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.Dd November 9, 2019
.Dt NTB_TRANSPORT 4
.Os
.Sh NAME
.Nm ntb_transport
.Nd Packet-oriented transport for Non-Transparent Bridges
.Sh SYNOPSIS
To compile this driver into your kernel,
place the following lines in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ntb"
.Cd "device ntb_transport"
.Ed
.Pp
Or, to load the driver as a module at boot, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
ntb_transport_load="YES"
.Ed
.Pp
The following tunables are settable from the
.Xr loader 8 :
.Bl -ohang
.It Va hw.ntb_transport.debug_level
Driver debug level.
The default value is 0, higher means more verbose.
.It Va hw.ntb_transport.max_mw_size
Limits maximum memory window usage.
Allocation of big physically contiguous memory buffer may be a problem,
while too big buffers makes no much sense for low latency network interface.
.It Va hint.ntb_transport. Ns Ar X Ns Va .config
Configures a set of the transport consumers, separated by commas.
Each consumer can be configured as: "[<name>][:<queues>]", where:
.Va name
is a name of the driver to attach (empty means any),
.Va queues
is a number of queues to allocate (empty means automatic).
The default configuration is empty string, which means single consumer
with one queue per memory window, allowing any driver to attach.
.It Va hint.ntb_transport. Ns Ar X Ns Va .compact
Non-zero value enables compact version of scratchpad protocol, using half
as many registers.
Enabled automatically if there is not enough registers to negotiate all
available memory windows.
The compact version does not support memory windows of 4GB and above.
.El
.Sh DESCRIPTION
The
.Nm
driver attaches on top of the
.Nm ntb
driver to utilize its resources to create a set of bidirectional queues,
delivering packets between the systems.
The primary purpose of this driver is to be used by
.Nm if_ntb
network interface, but other consumers may also be developed using KPI.
.Pp
Each
.Nm
require from underlying
.Nm ntb
instance:
.Bl -bullet -compact
.It
1 or more memory windows;
.It
6 scratchpads, plus 2 more for each additional memory window,
or 3 plus 1 in case of compact protocol;
.It
1 doorbell for each memory window or configured queue.
.El
.Sh SEE ALSO
.Xr if_ntb 4 ,
.Xr ntb 4 ,
.Xr ntb_hw_amd 4 ,
.Xr ntb_hw_intel 4 ,
.Xr ntb_hw_plx 4
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was developed by Intel and originally written by
.An Carl Delsey Aq Mt carl@FreeBSD.org .
Later improvements were done by
.An Conrad E. Meyer Aq Mt cem@FreeBSD.org
and
.An Alexander Motin Aq Mt mav@FreeBSD.org .