Any comments?

Generic comments.  Could you use *_compat instead of  *_old_*?
Another idea is do not touch current interface, just append new
function and associated structure to make a smooth transition of the
userspace stuff.

What about documentation (Documentation/hid/uhid.txt)? Could you
update it acordingly?

Subject: [PATCH] uhid: introduce new create event to fix 32/64-bit
 compatibility issue

Current create event has pointer in payload. It causes problem with
32/64-bit compatibility. In particular it's not possible to use 32-bit
userspace driver with 64-bit kernel.

This patch deprecates old create event and introduce a new one. The new
create event has padding for pointer on 32-bit system to extend pointer
correctly.

Old userspace driver binaries will use old create event. It requires
simple recompile to switch to new one.

That's what I afraid of. Better to try to avoid any excessive
requirement to the existing userspace.

-- 
With Best Regards,
Andy Shevchenko