> I thought as much, but maybe there is some driver which can offload
> whole i2c_transfer to HW, and has to pass the addresses of the buffers
> to the HW, and the HW can have problems if the buffers overlap
> somewhere...

Well, sure, you can never know what crazy HW is out there :) But that
shouldn't prevent us from doing legit I2C transfers. The likeliness of
such HW is low enough; They must process the whole transfer in one go
(rare) AND have the limitiation with the buffer pointers (at least I
don't know one) AND have no possibility of a fallback to a simpler mode
where they can handle the transfer per message. If such a controller
exists, it would need a new quirk flag, I'd say, and reject the
transfer. But that shouldn't stop you from fixing your issue.

Thanks for thinking thoroughly about drawbacks! Much appreciated.