dma_fence_unwrap_merge
f3 = dma_fence_unwrap_merge(f1, f2);
f2 = dma_fence_unwrap_merge(f1, f1);
f4 = dma_fence_unwrap_merge(f1, f2, f3);
a2 = dma_fence_unwrap_merge(a1, c2);
f3 = dma_fence_unwrap_merge(f1, f2);
f5 = dma_fence_unwrap_merge(f3, f4, dma_fence_get_stub());
f7 = dma_fence_unwrap_merge(f5, f6);
fence = dma_fence_unwrap_merge(a->fence, b->fence);
fence = dma_fence_unwrap_merge(vm->last_update,
fence = dma_fence_unwrap_merge(tmp);
vm->last_fence = dma_fence_unwrap_merge(submit->user_fence, last_fence);