[PATCH v3 2/3] kconfig: new macro IF_ENABLED()

[Heinrich Schuchardt]

We want to move from using #ifdef to using if in our code. A lot of our
code using #ifdef is structured like:

    #ifdef CONFIG_FOO
        fun(CONFIG_FOO_OPT);
    #endif

In Kconfig you will find

    config FOO
        bool "enable foo"

    config FOO_OPT
        string "value for foo"
        depends on FOO

We cannot use CONFIG_FOO_OPT in our code directly if CONFIG_FOO is not
defined.

     if (IS_ENABLED(CONFIG_FOO)
         fun(CONFIG_FOO_OPT);

This would result in an error due to the undefined symbol CONFIG_FOO_OPT.

The new macro IF_ENABLED(CONFIG_FOO, opt_cfg, def_val) which evaluates
to opt_cfg if CONFIG_FOO is set to 'y' and to def_val otherwise comes to
the rescue:

     if (IS_ENABLED(CONFIG_FOO)
         fun(IF_ENABLED(CONFIG_FOO, CONFIG_FOO_OPT, "");

If CONFIG_FOO is not defined, the compiler will see

    if (0)
        fun("");

and be happy.

If CONFIG_FOO is defined, the compiler will see

    if (1)
        fun(CONFIG_FOO_OPT)

and be equally happy.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
v3:
	new patch
---
 include/linux/kconfig.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index 2bc704e110..7fea72da1a 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -28,6 +28,13 @@
  */
 #define IS_ENABLED(option)	config_enabled(option, 0)
 
+/*
+ * IF_ENABLED(CONFIG_FOO, opt_cfg, def_val) evalutes to opt_cfg if
+ * CONFIG_FOO is set to 'y' and to def_val otherwise.
+ */
+#define IF_ENABLED(option, opt_cfg, def_val) \
+	config_opt_enabled(IS_ENABLED(option), opt_cfg, def_val)
+
 /*
  * U-Boot add-on: Helper macros to reference to different macros (prefixed by
  * CONFIG_, CONFIG_SPL_, CONFIG_TPL_ or CONFIG_TOOLS_), depending on the build
-- 
2.38.1