On Thu, Sep 12, 2019 at 11:29:00AM +0200, Arnd Bergmann wrote:

Generally speaking, the way that works best is

config SUBSYS_DRIVER_FOO
       tristate "SUBSYS support for FOO platform"
       depends on ARCH_FOO || COMPILE_TEST
       depends on SUBSYS
       default "m" if ARCH_FOO

This means it's enabled as a loadable module by default (use
default "y" instead where necessary) as long as the platform
is enabled, but an x86 allmodconfig build also includes it
because of COMPILE_TEST, while any configuration without
ARCH_FOO that is not compile-testing cannot enable it.

Indeed, though we shouldn't be adding any default m/y to things
that don't already default on.