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diff --git a/scripts/kconfig/lkc_spec b/scripts/kconfig/lkc_spec new file mode 100644 index 0000000..45c36eb --- a/dev/null +++ b/scripts/kconfig/lkc_spec @@ -0,0 +1,250 @@ +1. General Structure + +The configuration file describes a series of menu entries. These menu +entries are organized in a tree structure. The following statements +start a new menu entry definition (and end a previous menu entry): +- config +- choice +- comment +- menu +The following statements are control entries and also end the definition +of a previous menu entry: +- source +- if + +2. Dependencies + +Every menu entry has dependencies, which define it's visibility in the +menu structure. What makes these dependencies more difficult is that +they use three states instead of two, that most programmers are familiar +with. The additional 'mod' state is needed to describe drivers which +are not compiled into the kernel, but are compiled as modules, which +can be loaded at runtime. Nevertheless they should be straigthforward +to use. +Dependencies describe in first place the relation between configuration +symbols and consequently between different parts of the kernel. To +simplify the verification of the rule base, dependencies must be +hierarchical, that means no recursive dependencies are allowed. The only +possible non-hierarchical dependency are exclusions (aka choices), to +cover typical uses during kernel configuration the semantic of choice +statements has been extended (see the choice statement below). + +This allows to describe the following basic relationships: +- initialization order of kernel subsystems. That means which other + subsystems are required (initialized and working), before a specific + subsystem can be initialized itself. This allows above requirement of + hierarchical dependencies. +- mutual exclusions of kernel subsystems. This allows that only a single + of multiple possible subsystems is configured into the kernel. +These are the same relationships, which are reasonably representable +with cml1, but with this new config syntax it should be possible to +easily add further relationships and other properties. + +The important usage of the dependency information is for generation of +the menu structure. First it defines whether a symbol or statement is +visible at all. If the dependency expression evaluates to 'n', the symbol +is not visible (and is currently also not saved, this BTW corresponds to +the behavior of xconfig, which is noted as a bug in Documentation/ +kbuild/config-language.txt, that didn't seem to be a problem so far, but +that has to be considered). +If a symbol is visible, it defines the possible input range for tristate +symbols, if the dependency expression evaluates to 'm', a tristate symbol +can only be set to 'n' or 'm', otherwise also 'y' is possible. +Finally dependency information is also used to group symbols together. +If a symbol entry is followed by other symbol entries which depends on +the first one, the latter entries are associated with the first entry. +The text config front end uses this information to automatically indent +the entries, the qt interface creates further submenus. This can reduce +the amount of explicit menu information required. + +syntax: + +This is the syntax of dependency expressions: + +<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. An +expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 respectively +for calculations below). +There are two type 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 +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 '\'. +Nonconstant symbols which are nowhere defined with 'config' are a +special case, they behave like constant symbols, so that one can do +"FOO=123", it usage should restricted to number values (this might +be enforced later). + +expression syntax: + +(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/). + +3. "config" + +syntax: + + "config" <symbol> + <config options> + +Defines a new config symbol. A symbol can be defined multiple times as +long as the symbol type is always the same. + +config options: + + "depends" <expr> + +defines the visibility and the input range of the config symbol. + + "tristate" <prompt> "if" <expr> + "bool" <prompt> "if" <expr> + "int" <prompt> "if" <expr> + "hex" <prompt> "if" <expr> + "string" <prompt> "if" <expr> + +defines the type of the symbol and the prompt which is used to request a +value from the user. Additional constraints for the visibility and the +input range of the prompt can be defined after an "if" statement. The +prompt and the "if" statement are optional, but an "if" statement +without a prompt is not possible. + + "prompt" <prompt> "if" <expr> + +same as above, but without defining the type of the symbol. This was +generated by earlier versions of the converter and will likely +disappear unless needed otherwise. + + "default" <symbol> "if" <expr> + +defines a default value for the config symbol. Unless the config symbol +was previously set by the user, it will set to this value. This means +it will be used as default value for above input prompts or if no user +prompt is visible the config symbol will be saved with this value. If +multiple default statements are visible only the first is used. + + "help" + +defines a help text for this statement. The end of the help text +is determined by the level indentation, this means it ends at the first +line which has a smaller indentation than the first line of the help text. + +4. "choice" + +syntax: + + "choice" + <choice options> + <choice block> + "endchoice" + +defines a group of related config statements. There are two types of +choice statements - bool and tristate. + +bool choice: allows only single config statement to be selected and +set to "y". +tristate choice: extends the bool choice by also allowing multiple +config statement to be selected, but in this mode these will only be set +"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. + +choice options: + + "depends" <expr> + +defines the visibility and the input range of the choice. + + "prompt" <prompt> + +defines the prompt which is presented to the user. + + <optional> + +by default exactly one of the config statements of a bool choice has +to be selected, this option allows that also no config statement has to +be selected. + + "default" <symbol> + +defines the default choice presented to the user. The prompt must be a +one of symbols defined within this choice. + + "help" + +defines a help text for this choice statement. The end of the help text +is determined by the level indentation, this means it ends at the first +line which has a smaller indentation than the first line of the help text. + +choice block: + +right now only config statements allowed. (It's possible to also allow +other statements later.) + +5. "comment" + +syntax: + + "comment" <prompt> + <comment options> + +defines the prompt which is displayed to the user during the +configuration process and is also echoes it to the output files during +output. + +comment options: + + "depends" <expr> + +defines the visibility of the comment. + +6. "menu" + +syntax: + + "menu" <prompt> + <menu options> + <menu block> + "endmenu" + +menu options: + + "depends" <expr> + +defines the visibility of the menu. + +menu block: + +Any of the basic statements is allowed within a menu block. + +7. "if" + +syntax: + + "if" <expr> + <if block> + "endif" + +8. "source" + +syntax: + + "source" <prompt> + +reads the specified configuration file. this is done unconditionally, + |