Linux 7.2 To Add ACPI CPPC v4 Support Authored By NVIDIA
Linux 7.2 is poised to introduce support for ACPI's version 4 standard of the Collaborative Processor Performance Control interface. CPPC v4 introduces a new OSPM nominal performance feature for the OS to indicate to the platform what is "nominal" performance as the threshold between any boost performance or below that being throttled for power/thermal needs. CPPC v4 also adds resource priority for communicating resource priority levels.
CPPC v4 (ACPI 6.6, Section 8.4.6) adds two optional entries to the _CPC package:
1. OSPM Nominal Performance (8.4.6.1.2.6): A write-only register that lets OSPM inform the platform what it considers nominal performance. The platform classifies performance above this level as boost and below as throttle for its power/thermal decisions.
2. Resource Priority (8.4.6.1.2.7): A Package of Resource Priority Register Descriptor sub-packages that allow OSPM to set relative priority among processors for shared resources (boost, throttle, L2/L3 cache, memory bandwidth). Parsing the full structure is not yet supported; such entries are marked as unsupported.
This patch adding the ACPI CPPC v4 support to the common cppc_acpi driver was authored by NVIDIA engineer Sumit Gupta. This patch had been floated on the Linux kernel mailing list going back to April. With that patch now being in the power management subsystem's linux-pm.git linux-next Git branch, it should be submitted as part of the PM material for the upcoming Linux 7.2 merge window.
This ACPI CPPC v4 support is among the work done by NVIDIA as part of their Vera CPU platform. Other hardware vendors using the common ACPI CPPC code and supporting the CPPC v4 specifications will also be able to benefit from this kernel addition.
6 Comments