linux-kernel - Re:Re: [Regression] 6.11.0-rc1: AMD CPU boot with error when CPPC feature disabled by BIOS

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Message-ID: <51a44058.3913.19106dea781.Coremail.00107082@163.com>
Date: Wed, 31 Jul 2024 11:39:00 +0800 (CST)
From: "David Wang" <00107082@....com>
To: "Xiaojian Du" <xiaojidu@....com>
Cc: perry.yuan@....com, Alexander.Deucher@....com, Li.Meng@....com, 
	Mario.Limonciello@....com, Xiaojian.Du@....com, Xinmei.Huang@....com, 
	gautham.shenoy@....com, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, rafael.j.wysocki@...el.com, 
	viresh.kumar@...aro.org
Subject: Re:Re: [Regression] 6.11.0-rc1: AMD CPU boot with error when CPPC
 feature disabled by BIOS


At 2024-07-31 11:16:14, "Xiaojian Du" <xiaojidu@....com> wrote:
>
>On 2024/7/31 8:25, David Wang wrote:
>> Hi Du,
>>
>> Thanks for the quick response
>>
...
>>>
>>> Target system, including CPU+baseboard+BIOS, is supposed to enable and
>>> use CPPC feature for better Performance per Watt.
>> I agree that the warning guide makes total sense,  but  the  *errors* does not, why bother trying and report error when the feature is disabled by BIOS.
>>
>It has to do that.
>AMD strongly recommends users to enable this feature, but each OEM will 
>have customized BIOS, some support CPPC but disable by default,
>some support CPPC and enable by default, and some disable CPPC directly 
>without providing switch option.
>
>Since newer Linux kernel enables the amd-pstate driver by default, and 
>newer AMD Zen X CPU supports this feature,
>but user find that CPPC is not effective under their software and 
>hardware combination,
>if this driver does not try to load module and print no information, it 
>will mislead users that the problem is caused by the amd-pstate driver.
>
>Thanks,
>Xiaojian
>

I feel that you are arguing for the warning and the errors separately.
Separately,   I agree warning or error message make sense as you explained,  but together I feel confused:
Receiving a warning that CPPC feature is disable by BIOS already notify users that amd-pstate would not work, right?
Is it possible, that those two condition coexists: CPPC is disabled by BIOS, and  amd-pstate could function properly?


Thanks
David