linux-kernel - Re: [Add SMP support for Allwinner A20: PATCH V5 3/3] Add arch count timer node in dts for Allwinner A20(sunxi 7i).

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Date:	Wed, 23 Oct 2013 12:28:09 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Fan Rong <cinifr@...il.com>
Cc:	coosty@....com, daniel.lezcano@...aro.org, linux@....linux.org.uk,
	tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, mark.rutland@....com,
	pawel.moll@....com, rob.herring@...xeda.com,
	linux-sunxi@...glegroups.com
Subject: Re: [Add SMP support for Allwinner A20: PATCH V5 3/3] Add arch count
 timer node in dts for Allwinner A20(sunxi 7i).

On Fri, Oct 18, 2013 at 12:37:07AM +0800, Fan Rong wrote:
> Linux kernel usually use virtual arch timer for smp cpu tick. But the
> arch timer register VCTOFF normally is very different between the two
> cpus in A20 afer hardware reset, so SMP Cpus will see different time
> tick. It will cause kernel crash currently. You have two choices to
> fix it: 1 Simpley use physical arch timer, 2 Set VCTOFF to same value
> for each cpu in bootloader. The first choice will cause some other
> problem for kernel, especially for KVM, guest OS want to use virtual
> arch timer. So the second choice is perfect. So if you want to use
> arch timer for smp cpu tick, you must ensure you bootload have set
> same VCTOFF for all cpus.
> 

Is your patchset working without that last patch?

I'm not really wanting to apply it right now.

It relies on a bootloader behaviour that is not implemented by any
bootloader we have openly available right now. I will apply it after
it's been merged in at least u-boot-sunxi.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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