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

[Gautham R.Shenoy <gautham.shenoy@amd.com>]

Hello David,

"David Wang" <00107082@163.com> writes:

> Hi,
>
> At 2024-07-31 18:12:12, "Gautham R.Shenoy" <gautham.shenoy@amd.com> wrote:
>>Hello David,
>>
>>David Wang <00107082@163.com> writes:
>>
>>> Hi,
>>>
>>> I notice some kernel warning and errors when I update to 6.11.0-rc1:
>>>
>>>  kernel: [    1.022739] amd_pstate: The CPPC feature is supported but currently disabled by the BIOS.
>>>  kernel: [    1.022739] Please enable it if your BIOS has the CPPC option.
>>>  kernel: [    1.098054] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.110058] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.122057] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.134062] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.134641] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.135128] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.135693] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.136371] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.136390] amd_pstate: failed to register with return -19
>>>  kernel: [    1.138410] ledtrig-cpu: registered to indicate activity on CPUs
>>>
>>>
>>> Those warning message was introduced by commit:
>>>  bff7d13c190ad98cf4f877189b022c75df4cb383 ("cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS)
>>> , which make sense.
>>
>>
>>If CPPC is disabed in the BIOS, then the _CPC objects shouldn't have
>>been created. And the error message that you should have seen is
>>"the _CPC object is not present in SBIOS or ACPI disabled".
>>
>>
>>Could you please share the family and model number of the platform where
>>you are observing this ?
>
> My `cat /proc/cpuinfo` shows something as following:
> processor	: 0
> vendor_id	: AuthenticAMD
> cpu family	: 23
> model		: 113


This is Family 0x17 (Zen2), Model 0x71. AFAIK, this processor supports
CPPC but does not have the support for the CPPC MSRs. Hence the CPPC
communication occurs via shared-memory.

Hence the warning introduced by the commit bff7d13c190a ("cpufreq:
amd-pstate: add debug message while CPPC is supported and disabled by
SBIOS") is not applicable on your platform. I will send a patch to
rectify this which avoids the warning for Zen2 Models 0x70-0x7F.

Regarding the following errors that you are observing 

>>>  kernel: [    1.098054] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.110058] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.122057] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.134062] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.134641] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.135128] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.135693] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.136371] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
>>>  kernel: [    1.136390] amd_pstate: failed to register with return -19


it appears that the CPPC version on your platform is v2 which does not
advertise the nominal_freq and the lowest_freq. In the absence of these,
it is not possible for the amd-pstate driver to infer the
min/max_freq. Which is why the driver bails at this later stage.

The way around it is to add a quirk for your BIOS as done in this commit
from Perry:
eb8b6c368202 ("cpufreq: amd-pstate: Add quirk for the pstate CPPC capabilities missing")


--
Thanks and Regards
gautham.