Intel Comet Lake Added To RAPL Driver With Linux 5.5, New "HMEM" Driver

The ACPI and power management updates were sent in back on Tuesday for the Linux 5.5 kernel and punctually landed in the mainline tree.

The Linux 5.5 power management code doesn't bring any big changes on the Intel or AMD front this round, but there is Comet Lake mobile and desktop IDs added to the Intel RAPL (Run-time Average Power Limiting) driver used for scaling back the power-limit as well as monitoring it. That's about it with no big CPUfreq or P-State changes, including nothing to report on the AMD CPPC front for newer processors.

The other power management and ACPI work for Linux 5.5 includes:

- Switching from microseconds to nanoseconds for the CPU idle core handling. The idle injection infrastructure can now handle the durations in nanoseconds as well as allowing an exit latency limit.

- Various updates to the smaller ARM/embedded CPUFreq drivers.

- The aforementioned CPU IDs for Intel Comet Lake mobile and desktop within their power-capping driver.

- The ACPI tree meanwhile has the new HMEM driver with support for EFI specific purpose memory (like Intel Optane DC Persistent Memory) to allow either application-exclusive or core kernel memory management access to these specialized memory pools.

- Improved ACPI device enumeration for some Intel Bay Trail platforms.

More details via the PM pull and ACPI pull.