Re: [libvirt-users] pcie-expander-bus doesn't support pcie-pci-bridge and pcie-switch-upstream-port

On Wed, 2018-10-17 at 10:50 +0800, Han Han wrote: > In libvirt, I found pcie-expander-bus controller doesn't support pcie-to-pci-bridge and pcie-switch-upstream-port. [...] > # virsh -k0 -K0 define /tmp/c.xml Aside: the -k and -K virsh options are documented as -k | --keepalive-interval=NUM keepalive interval in seconds, 0 for disable -K | --keepalive-count=NUM number of possible missed keepalive messages So -k0 disables keepalive entirely, making -K0 unnecessary :) > error: Failed to define domain from /tmp/c.xml > error: XML error: The device at PCI address 0000:01:00.0 cannot be plugged into the PCI controller with index='1'. It requires a controller that accepts a pcie-to-pci-bridge. [...] > In function virDomainPCIAddressBusSetModel, I find pcie-expander-bus only supports pcie-root-port and dmi-to-pci-bridge > 353 case VIR_DOMAIN_CONTROLLER_MODEL_PCIE_EXPANDER_BUS: > 354 ┆ /* 32 slots, no hotplug, only accepts pcie-root-port or > 355 ┆ ┆* dmi-to-pci-bridge > 356 ┆ ┆*/ > 357 ┆ bus->flags = (VIR_PCI_CONNECT_TYPE_PCIE_ROOT_PORT | > 358 ┆ ┆ ┆ ┆ ┆ VIR_PCI_CONNECT_TYPE_DMI_TO_PCI_BRIDGE); > 359 ┆ bus->minSlot = 0; > 360 ┆ bus->maxSlot = VIR_PCI_ADDRESS_SLOT_LAST; > 361 ┆ break; The above is consistent with pcie-root itself, which also doesn't support plugging a pcie-to-pci-bridge directly into it but requires a pcie-root <- pcie-root-port <- pcie-to-pci-bridge topology. Now, I don't quite recall *why* that is the case - perhaps Laine does? - but I'm sure we had very compelling reasons O:-)

> But it works in qemu: > # /usr/libexec/qemu-kvm -machine q35 -m 1024 -device pxb-pcie,bus_nr=250,id=pci.1,bus=pcie.0,addr=0x4 -device pcie-pci-bridge,id=pci.250,bus=pci.1,addr=0x0 -device pcie-pci-bridge,id=pci.251,bus=pci.1,addr=0x1 -spice port=5902,addr=0.0.0.0,disable-ticketing /var/lib/libvirt/images/q35.qcow2 It should be noted that QEMU in general allows users to make pretty unwise device placement choices without so much of a warning, so I would not take the above as proof the pcie-to-pci-bridge should be allowed to plug into pcie-expander-bus (or pcie-root) directly :)