linux-kernel - Re: [RFC PATCH v2 5/6] dt-bindings: cpufreq: add bindings for virtual kvm cpufreq

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Message-ID: <CAL_JsqJErVOZZ==i1HpMABfuVEDC+drboLTntMDB0sUC9ZdQ_Q@mail.gmail.com>
Date:   Fri, 31 Mar 2023 07:46:52 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     David Dai <davidai@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Saravana Kannan <saravanak@...gle.com>,
        kernel-team@...roid.com, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Subject: Re: [RFC PATCH v2 5/6] dt-bindings: cpufreq: add bindings for virtual
 kvm cpufreq

On Thu, Mar 30, 2023 at 8:45 PM David Dai <davidai@...gle.com> wrote:
>
> Add devicetree bindings for a virtual kvm cpufreq driver.
>
> Co-developed-by: Saravana Kannan <saravanak@...gle.com>
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> Signed-off-by: David Dai <davidai@...gle.com>
> ---
>  .../bindings/cpufreq/cpufreq-virtual-kvm.yaml | 39 +++++++++++++++++++
>  1 file changed, 39 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/cpufreq/cpufreq-virtual-kvm.yaml
>
> diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-virtual-kvm.yaml b/Documentation/devicetree/bindings/cpufreq/cpufreq-virtual-kvm.yaml
> new file mode 100644
> index 000000000000..31e64558a7f1
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-virtual-kvm.yaml
> @@ -0,0 +1,39 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/cpufreq/cpufreq-virtual-kvm.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Virtual KVM CPUFreq
> +
> +maintainers:
> +  - David Dai <davidai@...gle.com>
> +
> +description: |
> +
> +  KVM CPUFreq is a virtualized driver in guest kernels that sends utilization
> +  of its vCPUs as a hint to the host. The host uses hint to schedule vCPU
> +  threads and select CPU frequency. It enables accurate Per-Entity Load
> +  Tracking for tasks running in the guest by querying host CPU frequency
> +  unless a virtualized FIE exists(Like AMUs).
> +
> +properties:
> +  compatible:
> +    const: virtual,kvm-cpufreq
> +
> +required:
> +  - compatible
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    {
> +      #address-cells = <2>;
> +      #size-cells = <2>;
> +
> +      cpufreq {
> +            compatible = "virtual,kvm-cpufreq";
> +      };

The same thing was tried on non-virtual h/w too. This is not a device
so it doesn't go in DT. It is just an abuse of DT as a kernel driver
instantiation mechanism.

Rob