[iam4722202468]

Yeah, this is still needed even with coreboot. The attiny isn't doing anything too complicated, it's just there to tell the laptop the status of the battery. In the testing I did, if you supply 12v without any of the SMBus stuff the laptop will shut off after a few minutes of use.

I'm actually looking in to making a slice battery, it should be possible but sourcing the docking connector seems to be much harder than getting the battery connector.

[castratikron]

Would it be possible to write directly to /dev/i2c in Linux and spoof the messages? Not sure what the use case of this would be, but might be useful for something.

[iam4722202468]

Yep definitely, I had this exact thought last night and found an example kernel module to spoof a battery, and one to read i2c messages. There's probably all kinds of cool things you can do with a kernel module to communicate between the laptop's i2c port and a microcontroller. The docking connector conveniently has an i2c port on it, maybe I'll look in to this in the future