qemu/docs/pcie.txt

34 PCI Express devices should be plugged only into PCI Express Root Ports and
35 PCI Express Downstream ports.
51     (2) PCI Express Root Ports (pcie-root-port), for starting exclusively
71       PCI Express Root Ports and PCI Express to PCI bridges can be
79 Always use PCI Express Root Ports to start PCI Express hierarchies.
84 number of PCI Express Root Ports per PCI Express Root Bus is 256.
86 Prefer grouping PCI Express Root Ports into multi-function devices
89 if there is no more room for PCI Express Root Ports.
92 Plug only PCI Express devices into PCI Express Ports.
117 2.2.2 Using multi-function PCI Express Root Ports:
173 The PCI Express Root Ports and PCI Express Downstream ports are seen by
185 The IO space is very limited, to 65536 byte-wide IO ports, and may even be
186 fragmented by fixed IO ports owned by platform devices resulting in at most
187 10 PCI Express Root Ports or PCI Express Downstream Ports per system
193 without using IO ports. The PCI hierarchy has no such limitations.
203 PCI Express Root Ports, PCI Express Downstream/Upstream ports)
211 Upstream Ports.
226     (2) PCI Express Root Ports
230 Be aware that PCI Express Downstream Ports can't be hot-plugged into
239 PCI Express Root Ports (and PCI Express Downstream Ports).
255         Leave enough PCI Express Root Ports empty. Use multifunction
256         PCI Express Root Ports (up to 8 ports per pcie.0 slot)
273 PCI Express Root Ports or PCI Express Downstream Ports.
304 Virtio devices plugged into PCI Express ports are PCI Express devices and