# PCI devices on s390x

PCI devices on s390x work differently than on other architectures and need to be configured in a slightly different way.

Every PCI device is linked with an additional `zpci` device. While the `zpci` device will be autogenerated if not specified, it is recommended to specify it explicitly so that you can pass s390-specific PCI configuration.

For example, in order to pass a PCI device `0000:00:00.0` through to the guest, you would specify:

    qemu-system-s390x ... \
                      -device zpci,uid=1,fid=0,target=hostdev0,id=zpci1 \
                      -device vfio-pci,host=0000:00:00.0,id=hostdev0

Here, the zpci device is joined with the PCI device via the `target` property.

Note that we don't set bus, slot or function here for the guest as is common in other PCI implementations. Topology information is not available on s390x, and the guest will not see any of the bus, slot or function information specified on the command line.

Instead, `uid` and `fid` determine how the device is presented to the guest operating system.

In case of Linux, `uid` will be used in the `domain` part of the PCI identifier, and `fid` identifies the physical slot, i.e.:

    qemu-system-s390x ... \
                      -device zpci,uid=7,fid=8,target=hostdev0,id=zpci1 \
                      ...

will be presented in the guest as:

    # lspci -v
    0007:00:00.0 ...
    Physical Slot: 00000008
    ...