[PATCH 2/6] kconfig: Add support for conditional values

[Simon Glass]

At present if an optional Kconfig value needs to be used it must be
bracketed by #ifdef. For example, with this Kconfig setup:

config WIBBLE
	bool "Support wibbles, the world needs more wibbles"

config WIBBLE_ADDR
	hex "Address of the wibble"
	depends on WIBBLE

then the following code must be used:

 #ifdef CONFIG_WIBBLE
 static void handle_wibble(void)
 {
 	int val = CONFIG_WIBBLE_ADDR;

	...
 }
 #endif

 static void init_machine()
 {
 ...
 #ifdef CONFIG_WIBBLE
	handle_wibble();
 #endif
 }

Add a new IF_ENABLED_INT() to help with this. So now it is possible to
write, without #ifdefs:

 static void handle_wibble(void)
 {
        int val = IF_ENABLED_INT(CONFIG_WIBBLE, CONFIG_WIBBLE_ADDR);

	...
 }

 static void init_machine()
 {
 ...
 if (IS_ENABLED(CONFIG_WIBBLE))
	handle_wibble();
 }

The value will be 0 if CONFIG_WIBBLE is not defined, and
CONFIG_WIBBLE_ADDR if it is. This allows us to reduce the use of #ifdef in
the code, ensuring that the compiler still checks the code even if it is
not ultimately used for a particular build.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 include/linux/kconfig.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index 3a2da738c4..86cd266540 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -79,6 +79,18 @@
  */
 #define CONFIG_VAL(option)  config_val(option)
 
+/* This use a similar mechanism to config_enabled() above */
+#define config_opt_enabled(cfg, opt_cfg) _config_opt_enabled(cfg, opt_cfg)
+#define _config_opt_enabled(cfg_val, opt_value) \
+	__config_opt_enabled(__ARG_PLACEHOLDER_##cfg_val, opt_value)
+#define __config_opt_enabled(arg1_or_junk, arg2) \
+	___config_opt_enabled(arg1_or_junk arg2, 0)
+#define ___config_opt_enabled(__ignored, val, ...) val
+
+/* Evaluates to 0 if option is not defined, int_option if it is defined */
+#define IF_ENABLED_INT(option, int_option) \
+	config_opt_enabled(option, int_option)
+
 /*
  * CONFIG_IS_ENABLED(FOO) evaluates to
  *  1 if CONFIG_SPL_BUILD is undefined and CONFIG_FOO is set to 'y' or 'm',
-- 
2.27.0.rc0.183.gde8f92d652-goog