[PATCH] rtc: rzn1: Fix RTC_RD_TIME: Invalid argument

[Biju Das <biju.das.jz@xxxxxxxxxxxxxx>]

This patch fixes the issue RTC_RD_TIME: Invalid argument with the below
use case.

Steps to reproduce:
------------------
date -s "2022-12-31 23:59:55";hwclock -w
hwclock; sleep 10; hwclock

Original result:
---------------
Sat Dec 31 23:59:55 UTC 2022
Sat Dec 31 23:59:56 2022  0.000000 seconds
hwclock: RTC_RD_TIME: Invalid argument

Result after the fix:
--------------------
Sat Dec 31 23:59:55 UTC 2022
Sat Dec 31 23:59:56 2022  0.000000 seconds
Sun Jan  1 00:00:06 2023  0.000000 seconds

Fixes: deeb4b5393e1 ("rtc: rzn1: Add new RTC driver")
Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
---
This patch fix is based on [1]
[1] https://github.com/renesas-rz/rzn1_linux/blob/rzn1-stable-v4.19/drivers/rtc/rtc-rzn1.c
---
 drivers/rtc/rtc-rzn1.c | 47 ++++++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 15 deletions(-)

diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
index ac788799c8e3..0f99b4fd3c4b 100644
--- a/drivers/rtc/rtc-rzn1.c
+++ b/drivers/rtc/rtc-rzn1.c
@@ -88,6 +88,35 @@ static unsigned int rzn1_rtc_tm_to_wday(struct rtc_time *tm)
 	return (days + 4) % 7;
 }
 
+static void bcd2tm(struct rtc_time *tm)
+{
+	tm->tm_sec = bcd2bin(tm->tm_sec);
+	tm->tm_min = bcd2bin(tm->tm_min);
+	tm->tm_hour = bcd2bin(tm->tm_hour);
+	tm->tm_wday = bcd2bin(tm->tm_wday);
+	tm->tm_mday = bcd2bin(tm->tm_mday);
+	tm->tm_mon = bcd2bin(tm->tm_mon) - 1;
+	/* epoch == 1900 */
+	tm->tm_year = bcd2bin(tm->tm_year) + 100;
+}
+
+static int tm2bcd(struct rtc_time *tm)
+{
+	if (rtc_valid_tm(tm) != 0)
+		return -EINVAL;
+
+	tm->tm_sec = bin2bcd(tm->tm_sec);
+	tm->tm_min = bin2bcd(tm->tm_min);
+	tm->tm_hour = bin2bcd(tm->tm_hour);
+	tm->tm_wday = bin2bcd(rzn1_rtc_tm_to_wday(tm));
+	tm->tm_mday = bin2bcd(tm->tm_mday);
+	tm->tm_mon = bin2bcd(tm->tm_mon + 1);
+	/* epoch == 1900 */
+	tm->tm_year = bin2bcd(tm->tm_year - 100);
+
+	return 0;
+}
+
 static int rzn1_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
@@ -106,14 +135,7 @@ static int rzn1_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	if (tm->tm_sec != secs)
 		rzn1_rtc_get_time_snapshot(rtc, tm);
 
-	tm->tm_sec = bcd2bin(tm->tm_sec);
-	tm->tm_min = bcd2bin(tm->tm_min);
-	tm->tm_hour = bcd2bin(tm->tm_hour);
-	tm->tm_wday = bcd2bin(tm->tm_wday);
-	tm->tm_mday = bcd2bin(tm->tm_mday);
-	tm->tm_mon = bcd2bin(tm->tm_mon);
-	tm->tm_year = bcd2bin(tm->tm_year);
-
+	bcd2tm(tm);
 	return 0;
 }
 
@@ -123,13 +145,8 @@ static int rzn1_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	u32 val;
 	int ret;
 
-	tm->tm_sec = bin2bcd(tm->tm_sec);
-	tm->tm_min = bin2bcd(tm->tm_min);
-	tm->tm_hour = bin2bcd(tm->tm_hour);
-	tm->tm_wday = bin2bcd(rzn1_rtc_tm_to_wday(tm));
-	tm->tm_mday = bin2bcd(tm->tm_mday);
-	tm->tm_mon = bin2bcd(tm->tm_mon);
-	tm->tm_year = bin2bcd(tm->tm_year);
+	if (tm2bcd(tm) < 0)
+		return -EINVAL;
 
 	val = readl(rtc->base + RZN1_RTC_CTL2);
 	if (!(val & RZN1_RTC_CTL2_STOPPED)) {
-- 
2.25.1