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-rw-r--r--Documentation/kbuild/kconfig-language.txt22
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index 48a3981c717b..44e2649fbb29 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -389,3 +389,25 @@ config FOO
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.