linux-kernel - Re: [PATCH 5/9] clocksource: tegra: Enable ARM arch

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Message-ID: <20121220221348.GB19766@tbergstrom-lnx.Nvidia.com>
Date:	Fri, 21 Dec 2012 00:13:48 +0200
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Marc Zyngier <marc.zyngier@....com>
CC:	Hiroshi Doyu <hdoyu@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"johnstul@...ibm.com" <johnstul@...ibm.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 5/9] clocksource: tegra: Enable ARM arch_timer with TSC

> > 
> > "tegra114.dtsi" has the folloiwng "tsc" entry. So can we consider that
> > if dts has this entry, CNTFRQ is not set, which implies it's in secure
> > mode. kernel should set it up by itself? Otherwise, skip this setup
> > and use it. For example:
> > 
> >  	tsc {
> >  		compatible = "nvidia,tegra114-tsc";
> >  		reg = <0x700f0000 0x20000>;
> > +		setup-cntfrq;
> >  	};
> > 
> > Is this what you explained in the above?
> > At least, kernel can survive without bootloader/firmware support, ATM.
> 
> No. The DT should only describe the hardware, and not something that is
> Linux specific.
> 
> Just use the "clock-frequency" attribute in the timer arch-timer node,
> and get rid of this CNTFRQ setting. The driver already knows how to deal
> with this situation if this attribute is set.

The frequency is probed at boottime by the kernel though. It will not
necessarily be the same for every board.

Cheers,

Peter.
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