reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-52-g1cf3d98c-dirty
        git remote add drm-misc git://anongit.freedesktop.org/drm/drm-misc
        git fetch --no-tags drm-misc drm-misc-next
        git checkout d3e040f450ec8e46ff42fa495a433b976ab47686
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=um olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=um SHELL=/bin/bash drivers/gpu/drm/rockchip/