linux-kernel - Re: [PATCH v3 0/5] Apple SoC cpufreq driver

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Date:   Mon, 24 Oct 2022 09:28:50 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     "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>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.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 0/5] Apple SoC cpufreq driver

On Mon, 24 Oct 2022 05:39:20 +0100,
Hector Martin <marcan@...can.st> wrote:
> 
> Hi folks,
> 
> Third time's the charm? Here's v3 of the cpufreq driver for Apple SoCs.
> This version takes a page from both v1 and v2, keeping the dedicated
> cpufreq style (instead of pretending to be a clock controller) but using
> dedicated DT nodes for each cluster, which accurately represents the
> hardware. In particular, this makes supporting t6002 (M1 Ultra) a lot
> more reasonable on the DT side.
> 
> This version also switches to the standard performance-domains binding,
> so we don't need any more vendor-specific properties. In order to
> support this, I had to make the performance-domains parsing code more
> generic. This required a minor change to the only consumer
> (mediatek-cpufreq-hw).
> 
> The Linux driver probes based on platform compatible, and then attempts
> to locate the cluster nodes by following the performance-domains links
> from CPU nodes (this will then fail for any incompatible nodes, e.g. if
> a future SoC needs a new compatible and can't fall back). This approach
> was suggested by robh as the right way to handle the impedance mismatch
> between the hardware, which has separate controllers per cluster, and
> the Linux model where there can only be one CPUFreq driver instance.
> 
> Functionality-wise, there are no significant changes from v2. The only
> notable difference is support for t8112 (M2). This works largely the
> same as the other SoCs, but they ran out of bits in the current PState
> register, so that needs a SoC-specific quirk. Since that register is
> not used by macOS (it was discovered experimentally) and is not critical
> for functionality (it just allows accurately reporting the current
> frequency to userspace, given boost clock limitations), I've decided to
> only use it when a SoC-specific compatible is present. The default
> fallback code will simply report the requested frequency as actual.
> I expect this will work for future SoCs.
> 
> As usual, MAINTAINERS and DT changes are split. I expect patches #2~#4
> to go through the cpufreq tree, and we'll take care of #1 and #5 via
> the asahi-soc tree.
> 
> Hector Martin (5):
>   MAINTAINERS: Add entries for Apple SoC cpufreq driver
>   dt-bindings: cpufreq: apple,soc-cpufreq: Add binding for Apple SoC
>     cpufreq
>   cpufreq: Generalize of_perf_domain_get_sharing_cpumask phandle format
>   cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states
>   arm64: dts: apple: Add CPU topology & cpufreq nodes for t8103
> 
>  .../cpufreq/apple,cluster-cpufreq.yaml        | 119 ++++++
>  MAINTAINERS                                   |   2 +
>  arch/arm64/boot/dts/apple/t8103.dtsi          | 206 +++++++++-
>  drivers/cpufreq/Kconfig.arm                   |   9 +
>  drivers/cpufreq/Makefile                      |   1 +
>  drivers/cpufreq/apple-soc-cpufreq.c           | 352 ++++++++++++++++++
>  drivers/cpufreq/cpufreq-dt-platdev.c          |   2 +
>  drivers/cpufreq/mediatek-cpufreq-hw.c         |  14 +-
>  include/linux/cpufreq.h                       |  28 +-
>  9 files changed, 706 insertions(+), 27 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/cpufreq/apple,cluster-cpufreq.yaml
>  create mode 100644 drivers/cpufreq/apple-soc-cpufreq.c

FWIW, and for the whole series:

Acked-by: Marc Zyngier <maz@...nel.org>

	M.

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