FreeBSD doesn't have Wi-Fi driver for my old MacBook. AI build one for me
My old 2016 MacBook Pro has been collecting dust in a cabinet for some time now. The laptop suffers from a “flexgate” problem, and I don’t have any practical use for it. For quite some time, I’ve been thinking about repurposing it as a guinea pig, to play with FreeBSD — an OS that I’d aspired to play with for a long while, but had never had a real reason to.
During the recent holiday season, right after FreeBSD 15 release, I’ve finally found time to set the laptop up. Doing that I didn’t plan, or even think, this may turn into a story about AI coding.
Background
2016 MacBook Pro models use Broadcom BCM4350 Wi-Fi chip. FreeBSD doesn’t have native support for this chip. To have a working Wi-Fi, a typical suggestion on FreeBSD forums, is to run wifibox — a tiny Linux VM, with the PCI Wi-Fi device in pass through, that allows Linux to manage the device through its brcmfmac driver.
Brcmfmac is a Linux driver (ISC licence) for set of FullMAC chips from Broadcom. The driver offloads the processing jobs, like 802.11 frame movement, WPA encryption and decryption, etc, to the firmware, which is running inside the chip. Meanwhile, the driver and the OS do high-level management work (ref Broadcom brcmfmac(PCIe) in Linux Wireless documentation).
Say we want to build a native FreeBSD kernel module for the BCM4350 chip. In theory, this separation of jobs between the firmware and the driver sounds perfect. The “management” part of work is what FreeBSD already does for other supported Wi-Fi devices. We need to port some amount of existing “glue code” from specifics of Linux to FreeBSD. If we ignore a lot of details, the problem doesn’t sound too complicated, right?
Act 1
A level-zero idea, when one hears about “porting a bunch of existing code from A to B”, in 2026 is, of course, to use AI. So that was what I tried.
I cloned the brcmfmac subtree, and asked Claude Code to make it work for FreeBSD. FreeBSD already has drivers that work through LinuxKPI — compatibility layer for running Linux kernel drivers. So I specifically pointed Claude at the iwlwifi driver (a softmac driver for Intel wireless network card), asking “do as they did it”. And, at first, this even looked like this can work — Claude told me so.
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