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Date: Wed, 14 May 2014 13:06:34 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-trivial] [PATCH v2] serial-pci: Set prog
 interface field of pci config to 16550 compatible
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To: BALATON Zoltan <balaton@eik.bme.hu>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-trivial@nongnu.org, Michael Tokarev <mjt@tls.msk.ru>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>

Il 14/05/2014 12:59, BALATON Zoltan ha scritto:
> On Wed, 14 May 2014, Michael S. Tsirkin wrote:
>> On Wed, May 14, 2014 at 01:39:03AM +0200, BALATON Zoltan wrote:
>>> On Thu, 8 May 2014, Michael Tokarev wrote:
>>>> 27.02.2014 05:05, BALATON Zoltan wrote:
>>>>
>>>> Shoudl we actually make it machine-specific, to keep even prog-if value
>>>> of these things the same as before for older machine types?  I dunno.
>>>> mst says we should, I think this is not a very important property to
>>>> keep.
>>>
>>> So what's the decision? Can it be taken as it is now or do you want
>>> any more changes? (If you want it version specific then please tell
>>> me how to do that or show me an example because I don't know how to
>>> do that.)
>>>
>>
>> If you change it migration to old qemu breaks.
>
> This is unlikely as this pci serial card is not used by default in any
> machine version AFAIK. Is it still desired to keep backward
> compatibility for a device that can only be added by users explicitely?

Yes, after all not even virtio-blk is used by default.

Paolo