Re: [PATCH v4 7/7] clocksource: mips-gic-timer: Mark GIC timer as unstable if ref clock changes
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: 2020-05-21 09:10:03
Also in:
linux-mips, linux-rtc, lkml
Hi Serge, On Thu, May 21, 2020 at 2:54 AM Serge Semin [off-list ref] 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 <redacted>
Thanks for your patch!
quoted hunk ↗ jump to hunk
--- 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
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when I'm talking to journalists I just say "programmer" or something like that.
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