NTB_HW_INTEL(4)        FreeBSD Kernel Interfaces Manual        NTB_HW_INTEL(4)

NAME
     ntb_hw_intel - Intel(R) Non-Transparent Bridge driver

SYNOPSIS
     To compile this driver into your kernel, place the following lines in
     your kernel configuration file:

           device ntb
           device ntb_hw_intel

     Or, to load the driver as a module at boot, place the following line in
     loader.conf(5):

           ntb_hw_intel_load="YES"

DESCRIPTION
     The ntb_hw_intel driver provides support for the Non-Transparent Bridge
     (NTB) hardware in Intel Xeon E3/E5 and S1200 processor families, which
     allow one of their PCIe ports to be switched from transparent to non-
     transparent bridge mode.  In this mode the bridge looks not like a PCI
     bridge, but like a PCI endpoint device.  The driver hides hardware
     details, exposing memory windows, scratchpads and doorbells of the other
     side via a hardware independent KPI to the ntb(4) subsystem.

     The hardware provides 2 or 3 memory windows to the other system's memory,
     16 scratchpad registers and 14, 31 or 34 doorbells to interrupt the other
     system, depending on the platform.  On Xeon processors one of the memory
     windows is typically consumed by the driver itself to work around
     multiple hardware errata.

CONFIGURATION
     The NTB configuration should be set by BIOS.  It includes enabling NTB,
     choosing between NTB-to-NTB (back-to-back) or NTB-to-Root Port mode,
     enabling split BAR mode (one of two 64-bit BARs can be split into two
     32-bit ones) and configuring BAR sizes in bits (from 12 to 29/39) for
     both NTB sides.

     The recommended configuration is NTB-to-NTB mode, split bar enabled and
     all BAR sizes set to 20 (1 MiB).  This needs to be done on both systems.
     Note, on Xeon SkyLake and newer platforms, split bar mode is not
     available.

SEE ALSO
     if_ntb(4), ntb_transport(4), ntb(4),

AUTHORS
     The ntb_hw_intel driver was developed by Intel and originally written by
     Carl Delsey <carl@FreeBSD.org>.  Later improvements were done by Conrad
     E. Meyer <cem@FreeBSD.org> and Alexander Motin <mav@FreeBSD.org>.

BUGS
     NTB-to-Root Port mode is not yet supported, but it doesn't look very
     useful.

     On Xeon v2/v3/v4 processors split BAR mode should be enabled to allow
     SB01BASE_LOCKUP errata workaround to be applied by the driver.

     There is no way to protect your system from malicious behavior on the
     other system once the link is brought up.  Anyone with root or kernel
     access on the other system can read or write to any location on your
     system.  In other words, only connect two systems that completely trust
     each other.

FreeBSD 13.1-RELEASE-p6        October 11, 2020        FreeBSD 13.1-RELEASE-p6