reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/srini/nvmem.git/commit/?id=117c3f3014a929464c01622cb95b566bd27244f8
        git remote add srini-nvmem https://git.kernel.org/pub/scm/linux/kernel/git/srini/nvmem.git
        git fetch --no-tags srini-nvmem for-next
        git checkout 117c3f3014a929464c01622cb95b566bd27244f8
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash drivers/nvmem/