Kernel module to connect ps/2 keyboard to usb?
Is it technically possible to write a kernel module to physically connect a PS/2 keyboard to a USB port using a passive converter? If not, why?
(If I simply wanted my keyboard to work I would buy an active adapter, but the purpose of this question is to learn something)
No.
No USB standard implements backwards compatibility with PS/2. PS/2 mice which predate USB do not contain time-travelled USB descriptors. Nor can an arbitrary USB port be accessed as a GPIO.
USB descriptors: https://blog.digital-scurf.org/posts/stm32-and-rtfm/
https://en.wikipedia.org/wiki/Gpio & https://en.wikipedia.org/wiki/Bit_banging
(Wiki links aren’t going to be great, but the introductions here should give the idea).
Converting the opposite way round, passive USB to PS/2 converters require USB support in the USB input device, and recent USB devices don’t bother with it: https://en.wikipedia.org/wiki/PS/2_port#Conversion_between_PS.2F2_and_USB
Enabling "legacy usb" in BIOS let’s you use passive USB/PS2 (pin to pin) converters. And they work on windows.
I’ve never tried with linux though.