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

From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
To: 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>,
	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>
Cc: 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
Subject: Re: [RFC PATCH v2 5/6] dt-bindings: cpufreq: add bindings for virtual kvm cpufreq
Date: Fri, 31 Mar 2023 10:55:46 +0200	[thread overview]
Message-ID: <e28e76e2-f392-44d9-e88c-27c6d26115d0@linaro.org> (raw)
In-Reply-To: <20230331014356.1033759-6-davidai@google.com>

On 31/03/2023 03:43, David Dai wrote:
> Add devicetree bindings for a virtual kvm cpufreq driver.

Why? Why virtual devices should be documented in DT? DT is for
non-discoverable hardware, right? You have entire commit msg to explain
it instead of saying something easily visible by the diff.

> 
> 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-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@google.com>
> +
> +description: |

Do not need '|'.
> +

Drop stray blank line.

> +  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).

No clue why you need DT bindings for this. KVM has interfaces between
host and guests.

> +
> +properties:
> +  compatible:
> +    const: virtual,kvm-cpufreq
> +
> +required:
> +  - compatible
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    {

This is some broken syntax and/or indentation.

I don't get what this node is about.

> +      #address-cells = <2>;
> +      #size-cells = <2>;

Why?

> +
> +      cpufreq {
> +            compatible = "virtual,kvm-cpufreq";
> +      };
> +

Drop stray blank lines

> +    };

Best regards,
Krzysztof

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