reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/commit/?id=108f3a1c25d4e9fa74d574cd49670ac5faffc8fa
        git remote add robh https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git
        git fetch --no-tags robh dt-convert
        git checkout 108f3a1c25d4e9fa74d574cd49670ac5faffc8fa
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs