linux-kernel - Re: [Qemu-devel] [PATCH v2] arm: change vendor ID for virtio-mmio

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Message-ID: <20150730180303-mutt-send-email-mst@redhat.com>
Date:	Thu, 30 Jul 2015 18:05:52 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Peter Maydell <peter.maydell@...aro.org>
Cc:	Shannon Zhao <shannon.zhao@...aro.org>,
	QEMU Developers <qemu-devel@...gnu.org>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	Shannon Zhao <zhaoshenglong@...wei.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Alex Bennée <alex.bennee@...aro.org>
Subject: Re: [Qemu-devel] [PATCH v2] arm: change vendor ID for virtio-mmio

On Thu, Jul 30, 2015 at 10:24:11AM +0100, Peter Maydell wrote:
> On 30 July 2015 at 09:04, Michael S. Tsirkin <mst@...hat.com> wrote:
> > On Thu, Jul 30, 2015 at 09:23:20AM +0800, Shannon Zhao wrote:
> >>
> >> Why do we drop the previous way using "QEMUXXXX"? Something I missed?
> >
> > So that guests that bind to this interface will work fine with non QEMU
> > implementations of virtio-mmio.
> 
> I don't understand this sentence. If there are pre-existing
> non-QEMU virtio-mmio implementations, then they're using
> LNRO0005, and we should use it too. If there are going to
> be implementations of virtio-mmio in future, then they will
> use whatever identifier we pick here. Either way, we get
> interoperability. I don't see any difference between our
> saying "the ID for virtio-mmio is QEMU0005" and saying
> "the ID for virtio-mmio is 1AF4103F".

I agree. It's just that 1AF4 is already reserved for virtio.

> (The latter seems unnecessarily opaque to me, to be honest.
> At least an ID string QEMUxxxx gives you a clue where to
> look for who owns the thing.)

Well - if one looks in the ACPI spec, that says if ID uses numbers, then
one has to find the vendor from PCI SIG, and that has a database mapping
IDs to vendors.

> 
> Note also that strictly you don't mean "non-QEMU implementations
> of virtio-mmio", you mean "non-QEMU implementations of the
> ACPI tables".

Yes.

> The hardware implementation of virtio-mmio
> doesn't care at all about the ACPI ID. (In fact the most
> plausible other-implementation would be UEFI using its
> own (hard-coded) ACPI tables on top of a QEMU vexpress-a15
> model or something similar.)
> 
> -- PMM
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