Re: [PATCH v2] cpufreq/amd-pstate: Bail out early if !X86_FEATURE_HW_PSTATE

[Mario Limonciello <mario.limonciello@amd.com>]

On 7/20/26 00:14, K Prateek Nayak wrote:
> Hello Rong,
> 
> On 7/18/2026 8:45 PM, Rong Zhang wrote:
>> When booting a VM that simulates or passes-through a relatively new CPU
>> model, these warning messages are printed to kmsg:
>>
>>      amd_pstate: The CPPC feature is supported but currently disabled by the BIOS.
>>      Please enable it if your BIOS has the CPPC option.
> 
> This is message is printed from amd_cppc_supported() ...
> 
>>      amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled
>>
> 
> [..snip..]
> 
>> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
>> index a74a4cf99d22..877b4b30ecd0 100644
>> --- a/drivers/cpufreq/amd-pstate.c
>> +++ b/drivers/cpufreq/amd-pstate.c
>> @@ -2228,6 +2228,13 @@ static int __init amd_pstate_init(void)
>>   	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
>>   		return -ENODEV;
>>   
>> +	/*
>> +	 * Do not continue on the following checks and emit bogus warning
>> +	 * messages if the platform doesn't support frequency scaling at all.
>> +	 */
>> +	if (!cpu_feature_enabled(X86_FEATURE_HW_PSTATE))
>> +		return -ENODEV;
> 
> ... so why add this check in amd_pstate_init()?
> 
> I personally prefer having the check in amd_cppc_supported() and
> returning false from there with a pr_debug_once() saying processor does
> not support frequency scaling.
> 

FWIW I agree with Prateek here.

>> +
>>   	/* show debug message only if CPPC is not supported */
>>   	if (!amd_cppc_supported())
>>   		return -EOPNOTSUPP;
>>
>> ---
>> base-commit: 94515f3a7d4256a5062176b7d6ed0471938cd51a
>> change-id: 1cc24037-amd-pstate-vm-d6ab4c959bd3
>>
>> Thanks,
>> Rong
>>
>