reproduce (this is a W=1 build):
        # https://github.com/morimoto/linux/commit/a38f29304a2545aeef3d38033e6a76fea04178d4
        git remote add morimoto https://github.com/morimoto/linux
        git fetch --no-tags morimoto renesas-lts/v6.18.0-2025-12-01-x5h-ironhide
        git checkout a38f29304a2545aeef3d38033e6a76fea04178d4

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/mailbox/