From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <ian.campbell@citrix.com>
Subject: Re: [RFC PATCH 11/13] cpufreq: add xen-cpufreq driver
Date: Wed, 15 Oct 2014 13:34:53 +0100
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To: Andrii Tseglytskyi <andrii.tseglytskyi@globallogic.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Oleksandr Dmytryshyn <oleksandr.dmytryshyn@globallogic.com>, Tim Deegan <tim@xen.org>, xen-devel <xen-devel@lists.xen.org>, Stefano Stabellini <Stefano.Stabellini@citrix.com>, Jan Beulich <JBeulich@suse.com>
List-Id: xen-devel@lists.xenproject.org

On Wed, 2014-10-15 at 14:17 +0300, Andrii Tseglytskyi wrote:
> > Jan and I have been discussing this face to face yesterday (thanks to
> > LinuxCon being located in Germany this year).
> >
> > We should keep in mind that actually both approaches can coexist and we
> > should be able to choose the best one for each platform.
> >
> 
> What if we try to implement both and see which one is better? But I
> would prefer to implement solution without I2C in hypervisor frirst ))
> And post it as RFC of course.

My preference would be to implement the in hypervisor based one first
(since this is the architecturally cleaner option) and then only do the
out of hypervisor one if it turns out to be unworkable in practice.

> > Also it would be nice to know how many I2C bus accesses per seconds the
> > drivers on your board actually make. You could take a measurement by
> > editing your Linux kernel and adding a counter in the I2C subsystem.
> >
> 
> IMO - synchronization of I2C access between dom0 and hypervisot will be painful.

I think this supposition needs backing with evidence of the type Stefano
is asking for, or by actually building it and showing it doesn't work on
this particular platform.

Ian.