applesmc-next

Kernel patches that expose battery charge thresholds on Intel Apple laptops running Linux. Adds charge_control_end_threshold (and friends) to /sys/class/power_supply/BAT0/, mapping writes to the SMC BCLM key so the limit is stored in SMC NVRAM and survives reboots — even back into macOS.

This is the netlinux-ai fork of c---/applesmc-next. It carries fixes and packaging for recent Debian / Ubuntu kernels in addition to the upstream features.

What it does

Once the modules are loaded, the kernel battery exposes:

/sys/class/power_supply/BAT0/charge_control_end_threshold     # BCLM
/sys/class/power_supply/BAT0/charge_control_full_threshold    # BFCL (cosmetic)
/sys/class/power_supply/BAT0/charge_control_start_threshold   # stock kernel; not driven by BCLM

Writing an integer 20–100 to charge_control_end_threshold makes the SMC stop charging at that percentage. The setting is persistent in SMC NVRAM across reboots and operating systems unless the SMC is reset.

echo 80 | sudo tee /sys/class/power_supply/BAT0/charge_control_end_threshold

charge_control_full_threshold only controls when the charging LED turns green and is cosmetic. For it to work, set it at least 2% below the end threshold, because the battery floats slightly under its target.

What's in this fork

• Two-module DKMS package (applesmc-next-dkms) — replaces stock applesmc and sbs with patched copies in /lib/modules/.../updates/dkms/. AUTOINSTALL=yes means it rebuilds on every kernel upgrade.
• GitHub Actions that build .deb packages for Debian Bookworm and Ubuntu Resolute (26.04) on every release.
• Fix for kernels where sbshc is a platform_driver (notably the Ubuntu 7.0 kernel in Resolute). On those kernels the host controller pointer lives in the parent's platform device drvdata rather than its ACPI driver_data; without this fix the probe oopses on a NULL acpi_smb_hc pointer and the module is unrecoverable until reboot.
• TLP integration — drop 45-apple into /usr/share/tlp/bat.d/ for charge-threshold control via TLP profiles.

Install

From the .deb (Debian / Ubuntu)

Grab the .deb for your release from the releases page, then:

sudo apt install ./applesmc-next-dkms_*.deb

This pulls in dkms, builds and signs both modules against your running kernel, and installs them into /lib/modules/$(uname -r)/updates/dkms/. After install:

sudo modprobe -r applesmc sbs           # drop the stock modules
sudo modprobe sbs                       # load the patched sbs first
sudo modprobe applesmc                  # then applesmc (it hooks into sbs)
ls /sys/class/power_supply/BAT0/        # should now contain charge_control_*_threshold

From source (any distro)

sudo apt install dkms linux-headers-$(uname -r)
sudo git clone https://github.com/netlinux-ai/applesmc-next /usr/src/applesmc-next-0.1.6
sudo dkms add     -m applesmc-next -v 0.1.6
sudo dkms install -m applesmc-next -v 0.1.6

From the AUR (Arch)

applesmc-next-dkms on the AUR points at the original c---/applesmc-next upstream.

Use

Direct sysfs:

echo 80 | sudo tee /sys/class/power_supply/BAT0/charge_control_end_threshold
cat /sys/class/power_supply/BAT0/charge_control_end_threshold        # -> 80

To remove the limit, write 100.

With TLP

Copy 45-apple into TLP's plugin directory:

sudo install -Dm755 45-apple /usr/share/tlp/bat.d/45-apple

Then add the standard TLP keys to /etc/tlp.conf:

START_CHARGE_THRESH_BAT0=0      # not used; SMC BCLM has no start threshold
STOP_CHARGE_THRESH_BAT0=80

GUI

If you want a tray app to drive the same sysfs file, see netlinux-ai/battery-tray.

Kernel compatibility

Kernel	Status
6.1 – 6.17	builds against acpi_driver-based sbshc
6.18+ / Ubuntu 7.0 (Resolute)	builds against platform_driver-based sbshc — needs the fix in this fork
< 6.1	legacy device->parent lookup path

Tested on:

• MacBookPro9,2 (Ivy Bridge HD 4000) — Ubuntu 26.04, kernel 7.0.0-14-generic
• MacBookPro models with Smart Battery System (ACPI device SBS0 under SBSH)

Troubleshooting

• charge_control_end_threshold doesn't appear — patched modules aren't loaded. Check dkms status applesmc-next and modinfo sbs | head -1 (it should resolve to /lib/modules/.../updates/dkms/sbs.ko.zst, not the in-tree /kernel/drivers/acpi/sbs.ko.zst). If stock modules are still loaded, modprobe -r them and modprobe again.

• modprobe sbs returns 0 but BAT0 is missing — sbs probably hit -EPROBE_DEFER. Check sudo cat /sys/kernel/debug/devices_deferred — if ACPI0002:00 is parked there and you're on a recent kernel without this fork's fix, you need to update.

• Kernel oops with mutex_lock+0x1c and CR2: 0x0000000000000008 — this fork's commit history fixes exactly that. Pre-fix builds (0.1.6 and earlier) are unrecoverable without a reboot once they hit this.

• Writes to charge_control_full_threshold return I/O error — the BFCL SMC key doesn't exist on all models (e.g. MacBookPro9,2). The end threshold still works; full is cosmetic-only.

License

GPL-2.0 — see LICENSE.

Credits

• Original work by @c--- and contributors.
• Platform-driver / Ubuntu-Resolute fix and Debian/Ubuntu packaging by netlinux-ai.