diff options
Diffstat (limited to 'package/config/kconfig-language.txt')
| -rw-r--r-- | package/config/kconfig-language.txt | 102 |
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). + |