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From:   Rob Herring <robh+dt@kernel.org>
Date:   Fri, 31 Mar 2023 07:46:52 -0500
Message-ID: <CAL_JsqJErVOZZ==i1HpMABfuVEDC+drboLTntMDB0sUC9ZdQ_Q@mail.gmail.com>
Subject: Re: [RFC PATCH v2 5/6] dt-bindings: cpufreq: add bindings for virtual
 kvm cpufreq
To:     David Dai <davidai@google.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Saravana Kannan <saravanak@google.com>,
        kernel-team@android.com, linux-pm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
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On Thu, Mar 30, 2023 at 8:45=E2=80=AFPM David Dai <davidai@google.com> wrot=
e:
>
> Add devicetree bindings for a virtual kvm cpufreq driver.
>
> Co-developed-by: Saravana Kannan <saravanak@google.com>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> Signed-off-by: David Dai <davidai@google.com>
> ---
>  .../bindings/cpufreq/cpufreq-virtual-kvm.yaml | 39 +++++++++++++++++++
>  1 file changed, 39 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/cpufreq/cpufreq-vir=
tual-kvm.yaml
>
> diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-virtual-kv=
m.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@google.com>
> +
> +description: |
> +
> +  KVM CPUFreq is a virtualized driver in guest kernels that sends utiliz=
ation
> +  of its vCPUs as a hint to the host. The host uses hint to schedule vCP=
U
> +  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 =3D <2>;
> +      #size-cells =3D <2>;
> +
> +      cpufreq {
> +            compatible =3D "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