Re: [PATCH v1] ACPI: CPPC: Drop two compliance checks involving nominal performance

[Christian Loehle <christian.loehle@arm.com>]

On 11/12/26 21:02, Rafael J. Wysocki (Intel) wrote:
> On Thu, Nov 12, 2026 at 9:55 PM Christian Loehle
> <christian.loehle@arm.com> wrote:
>>
>> On 11/12/26 17:42, Rafael J. Wysocki (Intel) wrote:
>>> On Thu, Nov 12, 2026 at 6:39 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>>>>
>>>> From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>>>>
>>>> On a number of Intel platforms in the field, the nominal performance
>>>> value in ACPI _CPC (which is an integer) is larger than the guaranteed
>>>
>>> I said "larger", but should have said "less".  Sorry about this.
>>>
>>> Will fix this when applying the patch unless there are other comments.
>>>
>>>> performance value and it may even be larger than the highest performance
>>>> value (that come from register reads).
>>>>
>>>> The new specification compliance checks involving those values added
>>>> by commit 32299b29a887 ("ACPI: CPPC: Validate _CPC entry and control
>>>> semantics") cause the CPPC library to refuse to work for some CPUs
>>>> on the affected systems which in turn causes the intel_pstate driver
>>>> to overestimate the maximum performance levels for those CPUs.  One
>>>> of the affected systems is Dell Pro 5 14 P514260.
>>>>
>>>> In this particular case, the fact that the specification is not
>>>> exactly followed has no implications and the checks enforcing
>>>> compliance are not useful, so drop them from the CPPC library.
>>>>
>>>> If really necessary, they will need to be done elsewhere.
>>
>> They would've made things a littler clearer but I don't see why
>> we strictly need them right now.
>>
>>>>
>>>> Fixes: 32299b29a887 ("ACPI: CPPC: Validate _CPC entry and control semantics")
>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>
>> Reviewed-by: Christian Loehle <christian.loehle@arm.com>
> 
> Thank you!
> 
> I will need to update the patch because the nom vs min_nonlinear check
> is also affected.
> 
> I'll send a v2 tomorrow with your R-by if that's OK.

All good!

> [snip]