Apple Silicon CPUFreq Driver Heading To Linux 6.2

Written by Michael Larabel in Apple on 7 December 2022 at 06:18 AM EST. 2 Comments
With the upcoming Linux 6.2 kernel cycle the Apple Silicon CPU frequency scaling driver is set to be mainlined for further improving the Apple M1/M2 SoC support on the mainline kernel.

Sent in yesterday were the Arm CPUFreq updates to queue in the Linux power management tree ahead of the Linux 6.2 merge window. Linux power management subsystem maintainer Rafael Wysocki has pulled these Arm driver updates, which most notably includes the new CPUFreq driver for Apple SoC CPU P-states handling.

This "apple-soc-cpufreq" driver implements CPU frequency scaling for Apple Silicon SoCs -- currently the M1, M1 Max/Pro/Ultra, and the M2.

Apple M2

Asahi Linux lead developer Hector Martin summed up the new Apple CPUFreq driver in the patch:
This driver implements CPU frequency scaling for Apple Silicon SoCs, including M1 (t8103), M1 Max/Pro/Ultra (t600x), and M2 (t8112).

Each CPU cluster has its own register set, and frequency management is fully automated by the hardware; the driver only has to write one register. There is boost frequency support, but the hardware will only allow their use if only a subset of cores in a cluster are in non-deep-idle. Since we don't support deep idle yet, these frequencies are not achievable, but the driver supports them. They will remain disabled in the device tree until deep idle is implemented, to avoid confusing users.

This driver does not yet implement the memory controller performance state tuning that usually accompanies higher CPU p-states. This will be done in a future patch.

The new driver is now in linux-pm.git's "linux-next" branch ahead of the Linux 6.2 merge window opening next week.
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