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 10.10.14 at 11:39, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > 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.
> 
> Okay, but that doesn't change the picture: I2C support is going to
> be useful (needed?) for ACPI sooner or later, so having something
> (hopefully minimalistic) in the hypervisor doesn't sound like all that
> bad an idea, and could then be used outside of ACPI too for ARM.

Why is I2C needed for ACPI? I thought that all the freq changing ops
would be hidden behind AML methods.

Honestly not knowing how much code is required to have I2C support in
Xen, it is difficult for me to guess what would be the best approach.
The GlobalLogic guys seem to think too much.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel