linux-kernel - Re: [PATCH] watchdog: s3c2410_wdt: Only register for cpufreq on CPU_FREQ

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Date:	Tue, 26 Nov 2013 00:31:30 +0100
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Wim Van Sebroeck <wim@...ana.be>,
	Leela Krishna Amudala <l.krishna@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Ben Dooks <ben-linux@...ff.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	linux-watchdog@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] watchdog: s3c2410_wdt: Only register for cpufreq on CPU_FREQ_S3C24XX

On Monday 25 of November 2013 15:28:29 Doug Anderson wrote:
> Guenter,
> 
> On Mon, Nov 25, 2013 at 3:23 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> > On 11/25/2013 02:55 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
> >> CPU_FREQ_S3C24XX 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 CPU_FREQ_S3C24XX 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@...omium.org>
> >> ---
> >>   drivers/watchdog/s3c2410_wdt.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/watchdog/s3c2410_wdt.c
> >> b/drivers/watchdog/s3c2410_wdt.c
> >> index 7d8fd04..4980f84 100644
> >> --- a/drivers/watchdog/s3c2410_wdt.c
> >> +++ b/drivers/watchdog/s3c2410_wdt.c
> >> @@ -264,7 +264,7 @@ static irqreturn_t s3c2410wdt_irq(int irqno, void
> >> *param)
> >>         return IRQ_HANDLED;
> >>   }
> >>
> >> -#ifdef CONFIG_CPU_FREQ
> >> +#ifdef CONFIG_CPU_FREQ_S3C24XX
> >>
> > Where is the CPU_FREQ_S3C24XX configuration option defined ? I don't see it
> > in the current upstream kernel, so it appears that this depends on some
> > out-of-tree changes.
> 
> Whoops!  I guess I just trusted another patch and didn't dig.  I was
> basing this on https://patchwork.kernel.org/patch/3023421/
> 
> Ah, I see that Tomasz just found the answer.  I'll update my patch.

Seems like I originally gave you the wrong symbol name, looking at our
internal 3.10 tree, where the rename is not present yet, and nobody
noticed. Sorry for that.

Best regards,
Tomasz

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