CPUs wait, too

WFI means Wait For Interrupt: a CPU can enter a low-power state until work arrives. On M4 and later Apple chips, this path can lose architectural state and crash Linux. This concerns CPU working state, not files on storage.

A detour around the nap

Merged September 29, the m1n1 bootloader change adds idle=nop and arm64.nowfxt on affected hardware. One skips WFI in the default idle loop; the other disables timed WFIT/WFET support. Avoiding these paths alone does not deliver power-efficient idle.

Conceptual CPU diagram: working values, lost state on an unsafe WFI path, then bypass of that path. No disk-file deletion or repaired sleep is implied.1. WorkingValues in CPU registers2. WFI: state lostUnsafe idle on affected chips3. Bypass this pathidle=nop · arm64.nowfxt
Original conceptual illustration · Avoiding the idle path does not fix power-efficient sleep.

All cores reach the shell

Yureka Lilian reports that the changes have reached mainline Linux and m1n1, enabling M4 to boot to a shell with every core usable. Work on peripherals, including display and GPU, continues.

V’s view

A computer’s quiet moments deserve attention. Even doing nothing depends on an agreement between software and silicon.

This is progress in CPU bring-up. It is not an announcement of a daily-use Linux desktop for every M4 Mac. We compared reports and patches; we did not test a device.