qemu/docs/pcie.txt

1 PCI EXPRESS GUIDELINES
6 The doc proposes best practices on how to use PCI Express (PCIe) / PCI
7 devices in PCI Express based machines and explains the reasoning behind
17  (2) A comparison between PCI and PCI Express technologies.
26 and allows any PCI/PCI Express device to be plugged into any
27 PCI/PCI Express slot.
28 Plugging a PCI device into a PCI Express slot might not always work and
30 Plugging a PCI Express device into a PCI slot will hide the Extended
33 The recommendation is to separate the PCI Express and PCI hierarchies.
34 PCI Express devices should be plugged only into PCI Express Root Ports and
35 PCI Express Downstream ports.
45         Although the PCI Express spec does not forbid PCI Express devices as
48         strangely when PCI Express devices are integrated
51     (2) PCI Express Root Ports (pcie-root-port), for starting exclusively
52         PCI Express hierarchies.
54     (3) PCI Express to PCI Bridge (pcie-pci-bridge), for starting legacy PCI
57     (4) Extra Root Complexes (pxb-pcie), if multiple PCI Express Root Buses
69 2.1.2 To expose a new PCI Express Root Bus use:
71       PCI Express Root Ports and PCI Express to PCI bridges can be
77 2.2 PCI Express only hierarchy
79 Always use PCI Express Root Ports to start PCI Express hierarchies.
81 A PCI Express Root bus supports up to 32 devices. Since each
82 PCI Express Root Port is a function and a multi-function
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
88 Only use PCI Express Switches (x3130-upstream, xio3130-downstream)
89 if there is no more room for PCI Express Root Ports.
92 Plug only PCI Express devices into PCI Express Ports.
103     | PCIe Dev |                      |    PCI Express  | Upstream Port |              |
114 2.2.1 Plugging a PCI Express device into a PCI Express Root Port:
117 2.2.2 Using multi-function PCI Express Root Ports:
121 2.2.3 Plugging a PCI Express device into a Switch:
129     PCI Express Root Port. slot defaults to 0 when not specified.
138 Besides that use PCI Express to PCI Bridges (pcie-pci-bridge) in
141 Prefer flat hierarchies. For most scenarios a single PCI Express to PCI Bridge
145 PCI Express to PCI Bridge until is full and then plug a new PCI-PCI Bridge...
169       the PCI Bridge/PCI Express to PCI Bridge.
173 The PCI Express Root Ports and PCI Express Downstream ports are seen by
180 by not allocating IO space for each PCI Express Root / PCI Express
187 10 PCI Express Root Ports or PCI Express Downstream Ports per system
188 if devices with IO BARs are used in the PCI Express hierarchy. Using the
190 PCI Express devices within PCI Express hierarchy.
192 The PCI Express spec requires that PCI Express devices work properly
198 Each PCI domain can have up to only 256 buses and the QEMU PCI Express
202 Each element of the PCI Express hierarchy (Root Complexes,
203 PCI Express Root Ports, PCI Express Downstream/Upstream ports)
205 can be attached to a PCI Express Root Port or PCI Express Downstream
209 Avoiding PCI Express Switches (and thereby striving for a 'flatter' PCI
210 Express hierarchy) enables the hierarchy to not spend bus numbers on
222 The PCI Express root buses (pcie.0 and the buses exposed by pxb-pcie devices)
225     (1) PCI Express Integrated Endpoints
226     (2) PCI Express Root Ports
227     (3) PCI Express to PCI Bridges
230 Be aware that PCI Express Downstream Ports can't be hot-plugged into
231 an existing PCI Express Upstream Port.
233 PCI devices can be hot-plugged into PCI Express to PCI and PCI-PCI Bridges.
235 PCI Express to PCI bridges is SHPC-based. They both can work side by side with
236 the PCI Express native hot-plug.
238 PCI Express devices can be natively hot-plugged/hot-unplugged into/from
239 PCI Express Root Ports (and PCI Express Downstream Ports).
244         or more empty PCI-PCI Bridges to the PCI Express to PCI Bridge.
252         Integrated Endpoints. (The PCI Express Hierarchy needs no IO space).
254     (2) PCI Express hierarchy:
255         Leave enough PCI Express Root Ports empty. Use multifunction
256         PCI Express Root Ports (up to 8 ports per pcie.0 slot)
259         Don't use PCI Express Switches if you don't have
267 …device_add <dev>,id=<id>,bus=<PCI Express Root Port Id/PCI Express Downstream Port Id/PCI-PCI Brid…
272 Host devices are mostly PCI Express and should be plugged only into
273 PCI Express Root Ports or PCI Express Downstream Ports.
276 6.1 How to detect if a device is PCI Express:
285     Capabilities: [40] Express Endpoint, MSI 00
292 If you can see the "Express Endpoint" capability in the
293 output, then the device is indeed PCI Express.
304 Virtio devices plugged into PCI Express ports are PCI Express devices and
310 legacy behavior) for PCI Express virtio devices causing them to
318 and at the same time overcomes the PCI Express architecture limitations.