Re: [Qemu-ppc] PCI Express on pseries guests

[David Gibson]

On Mon, Sep 19, 2016 at 05:34:57PM +0200, Andrea Bolognani wrote:
> I was wondering whether it's possible to create a pseries guest
> that uses PCI Express instead of legacy PCI.
> 
> The host itself is using PCI Express only
> 
>   $ sudo lspci -vv | grep -Ec '^[0-9]'
>   28
>   $ sudo lspci -vv | grep -Ec '^.*Capabilities: \[..\] Express'
>   28
> 
> but pseries guests seem to use legacy PCI instead
> 
>   $ echo -e "info qtree\nquit" \
>     | ./ppc64-softmmu/qemu-system-ppc64 \
>       -nodefaults -nographic -no-user-config \
>       -M pseries,accel=kvm \
>       -cpu host \
>       -monitor stdio \
>     | grep \
>       -i pci
>   dev: spapr-pci-host-bridge, id ""
>       bus: pci.0
>             type PCI
> 
> AFAIU, the spapr-pci-host-bridge is connected to the
> main-system-bus and that creates a legacy PCI bridge that
> PCI devices can be attached to.
> 
> The corresponding spapr-pcie-host-bridge device doesn't seem
> to exist; pxb-pcie looks promising, but if I try using it
> QEMU rightfully complains
> 
>   pxb-pcie devices cannot reside on a PCI bus!
> 
> So at this point I'm pretty much stuck. Suggestions? :)

So, the thing is that because the PCI bridge is para-virtualized on
the pseries platform, the distinction between PCI and PCI-E isn't
really meaningful.  That's why everything appears to be legacy PCI
within the guest.

BenH, can you correct me if I'm wrong here?

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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