linux-kernel - Re: [PATCH] docs: kconfig: Mention IS_REACHABLE as way for optional dependency

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Message-ID: <c95582e4-9ac3-4636-8a4b-3d27ebcb28ee@linaro.org>
Date: Sat, 15 Feb 2025 13:44:09 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Masahiro Yamada <masahiroy@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>,
 Jonathan Corbet <corbet@....net>, linux-kbuild@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] docs: kconfig: Mention IS_REACHABLE as way for optional
 dependency

On 15/02/2025 12:42, Krzysztof Kozlowski wrote:
> @@ -580,10 +582,15 @@ Some drivers are able to optionally use a feature from another module
>  or build cleanly with that module disabled, but cause a link failure
>  when trying to use that loadable module from a built-in driver.
>  
> -The most common way to express this optional dependency in Kconfig logic
> -uses the slightly counterintuitive::
> +There are two ways to express this optional dependency:
>  
> -  config FOO
> +1. If pre-processor can discard entire optional code or module FOO does not
> +   provide !FOO stubs then in the C code :ref:`IS_REACHABLE<is_reachable>`
> +
> +2. Otherwise (and module FOO must provide all !FOO stubs) use the slightly

Obviously this should be "module BAR", similarly above.

I will send a v2.

> +   counterintuitive Kconfig syntax::
> +
> +     config FOO
>  	tristate "Support for foo hardware"
>  	depends on BAR || !BAR
>  


Best regards,
Krzysztof