parisc: Improve error return codes when setting rtc time

The HP 730 machine returned strange errors when I tried setting the rtc
time.  Add some debug code to improve the possibility to trace errors
and document that hppa probably has as Y2k38 problem.
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/kernel/time.c

@@ -180,9 +180,16 @@ static int rtc_generic_get_time(struct device *dev, struct rtc_time *tm)
 static int rtc_generic_set_time(struct device *dev, struct rtc_time *tm)
 {
 	time64_t secs = rtc_tm_to_time64(tm);
-
-	if (pdc_tod_set(secs, 0) < 0)
+	int ret;
+
+	/* hppa has Y2K38 problem: pdc_tod_set() takes an u32 value! */
+	ret = pdc_tod_set(secs, 0);
+	if (ret != 0) {
+		pr_warn("pdc_tod_set(%lld) returned error %d\n", secs, ret);
+		if (ret == PDC_INVALID_ARG)
+			return -EINVAL;
 		return -EOPNOTSUPP;
+	}
 
 	return 0;
 }