kconfig: environment symbol support
Add the possibility to import a value from the environment into kconfig
via the option syntax. Beside flexibility this has the advantage
providing proper dependencies.
Documented the options syntax.
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index 53ca12f..a43fcc6 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -127,6 +127,27 @@
used to help visually separate configuration logic from help within
the file as an aid to developers.
+- misc options: "option" <symbol>[=<value>]
+ Various less common options can be defined via this option syntax,
+ which can modify the behaviour of the menu entry and its config
+ symbol. These options are currently possible:
+
+ - "defconfig_list"
+ This declares a list of default entries which can be used when
+ looking for the default configuration (which is used when the main
+ .config doesn't exists yet.)
+
+ - "modules"
+ This declares the symbol to be used as the MODULES symbol, which
+ enables the third modular state for all config symbols.
+
+ - "env"=<value>
+ This imports the environment variable into Kconfig. It behaves like
+ a default, except that the value comes from the environment, this
+ also means that the behaviour when mixing it with normal defaults is
+ undefined at this point. The symbol is currently not exported back
+ to the build environment (if this is desired, it can be done via
+ another symbol).
Menu dependencies
-----------------
