linux-kernel - Re: [PATCH v3 4/5] cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states

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Message-ID: <3d4536c9-4b3b-8312-4868-5e5b42a87424@marcan.st>
Date:   Wed, 9 Nov 2022 21:13:33 +0900
From:   Hector Martin <marcan@...can.st>
To:     Marc Zyngier <maz@...nel.org>
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 4/5] cpufreq: apple-soc: Add new driver to control
 Apple SoC CPU P-states

On 24/10/2022 17.27, Marc Zyngier wrote:
> On Mon, 24 Oct 2022 05:39:24 +0100,
> Hector Martin <marcan@...can.st> wrote:
>>
>> This driver implements CPU frequency scaling for Apple Silicon SoCs,
>> including M1 (t8103), M1 Max/Pro/Ultra (t600x), and M2 (t8112).
>>
>> Each CPU cluster has its own register set, and frequency management is
>> fully automated by the hardware; the driver only has to write one
>> register. There is boost frequency support, but the hardware will only
>> allow their use if only a subset of cores in a cluster are in
>> non-deep-idle. Since we don't support deep idle yet, these frequencies
>> are not achievable, but the driver supports them. They will remain
>> disabled in the device tree until deep idle is implemented, to avoid
>> confusing users.
>>
>> This driver does not yet implement the memory controller performance
>> state tuning that usually accompanies higher CPU p-states. This will be
>> done in a future patch.
>>
>> Signed-off-by: Hector Martin <marcan@...can.st>
>> ---
>>  drivers/cpufreq/Kconfig.arm          |   9 +
>>  drivers/cpufreq/Makefile             |   1 +
>>  drivers/cpufreq/apple-soc-cpufreq.c  | 352 +++++++++++++++++++++++++++
>>  drivers/cpufreq/cpufreq-dt-platdev.c |   2 +
>>  4 files changed, 364 insertions(+)
>>  create mode 100644 drivers/cpufreq/apple-soc-cpufreq.c
>>
> 
> [...]
> 
>> +static struct freq_attr *apple_soc_cpufreq_hw_attr[] = {
>> +	&cpufreq_freq_attr_scaling_available_freqs,
>> +	NULL,
>> +	NULL,
> 
> nit: extra NULL?

That slot gets filled in later if boost is enabled, hence the need for
an extra terminating NULL in that case.

- Hector