linux-kernel - Re: [PATCH] rtc: Do not sync CMOS clock when CONFIG_RTC

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Message-ID: <875zdls2bi.fsf@nanos.tec.linutronix.de>
Date:   Mon, 27 Apr 2020 11:30:41 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Leonid Bloch <lb.workbox@...il.com>, linux-kernel@...r.kernel.org
Cc:     John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Leonid Bloch <lb.workbox@...il.com>
Subject: Re: [PATCH] rtc: Do not sync CMOS clock when CONFIG_RTC_SYSTOHC is not set

Leonid Bloch <lb.workbox@...il.com> writes:
> According to documentation in 'drivers/rtc/Kconfig', if
> 'CONFIG_RTC_SYSTOHC' is set, then:
>
> '''
> The system time (wall clock) will be stored in the RTC specified by
> RTC_HCTOSYS_DEVICE approximately every 11 minutes if userspace reports
> synchronized NTP status.
> '''
>
> However in reality, even if 'CONFIG_RTC_SYSTOHC' is not set, the RTC
> is still sometimes synced with the system time: at least when the RTC
> driver is 'rtc_cmos', in certain situations. This commit prevents
> that.

But in reality sync_cmos_clock() depends on CONFIG_GENERIC_CMOS_UPDATE
and has nothing to do with CONFIG_RTC_SYSTOHC.

That's a historical leftover from the days where RTCs were strictly a
platform/architecture specific issue.

Your change would break all architectures which still depend on that.

Thanks,

        tglx