Hopefully finishing my study of GRUB's terminal drivers...
On ARM machines there's a driver for initializing any "google,cros-ec-keyb" devices attached to the FDT bus. At which point it reads the keymap & validates (via a helper) the device, reformats the keymapping, & registers a corresponding driver with some flags set.
To read input it (via a helper) scans the keyboard, then iterates over the read columns XOR'd with the previous scan decoding scancodes & handing off to the PS/2 routines.
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