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

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Message-ID: <20110711094343.GB11247@e102109-lin.cambridge.arm.com>
Date:	Mon, 11 Jul 2011 10:43:43 +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

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.
 
That's highly platform dependent and it's not just ARM dev boards. Any
board with ARM11MPCore, Cortex-A9 or Cortex-A5 would need to find a way
to retrieve such information. If anyone is prepared to go through each
board and figure out how to get the information, it's fine by me.

-- 
Catalin
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