drm/amdgpu: fix lost sync_to if scheduler is enabled.

BugLink: http://bugs.launchpad.net/bugs/1553179

commit 888c9e33 upstream.

when scheduler is enabled, the semaphore isn't used at all.
Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c

@@ -293,7 +293,8 @@ int amdgpu_sync_rings(struct amdgpu_sync *sync,
 		fence = to_amdgpu_fence(sync->sync_to[i]);
 
 		/* check if we really need to sync */
-		if (!amdgpu_fence_need_sync(fence, ring))
+		if (!amdgpu_enable_scheduler &&
+		    !amdgpu_fence_need_sync(fence, ring))
 			continue;
 
 		/* prevent GPU deadlocks */
@@ -303,7 +304,7 @@ int amdgpu_sync_rings(struct amdgpu_sync *sync,
 		}
 
 		if (amdgpu_enable_scheduler || !amdgpu_enable_semaphores) {
-			r = fence_wait(&fence->base, true);
+			r = fence_wait(sync->sync_to[i], true);
 			if (r)
 				return r;
 			continue;