linux-kernel - Re: 回复: [PATCH RESENT] cpufreq: amd-pstate: add quirk for Ryzen 3000 series processor

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Message-ID: <ZsbT3WIkz5kTpfXx@BLRRASHENOY1.amd.com>
Date: Thu, 22 Aug 2024 11:29:57 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: David Wang <00107082@....com>
Cc: "Du, Xiaojian" <Xiaojian.Du@....com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"Limonciello, Mario" <Mario.Limonciello@....com>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"Huang, Ray" <Ray.Huang@....com>,
	"Petkov, Borislav" <Borislav.Petkov@....com>,
	"Huang, Shimmer" <Shimmer.Huang@....com>,
	"Meng, Li (Jassmine)" <Li.Meng@....com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Yuan, Perry" <Perry.Yuan@....com>
Subject: Re: 回复: [PATCH RESENT] cpufreq: amd-pstate: add quirk for Ryzen 3000 series processor

Hello David,

On Thu, Aug 22, 2024 at 01:43:12PM +0800, David Wang wrote:
> Hi, 
> >
> Thanks for the information.   (I did change my BIOS's CPPC config from "auto" to "enable", but error message still.)
> But according to   another mail from gautham.shenoy@....com,  my understanding is that my CPU(AMD Ryzen 3 3100 4-Core Processor) does not have this CPPC feature,  would upgrade my BIOS really help?
> ```

To clarify,

There are two ways in which the OS can communicate its CPPC
requirements with the platform firmware.

1. Via the following CPPC MSRs

#define MSR_AMD_CPPC_CAP1		0xc00102b0
#define MSR_AMD_CPPC_ENABLE		0xc00102b1
#define MSR_AMD_CPPC_CAP2		0xc00102b2
#define MSR_AMD_CPPC_REQ		0xc00102b3
#define MSR_AMD_CPPC_STATUS		0xc00102b4

2. Via the shared memory mechanism.

The presence of the CPPC MSRs is indicated via X86_FEATURE_CPPC (CPUID
0x80000008.EBX[27]). If available, the amd-pstate driver prefers that
over the shared-memory mechanism.

So the the following warning are intended only for platforms that are
known to have the MSR support, not for the platforms which don't have
the MSR support.

"The CPPC feature is supported but currently disabled by the BIOS.
Please enable it if your BIOS has the CPPC option"

Your platform has CPPC feature (evident from the fact that amd-pstate
worked for you with the BIOS quirk patch), and the amd-pstate driver can
work just as well using the shared-memory mechanism (2 above) as long
as your BIOS supports CPPC v3 (which advertises the nominal frequency
in addition to the nominal perf).

The current version of the BIOS that you are running doesn't seem to
support CPPC v3, which is why the amd-pstate driver won't work
out-of-box. This is why Xiaojian recommended upgrading the BIOS to the
latest version.

> 
> Anyway, I will give BIOS upgrading  a try.

Please do!

> 
> >If this issue is fixed in BIOS, no need to modify the upstream kernel code, right?
> 
> I think , even when upgrading BIOS would not help, the quirk just for my system is not worth be in kernel :)......
>

Fair point. However, in case you prefer to use amd-pstate, know that
this is one way of enabling it, if the BIOS upgrade doesn't help.

> 
> Thanks
> David

--
Thanks and Regards
gautham.