linux-kernel - Re: [PATCH] rtc: cmos: ignore bogus century byte

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Date:   Thu, 10 Jan 2019 22:33:34 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Eric Wong <e@...24.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Sylvain Chouleur <sylvain.chouleur@...el.com>,
        Patrick McDermott <patrick.mcdermott@...iquity.com>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: cmos: ignore bogus century byte

On 06/01/2019 08:21:03+0000, Eric Wong wrote:
> Older versions of Libreboot and Coreboot had an invalid value
> (`3' in my case) in the century byte affecting the GM45 in
> the Thinkpad X200.  Not everybody's updated their firmwares,
> and Linux <= 4.2 was able to read the RTC without problems,
> so workaround this by ignoring invalid values.
> 

Does this mean that it is set to an invalid value and that in is not
getting updated properly in mc146818_set_time?

> Fixes: 3c217e51d8a272b9 ("rtc: cmos: century support")
> 
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> Cc: Sylvain Chouleur <sylvain.chouleur@...el.com>
> Cc: Patrick McDermott <patrick.mcdermott@...iquity.com>
> Cc: linux-rtc@...r.kernel.org
> Signed-off-by: Eric Wong <e@...24.org>
> ---
>  drivers/rtc/rtc-mc146818-lib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> index 2f1772a358ca..18a6f15e313d 100644
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -82,7 +82,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
>  	time->tm_year += real_year - 72;
>  #endif
>  
> -	if (century)
> +	if (century > 20)
>  		time->tm_year += (century - 19) * 100;
>  
>  	/*
> -- 
> EW

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