Asahi Linux Releases Progress Report for Linux 7.2, Details Apple Silicon Power Management

Linux 7.2 Progress Report

Asahi Linux has released a progress report for Linux 7.2, detailing ongoing development efforts. The report primarily focuses on the technical challenges encountered while adapting Linux to run on Apple Silicon hardware, particularly concerning power management.

Apple Silicon Power Management Complexity

The Apple Silicon platform features a complex power management infrastructure, distributing responsibilities across multiple hardware blocks such as the SMC, PMGR, and PMP. These components are crucial for managing power consumption, with the application cores themselves posing a significant obstacle to improving battery life.

CPU Core Sleep Modes

CPU cores can enter various sleep states to conserve power. The basic Wait For Interrupt (WFI) instruction stops code execution but keeps the core powered. Apple cores include a "deep" WFI mode that shuts down more of the core, losing its state. Asahi's cpuidle driver utilizes this deep WFI mode by saving the core's state before entering the WFI loop.

PSCI Requirement for Upstreaming

The Linux kernel's arm64 architecture maintainers mandate the use of the Power State Coordination Interface (PSCI) for all upstream hardware power management. PSCI provides a standard interface for operating systems to interact with system firmware for CPU core power management functions. Due to this requirement, Asahi Linux's Apple-specific cpuidle driver cannot be upstreamed into the main Linux kernel.