# NTB Drivers

NTB (Non-Transparent Bridge) is a type of PCI-Express bridge chip that connects
the separate memory systems of two computers to the same PCI-Express fabric.
Existing NTB hardware supports a common feature set, including scratchpad
registers, doorbell registers, and memory translation windows.  Scratchpad
registers are read-and-writable registers that are accessible from either side
of the device, so that peers can exchange a small amount of information at a
fixed address.  Doorbell registers provide a way for peers to send interrupt
events.  Memory windows allow translated read and write access to the peer
memory.

## NTB Core Driver (ntb)

The NTB core driver defines an api wrapping the common feature set, and allows
clients interested in NTB features to discover NTB the devices supported by
hardware drivers.  The term "client" is used here to mean an upper layer
component making use of the NTB api.  The term "driver," or "hardware driver,"
is used here to mean a driver for a specific vendor and model of NTB hardware.

## NTB Client Drivers

NTB client drivers should register with the NTB core driver.  After
registering, the client probe and remove functions will be called appropriately
as ntb hardware, or hardware drivers, are inserted and removed.  The
registration uses the Linux Device framework, so it should feel familiar to
anyone who has written a pci driver.

## NTB Hardware Drivers

NTB hardware drivers should register devices with the NTB core driver.  After
registering, clients probe and remove functions will be called.