MEN Chameleon Bus (MCB) for industrial FPGA carrier boards
A bus subsystem that lets Linux enumerate and talk to FPGA-based I/O cores carried over MEN/duagon Chameleon Bus carriers, which sit on top of PCI or LPC. It is the glue used by rugged CompactPCI and embedded industrial boards from MEN Mikro Elektronik (now part of duagon) to expose their on-FPGA UARTs, GPIO, CAN, and similar function blocks to the kernel.
recommendation
Worth keeping but worth flagging as a niche industrial subsystem, because it serves a small audience of embedded and rugged-computing users rather than general Linux desktops or servers. The code is still actively maintained: a feature series in April 2026 expanded which PCI BARs MCB devices can register on, and a sanity-check fix was backported to stable in February 2026. duagon continues to sell the underlying CompactPCI hardware new in 2026, so the driver has both upstream attention and an ongoing commercial customer base.
repository signals
sources
- lore.kernel.org
An April 24, 2026 v3 series titled "mcb: enable register PCI devices using any BAR" shows active upstream feature work in this subsystem.
- lore.kernel.org
A February 25, 2026 stable backport of "mcb: fix incorrect sanity check" shows the code is still receiving bug fixes important enough for stable kernels.
- duagon.com
duagon still markets rugged CompactPCI industrial boards in 2026, indicating the surrounding MEN/duagon embedded hardware ecosystem remains commercially active.
- duagon.com
duagon advertises long-term availability for a current CompactPCI carrier product, supporting continued niche industrial deployments rather than total market disappearance.
codex reasoning notes (technical)
Local `rg`/Kconfig inspection shows this is a real bus driver for MEN FPGA devices over PCI/LPC, not a helper library. `lore_file_timeline` on `drivers/mcb/mcb-core.c` showed fresh 2025-2026 fixes including stable backports; `lore_regex` surfaced the April 24, 2026 MCB PCI BAR series, and did not surface any obvious removal/deprecation discussion. `web.search_query` found current duagon product pages showing the vendor ecosystem is still selling embedded CompactPCI hardware in 2026; that is indirect evidence for new-sales viability, so I treat deployments as niche/industrial and recommend keep-annotate rather than deprecate.