> just to give you an update: I do have some code, but it is a bit messy,
> and it doesn't work well for ds2482 (the chip behind it still hangs up
> if I access it in parallel through i2c-dev). On top of that, it causes
> pretty significant slow-downs when accessing other devices on the same
> bus at the same time. Not surprising, I guess, since it expands the scope
> of the bus lock significantly.

Just to get a better idea: Did you try taking the adapter_lock before
the two SMBus command which needed to be concatenated (and use
smbus_xfer directly)?