Re: [PATCH v2] docs/s390x/pcidevices: document pci devices on s390x

["Cédric Le Goater" <clegoate@redhat.com>]

On 1/27/23 09:46, Sebastian Mitterle wrote:
> Add some documentation about the zpci device and how
> to use it with pci devices on s390x.
> 
> Used source: Cornelia Huck's blog post
> https://people.redhat.com/~cohuck/2018/02/19/notes-on-pci-on-s390x.html
> 
> Signed-off-by: Sebastian Mitterle <smitterl@redhat.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
> v2: move section below 'Device support'
> ---
>   docs/system/s390x/pcidevices.rst | 34 ++++++++++++++++++++++++++++++++
>   docs/system/target-s390x.rst     |  1 +
>   2 files changed, 35 insertions(+)
>   create mode 100644 docs/system/s390x/pcidevices.rst
> 
> diff --git a/docs/system/s390x/pcidevices.rst b/docs/system/s390x/pcidevices.rst
> new file mode 100644
> index 0000000000..fec905d6e6
> --- /dev/null
> +++ b/docs/system/s390x/pcidevices.rst
> @@ -0,0 +1,34 @@
> +PCI devices on s390x
> +====================
> +
> +PCI devices on s390x work differently than on other architectures.
> +
> +To start with, using a PCI device requires the additional ``zpci`` device. For example,
> +in order to pass a PCI device ``0000:00:00.0`` through you'd 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. 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
> + ...
> +
> +Finally, note that you might have to enable the ``zpci`` feature in the cpu model in oder to use
> +it.
> diff --git a/docs/system/target-s390x.rst b/docs/system/target-s390x.rst
> index c636f64113..f6f11433c7 100644
> --- a/docs/system/target-s390x.rst
> +++ b/docs/system/target-s390x.rst
> @@ -26,6 +26,7 @@ or vfio-ap is also available.
>      s390x/css
>      s390x/3270
>      s390x/vfio-ccw
> +   s390x/pcidevices
>   
>   Architectural features
>   ======================