linux-kernel - Re: [PATCH v4] ACPI: cpufreq: use a platform device to load ACPI PPC and PCC drivers

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Message-ID: <ZFreh8SDMX67EaB6@kevinlocke.name>
Date:   Tue, 9 May 2023 18:00:07 -0600
From:   Kevin Locke <kevin@...inlocke.name>
To:     Petr Pavlu <petr.pavlu@...e.com>
Cc:     rafael@...nel.org, lenb@...nel.org, viresh.kumar@...aro.org,
        pmladek@...e.com, mcgrof@...nel.org, linux-acpi@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] ACPI: cpufreq: use a platform device to load ACPI PPC
 and PCC drivers

On Thu, 2023-03-16 at 16:10 +0100, Petr Pavlu wrote:
> The patch extends the ACPI parsing logic to check the ACPI namespace if
> the PPC or PCC interface is present and creates a virtual platform
> device for each if it is available. The acpi-cpufreq and pcc-cpufreq
> drivers are then updated to map to these devices.
> 
> This allows to try loading acpi-cpufreq and pcc-cpufreq only once during
> boot and only if a given interface is available in the firmware.

As a result of this patch (691a637123470bfe63bccf5836ead40fac4c7fab)
my ThinkPad T430 with an i5-3320M CPU configured with
CONFIG_X86_INTEL_PSTATE=y and CONFIG_X86_ACPI_CPUFREQ=m (Debian's
amd64 kernel config) now logs

kernel: acpi-cpufreq: probe of acpi-cpufreq failed with error -17

during boot.  Presumably this occurs because loading acpi-cpufreq
returns -EEXIST when intel-pstate is already loaded (or built-in, as
in this case).  I'm unsure why the message was not printed before;
perhaps a difference between driver probing for platform and cpu bus
types?  Although the error message is not wrong, it may lead to
unnecessary investigation by sysadmins, as it did for me.  I thought
it was worth reporting so you can consider whether the change is
desirable.

Cheers,
Kevin