timestamp: Apply factor to recorded stamps

If we dont have a constant TSC rate, timestamp table
has odd leaps and may appear to run backwards. Add
functionality to apply a factor such that all stamps
are in the same timebase.

Change-Id: Idab9c2c00e117c4d247db8cc9a2897640fa01edd
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/19330
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/timestamp.h

@@ -36,10 +36,15 @@ void timestamp_init(uint64_t base);
 void timestamp_add(enum timestamp_id id, uint64_t ts_time);
 /* Calls timestamp_add with current timestamp. */
 void timestamp_add_now(enum timestamp_id id);
+
+/* Apply a factor of N/M to all timestamps recorded so far. */
+void timestamp_rescale_table(uint16_t N, uint16_t M);
+
 #else
 #define timestamp_init(base)
 #define timestamp_add(id, time)
 #define timestamp_add_now(id)
+#define timestamp_rescale_table(N, M)
 #endif
 
 /* Implemented by the architecture code */