def build_fcos_dla_fpn_backbone_p6(cfg, input_shape):
    """
    Args:
        cfg: a detectron2 CfgNode

    Returns:
        backbone (Backbone): backbone module, must be a subclass of :class:`Backbone`.
    """
    bottom_up = build_dla_backbone(cfg, input_shape)
    in_features = cfg.FE.FPN.IN_FEATURES
    out_channels = cfg.FE.FPN.OUT_CHANNELS
    # in_channels_p6p7 = bottom_up.output_shape()["level5"].channels
    in_channels_p6 = out_channels
    backbone = FPN(
        bottom_up=bottom_up,
        in_features=in_features,
        out_channels=out_channels,
        norm=cfg.FE.FPN.NORM,
        top_block=LastLevelP6(in_channels_p6, out_channels, "p5"),
        fuse_type=cfg.FE.FPN.FUSE_TYPE,
    )

    backbone._size_divisibility *= 2

    return backbone

    Args:
        cfg: a detectron2 CfgNode

    Returns:
        backbone (Backbone): backbone module, must be a subclass of :class:`Backbone`.
    
tridet/modeling/feature_extractor/dla.py