Re: [PATCH v2 3/4] hw/display/vga-mmio: QOM'ify vga_mmio_init() as TYPE_VGA_MMIO

[Daniel P . Berrangé]

On Tue, Dec 14, 2021 at 01:05:29PM +0100, Juan Quintela wrote:
> Thomas Huth <thuth@redhat.com> wrote:
> > On 06/12/2021 23.45, Philippe Mathieu-Daudé wrote:
> >> Introduce TYPE_VGA_MMIO, a sysbus device.
> >> While there is no change in the vga_mmio_init()
> >> interface, this is a migration compatibility break
> >> of the MIPS Acer Pica 61 Jazz machine (pica61).
> >
> > It's unfortunate, but as far as I know, it would be pretty difficult
> > or even impossible to get this done without versioned machine types?
> > So IMHO it's ok to break this in this case here.
> 
> Hi
> 
> My understanding is that outside of x86*, and now ppc, arm and s390,
> no one else really cares about migration compatibility.  I am not even
> sure if they really care about migration at all O:-)
>
> So, if the code is better for other reasons, I will not wonder about
> migration compatibility.

Essentially if it has versioned machine types, then migration ABI
compat is mandatory. If it doesn't have versioned machine types
then migration API compat explicitly doesn't exist.

There are no versioned machine types for MIPS, so migration compat
is a non-issue.

Regards,
Daniel
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