linux-kernel - Re: [PATCH v3 2/5] dt-bindings: cpufreq: apple,soc-cpufreq: Add binding for Apple SoC cpufreq

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Date:   Tue, 25 Oct 2022 18:12:36 -0500
From:   Rob Herring <robh@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>, asahi@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] dt-bindings: cpufreq: apple,soc-cpufreq: Add
 binding for Apple SoC cpufreq

On Wed, Oct 26, 2022 at 02:22:40AM +0900, Hector Martin wrote:
> On 26/10/2022 01.01, Krzysztof Kozlowski wrote:
> > On 24/10/2022 00:39, Hector Martin wrote:
> >> This binding represents the cpufreq/DVFS hardware present in Apple SoCs.
> >> The hardware has an independent controller per CPU cluster, and we
> >> represent them as unique nodes in order to accurately describe the
> >> hardware. The driver is responsible for binding them as a single cpufreq
> >> device (in the Linux cpufreq model).
> >>
> >> Signed-off-by: Hector Martin <marcan@...can.st>
> >> ---
> >>  .../cpufreq/apple,cluster-cpufreq.yaml        | 119 ++++++++++++++++++
> >>  1 file changed, 119 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/cpufreq/apple,cluster-cpufreq.yaml
> >>
> >> diff --git a/Documentation/devicetree/bindings/cpufreq/apple,cluster-cpufreq.yaml b/Documentation/devicetree/bindings/cpufreq/apple,cluster-cpufreq.yaml
> >> new file mode 100644
> >> index 000000000000..b11452f91468
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/cpufreq/apple,cluster-cpufreq.yaml
> >> @@ -0,0 +1,119 @@
> >> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> >> +%YAML 1.2
> >> +---
> >> +$id: http://devicetree.org/schemas/cpufreq/apple,cluster-cpufreq.yaml#
> >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> >> +
> >> +title: Apple SoC cluster cpufreq device
> > 
> > Few nits, in general looks fine to me.
> > 
> >> +
> >> +maintainers:
> >> +  - Hector Martin <marcan@...can.st>
> >> +
> >> +description: |
> >> +  Apple SoCs (e.g. M1) have a per-cpu-cluster DVFS controller that is part of
> >> +  the cluster management register block. This binding uses the standard
> >> +  operating-points-v2 table to define the CPU performance states, with the
> >> +  opp-level property specifying the hardware p-state index for that level.
> >> +
> >> +properties:
> >> +  compatible:
> >> +    oneOf:
> >> +      - items:
> >> +          - const: apple,t8103-cluster-cpufreq
> >> +          - const: apple,cluster-cpufreq
> >> +      - items:
> >> +          - const: apple,t6000-cluster-cpufreq
> >> +          - const: apple,t8103-cluster-cpufreq
> >> +          - const: apple,cluster-cpufreq
> >> +      - items:
> >> +          - const: apple,t8112-cluster-cpufreq
> > 
> > With the first one (t8103) - it's an enum.
> 
> This is deliberate. t6000 is compatible with t8103, but t8112 is not
> (though all are compatible with what the generic apple,cluster-cpufreq
> compatible implies).

What does compatible mean here? IOW, what can a client do with 
'apple,cluster-cpufreq' alone? It's one thing for self-contained blocks 
to remain unchanged from chip to chip, but things like this tend to 
change frequently. It looks like for 4 chips we have 3 different 
versions.

Rob