Turning TSO off at netdev registration time with a warning will be a
cleaner IMO. Or alternatively introducing a kernel-config "I know what

You mean the qdisc should force TSO off on the underlying device? 

TSO is" option which is then used at netdev registration. From a
usability perspective it would make more sense to just keep ethtool as
the only way to configure TSO. 

Ok, reasonable point.

-Andi