NTB_HW_INTEL(4)

📦 version 15.1, in freebsd 14.5, freebsd 15.1, nixpkgs unstable

✨ NAME ✨

ntb_hw_intel — Intel(R) Non-Transparent Bridge driver. Okay bestie, welcome to NTB_HW_INTEL(4) from the Kernel Interfaces Manual — this is the Intel NTB page, and it's giving “hardware whisperer” energy fr fr. 🦋

🛠️ SYNOPSIS 🛠️

To compile this driver into your kernel, place these lines in your kernel configuration file:

device ntb
device ntb_hw_intel

Or, to load the driver as a module at boot, place this 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 way that hardware just changes its whole identity? Obsessed. 👑

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. It's literally the translator bestie between chaotic hardware and the NTB subsystem. Slay. 💅

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. Not me using a whole window for errata reasons 😭.

🎀 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)
  • 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. No cap — both sides gotta match, bestie, and that setup ate. 🫶

Note, on Xeon SkyLake and newer platforms, split bar mode is not available.

🔗 SEE ALSO 🔗

👑 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>. We love a collaborative glow-up ✨ — slay.

💀 BUGS 💀

NTB-to-Root Port mode is not yet supported, but it doesn't look very useful. Lowkey “we'll get to it” energy, but honestly it's not giving main character energy here. 🙈

On Xeon v2/v3/v4 processors split BAR mode should be enabled to allow SB01BASE_LOCKUP errata workaround to be applied by the driver. This is highkey important, iykyk. 🚨

Warning bestie: 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. Ngl, trust is the whole vibe check here. 💀

This cutie came from Debian, dated October 11, 2020 — periodt. 💅

📦 where this page comes from