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

From: Collin Walling <walling@linux.ibm.com>
To: Thomas Huth <thuth@redhat.com>,
	Markus Armbruster <armbru@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Palmer Dabbelt" <palmer@sifive.com>,
	"open list:RISC-V" <qemu-riscv@nongnu.org>,
	"Eduardo Habkost" <ehabkost@redhat.com>,
	"Sagar Karandikar" <sagark@eecs.berkeley.edu>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Helge Deller" <deller@gmx.de>,
	"Cornelia Huck" <cohuck@redhat.com>,
	"Mark Cave-Ayland" <mark.cave-ayland@ilande.co.uk>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Aurelien Jarno" <aurelien@aurel32.net>,
	"open list:S390" <qemu-s390x@nongnu.org>,
	qemu-arm <qemu-arm@nongnu.org>,
	"Alistair Francis" <Alistair.Francis@wdc.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>,
	qemu-ppc <qemu-ppc@nongnu.org>,
	"Richard Henderson" <rth@twiddle.net>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Artyom Tarasenko" <atar4qemu@gmail.com>,
	"David Gibson" <david@gibson.dropbear.id.au>
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	[thread overview]
Message-ID: <50befb09-d381-4362-9cd1-6fb11c96a719@linux.ibm.com> (raw)
In-Reply-To: <beb5fe93-991d-ba2b-d2c1-51e01b912dbe@redhat.com>

On 7/16/19 11:04 AM, Thomas Huth wrote:
> 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?
> 

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
> 