Awesome

Very simple, work in progress input driver for the SPI keyboard / trackpad found on 12" MacBooks (2015 and later) and newer MacBook Pros (late 2016 and later).

Using it:

If you're on any MacBook or MacBook Pro other than MacBook8,1 (2015), and you're running a kernel before 4.11, then you'll need to boot the kernel with intremap=nosid. In all cases make sure you don't have noapic in your kernel options.

On the 2015 MacBook you need to (re)compile your kernel with CONFIG_X86_INTEL_LPSS=n if running a kernel before 4.14. And on all kernels you need ensure the spi_pxa2xx_platform and spi_pxa2xx_pci modules are loaded too (if you don't have those module, rebuild your kernel with CONFIG_SPI_PXA2XX=m and CONFIG_SPI_PXA2XX_PCI=m).

On all other MacBook's and MacBook Pros you need to instead make sure both the spi_pxa2xx_platform and intel_lpss_pci modules are loaded (if these don't exist, you need to (re)compile your kernel with CONFIG_SPI_PXA2XX=m and CONFIG_MFD_INTEL_LPSS_PCI=m).

For best results everywhere, make sure all three modules (this applespi driver plus the two core ones mentioned above) are present in your initramfs/initrd so that the keyboard is functional by the time the prompt for the disk password appears. Also, having them loaded early also appears to remove the need for the irqpoll kernel parameter on MacBook8,1's.

DKMS module (Debian & co):

As root, do the following (all MacBook's and MacBook Pro's except MacBook8,1 (2015)):

echo -e "\n# applespi\napplespi\nspi_pxa2xx_platform\nintel_lpss_pci" >> /etc/initramfs-tools/modules

apt install dkms
git clone https://github.com/cb22/macbook12-spi-driver.git /usr/src/applespi-0.1
dkms install -m applespi -v 0.1

If you're on a MacBook8,1 (2015):

echo -e "\n# applespi\napplespi\nspi_pxa2xx_platform\nspi_pxa2xx_pci" >> /etc/initramfs-tools/modules

apt install dkms
git clone https://github.com/cb22/macbook12-spi-driver.git /usr/src/applespi-0.1
dkms install -m applespi -v 0.1

What works:

Basic Typing
FN keys
Driver unloading (no more hanging)
Basic touchpad functionality (even right click, handled by libinput)
MT touchpad functionality (two finger scroll, probably others)
Interrupts!
Suspend / resume

What doesn't work:

Key rollover (properly)
Wakeup on keypress / touchpad

Known bugs:

Occasionally, the SPI device can get itself into a state where it causes an interrupt storm. There should be a way of resetting it, or better yet avoiding this state altogether.

Interrupts:

Interrupts are now working! This means that the driver is no longer polled, and should no longer be a massive battery drain. For more information on how the driver receives interrupts, see the discussion here

Touchpad:

The touchpad protocol is the same as the bcm5974 driver. Perhaps there is a nice way of utilizing it? For now, bits of code have just been copy and pasted.

Debugging:

The debug module parameter can be used to turn debugging output on (and off) dynamically, and can be set in all the usual ways (e.g. via kernel command-line (applespi.debug=0x1), via sysfs (echo 0x10000 | sudo tee /sys/module/applespi/parameters/debug), etc.).

Some useful values are (since the value is a bitmask, these can be combined):

0x10000 - determine touchpad values range
0x1 - turn on logging of touchpad initialization packets
0x6 - turn on logging of backlight and caps-lock-led packets