(from, seqno))
+			goto await_dma_fence;
 
+		if (!__i915_spin_request(from, seqno, TASK_INTERRUPTIBLE, 2))
+			goto await_dma_fence;
+	} else {
 		if (seqno <= to->timeline->global_sync[from->engine->id])
 			return 0;
 
 		trace_i915_gem_ring_sync_to(to, from);
-	if (!i915.semaphores) {
-		if (!i915_spin_request(from, TASK_INTERRUPTIBLE, 2)) {
-			ret = i915_sw_fence_await_dma_fence(&to->submit,
-							    &from->fence, 0,
-							    GFP_KERNEL);
-			if (ret < 0)
-				return ret;
-		}
-	} else {
 		ret = to->engine->semaphore.sync_to(to, from);
 		if (ret)
 			return ret;
-	}
 
 		to->timeline->global_sync[from->engine->id] = seqno;
+	}
+
 	return 0;
+
+await_dma_fence:
+	ret = i915_sw_fence_await_dma_fence(&to->submit,
+					    &from->fence, 0,
+					    GFP_KERNEL);
+	return ret < 0 ? ret : 0;
 }
 
 int