Re: [Qemu-devel] machines and versions - why so many?

[Markus Armbruster <armbru@redhat.com>]

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> On 06/24/2014 03:15 PM, Paolo Bonzini wrote:
>> Il 23/06/2014 23:35, Alexey Kardashevskiy ha scritto:
>>> nec-usb-xhci is off for PC_COMPAT_1_3 because of what? PIIX emulation was
>>> broken in 1.3? Or nec-usb-xhci?
>> 
>> nec-usb-xhci is not "off".
>
> Yes, my bad, I understood (but explained this wrong) that XHCI is enabled
> but without MSI.
>
>
>> 
>>             .driver   = "nec-usb-xhci",\
>>             .property = "msi",\
>>             .value    = "off",\
>> 
>> What's off is MSI (and MSI-X), because it wasn't implemented.
>>
>>> If it is the latter, why is the tweak limited by PC?
>> 
>> Because at the time nobody cared about migration compatibility (even now
>> only pSeries is starting to care).
>
>
> "only pSeries"? There are plenty of x86 machines already and if it is not
> for migration support, then what are they all for? :)

At the time, nobody *else* cared.  Only PC did.

Back then gerd created a way to do the compatibility stuff without
getting into the other target's hair: compat_props.  They've served us
well enough, but now that more targets get interested in migration,
their shortcomings start to hurt.  Having to duplicate device
compatibility gunk in multiple places, all far away from the device, is
decidedly suboptimal.  Better ideas welcome.

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