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


From: Collin Walling
Subject: Re: [Qemu-devel] [qemu-s390x] [RFC PATCH 1/3] hw/Kconfig: PCI bus implies PCI_DEVICES
Date: Wed, 17 Jul 2019 08:59:30 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0

On 7/16/19 11:04 AM, Thomas Huth wrote:
On 16/07/2019 15.06, Markus Armbruster wrote:
Paolo Bonzini <address@hidden> 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?


MSI-X is mandatory for PCI devices in the s390 architecture.

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





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