Multiple Passes of the FreeBSD Device Tree

John Baldwin <>

The existing device driver framework in FreeBSD works fairly well for many tasks. However, there are a few problems that are not easily solved with the current design. These problems include having “real” device drivers for low-level hardware such as clocks and interrupt controllers, proper resource discovery and management, and allowing most drivers to always probe and attach in an environment where interrupts are enabled. I propose extending the device driver framework to support multiple passes over the device tree during boot. This would allow certain classes of drivers to be attached earlier and perform boot-time setup before other drivers are probed and attached. This in turn can be used to develop solutions to the earlier list of problems.