quoted

If SCL is stuck low, how do you want to send a STOP?

Fair point. I should probably drop that in the future and just do a
reset, and even then, doing a
reset is probably just wishful thinking. If a slave is holding down
SCL, we are pretty screwed.

Yes, you'd need to reset the client device. And that has to be done in
the client driver. I wonder if i2c_transfer and friends should return a
specific error value in that case... need to think about it.