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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-10-10 at 10:54 +0100, Stefano Stabellini wrote:
> On Fri, 10 Oct 2014, Jan Beulich wrote:
> > >> ACPI has obtained I2C resource handling a while ago,
> > >> 
> Why is I2C needed for ACPI? I thought that all the freq changing ops
> would be hidden behind AML methods.

From what Jan says it sounds to me like AML can now invoke i2c
operations...

> 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.

A simple i2c driver (without all the generic framework/bus
infrastructure which Linux has) is pretty simple.

I think the biggest complexity would come from i2c busses with both
cpufreq and other devices on them and managing the potentially shared
accesses.

Presumably ACPI systems must avoid having buses which are accessed both
via AML and by the OS directly. I expect DT has no such restriction.

Ian.


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