Linux Virtualization - Jul 2015 - [Qemu-devel] [PATCH v2] arm: change vendor ID for virtio-mmio

On 30 July 2015 at 09:04, Michael S. Tsirkin <mst at redhat.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".

(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.)

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

On 30 July 2015 at 10:24, Peter Maydell <peter.maydell at linaro.org>
wrote:
> On 30 July 2015 at 09:04, Michael S. Tsirkin <mst at redhat.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.
The only one I have come across is the ARM FVP model, and it happens
that I chose the ID and maintain the tables for that so I can change
it.

Graeme

On 30 July 2015 at 10:37, G Gregory <graeme.gregory at linaro.org>
wrote:
> On 30 July 2015 at 10:24, Peter Maydell <peter.maydell at linaro.org>
wrote:
>> On 30 July 2015 at 09:04, Michael S. Tsirkin <mst at redhat.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.
>
> The only one I have come across is the ARM FVP model, and it happens
> that I chose the ID and maintain the tables for that so I can change
> it.
>
In fact, I would just add

Name (_HID, "QEMUXXXX")
Name (_HID, "1AF4103F")

To the tables so tables work with old (internal) kernels and new!

Graeme

On Thu, Jul 30, 2015 at 10:24:11AM +0100, Peter Maydell
wrote:
> On 30 July 2015 at 09:04, Michael S. Tsirkin <mst at redhat.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