[PATCH] rtc: ds1347: fix value written to century register

[PATCH] rtc: ds1347: fix value written to century register

[Ian Abbott]

In `ds1347_set_time()`, the wrong value is being written to the
`DS1347_CENTURY_REG` register.  It needs to be converted to BCD.  Fix
it.

Fixes: 147dae76dbb9 ("rtc: ds1347: handle century register")
Cc: <stable@vger.kernel.org> # v5.5+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
 drivers/rtc/rtc-ds1347.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-ds1347.c b/drivers/rtc/rtc-ds1347.c
index 157bf5209ac4..a40c1a52df65 100644
--- a/drivers/rtc/rtc-ds1347.c
+++ b/drivers/rtc/rtc-ds1347.c
@@ -112,7 +112,7 @@ static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
 		return err;
 
 	century = (dt->tm_year / 100) + 19;
-	err = regmap_write(map, DS1347_CENTURY_REG, century);
+	err = regmap_write(map, DS1347_CENTURY_REG, bin2bcd(century));
 	if (err)
 		return err;
 
-- 
2.35.1

Re: [PATCH] rtc: ds1347: fix value written to century register

[Ian Abbott]

On 27/10/2022 17:32, Ian Abbott wrote:
> In `ds1347_set_time()`, the wrong value is being written to the
> `DS1347_CENTURY_REG` register.  It needs to be converted to BCD.  Fix
> it.
> 
> Fixes: 147dae76dbb9 ("rtc: ds1347: handle century register")
> Cc: <stable@vger.kernel.org> # v5.5+
> Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
> ---
>   drivers/rtc/rtc-ds1347.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-ds1347.c b/drivers/rtc/rtc-ds1347.c
> index 157bf5209ac4..a40c1a52df65 100644
> --- a/drivers/rtc/rtc-ds1347.c
> +++ b/drivers/rtc/rtc-ds1347.c
> @@ -112,7 +112,7 @@ static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
>   		return err;
>   
>   	century = (dt->tm_year / 100) + 19;
> -	err = regmap_write(map, DS1347_CENTURY_REG, century);
> +	err = regmap_write(map, DS1347_CENTURY_REG, bin2bcd(century));
>   	if (err)
>   		return err;
>   

I'm sure this isn't a commonly used driver, but I'd just like to mention 
that I consider it critically broken without this bug fix.  Any dates in 
the 21st century written to the RTC end up being in the 15th century 
inside the chip, and the kernel treats it as invalid when it is read 
back.  (The times are out of range of a 32-bit Unix time.  I'm not sure 
if 64-bit Unix times from the RTC before 1970 are supported or not.)

-- 
-=( Ian Abbott <abbotti@mev.co.uk> || MEV Ltd. is a company  )=-
-=( registered in England & Wales.  Regd. number: 02862268.  )=-
-=( Regd. addr.: S11 & 12 Building 67, Europa Business Park, )=-
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Re: [PATCH] rtc: ds1347: fix value written to century register

[Alexandre Belloni]

On Thu, 27 Oct 2022 17:32:49 +0100, Ian Abbott wrote:
> In `ds1347_set_time()`, the wrong value is being written to the
> `DS1347_CENTURY_REG` register.  It needs to be converted to BCD.  Fix
> it.
> 
> 

Applied, thanks!

[1/1] rtc: ds1347: fix value written to century register
      commit: c397361d7339fa3a2949758ffd5298231fb43173

Best regards,

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