[$] DMA addresses for UIO
The Userspace
I/O (UIO) subsystem was first https://git.kernel.org/linus/beafc54c4e2f
by
Hans J. Koch for the 2.6.32 release in 2007. Its purpose is to facilitate
the writing of drivers (mostly) in user space; to that end, it provides
access to a number of resources that user-space code normally cannot touch.
One piece that is missing, though, is DMA addresses. A proposal to
fill that gap from Bastien Curutchet is running into some opposition,
though.