reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/commit/?id=7199a0f557cb1538991c03eb3b183dc4b002d0aa
        git remote add pdx86-platform-drivers-x86 https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git
        git fetch --no-tags pdx86-platform-drivers-x86 review-ilpo-next
        git checkout 7199a0f557cb1538991c03eb3b183dc4b002d0aa
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs