I've tried to make it all generic enough that non-Intel NTBs should plug in with
minimal changes to ntb_hw.c.  If their design is too divergent, then a slight
redesign of ntb_hw.c might be necessary.  But from what I've seen of other
designs on the internet, they appear to be extremely similar.  The transport and
client drivers were written with the hardware abstracted away as much as
possible to prevent the need to modify it for different hardware.  If there is
anything which is Intel hardware specific, I'd be happy to change it to make it
more generic.

  In ntb_process_tx(), ntb uses hard-coding 'memcpy_toio' to copy data
to remote.
  Is it better to provide a function pointer like 'tx()' and call qp->tx().
  memcpy_toio is a slow operation. Some hardware can setup a dma
transfer and wait.

  IMHO, the best way is to handle tx in async mode. But it requires
lots of modification.