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

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Message-Id: <20210719202844.18281-1-rrichter@amd.com>
Date:   Mon, 19 Jul 2021 22:28:44 +0200
From:   Robert Richter <rrichter@....com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>
Cc:     Robert Richter <rrichter@....com>, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] 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>
---
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