On Sat, Feb 15, 2025, at 14:17, Krzysztof Kozlowski wrote:
> Several drivers express optional Kconfig dependency with FOO || !FOO,
> but for many choices this is neither suitable (lack of stubs for !FOO
> like in HWMON) nor really needed and driver can be built in even if FOO
> is the module. This is achieved with IS_REACHABLE, so move earlier
> section from "imply" chapter to "Optional dependencies" and grow the
> description.
>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
I think this needs to be more strongly worded to heavy discourage
the use of IS_REACHABLE(). In most cases, anyone trying this has
just given up on writing correct dependencies and works around
it in a user-hostile way.
> +1. If pre-processor can discard entire optional code or module BAR does not
> + provide !BAR stubs then call can be guarded with IS_REACHABLE()::
> +
> + foo_init()
> + {
> + if (IS_REACHABLE(CONFIG_BAR))
> + bar_register(&foo);
> + ...
> + }
> +
> + Drawback: this might lead to run-time debugging, when looking why
> + bar_register() was not called.
