linux-kernel - Re: [GIT PULL] omap changes for v2.6.39 merge window

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Message-ID: <1301988624.417.71.camel@e102391-lin.cambridge.arm.com>
Date:	Tue, 05 Apr 2011 08:30:24 +0100
From:	Marc Zyngier <Marc.Zyngier@....com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>, david@...g.hm,
	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nico@...xnic.net>,
	Tony Lindgren <tony@...mide.com>,
	Catalin Marinas <catalin.marinas@....com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-omap@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Detlef Vollmann <dv@...lmann.ch>,
	David Brown <davidb@...eaurora.org>
Subject: Re: [GIT PULL] omap changes for v2.6.39 merge window

On Mon, 2011-04-04 at 22:08 +0200, Linus Walleij wrote:
> 2011/4/4 Marc Zyngier <Marc.Zyngier@....com>:
> > On Mon, 2011-04-04 at 14:31 +0100, Russell King - ARM Linux wrote:
> >>
> >> If ARM are going to architect a set of timers into the hardware, let's
> >> make sure that all such hardware has them so we can dig ourselves out
> >> of this crappy mess that we find ourselves in today.
> >
> > As far as I know, A15 always has a set of generic timers.
> >
> > It may be that they are not available (frequency not programmed into the
> > CNTFREQ register), or that someone decided to use a better alternative
> > (for some particular interpretation of "better").
> 
> I guess this thing is inside that A15 core?
> 
> First, what happens the day any vendors start making SoCs on this is
> they turn the A15 core off whenever it is not used, loosing all state
> including this timer, I believe.

The main counter is located in an ALWAYS_ON power domain, and should
keep going whatever happens in the system.

[...]

> Second, have you taken into account the effect of changing the
> frequency of the A15 core, which is something every vendor also
> does, as you know Colin Cross already has a patch pending
> for that on the TWD localtimer which has not yet reached
> the kernel. (Or is A15 fixed frequency? Forgive my ignorance...)

Fixed frequency, with a minimal roll-over time of 40 years.

	M.
-- 
Reality is an implementation detail.


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