Re: [Xen-devel] [RFC PATCH 11/13] cpufreq: add xen-cpufreq driver

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 10 Oct 2014, Jan Beulich wrote:
> >>> On 08.10.14 at 15:51, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > On Tue, 7 Oct 2014, Jan Beulich wrote:
> >> >>> On 07.10.14 at 16:19, <oleksandr.dmytryshyn@xxxxxxxxxxxxxxx> wrote:
> >> > This driver uses Dom0 to change frequencies on CPUs
> >> 
> >> In which case its name should be dom0-cpufreq. But I very much
> >> question a model where it is not the hypervisor controlling aspects
> >> of physical CPUs.
> > 
> > Me too, however we had a long discussion (see
> > CAN58jiuVOJMX2-U=Odqrjtr1agNPSRnS1nXURYitc8AC8FgH3g@xxxxxxxxxxxxxx) and
> > Oleksandr and others thought that it would require too much drivers code
> > to change cpu frequency directly in Xen on ARM
> > (CAH_mUMNQLHeOWFC_SNB_8BjBz9rOs=moYOUFFhtOXo_WPZTa7w@xxxxxxxxxxxxxx and
> > CAH_mUMM0iSCcCcYz1B13p5YdS+wvgBOMVJh-871v0Ga0f1bH8Q@xxxxxxxxxxxxxx).
> > 
> > They might be right.
> 
> I continue to disagree, despite understanding some of the points
> they make. ACPI has obtained I2C resource handling a while ago,
> so rather than keeping I2C out of Xen we should rather consider
> updating the few ACPI pieces we have to be capable of handling
> that resource type. Of course that's only useful if systems also
> describe their frequency change procedure properly in ACPI (but
> if they don't do now, I think with ARM moving the ACPI way we
> can at least expect that to come).

ACPI is not coming to ARM in general, only to (some?) ARM servers.
Device Tree is alive and well and we have to keep supporting it for all
the other systems.

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