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

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Message-ID: <202501091546387cff95fd@mail.local>
Date: Thu, 9 Jan 2025 16:46:38 +0100
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Alexandre Mergnat <amergnat@...libre.com>
Cc: Eddie Huang <eddie.huang@...iatek.com>,
	Sean Wang <sean.wang@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Macpaul Lin <macpaul.lin@...iatek.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, linux-rtc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rtc: mt6359: fix year issue

On 09/01/2025 16:29:52+0100, Alexandre Mergnat wrote:
> 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.
> 

NAK, you'd have to investigate a bit more, I want to get rid of the
RTC_MIN_YEAR_OFFSET insanity.

> 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
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com