NTB_HW(4)

NAME
ntb, ntb_hw - 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_hw

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

    ntb_hw_load="YES"

The following tunables are settable from the loader(8):

hw.ntb.debug_level
Driver debug level. The default value is 0, higher means more verbose.

hint.ntb_hw.X.config
Configures NTB resources split between several consumer devices. Configuration of multiple consumer devices separated by commas. Each device can be configured as: "<name>[:<mw>[:<spad>[:<db>]]]", where: name is a name of the driver which should attach the device (empty means any), mw is a number of memory windows to allocate (empty means all available), spad is a number of scratchpad registers to allocate (empty means all available), db is a number of doorbells to allocate (empty means all available). The default configuration is empty string, which means single device with all available resources allowing any driver attachment.

DESCRIPTION
The NTB allows you to connect two computer systems using a PCIe link if they have the correct equipment and connectors. The ntb_hw driver provides support for the Non-Transparent Bridge (NTB) in the Intel S1200 and Xeon E3/E5 processor families. The ntb driver hides hardware details, exposing memory windows, scratchpads and doorbells via hardware independent KPI.

The hardware provides 2-3 memory windows to the other system's memory, 16 scratchpad registers and 14/34 doorbells to interrupt the other system. On Xeon processors one of memory windows is typically consumed by the driver to workaround multiple hardware erratas.

CONFIGURATION
The NTB configuration should be set by BIOS. It includes enabling NTB, choosing between NTB-to-NTB 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 is enabled and all BAR sizes are set to 20 (1 MiB). This needs to be done on both systems.

SEE ALSO
ntb_transport(4), if_ntb(4)

AUTHORS
-nosplit The ntb 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.