Add kconfig documentation

git-svn-id: https://nuttx.svn.sourceforge.net/svnroot/nuttx/trunk@4567 7fd9a85b-ad96-42d3-883c-3090e2eb8679

apps/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/adc/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/buttons/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/can/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/cdcacm/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/dhcpd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/ftpc/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/ftpd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/hello/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/helloxx/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/hidkbd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/igmp/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/lcdrw/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/mm/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/mount/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nettest/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nsh/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/null/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nx/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nxconsole/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nxffs/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nxflat/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nxhello/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nximage/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nxlines/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/nxtext/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/ostest/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/pashello/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/pipe/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/poll/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/pwm/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/qencoder/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/rgmp/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/romfs/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/sendmail/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/serloop/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/telnetd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/thttpd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/tiff/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/touchscreen/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/udp/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/uip/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/usbserial/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/usbstorage/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/usbterm/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/wget/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/examples/wlan/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/graphics/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/interpreters/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/interpreters/ficl/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/namedapp/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/dhcpc/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/dhcpd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/ftpc/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/ftpd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/resolv/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/smtp/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/thttpd/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/uiplib/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/webclient/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/netutils/webserver/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/nshlib/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/system/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/system/free/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/system/i2c/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/system/install/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/system/readline/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/vsn/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/vsn/poweroff/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/vsn/ramtron/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/vsn/sdcard/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

apps/vsn/sysinfo/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

misc/tools/kconfig-language.txt

@@ -0,0 +1,413 @@
+Introduction
+------------
+
+The configuration database is a collection of configuration options
+organized in a tree structure:
+
+	+- Code maturity level options
+	|  +- Prompt for development and/or incomplete code/drivers
+	+- General setup
+	|  +- Networking support
+	|  +- System V IPC
+	|  +- BSD Process Accounting
+	|  +- Sysctl support
+	+- Loadable module support
+	|  +- Enable loadable module support
+	|     +- Set version information on all module symbols
+	|     +- Kernel module loader
+	+- ...
+
+Every entry has its own dependencies. These dependencies are used
+to determine the visibility of an entry. Any child entry is only
+visible if its parent entry is also visible.
+
+Menu entries
+------------
+
+Most entries define a config option; all other entries help to organize
+them. A single configuration option is defined like this:
+
+config MODVERSIONS
+	bool "Set version information on all module symbols"
+	depends on MODULES
+	help
+	  Usually, modules have to be recompiled whenever you switch to a new
+	  kernel.  ...
+
+Every line starts with a key word and can be followed by multiple
+arguments.  "config" starts a new config entry. The following lines
+define attributes for this config option. Attributes can be the type of
+the config option, input prompt, dependencies, help text and default
+values. A config option can be defined multiple times with the same
+name, but every definition can have only a single input prompt and the
+type must not conflict.
+
+Menu attributes
+---------------
+
+A menu entry can have a number of attributes. Not all of them are
+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
+  definition optionally accepts an input prompt, so these two examples
+  are equivalent:
+
+	bool "Networking support"
+  and
+	bool
+	prompt "Networking support"
+
+- input prompt: "prompt" <prompt> ["if" <expr>]
+  Every menu entry can have at most one prompt, which is used to display
+  to the user. Optionally dependencies only for this prompt can be added
+  with "if".
+
+- default value: "default" <expr> ["if" <expr>]
+  A config option can have any number of default values. If multiple
+  default values are visible, only the first defined one is active.
+  Default values are not limited to the menu entry where they are
+  defined. This means the default can be defined somewhere else or be
+  overridden by an earlier definition.
+  The default value is only assigned to the config symbol if no other
+  value was set by the user (via the input prompt above). If an input
+  prompt is visible the default value is presented to the user and can
+  be overridden by him.
+  Optionally, dependencies only for this default value can be added with
+  "if".
+
+- type definition + default value:
+	"def_bool"/"def_tristate" <expr> ["if" <expr>]
+  This is a shorthand notation for a type definition plus a value.
+  Optionally dependencies for this default value can be added with "if".
+
+- dependencies: "depends on" <expr>
+  This defines a dependency for this menu entry. If multiple
+  dependencies are defined, they are connected with '&&'. Dependencies
+  are applied to all other options within this menu entry (which also
+  accept an "if" expression), so these two examples are equivalent:
+
+	bool "foo" if BAR
+	default y if BAR
+  and
+	depends on BAR
+	bool "foo"
+	default y
+
+- reverse dependencies: "select" <symbol> ["if" <expr>]
+  While normal dependencies reduce the upper limit of a symbol (see
+  below), reverse dependencies can be used to force a lower limit of
+  another symbol. The value of the current menu symbol is used as the
+  minimal value <symbol> can be set to. If <symbol> is selected multiple
+  times, the limit is set to the largest selection.
+  Reverse dependencies can only be used with boolean or tristate
+  symbols.
+  Note:
+	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.
+
+- limiting menu display: "visible if" <expr>
+  This attribute is only applicable to menu blocks, if the condition is
+  false, the menu block is not displayed to the user (the symbols
+  contained there can still be selected by other symbols, though). It is
+  similar to a conditional "prompt" attribude for individual menu
+  entries. Default value of "visible" is true.
+
+- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
+  This allows to limit the range of possible input values for int
+  and hex symbols. The user can only input a value which is larger than
+  or equal to the first symbol and smaller than or equal to the second
+  symbol.
+
+- help text: "help" or "---help---"
+  This defines a help text. The end of the help text is determined by
+  the indentation level, this means it ends at the first line which has
+  a smaller indentation than the first line of the help text.
+  "---help---" and "help" do not differ in behaviour, "---help---" is
+  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
+-----------------
+
+Dependencies define the visibility of a menu entry and can also reduce
+the input range of tristate symbols. The tristate logic used in the
+expressions uses one more state than normal boolean logic to express the
+module state. Dependency expressions have the following syntax:
+
+<expr> ::= <symbol>                             (1)
+           <symbol> '=' <symbol>                (2)
+           <symbol> '!=' <symbol>               (3)
+           '(' <expr> ')'                       (4)
+           '!' <expr>                           (5)
+           <expr> '&&' <expr>                   (6)
+           <expr> '||' <expr>                   (7)
+
+Expressions are listed in decreasing order of precedence. 
+
+(1) Convert the symbol into an expression. Boolean and tristate symbols
+    are simply converted into the respective expression values. All
+    other symbol types result in 'n'.
+(2) If the values of both symbols are equal, it returns 'y',
+    otherwise 'n'.
+(3) If the values of both symbols are equal, it returns 'n',
+    otherwise 'y'.
+(4) Returns the value of the expression. Used to override precedence.
+(5) Returns the result of (2-/expr/).
+(6) Returns the result of min(/expr/, /expr/).
+(7) Returns the result of max(/expr/, /expr/).
+
+An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
+respectively for calculations). A menu entry becomes visible when its
+expression evaluates to 'm' or 'y'.
+
+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
+other character is allowed and the quotes can be escaped using '\'.
+
+Menu structure
+--------------
+
+The position of a menu entry in the tree is determined in two ways. First
+it can be specified explicitly:
+
+menu "Network device support"
+	depends on NET
+
+config NETDEVICES
+	...
+
+endmenu
+
+All entries within the "menu" ... "endmenu" block become a submenu of
+"Network device support". All subentries inherit the dependencies from
+the menu entry, e.g. this means the dependency "NET" is added to the
+dependency list of the config option NETDEVICES.
+
+The other way to generate the menu structure is done by analyzing the
+dependencies. If a menu entry somehow depends on the previous entry, it
+can be made a submenu of it. First, the previous (parent) symbol must
+be part of the dependency list and then one of these two conditions
+must be true:
+- the child entry must become invisible, if the parent is set to 'n'
+- the child entry must only be visible, if the parent is visible
+
+config MODULES
+	bool "Enable loadable module support"
+
+config MODVERSIONS
+	bool "Set version information on all module symbols"
+	depends on MODULES
+
+comment "module support disabled"
+	depends on !MODULES
+
+MODVERSIONS directly depends on MODULES, this means it's only visible if
+MODULES is different from 'n'. The comment on the other hand is always
+visible when MODULES is visible (the (empty) dependency of MODULES is
+also part of the comment dependencies).
+
+
+Kconfig syntax
+--------------
+
+The configuration file describes a series of menu entries, where every
+line starts with a keyword (except help texts). The following keywords
+end a menu entry:
+- config
+- menuconfig
+- choice/endchoice
+- comment
+- menu/endmenu
+- if/endif
+- source
+The first five also start the definition of a menu entry.
+
+config:
+
+	"config" <symbol>
+	<config options>
+
+This defines a config symbol <symbol> and accepts any of above
+attributes as options.
+
+menuconfig:
+	"menuconfig" <symbol>
+	<config options>
+
+This is similar to the simple config entry above, but it also gives a
+hint to front ends, that all suboptions should be displayed as a
+separate list of options.
+
+choices:
+
+	"choice" [symbol]
+	<choice options>
+	<choice block>
+	"endchoice"
+
+This defines a choice group and accepts any of the above attributes as
+options. A choice can only be of type bool or tristate, while a boolean
+choice only allows a single config entry to be selected, a tristate
+choice also allows any number of config entries to be set to 'm'. This
+can be used if multiple drivers for a single hardware exists and only a
+single driver can be compiled/loaded into the kernel, but all drivers
+can be compiled as modules.
+A choice accepts another option "optional", which allows to set the
+choice to 'n' and no entry needs to be selected.
+If no [symbol] is associated with a choice, then you can not have multiple
+definitions of that choice. If a [symbol] is associated to the choice,
+then you may define the same choice (ie. with the same entries) in another
+place.
+
+comment:
+
+	"comment" <prompt>
+	<comment options>
+
+This defines a comment which is displayed to the user during the
+configuration process and is also echoed to the output files. The only
+possible options are dependencies.
+
+menu:
+
+	"menu" <prompt>
+	<menu options>
+	<menu block>
+	"endmenu"
+
+This defines a menu block, see "Menu structure" above for more
+information. The only possible options are dependencies and "visible"
+attributes.
+
+if:
+
+	"if" <expr>
+	<if block>
+	"endif"
+
+This defines an if block. The dependency expression <expr> is appended
+to all enclosed menu entries.
+
+source:
+
+	"source" <prompt>
+
+This reads the specified configuration file. This file is always parsed.
+
+mainmenu:
+
+	"mainmenu" <prompt>
+
+This sets the config program's title bar if the config program chooses
+to use it. It should be placed at the top of the configuration, before any
+other statement.
+
+
+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).
+
+Kconfig symbol existence
+~~~~~~~~~~~~~~~~~~~~~~~~
+The following two methods produce the same kconfig symbol dependencies
+but differ greatly in kconfig symbol existence (production) in the
+generated config file.
+
+case 1:
+
+config FOO
+	tristate "about foo"
+	depends on BAR
+
+vs. case 2:
+
+if BAR
+config FOO
+	tristate "about foo"
+endif
+
+In case 1, the symbol FOO will always exist in the config file (given
+no other dependencies).  In case 2, the symbol FOO will only exist in
+the config file if BAR is enabled.

nuttx/Kconfig

@@ -1,6 +1,6 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #
 mainmenu "Nuttx/$ARCH Configuration"
 

nuttx/arch/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/arm/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/avr/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/hc/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/mips/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/rgmp/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/sh/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/x86/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/z16/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/arch/z80/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/binfmt/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/binfmt/libnxflat/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/amber/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/avr32dev1/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/c5471evm/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/compal_e88/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/compal_e99/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/demo9s12ne64/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/ea3131/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/ea3152/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/eagle100/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/ez80f910200kitg/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #

nuttx/configs/ez80f910200zco/Kconfig

@@ -1,4 +1,4 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see misc/tools/kconfig-language.txt.
 #