linux-kernel - [PATCH v2] watchdog: s3c2410_wdt: Only register for cpufreq on ARM_S3C24XX

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Date:	Mon, 25 Nov 2013 15:36:43 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Wim Van Sebroeck <wim@...ana.be>,
	Guenter Roeck <linux@...ck-us.net>
Cc:	Leela Krishna Amudala <l.krishna@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Doug Anderson <dianders@...omium.org>,
	Ben Dooks <ben-linux@...ff.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] watchdog: s3c2410_wdt: Only register for cpufreq on ARM_S3C24XX_CPUFREQ

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@...omium.org>
---
Changes in v2:
- Use the updated config name.

 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..c1ada33 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_ARM_S3C24XX_CPUFREQ

 static int s3c2410wdt_cpufreq_transition(struct notifier_block *nb,
 					  unsigned long val, void *data)
-- 
1.8.4.1

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