Re: [PATCH] hw/arm: Move the "arm-cpu" compat settings out of hw/core/machine.c

[Cornelia Huck <cohuck@redhat.com>]

On Tue, Jan 20 2026, Peter Maydell <peter.maydell@linaro.org> wrote:

> On Tue, 20 Jan 2026 at 14:15, Thomas Huth <thuth@redhat.com> wrote:
>>
>> On 20/01/2026 13.55, Peter Maydell wrote:
>> > On Tue, 20 Jan 2026 at 12:21, Thomas Huth <thuth@redhat.com> wrote:
>> >>
>> >> From: Thomas Huth <thuth@redhat.com>
>> >>
>> >> The hw_compat_* arrays in hw/core/machine.c should be used for generic
>> >> compat settings that might affect all (or at least multiple) machines.
>> >> Target specific settings should rather go into the target specific
>> >> source files instead. For arm/aarch64, the virt machine is the only
>> >> one that cares about compat settings, so move the "arm-cpu" related
>> >> switches to hw/arm/virt.c now.

FWIW, this is not the only arch-specific setting in there, and I don't
think it's really bothersome. There are many compat settings that might
not be applicable when you spin up a machine, and that's fine.

>> >
>> > I think it makes more sense for all the compat stuff to
>> > live in one place, rather than being scattered around,
>> > unless it is truly machine-specific (which this isn't).
>>
>> It's only used by the arm virt machine, so it's IMHO machine specific.
>> If we will ever get other versionized arm machines, they won't use these
>> config knobs, so this never will be shared with another machine.
>
> It happens to be only used by the virt board, but that's just
> a coincidence that we only have one versioned arm board right
> now. The config knob itself is not at all board specific:
> it applies to a device object that is used by many boards and
> sets a behaviour that would usefully apply to all of them.
> If we ever did have more arm versioned machines in the future
> we'd end up with a weird split where compat properties of the CPU
> object that happened to pre-date the addition of that second
> machine type would be in one place in the source code, and
> properties that happened to post-date the second machine
> type would be somewhere else.

I think there are only two options that really make sense:
- keep the compat setting where it is
- introduce an arm specific compat array that can be included by the
  virt machine and any future versioned arm machine

Not sure if the latter is actually worth the hassle.