Implement log framework

This patch gives users control over logging messages printed from the C
code using the LOG macros defined in debug.h Users now have the ability
to reduce the log_level at run time using the tf_log_set_max_level()
function. The default prefix string can be defined by platform by
overriding the `plat_log_get_prefix()` platform API which is also
introduced in this patch.

The new log framework results in saving of some RO data. For example,
when BL1 is built for FVP with LOG_LEVEL=LOG_LEVEL_VERBOSE, resulted
in saving 384 bytes of RO data and increase of 8 bytes of RW data. The
framework also adds about 108 bytes of code to the release build of FVP.

Fixes ARM-software/tf-issues#462

Change-Id: I476013d9c3deedfdd4c8b0b0f125665ba6250554
Co-authored-by: Eleanor Bonnici <Eleanor.bonnici@arm.com>
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/include/common/debug.h b/include/common/debug.h
index b858241..3f0f84a 100644
--- a/include/common/debug.h
+++ b/include/common/debug.h
@@ -27,47 +27,59 @@
 #include <stdarg.h>
 #include <stdio.h>
 
+/*
+ * Define Log Markers corresponding to each log level which will
+ * be embedded in the format string and is expected by tf_log() to determine
+ * the log level.
+ */
+#define LOG_MARKER_ERROR		"\xa"	/* 10 */
+#define LOG_MARKER_NOTICE		"\x14"	/* 20 */
+#define LOG_MARKER_WARNING		"\x1e"	/* 30 */
+#define LOG_MARKER_INFO			"\x28"	/* 40 */
+#define LOG_MARKER_VERBOSE		"\x32"	/* 50 */
+
 #if LOG_LEVEL >= LOG_LEVEL_NOTICE
-# define NOTICE(...)	tf_printf("NOTICE:  " __VA_ARGS__)
+# define NOTICE(...)	tf_log(LOG_MARKER_NOTICE __VA_ARGS__)
 #else
 # define NOTICE(...)
 #endif
 
 #if LOG_LEVEL >= LOG_LEVEL_ERROR
-# define ERROR(...)	tf_printf("ERROR:   " __VA_ARGS__)
+# define ERROR(...)	tf_log(LOG_MARKER_ERROR __VA_ARGS__)
 #else
 # define ERROR(...)
 #endif
 
 #if LOG_LEVEL >= LOG_LEVEL_WARNING
-# define WARN(...)	tf_printf("WARNING: " __VA_ARGS__)
+# define WARN(...)	tf_log(LOG_MARKER_WARNING __VA_ARGS__)
 #else
 # define WARN(...)
 #endif
 
 #if LOG_LEVEL >= LOG_LEVEL_INFO
-# define INFO(...)	tf_printf("INFO:    " __VA_ARGS__)
+# define INFO(...)	tf_log(LOG_MARKER_INFO __VA_ARGS__)
 #else
 # define INFO(...)
 #endif
 
 #if LOG_LEVEL >= LOG_LEVEL_VERBOSE
-# define VERBOSE(...)	tf_printf("VERBOSE: " __VA_ARGS__)
+# define VERBOSE(...)	tf_log(LOG_MARKER_VERBOSE __VA_ARGS__)
 #else
 # define VERBOSE(...)
 #endif
 
-
 void __dead2 do_panic(void);
 #define panic()	do_panic()
 
 /* Function called when stack protection check code detects a corrupted stack */
 void __dead2 __stack_chk_fail(void);
 
+void tf_log(const char *fmt, ...) __printflike(1, 2);
 void tf_printf(const char *fmt, ...) __printflike(1, 2);
 int tf_snprintf(char *s, size_t n, const char *fmt, ...) __printflike(3, 4);
 void tf_vprintf(const char *fmt, va_list args);
 void tf_string_print(const char *str);
+void tf_log_set_max_level(unsigned int log_level);
 
 #endif /* __ASSEMBLY__ */
 #endif /* __DEBUG_H__ */