Re: [Qemu-devel] [qemu-s390x] [RFC PATCH 1/3] hw/Kconfig: PCI bus implies PCI_DEVICES

[Thomas Huth <thuth@redhat.com>]

On 16/07/2019 15.06, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
>> On 15/07/19 18:12, Cornelia Huck wrote:
>>>> Is it INTx vs. MSI vs. MSI-X?
>>>
>>> I think for s390x we need (INTx || MSI) vs MSI-X...
>>
>> I think MSI vs MSI-X is just how it's configured, not the actual
>> behavior, so it should be irrelevant.
> 
> My best guesses from confusing information, please correct
> misunderstandings:
> 
> 1. PCI devices need to support MSI or MSI-X to work with s390x.

I think Cornelia mentioned that we might even require MSI-X there ...
Collin (being listed as "S390 PCI" maintainer), can you confirm?

> 2. We want a way to Kconfig the PCI devices that work, i.e. only the
>    ones that support MSI or MSI-X.
> 
> I don't like calling devices without any MSI capability "classic" or
> "conventional devices".  I'd rather call them "MSI-capable" or
> "MSI/MSI-X devices".

But you still need a config switch that you can set to enable the
non-MSI devices ... what's so wrong with "conventional" if that's even
the wording from the PCI SIG?

> Since PCI-E devices must implement MSI or MSI-X, we could perhaps
> configure just the PCI-E devices for s390x.  No need to invent a new
> name then.  Do we even have device models that can do MSI but not E?

I don't know if anybody ever tried a non-virtio PCIe device from QEMU on
s390x ... I guess there will be quite a bit of other hurdles, too (e.g.
the Linux driver also has to work without MMIO), so I'm not sure whether
we really want to enable all PCIe devices there...

 Thomas