Initial USB4 code written by Scott Long and originally passed on to HPS (source: https://github.com/hselasky/usb4).
I have removed the ICM code already as suggested by Scott. For context, older TB chips implemented the connection manager in firmware instead of in the OS (HCM).
Mostly completed work:
- Debug/Trace framework
- NHI controller driver
- PCIe bridge driver
- WMI driver -> don't quite know how useful this will be considering we're not going to support ICM devices?
Integrated Connection Manager handshake and authentication handlingI have removed the code for this.- Router and Config Space layer handling (in progress, almost complete, writing has been added in D49452)
Remaining work:
- tbtconfig (userland tool)
- man pages
- DMAR/IOMMU integration, PCIe tunnelling control
- Support for resetting and firmware flashing on the NHI via out-of-band control
- Host Connection Manager
- Cross-domain login
- ThunderboltIP
- Proper power management
Here are the comments Scott added alongside his code:
The driver originally targeted the Thunderbolt 3 controllers that were sold under the names “AlpineRidge" and “Icelake”, in the late 2010's, before the USB standards group publicly released the USB4 spec. The driver set I wrote was complete enough to activate Thunderbolt3 peripherals that otherwise would be disabled by default when plugged in. The driver also attempted to make it easier to identify things like PCIe tunnels in the topology, but that was mostly cosmetic. Unfortunately, the AlpineRidge chips proved to be extremely hard to work with despite their wide availability, and I spent way too much time fighting them and not enough time developing more useful functionality. The WMI driver was written to work around vexing problems with the Alpine Ridge controller that I never figured out. Much of the infrastructure from the TBT3 support extends to modern USB4 controllers, but there are still a lot of missing pieces. The NHI driver doesn't know how to probe a USB4 controller yet, but that should be easy to fix. Even more important, though, is that the code lacks a functional USB4 Connection Manager. Most of the pieces required to traverse the topology, discover routers and adapters, read and write their properties, and build routes between endpoints exists now, but there's no state machine yet that integrates those pieces together into a real Connection Manager. Without that, no attached peripherals will actually run. The TBT3 controllers like AlpineRidge and IceLake have a connection manager in firmware, so that's why those controllers function even with minimal host OS support. This isn't especially hard code to write, but it's missing nonetheless. Once the connection manager is written, it'll need to configure connections with the USB3, PCIe, and DisplayPort devices that operate over tunnels, and it'll need a cross domain handler for connecting to another host. USB3 tunnel support might require significant changes in the USB3 stack in order to work with USB4. Additionally you might need to write a USB-PD driver. Without it, negotiation on USB-C connectors for power delivery advertisements, cable orientation, alt mode configuration, and USB3 vs USB4 lane assignment might not work. If those negotiations are not handled then nothing that you plug into the port will even be seen by the controller. I'd totally stay away from spending time on supporting Falcon Ridge, Alpine Ridge, and Titan Ridge controllers. They're old, they're extremely difficult to work with, and they're not worth the headache. In fact, just ignore all TBT3 controllers, and remove the Internal Connection Manager code. The ICM module isn't code that I'm all that proud of anyways =-). Focus on writing an HCM, supporting PCIe and DP tunneling, and integrating IOMMU protections into both the NHI driver and the PCIe tunnel drivers. One thing that would be pretty awesome is ThunderboltIP support. It turns out that these controllers are really cheap 40Gbps devices, and have the potential to perform pretty well at line rate as a replacement for traditional 40Gb ethernet controllers, at least in a point-to-point configuration.
Useful links:
- USB4 v2.0 spec: https://www.usb.org/document-library/usb4r-specification-v20
- Email with the details Scott shared (where the above comes from): https://lists.freebsd.org/archives/freebsd-hackers/2024-July/003411.html