[v2] Documentation/kbuild: Document the kconfig choice default value

Commit Message

Robert Richter July 19, 2021, 9:16 a.m. UTC

On 18.07.21 18:36:31, Masahiro Yamada wrote:
> On Thu, Jul 15, 2021 at 6:26 PM Robert Richter <[e-mail]> 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 <[e-mail]>
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 <[e-mail]>
---
v2: clarification on 'default' attribute of a choice
    added example
---
 Documentation/kbuild/kconfig-language.rst | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

Comments

Robert Richter July 19, 2021, 8:20 p.m. UTC | #1

On 19.07.21 11:16:09, Robert Richter wrote:
> @@ -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.

This patch was not properly rebased and does not apply. Will resend a v3.

Sorry for that.

-Robert

> +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
>

Patch

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::