On Wed, Sep 13, 2023 at 01:37:52PM +0200 Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> This problem frequently comes up in randconfig testing, with
> drivers failing to link because of a dependency on an optional
> feature.
>
> The Kconfig language for this is very confusing, so try to
> document it in "Kconfig hints" section.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
Hi Arnd,
thanks for documenting this! Three questions below:
> Documentation/kbuild/kconfig-language.rst | 26 +++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index 858ed5d80defe..89dea587a469a 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -573,6 +573,32 @@ above, leading to:
> bool "Support for foo hardware"
> depends on ARCH_FOO_VENDOR || COMPILE_TEST
>
> +Optional dependencies
> +~~~~~~~~~~~~~~~~~~~~~
> +
> +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 slighly counterintuitive
slighly -> slightly
For better RST compliance: could you explicitly start the code block e.g. by
appending '::' as in "... counterintuitive::"?
> +
> + config FOO
> + bool "Support for foo hardware"
> + depends on BAR || !BAR
are you sure that this is enough? While testing, I needed to explicitly use
=y|=n:
depends on BAR=y || BAR=n
to prevent FOO to be selectable iff BAR=m.
> +
> +This means that there is either a dependency on BAR that disallows
> +the combination of FOO=y with BAR=m, or BAR is completely disabled.
For me, this sentence is hard to parse (but I am not a native speaker); what
about something like this:
This means that FOO can only be enabled, iff BAR is either built-in or
completely disabled. If BAR is built as a module, FOO cannot be enabled.
Kind regards,
Nicolas
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