[coldtea]

>what is so complicated about writing device drivers, whose sole purpose typically is to transport data from input to output, and vice versa?

What you ask if valid, and very true, but for cable construction, not driver writing.

There are tons of protocols and issues to handle when designing a device driver. Negotiate device capabilities. Handle hot plugging and unplugging. Handle intermittent state changes in the device. Handle buffering. Handle different versions of the protocol (or multiple protocols from the same bus). Handle throttling. Initialize and configure the device correctly (and infinite variations of devices from different vendors with perhaps slight or big inconsistencies in their implementation).

And of course device drivers are not just about I/O.

[JoeAltmaier]

Add discovery, error handling, system resource allocation(dma, memory, interrupts, pins, clocks and timers).