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

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Message-ID: <20110710103922.GB4812@n2100.arm.linux.org.uk>
Date:	Sun, 10 Jul 2011 11:39:22 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nico@...xnic.net>,
	Marc Zyngier <marc.zyngier@....com>,
	John Stultz <johnstul@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	"arm@...nel.org" <arm@...nel.org>,
	Vitaly Kuzmichev <vkuzmichev@...sta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2 0/6] arm_smp_twd: mpcore_wdt: Fix MPCORE watchdog
	setup

On Wed, Jul 06, 2011 at 12:16:03PM +0100, Russell King - ARM Linux wrote:
> On Wed, Jul 06, 2011 at 12:05:48PM +0100, Catalin Marinas wrote:
> > On Wed, Jul 06, 2011 at 11:14:56AM +0100, Russell King - ARM Linux wrote:
> > > 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.
> 
> Okay, that implies we can't have a fixed frequency built into the kernel
> then.  For such platforms like the ARM dev boards (realview + vexpress),
> I expect we can read the CPU frequency from somewhere like one of the
> ICST PLLs.

So how do we do that?  I see this as a blocker on these patches.
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