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From:   Saravana Kannan <saravanak@google.com>
Date:   Thu, 7 Dec 2023 14:44:36 -0800
Message-ID: <CAGETcx9-n0z5buWgtLZ+6VxW2jEko1GWzkGtGhFiZEq-x_G4nw@mail.gmail.com>
Subject: Re: [PATCH v4 1/2] dt-bindings: cpufreq: add virtual cpufreq device
To:     Marc Zyngier <maz@kernel.org>
Cc:     David Dai <davidai@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Quentin Perret <qperret@google.com>,
        Masami Hiramatsu <mhiramat@google.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Pavan Kondeti <quic_pkondeti@quicinc.com>,
        Gupta Pankaj <pankaj.gupta@amd.com>,
        Mel Gorman <mgorman@suse.de>, kernel-team@android.com,
        linux-pm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Wed, Nov 15, 2023 at 12:49=E2=80=AFAM Marc Zyngier <maz@kernel.org> wrot=
e:
>
> On Sat, 11 Nov 2023 01:49:29 +0000,
> David Dai <davidai@google.com> wrote:
> >
> > Adding bindings to represent a virtual cpufreq device.
> >
> > Virtual machines may expose MMIO regions for a virtual cpufreq device
> > for guests to read frequency information or to request frequency
> > selection. The virtual cpufreq device has an individual controller for
> > each frequency domain.
>
> I would really refrain form having absolute frequencies here. A
> virtual machine can be migrated, and there are *zero* guarantees that
> the target system has the same clock range as the source.
>
> This really should be a relative number, much like the capacity. That,
> at least, can be migrated across systems.

There's nothing in this patch that mandates absolute frequency.
In true KVM philosophy, we leave it to the VMM to decide.

-Saravana