linux-kernel - Re: [PATCH 3/3] cpufreq/amd-pstate: Remove warning for X86_FEATURE

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Message-ID: <ZsV+DI4IxQCSTWGY@BLRRASHENOY1.amd.com>
Date: Wed, 21 Aug 2024 11:11:32 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Xiaojian Du <xiaojidu@....com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Mario Limonciello <mario.limonciello@....com>,
	Huang Rui <ray.huang@....com>, Perry Yuan <perry.yuan@....com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
	David Wang <00107082@....com>
Subject: Re: [PATCH 3/3] cpufreq/amd-pstate: Remove warning for
 X86_FEATURE_CPPC on Zen1 and Zen2

Hello Xiaojian,

On Wed, Aug 14, 2024 at 05:29:04PM +0800, Xiaojian Du wrote:
> Hi Gautham,
> 
> On 2024/8/13 17:54, Gautham R. Shenoy wrote:
> > ...
> > 
> > This feature bit corresponds to CPUID 0x80000008.ebx[27] which is a
> > reserved bit on the Zen1 and Zen2 platforms, and is expected to be
> > cleared on these platforms. Thus printing the warning message for Zen1
> > and Zen2 models when X86_FEATURE_CPPC is incorrect. Fix this.
> > 
> > ...
> >   	if (!cpu_feature_enabled(X86_FEATURE_CPPC)) {
> > -		if (cpu_feature_enabled(X86_FEATURE_ZEN1) || cpu_feature_enabled(X86_FEATURE_ZEN2)) {
> > -			if (c->x86_model > 0x60 && c->x86_model < 0xaf)
> > -				warn = true;
> 
> Some models of ZEN2 APU/CPU require this warning info, like Renoir (Ryzen 7
> 4800H mobile APU/4750G desktop APU,
> Ryzen 5 4600 desktop CPU), Lucienne (Ryzen 5 5500U mobile APU) and Aerith
> (APU of Steam Deck console).
> 
> So it has to use model ID to narrow down the coverage.
> 

I checked the publicly available PPRs of the Family 17h models 0x60
(Renoir) [1] and Family 17h model 0x71 (Matisse) [2]. In both these
PPRs, CPUID 0x80000008 EBX[27] is a reserved bit.

In fact, David reported this issue on Matisse system.

I am happy to retain the warnings for specific models which are known
to have support for the CPPC MSRs (which is what CPUID 0x80000008
EBX[27] advertises). Could you please share the model numbers of those
that you are aware of?


[1] PPR Family 17h Model 0x60 : https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/55922-A1-PUB.zip
[2] PPR Family 17h Model 0x71 : https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/56176_ppr_Family_17h_Model_71h_B0_pub_Rev_3_06.zip

> For ZEN1 APU/CPU, this warning can be removed completely, because ZEN1
> doesn't support CPPC.

Agreed.

> 
> Thanks,
> Xiaojian

--
Thanks and Regards
gautham.