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From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Serge Semin <fancer.lancer@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Paul Burton <paulburton@kernel.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Alessandro Zummo <a.zummo@towertech.it>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
	"open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
	<linux-rtc@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	Paul Cercueil <paul@crapouillou.net>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Randy Dunlap <rdunlap@infradead.org>,
	Claudiu Beznea <claudiu.beznea@microchip.com>,
	Maarten ter Huurne <maarten@treewalker.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 7/7] clocksource: mips-gic-timer: Mark GIC timer as unstable if ref clock changes
Date: Thu, 21 May 2020 17:22:19 +0300	[thread overview]
Message-ID: <20200521142219.ejsl4y5eaqqfsp5k@mobilestation> (raw)
In-Reply-To: <CAMuHMdW5TqfDTZZCscXCK-Fkd7Gq1Ciyu1_sDzzR0B+_W-2hfg@mail.gmail.com>

On Thu, May 21, 2020 at 11:09:50AM +0200, Geert Uytterhoeven wrote:
> 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)

This is the most used word lately. So my hands write git everywhere by itself.)
Thanks for noticing this.

-Sergey

> 
> 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

      reply	other threads:[~2020-05-21 14:23 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-21  0:53 [PATCH v4 0/7] clocksource: Fix MIPS GIC and DW APB Timer for Baikal-T1 SoC support Serge Semin
2020-05-21  0:53 ` [PATCH v4 1/7] dt-bindings: rtc: Convert snps,dw-apb-timer to DT schema Serge Semin
2020-05-21  0:53 ` [PATCH v4 2/7] dt-bindings: timer: Move snps,dw-apb-timer DT schema from rtc Serge Semin
2020-05-21  0:53 ` [PATCH v4 3/7] dt-bindings: interrupt-controller: Convert mti,gic to DT schema Serge Semin
2020-05-21  0:53 ` [PATCH v4 4/7] clocksource: dw_apb_timer: Set clockevent any-possible-CPU mask Serge Semin
2020-05-21 15:04   ` Serge Semin
2020-05-21  0:53 ` [PATCH v4 5/7] clocksource: dw_apb_timer_of: Fix missing clockevent timers Serge Semin
2020-05-21  0:53 ` [PATCH v4 6/7] clocksource: mips-gic-timer: Register as sched_clock Serge Semin
2020-05-21  0:53 ` [PATCH v4 7/7] clocksource: mips-gic-timer: Mark GIC timer as unstable if ref clock changes Serge Semin
2020-05-21  9:09   ` Geert Uytterhoeven
2020-05-21 14:22     ` Serge Semin [this message]

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