linux-kernel - [PATCH 2/2] rtc: mt6359: fix year issue

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Message-Id: <20250109-enable-rtc-v1-2-e8223bf55bb8@baylibre.com>
Date: Thu, 09 Jan 2025 16:29:52 +0100
From: Alexandre Mergnat <amergnat@...libre.com>
To: Eddie Huang <eddie.huang@...iatek.com>, 
 Sean Wang <sean.wang@...iatek.com>, 
 Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Macpaul Lin <macpaul.lin@...iatek.com>
Cc: linux-arm-kernel@...ts.infradead.org, 
 linux-mediatek@...ts.infradead.org, linux-rtc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Alexandre Mergnat <amergnat@...libre.com>
Subject: [PATCH 2/2] rtc: mt6359: fix year issue

Removing the RTC_MIN_YEAR_OFFSET addition and subtraction has
introduced a regression.

~# hwclock -r --verbose
hwclock from util-linux 2.37.4
System Time: 1262312013.143552
Trying to open: /dev/rtc0
Using the rtc interface to the clock.
Assuming hardware clock is kept in UTC time.
Waiting for clock tick...
hwclock: select() to /dev/rtc0 to wait for clock tick timed out
...synchronization failed

Bring back the RTC_MIN_YEAR_OFFSET to fix the RTC.

Fixes: 34bbdc12d04e ("rtc: mt6359: Add RTC hardware range and add support for start-year")
Signed-off-by: Alexandre Mergnat <amergnat@...libre.com>
---
 drivers/rtc/rtc-mt6397.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/rtc/rtc-mt6397.c b/drivers/rtc/rtc-mt6397.c
index 55e75712edd4..9930b6bdb6ca 100644
--- a/drivers/rtc/rtc-mt6397.c
+++ b/drivers/rtc/rtc-mt6397.c
@@ -96,6 +96,12 @@ static int mtk_rtc_read_time(struct device *dev, struct rtc_time *tm)
 			goto exit;
 	} while (sec < tm->tm_sec);
 
+	/* HW register use 7 bits to store year data, minus
+	 * RTC_MIN_YEAR_OFFSET before write year data to register, and plus
+	 * RTC_MIN_YEAR_OFFSET back after read year from register
+	 */
+	tm->tm_year += RTC_MIN_YEAR_OFFSET;
+
 	/* HW register start mon/wday from one, but tm_mon/tm_wday start from zero. */
 	tm->tm_mon--;
 	tm->tm_wday--;
@@ -110,6 +116,7 @@ static int mtk_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	int ret;
 	u16 data[RTC_OFFSET_COUNT];
 
+	tm->tm_year -= RTC_MIN_YEAR_OFFSET;
 	tm->tm_mon++;
 	tm->tm_wday++;
 
@@ -167,6 +174,7 @@ static int mtk_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
 	tm->tm_mon = data[RTC_OFFSET_MTH] & RTC_AL_MTH_MASK;
 	tm->tm_year = data[RTC_OFFSET_YEAR] & RTC_AL_YEA_MASK;
 
+	tm->tm_year += RTC_MIN_YEAR_OFFSET;
 	tm->tm_mon--;
 
 	return 0;
@@ -182,6 +190,7 @@ static int mtk_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
 	int ret;
 	u16 data[RTC_OFFSET_COUNT];
 
+	tm->tm_year -= RTC_MIN_YEAR_OFFSET;
 	tm->tm_mon++;
 
 	mutex_lock(&rtc->lock);

-- 
2.25.1