rtc: test: Test date conversion for dates starting in 1900

While the RTC framework intends to only handle dates after 1970 for
consumers, time conversion must also work for earlier dates to cover
e.g. storing dates beyond an RTC's range_max. This is most relevant for
the rtc-mt6397 driver that has

	range_min = RTC_TIMESTAMP_BEGIN_1900;
	range_max = mktime64(2027, 12, 31, 23, 59, 59);

and so needs working support for timestamps in 1900 starting in less than
three years.

So shift the tested interval of timestamps to also cover years 1900 to
1970.

Signed-off-by: Uwe Kleine-König <[email protected]>
Signed-off-by: Alexandre Mergnat <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexandre Belloni <[email protected]>

Author: ukleinek

drivers/rtc/lib_test.c

@@ -41,15 +41,15 @@ static void rtc_time64_to_tm_test_date_range(struct kunit *test, int years)
 	 */
 	time64_t total_secs = ((time64_t)years) / 400 * 146097 * 86400;
 
-	int year	= 1970;
+	int year	= 1900;
 	int month	= 1;
 	int mday	= 1;
 	int yday	= 1;
-	int wday	= 4; /* Jan 1st 1970 was a Thursday */
+	int wday	= 1; /* Jan 1st 1900 was a Monday */
 
 	struct rtc_time result;
 	time64_t secs;
-	const time64_t sec_offset = ((1 * 60) + 2) * 60 + 3;
+	const time64_t sec_offset = RTC_TIMESTAMP_BEGIN_1900 + ((1 * 60) + 2) * 60 + 3;
 
 	for (secs = 0; secs <= total_secs; secs += 86400) {
 
@@ -72,7 +72,7 @@ static void rtc_time64_to_tm_test_date_range(struct kunit *test, int years)
 }
 
 /*
- * Checks every day in a 160000 years interval starting on 1970-01-01
+ * Checks every day in a 160000 years interval starting on 1900-01-01
  * against the expected result.
  */
 static void rtc_time64_to_tm_test_date_range_160000(struct kunit *test)
@@ -81,7 +81,7 @@ static void rtc_time64_to_tm_test_date_range_160000(struct kunit *test)
 }
 
 /*
- * Checks every day in a 1000 years interval starting on 1970-01-01
+ * Checks every day in a 1000 years interval starting on 1900-01-01
  * against the expected result.
  */
 static void rtc_time64_to_tm_test_date_range_1000(struct kunit *test)