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.Dd August 29, 2019
.Dt NTB 4
.Os
.Sh NAME
.Nm ntb
.Nd Non-Transparent Bridge subsystem
.Sh SYNOPSIS
To compile it into your kernel,
place the following lines in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ntb"
.Ed
.Pp
Or, to load it as a module at boot, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
ntb_load="YES"
.Ed
.Pp
The following tunables are settable from the
.Xr loader 8 :
.Bl -ohang
.It Va hw.ntb.debug_level
Driver debug level.
The default value is 0, higher means more verbose.
.It Va hint.ntb_hw. Ns Ar X Ns Va .config
Configures a set of NTB functions, separated by commas,
and their resource allocation.
Each function can be configured as: "[<name>][:<mw>[:<spad>[:<db>]]]", where:
.Va name
is a name of the driver to attach (empty means any),
.Va mw
is a number of memory windows to allocate (empty means all available),
.Va spad
is a number of scratchpad registers to allocate (empty means all available),
.Va db
is a number of doorbells to allocate (empty means all available).
The default configuration is empty string, which means single function
with all available resources, allowing any driver to attach.
.El
.Sh DESCRIPTION
Non-Transparent Bridges connect two computer systems with PCIe
link(s), providing each of them limited access to others memory space,
scratchpad registers and interrupts.
The
.Nm
subsystem uses those resources provided in generic way by hardware drivers
and splits them between several functions, according to specified
configuration.
.Sh SEE ALSO
.Xr if_ntb 4 ,
.Xr ntb_hw_amd 4 ,
.Xr ntb_hw_intel 4 ,
.Xr ntb_hw_plx 4 ,
.Xr ntb_transport 4
.Sh AUTHORS
.An -nosplit
The
.Nm
subsystem 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 .