linux-kernel - Re: [PATCH v3] Documentation/kbuild: Document the kconfig choice default value

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Date:   Thu, 5 Aug 2021 21:47:18 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Robert Richter <rrichter@....com>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] Documentation/kbuild: Document the kconfig choice
 default value

On Tue, Jul 20, 2021 at 5:29 AM Robert Richter <rrichter@....com> wrote:
>
> Document how choice defaults are determined:
>
> Default of a choice is its first visible choice element unless it is
> explicitly set by the 'default' property [1]. Choice elements do not
> support default attributes. [2]
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/kconfig/symbol.c?h=v5.14-rc1#n245
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/kconfig/menu.c?h=v5.14-rc1#n494
>
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
> v3: Fix base of v2 (rebased onto v5.14-rc2)
> v2: clarification on 'default' attribute of a choice
>     added example
> ---
>  Documentation/kbuild/kconfig-language.rst | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index 98c24183d8c3..d919dde0bcbf 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -417,6 +417,21 @@ definitions of that choice. If a [symbol] is associated to the choice,
>  then you may define the same choice (i.e. with the same entries) in another
>  place.
>
> +The default value of a choice is set to the first visible choice
> +element unless it is explicitly set by the 'default' property.
> +
> +Note:
> +       Choice options do not support the 'default' attribute.
> +
> +E.g.::
> +
> +  choice
> +       default C1
> +  config C0
> +  config C1
> +       # no default attribute here
> +  endchoice
> +
>  comment::
>
>         "comment" <prompt>
> --
> 2.29.2
>


I am not sure whether this note is needed or not,
anyway the code example is wrong.

Kconfig:3:warning: config symbol defined without type
Kconfig:4:warning: config symbol defined without type
Kconfig:3:warning: choice value must have a prompt
Kconfig:4:warning: choice value must have a prompt
Kconfig:1:warning: config symbol defined without type
Kconfig:1:warning: choice must have a prompt







-- 
Best Regards
Masahiro Yamada