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Message-ID: <CAMuHMdXmxV03tza_4M3+YJg9TT6yJKuvmNh9=JvdM7r-r-kR7A@mail.gmail.com> Date: Sun, 6 Jul 2025 11:08:11 +0200 From: Geert Uytterhoeven <geert@...ux-m68k.org> To: Finn Thain <fthain@...ux-m68k.org> Cc: Joshua Thompson <funaho@...ai.org>, linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] m68k/mac: Improve clocksource driver commentary On Tue, 24 Jun 2025 at 06:36, Finn Thain <fthain@...ux-m68k.org> wrote: > qemu-system-m68k -M q800 has an old bug that causes the kernel to > occasionally complain about a soft lockup: > > watchdog: BUG: soft lockup - CPU#0 stuck for 5107s! > > There isn't any actual lockup. The via1 clocksource produced a large > jump in jiffies, causing the watchdog to detect a stale timestamp. > > The 32-bit clocksource counter runs at 783360 Hz and its period is > about 5482 seconds. Applying the "nanosecond" approximation used in > get_timestamp() in kernel/watchdog.c then yields the duration reported > in the log message above (always 5107 or 5108 in my tests): > > 0xffffffff / VIA_CLOCK_FREQ * 10**9 / 2**30 = 5106.209 seconds > > It is notoriously difficult to correctly emulate a MOS6522 VIA chip. So > it seems wise to document the VIA clocksource driver better, especially > those hardware behaviours which the kernel relies upon. > > Cc: Joshua Thompson <funaho@...ai.org> > Signed-off-by: Finn Thain <fthain@...ux-m68k.org> > --- > Changed since v1: > - The letters A through E could be mistaken for hex digits so number the > states using roman numerals instead. LGTM, so Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org> i.e. will queue in the m68k tree for v6.17. 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
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