From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter De Schrijver <pdeschrijver-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 5/9] clocksource: tegra: Enable ARM arch_timer with TSC
Date: Thu, 20 Dec 2012 14:22:46 +0200
Message-ID: <20121220122246.GA6819@tbergstrom-lnx.Nvidia.com>
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To: Marc Zyngier <marc.zyngier-5wv7dgnIgG8@public.gmane.org>
Cc: "andrew-g2DYL2Zd6BY@public.gmane.org" <andrew-g2DYL2Zd6BY@public.gmane.org>, "linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org" <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>, "jason-NLaQJdtUoK4Be96aLqz0jA@public.gmane.org" <jason-NLaQJdtUoK4Be96aLqz0jA@public.gmane.org>, "linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "johnstul-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org" <johnstul-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>, "devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org" <devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org>, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org" <rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>, "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org" <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>, Hiroshi Doyu <hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
List-Id: devicetree@vger.kernel.org

> >>> +
> >>> +	/* CNTFRQ */
> >>> +	asm("mcr p15, 0, %0, c14, c0, 0\n" : : "r" (freq));
> >>> +	asm("mrc p15, 0, %0, c14, c0, 0\n" : "=r" (val));
> >>> +	BUG_ON(val != freq);
> >>
> >> This is scary. CNTFRQ is only writable from secure mode, and will
> >> explode in any other situation.
> >>
> >> Also, writing to CNTFRQ doesn't change the timer frequency! This is just
> >> a way for secure mode to tell the rest of the world the frequency the
> >> timer is ticking at. Unless you've wired the input clock to be able to
> >> change the frequency?
> > 
> > ATM, our upstream kernel is expected in secure mode. This situation
> > may be changed later, though....
> 
> I appreciate this. But I expect this kernel to be also used on the
> non-secure side if someone tried to run KVM with it. And this would go
> bang right away.
> 

But the guest wouldn't necessarily have this peripheral, or any other Tegra114
peripheral for that matter?

Cheers,

Peter.