kconfig: Document the 'symbol' struct

Visibility and choices in particular might be a bit tricky to figure
out.

Also fix existing comment to point out that P_MENU is also used for
menus.

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

1 files changed, 44 insertions, 1 deletions

diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index ae7583c3a7b1..e7d7a5e3da68 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -74,17 +74,60 @@ enum {
         S_DEF_COUNT
 };
 
+/*
+ * Represents a configuration symbol.
+ *
+ * Choices are represented as a special kind of symbol and have the
+ * SYMBOL_CHOICE bit set in 'flags'.
+ */
 struct symbol {
+        /* The next symbol in the same bucket in the symbol hash table */
         struct symbol *next;
+
+        /* The name of the symbol, e.g. "FOO" for 'config FOO' */
         char *name;
+
+        /* S_BOOLEAN, S_TRISTATE, ... */
         enum symbol_type type;
+
+        /*
+         * The calculated value of the symbol. The SYMBOL_VALID bit is set in
+         * 'flags' when this is up to date. Note that this value might differ
+         * from the user value set in e.g. a .config file, due to visibility.
+         */
         struct symbol_value curr;
+
+        /*
+         * Values for the symbol provided from outside. def[S_DEF_USER] holds
+         * the .config value.
+         */
         struct symbol_value def[S_DEF_COUNT];
+
+        /*
+         * An upper bound on the tristate value the user can set for the symbol
+         * if it is a boolean or tristate. Calculated from prompt dependencies,
+         * which also inherit dependencies from enclosing menus, choices, and
+         * ifs. If 'n', the user value will be ignored.
+         *
+         * Symbols lacking prompts always have visibility 'n'.
+         */
         tristate visible;
+
+        /* SYMBOL_* flags */
         int flags;
+
+        /* List of properties. See prop_type. */
         struct property *prop;
+
+        /* Dependencies from enclosing menus, choices, and ifs */
         struct expr_value dir_dep;
+
+        /* Reverse dependencies through being selected by other symbols */
         struct expr_value rev_dep;
+
+        /*
+         * "Weak" reverse dependencies through being implied by other symbols
+         */
         struct expr_value implied;
 };
 
@@ -133,7 +176,7 @@ enum prop_type {
         P_UNKNOWN,
         P_PROMPT,   /* prompt "foo prompt" or "BAZ Value" */
         P_COMMENT,  /* text associated with a comment */
-        P_MENU,     /* prompt associated with a menuconfig option */
+        P_MENU,     /* prompt associated with a menu or menuconfig symbol */
         P_DEFAULT,  /* default y */
         P_CHOICE,   /* choice value */
         P_SELECT,   /* select BAR */