linux-kernel - Re: [PATCH v3 10/11] cpufreq: amd-pstate: Add documentation for `amd_pstate_hw

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Message-ID: <f2ae5b0e-9864-45c1-a5a8-d968909ec247@amd.com>
Date: Tue, 10 Sep 2024 11:36:03 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Russell Haley <yumpusamongus@...il.com>,
 Mario Limonciello <superm1@...nel.org>,
 "Gautham R . Shenoy" <gautham.shenoy@....com>,
 Perry Yuan <perry.yuan@....com>
Cc: Borislav Petkov <bp@...en8.de>,
 "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
 <linux-kernel@...r.kernel.org>, "open list:ACPI"
 <linux-acpi@...r.kernel.org>,
 "open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3 10/11] cpufreq: amd-pstate: Add documentation for
 `amd_pstate_hw_prefcore`

On 9/10/2024 05:19, Russell Haley wrote:
> On 9/5/24 11:30 AM, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@....com>
>>
>> Explain that the sysfs file represents both preferred core being
>> enabled by the user and supported by the hardware.
>>
>> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>> v2->v3:
>>   * Add tag
>> ---
>>   Documentation/admin-guide/pm/amd-pstate.rst | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
>> index e13915c540648..d5c050ea390dc 100644
>> --- a/Documentation/admin-guide/pm/amd-pstate.rst
>> +++ b/Documentation/admin-guide/pm/amd-pstate.rst
>> @@ -263,6 +263,11 @@ lowest non-linear performance in `AMD CPPC Performance Capability
>>   <perf_cap_>`_.)
>>   This attribute is read-only.
>>   
>> +``amd_pstate_hw_prefcore``
>> +
>> +Whether the platform supports the preferred core feature and it has been
>> +enabled. This attribute is read-only.
>> +
>>   ``energy_performance_available_preferences``
>>   
>>   A list of all the supported EPP preferences that could be used for
> 
> I notice I am confused. If the attribute is read only, how can it be
> enabled by the user?

It is enabled by default.  It can be disabled by the user via the kernel 
command line:

amd_prefcore=disable

This is documented separately in kernel-parameters.txt.