Configuration Transactions Are Originated by the Processor

Only the Root Complex Can Originate Configuration Transactions

The spec states that only the Root Complex is permitted to originate configuration transactions. The Root Complex acts as the processor's surrogate to inject transaction requests into the fabric, as well as to pass completions back to the processor. The configuration software executing on the processor is responsible for detecting and configuring all devices in the system.

The ability to originate configuration transactions is restricted to the processor/Root Complex to avoid the anarchy that would result if any device had the ability to change the configuration of other devices.

Configuration Transactions Only Move DownStream

This restriction exists for the same reason stated in the previous section.

No Peer-to-Peer Configuration Transactions

The following rule applies to Root Ports, Switches, and PCI Express-to-PCI Bridges: Propagation of Configuration Requests from peer-to-peer are not supported.