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From: Finn Thain <>
To: Arnd Bergmann <>
Cc:, Mathieu Malaterre <>,
	Michael Ellerman <>,
	Meelis Roos <>, LKML <>,
	y2038 Mailman List <>,
	Paul Mackerras <>,
	Benjamin Herrenschmidt <>,
	Andreas Schwab <>,
	Geert Uytterhoeven <>,
	linuxppc-dev <>,
	Greg Ungerer <>,
	Joshua Thompson <>
Subject: Re: [PATCH 1/3] [v2] powerpc: mac: fix rtc read/write functions
Date: Tue, 10 Jul 2018 11:18:34 +1000 (AEST)	[thread overview]
Message-ID: <alpine.LNX.2.21.1807101105130.12@nippy.intranet> (raw)
In-Reply-To: <>

On Mon, 9 Jul 2018, Arnd Bergmann wrote:

> The most likely explanation I have here is that the RTC was indeed set 
> to an incorrect date, either because of a depleted battery (not unlikely 
> for a ~15 year old box) or because it was previously stored incorrectly.

The PowerMac stores the GMT offset in NVRAM, and this gets used to 
initialize timezone_offset.

If timezone_offset was negative and now.tv_sec was zero, I think this 
could store a 1969 date in the RTC:

int update_persistent_clock64(struct timespec64 now)
        struct rtc_time tm;

        if (!ppc_md.set_rtc_time)
                return -ENODEV;

        rtc_time64_to_tm(now.tv_sec + 1 + timezone_offset, &tm);

        return ppc_md.set_rtc_time(&tm);

But maybe now.tv_sec can be shown to be greater than timezone_offset.

Then, what would happen when the timezone in /etc/localtime disagrees with 
the timezone_offset stored in NVRAM (PRAM)?

Besides that, if the battery went flat, what use is a backtrace? Why not 
scrap the WARN_ON()?

Y2038 mailing list

      reply	other threads:[~2018-07-10  1:18 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
     [not found] ` <>
2018-07-01 15:47   ` [PATCH 1/3] [v2] powerpc: mac: fix rtc read/write functions Meelis Roos
2018-07-09 21:31     ` Arnd Bergmann
2018-07-10  1:18       ` Finn Thain [this message]

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