Re: [libvirt-users] pcie-expander-bus doesn't support pcie-pci-bridge and pcie-switch-upstream-port
Hi Laine,
On 10/17/18 8:29 PM, Laine Stump wrote:
On 10/17/2018 08:56 AM, Andrea Bolognani wrote:
> 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:-)
Umm, because Marcel told us that was the proper behavior ? Right, Marcel?
Yes it is.
The pcie-pxb expander does not support "embedded" devices, any devices
should be plugged into pcie ports.
Even if QEMU cmd line allows embedded devices, it is not a supported
configuration.
Zooming it into the specific case of the pcie-pci bridge, this is a PCI
Express device,
and PCI Express devices may miss-behave if plugged as Integrated Devices.
Thanks,
Marcel
>> 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 :)
>