BSDCan2009 - Final Release
BSDCan 2009
The Technical BSD Conference
| Speakers | |
|---|---|
|
John Baldwin |
| Schedule | |
|---|---|
| Day | Talks - 2 - 2009-05-09 |
| Room | MNT 201 |
| Start time | 15:00 |
| Duration | 01:00 |
| Info | |
| ID | 118 |
| Event type | Lecture |
| Track | Hacking |
| Language used for presentation | English |
Multiple Passes of the FreeBSD Device Tree
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.
A brief outline of the paper follows:
- An overview of the existing single-pass system
- Problems that are not easily solved in the current system
- "Real" devices for low-level hardware such as clocks and interrupt controllers
- Resource discovery and management (finally supporting "PnP OS = yes")
- cold vs non-cold probing
- Supporting multiple passes
- Description of the current proposed passes
- Easy to add new passes in the future similar to SYSINIT SISUB*
- Most device drivers need no modification and attach in the final pass
- Writing an early pass driver
- Use EARLYDRIVERMODULE() instead of DRIVER_MODULE() to specify pass number
- New semantics for busgenericprobe() and busgenericattach()
- The BUSNEWPASS() method and busgenericnew_pass()
- If the driver can be attached after boot (e.g. via kldload or hotplug) it must account for this in its attach routine
- Possible solutions to the earlier list of problems
- Use "early" drivers for clocks, interrupt controllers, etc.
- Resource discovery
- Use "early" drivers for buses and bridges
- Possibly add new methods for determining resource requirements and assigning ranges to buses
- Earlier scheduler start
- Start up callouts before final pass