linux-kernel - Re: [PATCH v4 1/2] dt-bindings: cpufreq: add virtual cpufreq device

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Message-ID: <865y231jvj.wl-maz@kernel.org>
Date:   Wed, 15 Nov 2023 08:49:36 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     David Dai <davidai@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Saravana Kannan <saravanak@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Masami Hiramatsu <mhiramat@...gle.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Gupta Pankaj <pankaj.gupta@....com>,
        Mel Gorman <mgorman@...e.de>, kernel-team@...roid.com,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] dt-bindings: cpufreq: add virtual cpufreq device

On Sat, 11 Nov 2023 01:49:29 +0000,
David Dai <davidai@...gle.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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.