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

[Thomas Huth]

On 27/01/2023 09.46, Sebastian Mitterle wrote:
> Add some documentation about the zpci device and how
> to use it with pci devices on s390x.

Thanks for tackling this! ... some comments below...

> 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>
> ---
> 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,

Please wrap lines at 80 columns (if possible)

> +in order to pass a PCI device ``0000:00:00.0`` through you'd specify::

I'd suggest to be more explicit here:

in order to pass a host 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

"as *it* is common" ?

> +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

s/oder/order/

(and it's a very long line again, please wrap at 80 columns)

> +it.

Should we also add some information about virtio devices? (can also be added 
later, not necessarily in your patch already)

 Thomas