linux-kernel - Re: [PATCH] ARM: Drop fixed 200 Hz timer requirement from Exynos platforms

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Date:   Fri, 18 Nov 2016 08:47:49 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Kukjin Kim <kgene@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Lee Jones <lee.jones@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] ARM: Drop fixed 200 Hz timer requirement from Exynos
 platforms

On Thu, Nov 17, 2016 at 01:35:45PM +0100, Arnd Bergmann wrote:
> On Monday, November 14, 2016 8:27:05 PM CET Krzysztof Kozlowski wrote:
> > @@ -1497,7 +1497,7 @@ source kernel/Kconfig.preempt
> >  config HZ_FIXED
> >         int
> >         default 200 if ARCH_EBSA110 || ARCH_S3C24XX || \
> > -               ARCH_S5PV210 || ARCH_EXYNOS4
> > +               ARCH_S5PV210
> >         default 128 if SOC_AT91RM9200
> >         default 0
> 
> After further research, I've concluded that we should also drop the
> settings for ARCH_S5PV210 and ARCH_S3C24XX here.
> 
> ARCH_S5PV210 behaves exactly like EXYNOS here, it has 32-bit timers
> so there won't be any overflow with 100Hz.
> 
> For ARCH_S3C24XX, it the requirement was that HZ_100 could not
> be used with the old arch/arm/plat-samsung/time.c code that would
> overflow its 16-bit counter.
> However, the new drivers/clocksource/samsung_pwm_timer.c configures
> the clock divider to '50' instead of '6', so there is no longer
> a 16-bit overflow before the 100Hz tick, it now overflows every
> 3.7ms for the typical 12MHz clock.

I can send an updated version however testing would be nice... I know
Sylwester has a S3C6410 platform running, maybe S3C24xx as well.

Best regards,
Krzysztof