linux-kernel - [PATCH v2] Documentation/kbuild: Document the kconfig choice default value

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Date:   Mon, 19 Jul 2021 11:16:01 +0200
From:   Robert Richter <rrichter@....com>
To:     Masahiro Yamada <masahiroy@...nel.org>
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: [PATCH v2] Documentation/kbuild: Document the kconfig choice default
 value

On 18.07.21 18:36:31, Masahiro Yamada wrote:
> On Thu, Jul 15, 2021 at 6:26 PM Robert Richter <rrichter@....com> wrote:

> > --- a/Documentation/kbuild/kconfig-language.rst
> > +++ b/Documentation/kbuild/kconfig-language.rst
> > @@ -417,6 +417,9 @@ 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.
> 
> 
> The default value of a choice is set to the first visible choice element
> unless it is explicitly set by the 'default' property.
> 
> ... is more precise.

Ah, ok. It becomes clear now, but how a value is set then in case the
type is tristate?

> 
> 
> 
> 
> > +Choice elements do not support the default attribute like menu entries do.
> 
> I doubt this info is useful.
> Rather, is it even confusing?
> 
> 
> choices support 'default' but
> choice elements (i.e. choice values) do not.

I have added an example to the doc for clarification, v2 below.

Thanks,

-Robert


>From 46ebd10dc11388ddce40aea70890000697a27165 Mon Sep 17 00:00:00 2001
From: Robert Richter <rrichter@....com>
Date: Wed, 14 Jul 2021 12:24:16 +0200
Subject: [PATCH v2] Documentation/kbuild: Document the kconfig choice default
 value

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>
---
v2: clarification on 'default' attribute of a choice
    added example
---
 Documentation/kbuild/kconfig-language.rst | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index e4d3463594e1..d919dde0bcbf 100644
--- a/Documentation/kbuild/kconfig-language.rst
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -417,8 +417,20 @@ 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.
-Choice elements do not support the default attribute like menu entries do.
+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::
 
-- 
2.29.2