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    SubjectRe: [PATCH v4 7/7] clocksource: mips-gic-timer: Mark GIC timer as unstable if ref clock changes
    Hi Serge,

    On Thu, May 21, 2020 at 2:54 AM Serge Semin
    <Sergey.Semin@baikalelectronics.ru> wrote:
    > Currently clocksource framework doesn't support the clocks with variable
    > frequency. Since MIPS GIC timer ticks rate might be unstable on some
    > platforms, we must make sure that it justifies the clocksource
    > requirements. MIPS GIC timer is incremented with the CPU cluster reference
    > clocks rate. So in case if CPU frequency changes, the MIPS GIC tick rate
    > changes synchronously. Due to this the clocksource subsystem can't rely on
    > the timer to measure system clocks anymore. This commit marks the MIPS GIC
    > based clocksource as unstable if reference clock (normally it's a CPU
    > reference clocks) rate changes. The clocksource will execute a watchdog
    > thread, which lowers the MIPS GIC timer rating to zero and fallbacks to a
    > new stable one.
    >
    > Note we don't need to set the CLOCK_SOURCE_MUST_VERIFY flag to the MIPS
    > GIC clocksource since normally the timer is stable. The only reason why
    > it gets unstable is due to the ref clock rate change, which event we
    > detect here in the driver by means of the clocks event notifier.
    >
    > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>

    Thanks for your patch!

    > --- a/drivers/clocksource/mips-gic-timer.c
    > +++ b/drivers/clocksource/mips-gic-timer.c
    > @@ -24,6 +24,9 @@
    > static DEFINE_PER_CPU(struct clock_event_device, gic_clockevent_device);
    > static int gic_timer_irq;
    > static unsigned int gic_frequency;
    > +static bool __read_mostly gic_clock_unstable;
    > +
    > +static void git_clocksource_unstable(char *reason);

    gic_clocksource_unstable? (everywhere)

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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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