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>

2 files changed, 33 insertions, 0 deletions

diff --git a/src/include/timestamp.h b/src/include/timestamp.h
index d0735294df..95470f53d6 100644
--- a/src/include/timestamp.h
+++ b/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 */
diff --git a/src/lib/timestamp.c b/src/lib/timestamp.c
index 816f28fd85..30f7c13fb8 100644
--- a/src/lib/timestamp.c
+++ b/src/lib/timestamp.c
@@ -299,6 +299,34 @@ static void timestamp_sync_cache_to_cbmem(int is_recovery)
 	ts_cache->cache_state = TIMESTAMP_CACHE_NOT_NEEDED;
 }
 
+void timestamp_rescale_table(uint16_t N, uint16_t M)
+{
+	uint32_t i;
+	struct timestamp_table *ts_table;
+
+	if (!timestamp_should_run())
+		return;
+
+	if (N == 0 || M == 0)
+		return;
+
+	ts_table = timestamp_table_get();
+
+	/* No timestamp table found */
+	if (ts_table == NULL) {
+		printk(BIOS_ERR, "ERROR: No timestamp table found\n");
+		return;
+	}
+
+	ts_table->base_time /= M;
+	ts_table->base_time *= N;
+	for (i = 0; i < ts_table->num_entries; i++) {
+		struct timestamp_entry *tse = &ts_table->entries[i];
+		tse->entry_stamp /= M;
+		tse->entry_stamp *= N;
+	}
+}
+
 ROMSTAGE_CBMEM_INIT_HOOK(timestamp_sync_cache_to_cbmem)
 RAMSTAGE_CBMEM_INIT_HOOK(timestamp_sync_cache_to_cbmem)