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authorAlper Yildirim <ayildirim@aselsan.com>2009-07-20 18:50:58 +0200
committerThomas Petazzoni <thomas.petazzoni@free-electrons.com>2009-07-27 16:06:50 +0200
commit4b3e11b3e7d00881878f45cddbfe8f4bf07d1ebe (patch)
tree3740632b5196497242055f7ecdfe4be3c6210409 /package/config/kconfig-language.txt
parentea536503331aea875e84ae598b4610fbd059f167 (diff)
downloadbuildroot-novena-4b3e11b3e7d00881878f45cddbfe8f4bf07d1ebe.tar.gz
buildroot-novena-4b3e11b3e7d00881878f45cddbfe8f4bf07d1ebe.zip
config: Update package/config to Kconfig 2.6.30
Update the package/config stuff with the code available in the Linux kernel 2.6.30. Signed-off-by: Alper Yildirim <ayildirim@aselsan.com>
Diffstat (limited to 'package/config/kconfig-language.txt')
-rw-r--r--package/config/kconfig-language.txt102
1 files changed, 89 insertions, 13 deletions
diff --git a/package/config/kconfig-language.txt b/package/config/kconfig-language.txt
index 616043a6d..c412c2458 100644
--- a/package/config/kconfig-language.txt
+++ b/package/config/kconfig-language.txt
@@ -24,7 +24,7 @@ visible if its parent entry is also visible.
Menu entries
------------
-Most entries define a config option, all other entries help to organize
+Most entries define a config option; all other entries help to organize
them. A single configuration option is defined like this:
config MODVERSIONS
@@ -50,7 +50,7 @@ applicable everywhere (see syntax).
- type definition: "bool"/"tristate"/"string"/"hex"/"int"
Every config option must have a type. There are only two basic types:
- tristate and string, the other types are based on these two. The type
+ tristate and string; the other types are based on these two. The type
definition optionally accepts an input prompt, so these two examples
are equivalent:
@@ -104,14 +104,15 @@ applicable everywhere (see syntax).
Reverse dependencies can only be used with boolean or tristate
symbols.
Note:
- select is evil.... select will by brute force set a symbol
- equal to 'y' without visiting the dependencies. So abusing
- select you are able to select a symbol FOO even if FOO depends
- on BAR that is not set. In general use select only for
- non-visible symbols (no promts anywhere) and for symbols with
- no dependencies. That will limit the usefulness but on the
- other hand avoid the illegal configurations all over. kconfig
- should one day warn about such things.
+ select should be used with care. select will force
+ a symbol to a value without visiting the dependencies.
+ By abusing select you are able to select a symbol FOO even
+ if FOO depends on BAR that is not set.
+ In general use select only for non-visible symbols
+ (no prompts anywhere) and for symbols with no dependencies.
+ That will limit the usefulness but on the other hand avoid
+ the illegal configurations all over.
+ kconfig should one day warn about such things.
- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
This allows to limit the range of possible input values for int
@@ -127,6 +128,27 @@ applicable everywhere (see syntax).
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
-----------------
@@ -162,9 +184,9 @@ An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
respectively for calculations). A menu entry becomes visible when it's
expression evaluates to 'm' or 'y'.
-There are two types of symbols: constant and nonconstant symbols.
-Nonconstant symbols are the most common ones and are defined with the
-'config' statement. Nonconstant symbols consist entirely of alphanumeric
+There are two types of symbols: constant and non-constant symbols.
+Non-constant symbols are the most common ones and are defined with the
+'config' statement. Non-constant symbols consist entirely of alphanumeric
characters or underscores.
Constant symbols are only part of expressions. Constant symbols are
always surrounded by single or double quotes. Within the quote, any
@@ -301,3 +323,57 @@ mainmenu:
This sets the config program's title bar if the config program chooses
to use it.
+
+
+Kconfig hints
+-------------
+This is a collection of Kconfig tips, most of which aren't obvious at
+first glance and most of which have become idioms in several Kconfig
+files.
+
+Adding common features and make the usage configurable
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is a common idiom to implement a feature/functionality that are
+relevant for some architectures but not all.
+The recommended way to do so is to use a config variable named HAVE_*
+that is defined in a common Kconfig file and selected by the relevant
+architectures.
+An example is the generic IOMAP functionality.
+
+We would in lib/Kconfig see:
+
+# Generic IOMAP is used to ...
+config HAVE_GENERIC_IOMAP
+
+config GENERIC_IOMAP
+ depends on HAVE_GENERIC_IOMAP && FOO
+
+And in lib/Makefile we would see:
+obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
+
+For each architecture using the generic IOMAP functionality we would see:
+
+config X86
+ select ...
+ select HAVE_GENERIC_IOMAP
+ select ...
+
+Note: we use the existing config option and avoid creating a new
+config variable to select HAVE_GENERIC_IOMAP.
+
+Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
+introduced to overcome the limitation of select which will force a
+config option to 'y' no matter the dependencies.
+The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
+situation where select forces a symbol equals to 'y'.
+
+Build as module only
+~~~~~~~~~~~~~~~~~~~~
+To restrict a component build to module-only, qualify its config symbol
+with "depends on m". E.g.:
+
+config FOO
+ depends on BAR && m
+
+limits FOO to module (=m) or disabled (=n).
+