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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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).

Jan


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