Raspberry Pi CPUFreq Driver & Other Power Management Work For Linux 5.3

The power management changes for Linux 5.3 merge window don't offer any P-State changes or other prominent Intel changes this cycle but there is some other improvements as well as new CPUFreq drivers for CPU frequency scaling.

Arguably the biggest Linux 5.3 power management change is the mainline addition of a CPUFreq driver for Raspberry Pi. This CPUFreq driver communicates with the firmware running on the dedicated processor responsible for clock adjustments. This firmware ends up making the final call on whether to honor requests for CPU clock changes based upon thermal and power criteria.

Also on the Arm front is a new CPUFreq driver for i.MX8M SoCs.

Some of the other PM work for Linux 5.3 includes better handling of shared ACPI power resources on PCI, other PCI bus type layer improvements, reworking of the hibernation handling code in ACPI core, extending the operating performance points (OPP) framework, and other fixes.

Power management maintainer Rafael Wysocki also submitted the ACPI changes to which there is now support for ACPI AC/battery drivers supported for non-x86, allowing the UEFI BGRT to be overriden via initrd or configfs, and other fixes.