reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=ef37a1e2485724f5287db1584d8aba48e8ba3f41
        git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
        git fetch --no-tags linux-next master
        git checkout ef37a1e2485724f5287db1584d8aba48e8ba3f41
        # choose either of the following two methods to reproduce the issue
        # 1. reproduce by kismet
           # install kmax per https://github.com/paulgazz/kmax/blob/master/README.md
           kismet --linux-ksrc=linux --selectees CONFIG_MFD_AT91_USART --selectors CONFIG_SERIAL_ATMEL -a=arm
        # 2. reproduce by make
           cd linux
           # download the config file from the "config:" link in the report, and save it as .config
           make ARCH=arm olddefconfig