power: supply: macsmc: support charge_behaviour on newer SMC firmware

[IntegralPilot]

Newer Apple SMC firmware (found on M3 devices and updated M1/M2) has removed the legacy CH0C (Inhibit Charge) and CH0I (Force Discharge) keys. Reading these missing keys results in -EIO (-5) errors, causing the charge_behaviour sysfs property to fail completely.

This patch adds support for the new CHTE key used for charge inhibition on these devices.

For now, it seems that auto and inhibit-charge are the only possible behaviours to set using this new key, however further macOS tracing may reveal additional behaviour states in future.

Changes:

1. Detects the presence of CHTE, CH0C, and CH0I during probe.
2. Only exposes force_discharge capability if CH0I is actually present.
3. Implements read/write support for CHTE using raw byte buffers (this is to avoid endianness issues with the kernel's u32 helpers)

Fully backwards compatible with both old and new firmwares. Tested on M3 with new firmware.

[IntegralPilot]

Oh sorry just realised there's an unrelated 2-line whitespace change in macsmc_log_power_ops, that was caused by check patch.pl --fix so probably is the correct whitespace, although I can undo this change if you'd like as it's not related to the patch.

[IntegralPilot]

Just moved a comment to a more logical place.

[nukelet]

thanks a ton for looking into this issue! i upgraded MacOS earlier today and was extremely disappointed to find out about this regression.

this patch does fix the -EIO error when reading from charge-behavior for me, but it seems that uevent is broken (the sysfs file reads empty). i can try looking into this later today if you don't have the time

[IntegralPilot]

Thank you for testing this out! I can't reproduce the uevent issue on M3 sorry, it is working fine for me. Can you please check if this patch introduced uevent issues, or if they occurred before it?

[nukelet]

somehow the error seems to be gone now. i did find out that i was loading the wrong device trees due to a minor corner case in my distro's kernel install hooks, but i haven't fixed the issue and yet the empty read on uevent issue seems to be gone; i wonder if it's somehow transient due to some firmware weirdness? i'm testing on a t8103-j293 (macbook pro m1 13''), fwiw.

either way, it seems to be working fine now. thanks again for looking into this!

[hexchain]

Tested on 16-inch M2 Pro 2023. Before applying this patch, setting the charge threshold is flaky, and there are a lot of the following logs:

kernel: power_supply macsmc-battery: driver failed to report `charge_behaviour' property: -5

These are all gone now. Thanks for working on this!

[IntegralPilot]

I sent this driver upstream, including this and other improvements: https://lore.kernel.org/asahi/20260105-b4-macsmc-power-v1-0-62954c42a555@gmail.com, though it will probably take several weeks of review, then several weeks for it to land here, so I'll leave this open in case anyone wants just the charge_behaviour patch so optimised charging works, though feel free to close if it's better to wait for upstream.

Happy to help, it was fun reverse engineering to find out how to fix this.