- pull kconfig from 2.6.25.4

  It has nicer "-*-" etc hints

1 files changed, 126 insertions, 6 deletions

diff --git a/extra/config/kconfig-language.txt b/extra/config/kconfig-language.txt
index 536d5bfbd..649cb8799 100644
--- a/extra/config/kconfig-language.txt
+++ b/extra/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:
 
@@ -77,7 +77,12 @@ applicable everywhere (see syntax).
   Optionally, dependencies only for this default value can be added with
   "if".
 
-- dependencies: "depends on"/"requires" <expr>
+- 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
@@ -98,6 +103,15 @@ applicable everywhere (see syntax).
   times, the limit is set to the largest selection.
   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 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
@@ -113,6 +127,27 @@ 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
 -----------------
@@ -148,9 +183,9 @@ 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
@@ -280,3 +315,88 @@ 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.
+
+
+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-$(CONFIG_GENERIC_IOMAP) += iomap.o
+
+For each architecture using the generic IOMAP functionality we would see:
+
+config X86
+	select ...
+	select HAVE_GENERIC_IOMAP
+	select ...
+
+Note: we use the existing config option and avoid creating a new
+config variable to select HAVE_GENERIC_IOMAP.
+
+Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
+introduced to overcome the limitation of select which will force a
+config option to 'y' no matter the dependencies.
+The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
+situation where select forces a symbol equals to 'y'.
+
+Build as module only
+~~~~~~~~~~~~~~~~~~~~
+To restrict a component build to module-only, qualify its config symbol
+with "depends on m".  E.g.:
+
+config FOO
+	depends on BAR && m
+
+limits FOO to module (=m) or disabled (=n).
+
+
+Build limited by a third config symbol which may be =y or =m
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A common idiom that we see (and sometimes have problems with) is this:
+
+When option C in B (module or subsystem) uses interfaces from A (module
+or subsystem), and both A and B are tristate (could be =y or =m if they
+were independent of each other, but they aren't), then we need to limit
+C such that it cannot be built statically if A is built as a loadable
+module.  (C already depends on B, so there is no dependency issue to
+take care of here.)
+
+If A is linked statically into the kernel image, C can be built
+statically or as loadable module(s).  However, if A is built as loadable
+module(s), then C must be restricted to loadable module(s) also.  This
+can be expressed in kconfig language as:
+
+config C
+	depends on A = y || A = B
+
+or for real examples, use this command in a kernel tree:
+
+$ find . -name Kconfig\* | xargs grep -ns "depends on.*=.*||.*=" | grep -v orig
+