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Date: Tue, 26 Nov 2013 10:14:54 -0800
From: Guenter Roeck <linux@roeck-us.net>
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To: Doug Anderson <dianders@chromium.org>, Wim Van Sebroeck <wim@iguana.be>
CC: Leela Krishna Amudala <l.krishna@samsung.com>,
        Olof Johansson <olof@lixom.net>, Tomasz Figa <tomasz.figa@gmail.com>,
        Kukjin Kim <kgene.kim@samsung.com>, Ben Dooks <ben-linux@fluff.org>,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-watchdog@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] watchdog: s3c2410_wdt: Only register for cpufreq on
 ARM_S3C24XX_CPUFREQ
References: <1385420137-32725-1-git-send-email-dianders@chromium.org> <1385422603-22684-1-git-send-email-dianders@chromium.org>
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On 11/25/2013 03:36 PM, Doug Anderson wrote:
> On modern SoCs the watchdog timer is parented on a clock that doesn't
> change every time we have a cpufreq change.  That means we don't need
> to constantly adjust the watchdog timer, so avoid registering for and
> dealing with cpufreq transitions unless we've actually got
> CONFIG_ARM_S3C24XX_CPUFREQ defined.
>
> Note that this is more than just an optimization.  The s3c2410
> watchdog driver actually pats the watchdog on every CPU frequency
> change.  On modern systems these happen many times per second (even in
> a system where "nothing" is happening).  That effectively makes any
> userspace watchdog program useless (the watchdog is constantly patted
> by the kernel).  If we need ARM_S3C24XX_CPUFREQ defined on a
> multiplatform kernel we'll need to make sure that kernel supports
> common clock and change this to user common clock framework.
>
> Signed-off-by: Doug Anderson <dianders@chromium.org>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>