add config option KERNEL_PRINTK to disable printing completely

include/kernel/printk.h

@@ -7,6 +7,10 @@
 
 #include <kernel/kernel_levels.h>
 
+#ifdef CONFIG_KERNEL_PRINTK
 int printk(const char *fmt, ...);
+#else
+#define printk(fmt, ...)
+#endif
 
 #endif /* _KERNEL_KERNEL_LEVELS_H_ */

kernel/Kconfig

+config KERNEL_PRINTK
+	bool "Enable printing in kernel"
+	default y
+
 config KERNEL_LEVEL
 	int "Kernel debug level"
 	default "7"
+	range 0 8
+	depends on KERNEL_PRINTK
 	help
 	 Limit the kernel's debug message level:
-	 0: emergency
-	 1: alerts
-	 2: critical conditions
-	 3: error conditions
-	 4: warnings
-	 5: notices
-	 6: informational
-	 7: debug
+	 1: emergency
+	 2: alerts
+	 3: critical conditions
+	 4: error conditions
+	 5: warnings
+	 6: notices
+	 7: informational
+	 8: debug
+

kernel/Makefile

 obj-y += ksym.o
-obj-y += printk.o
+obj-$(CONFIG_KERNEL_PRINTK) += printk.o
 obj-y += bitmap.o
 obj-y += module.o
 obj-m += testmodule.o