Re: [PATCH] ACPI: CPPC: Add helper to get effective guaranteed performance

在 2026/5/29 23:33, srinivas pandruvada 写道:
> On Fri, 2026-05-29 at 16:18 +0800, Xueqin Luo wrote:
>> According to the ACPI CPPC specification, if the Guaranteed
>> Performance register is not implemented, OSPM assumes the
>> guaranteed performance is equal to nominal performance.
>>
>> Add cppc_get_effective_guaranteed_perf() helper to provide a
>> spec-compliant effective guaranteed performance value while
>> preserving the raw values returned by cppc_get_perf_caps().
>>
> Hi Luo,
>
> Are you trying to fix any issue where you have issue with
> "base_frequency" display? intel_pstate will revert to native MSR, which
> is always present when we are using CPPC.
>
> I worry about some bad nominal perf in some platforms as we will be
> dependent on OEM BIOS.
>
> Thanks,
> Srinivas
>
Thanks Srinivas.

The intent is not to fix any issue in intel_pstate. It already
implements the fallback correctly today.

My goal was to provide a common helper encapsulating the ACPI
CPPC semantics, with intel_pstate serving as the first user.
That said, I agree the benefit may not justify a new exported
helper at this point.
>> Signed-off-by: Xueqin Luo <[email protected]>
>> ---
>>   drivers/acpi/cppc_acpi.c       | 26 ++++++++++++++++++++++++++
>>   drivers/cpufreq/intel_pstate.c | 10 ++++------
>>   include/acpi/cppc_acpi.h       |  5 +++++
>>   3 files changed, 35 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index f370be8715ae..6dc11030707a 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1328,6 +1328,32 @@ int cppc_get_highest_perf(int cpunum, u64
>> *highest_perf)
>>   }
>>   EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
>>   
>> +/**
>> + * cppc_get_effective_guaranteed_perf - get effective guaranteed
>> performance
>> + * @cpunum: CPU number
>> + * @guaranteed_perf: Effective guaranteed performance value
>> + *
>> + * The ACPI CPPC specification states that if the Guaranteed
>> + * Performance register is not implemented, OSPM assumes the
>> + * guaranteed performance is equal to nominal performance.
>> + *
>> + * Return: 0 on success, negative errno on failure.
>> + */
>> +int cppc_get_effective_guaranteed_perf(int cpunum, u64
>> *guaranteed_perf)
>> +{
>> +	struct cppc_perf_caps perf_caps;
>> +	int ret;
>> +
>> +	ret = cppc_get_perf_caps(cpunum, &perf_caps);
>> +	if (ret)
>> +		return ret;
>> +	*guaranteed_perf = perf_caps.guaranteed_perf ?:
>> +			   perf_caps.nominal_perf;
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(cppc_get_effective_guaranteed_perf);
>> +
>>   /**
>>    * cppc_get_epp_perf - Get the epp register value.
>>    * @cpunum: CPU from which to get epp preference value.
>> diff --git a/drivers/cpufreq/intel_pstate.c
>> b/drivers/cpufreq/intel_pstate.c
>> index 8dc22a65e025..8934e48f71a2 100644
>> --- a/drivers/cpufreq/intel_pstate.c
>> +++ b/drivers/cpufreq/intel_pstate.c
>> @@ -404,17 +404,15 @@ static void intel_pstate_set_itmt_prio(int cpu)
>>   
>>   static int intel_pstate_get_cppc_guaranteed(int cpu)
>>   {
>> -	struct cppc_perf_caps cppc_perf;
>> +	u64 guaranteed_perf;
>>   	int ret;
>>   
>> -	ret = cppc_get_perf_caps(cpu, &cppc_perf);
>> +	ret = cppc_get_effective_guaranteed_perf(cpu,
>> &guaranteed_perf);
>> +
>>   	if (ret)
>>   		return ret;
>>   
>> -	if (cppc_perf.guaranteed_perf)
>> -		return cppc_perf.guaranteed_perf;
>> -
>> -	return cppc_perf.nominal_perf;
>> +	return guaranteed_perf;
>>   }
>>   
>>   static int intel_pstate_cppc_get_scaling(int cpu)
>> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
>> index d1f02ceec4f9..c02f3bc1fc1a 100644
>> --- a/include/acpi/cppc_acpi.h
>> +++ b/include/acpi/cppc_acpi.h
>> @@ -155,6 +155,7 @@ struct cppc_cpudata {
>>   extern int cppc_get_desired_perf(int cpunum, u64 *desired_perf);
>>   extern int cppc_get_nominal_perf(int cpunum, u64 *nominal_perf);
>>   extern int cppc_get_highest_perf(int cpunum, u64 *highest_perf);
>> +extern int cppc_get_effective_guaranteed_perf(int cpunum, u64
>> *guaranteed_perf);
>>   extern int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs
>> *perf_fb_ctrs);
>>   extern int cppc_get_perf(int cpu, struct cppc_perf_ctrls
>> *perf_ctrls);
>>   extern int cppc_set_perf(int cpu, struct cppc_perf_ctrls
>> *perf_ctrls);
>> @@ -198,6 +199,10 @@ static inline int cppc_get_highest_perf(int
>> cpunum, u64 *highest_perf)
>>   {
>>   	return -EOPNOTSUPP;
>>   }
>> +static inline int cppc_get_effective_guaranteed_perf(int cpunum, u64
>> *guaranteed_perf)
>> +{
>> +	return -EOPNOTSUPP;
>> +}
>>   static inline int cppc_get_perf_ctrs(int cpu, struct
>> cppc_perf_fb_ctrs *perf_fb_ctrs)
>>   {
>>   	return -EOPNOTSUPP;