linux-kernel - Re: [PATCH V2 0/6] arm_smp_twd: mpcore

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Message-ID: <20110706110548.GA31936@1n450.cable.virginmedia.net>
Date:	Wed, 6 Jul 2011 12:05:48 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Vitaly Kuzmichev <vkuzmichev@...sta.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	"arm@...nel.org" <arm@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	John Stultz <johnstul@...ibm.com>,
	Nicolas Pitre <nico@...xnic.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V2 0/6] arm_smp_twd: mpcore_wdt: Fix MPCORE watchdog
 setup

(sorry for reposting - did something wrong with the SMTP configuration
and the original mail was rejected as spam by most recipients)

On Wed, Jul 06, 2011 at 11:14:56AM +0100, Russell King - ARM Linux wrote:
> On Wed, Jul 06, 2011 at 11:05:51AM +0100, Marc Zyngier wrote:
> > On 05/07/11 20:00, Vitaly Kuzmichev wrote:
> > > The series of patches fixes various bugs in ARM MPCORE watchdog setup.
> > > They also introduce some changes in common ARM_SMP_TWD timer setup code.
> > > The PATCH 2/6 adds an exported function to obtain twd timer rate in
> > > mpcore_wdt. However, this solution might be unacceptable, and the
> > > better is to copy calibration loop and clk_get_rate calling to mpcore_wdt.
> > 
> > My take on this is that the calibration loop should simply be killed
> > once Colin's patch using the "smp_twd" clock is merged and relevant
> > platforms updated. Once this is done, the watchdog driver should use the
> > clock directly, without exporting a symbol.
> 
> Do we know why the calibration was initially introduced?  FWIR, it came
> from the SMP group in ARM, so I guess they had a reason for it rather
> than copying x86.

I think it was introduced because the TWD frequency is half of the CPU
frequency but the latter may not be known - boot monitor configuration
could change it.

-- 
Catalin
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