sa53: adjust GNSS fix calculations

To check the HOLDOVER duration we compare the timestamp of the last
known GNSS fix and current time and use this comparison to adjust the
state of the card and MAC. Unfortunately, the last known GNSS fix
timestamp was stored as UTC time came from GNSS, but later compared to
monotonic clock timestamp. This comparison is incorrect. Store monotonic
clock timestamp every time we recieve good GNSS time and use it later in
all comparisons.

Signed-off-by: Vadim Fedorenko <vadfed@meta.com>

src/oscillators/sa5x_oscillator.c

@@ -90,6 +90,7 @@ struct sa5x_oscillator {
 	struct sa5x_disciplining_status status;
 	struct timespec disciplining_start;
 	struct timespec gnss_last_fix;
+	struct timespec gnss_last_fix_utc;
 	struct timespec mac_last_latch;
 	bool gnss_fix_status;
 	bool latch_fixed;
@@ -635,8 +636,10 @@ static int sa5x_oscillator_push_gnss_info(struct oscillator *oscillator, bool fi
 {
 	struct sa5x_oscillator *sa5x = container_of(oscillator, struct sa5x_oscillator, oscillator);
 	sa5x->gnss_fix_status = fixOk;
-	if (fixOk && last_fix_utc_time)
-		sa5x->gnss_last_fix = *last_fix_utc_time;
+	if (fixOk && last_fix_utc_time) {
+		sa5x->gnss_last_fix_utc = *last_fix_utc_time;
+		clock_gettime(CLOCK_MONOTONIC, &sa5x->gnss_last_fix);
+	}
 	return 0;
 }