linux-kernel - Re: [PATCH] m68k: Fix off-by-one calendar month

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Date:   Tue, 24 Apr 2018 12:06:30 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     Sam Creasey <sammy@...my.net>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH] m68k: Fix off-by-one calendar month

Hi Finn,

On Mon, Apr 23, 2018 at 3:02 AM, Finn Thain <fthain@...egraphics.com.au> wrote:
> This fixes a bug in read_persistent_clock() which causes the system
> clock to lag the Real Time Clock by one month. The problem was noticed
> on a Mac, but theoretically it must also affect Atari, BVME6000 and Q40.
>
> The tm_mon value in the struct rtc_time passed to mach_hwclk() is
> zero-based, and atari_mste_hwclk(), atari_tt_hwclk(), bvme6000_hwclk(),
> mac_hwclk() and q40_hwclk() all make this adjustment. Unfortunately,
> dn_dummy_hwclk(), mvme147_hwclk(), mvme16x_hwclk(), sun3_hwclk() and
> sun3x_hwclk() fail to decrement tm_mon.
>
> Bring these platforms into line and fix read_persistent_clock() so it
> works correctly on all m68k platforms.
>
> The datasheets for the RTC devices found on the affected platforms
> all confirm that the year is stored as a value in the range 0-99 and
> the month is stored as a value in the range 1-12. Please refer to the
> datasheets for MC146818 (Apollo), DS1643 (MVME), ICM7170 (Sun 3)
> and M48T02 (Sun 3x).
>
> Reported-by: Stan Johnson <userm57@...oo.com>
> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>

Thanks, applied and queued for v4.18.

<snip>

> --- a/arch/m68k/kernel/time.c
> +++ b/arch/m68k/kernel/time.c
> @@ -74,17 +74,17 @@ static irqreturn_t timer_interrupt(int irq, void *dummy)
>  void read_persistent_clock(struct timespec *ts)
>  {
>         struct rtc_time time;
> +
>         ts->tv_sec = 0;
>         ts->tv_nsec = 0;
>
> -       if (mach_hwclk) {
> -               mach_hwclk(0, &time);
> +       if (!mach_hwclk)
> +               return;
> +
> +       mach_hwclk(0, &time);
>
> -               if ((time.tm_year += 1900) < 1970)
> -                       time.tm_year += 100;
> -               ts->tv_sec = mktime(time.tm_year, time.tm_mon, time.tm_mday,
> -                                     time.tm_hour, time.tm_min, time.tm_sec);
> -       }
> +       ts->tv_sec = mktime(time.tm_year + 1900, time.tm_mon + 1, time.tm_mday,
> +                           time.tm_hour, time.tm_min, time.tm_sec);

That might explain why my Amiga spends so much time on file system checks
since I wrote the rp5c01 RTC driver...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds