Re: [RFC PATCH 00/40] Toward class init of cpu features

[Richard Henderson <richard.henderson@linaro.org>]

On 1/6/23 13:59, Peter Maydell wrote:
> We also set some properties in code -- eg aspeed_ast2600.c clears
> the 'neon' property on its CPUs, lots of the boards clear
> has_el3 and has_el2, etc.

Yes indeed, but in all of those cases we want all of the cpus to act identically.  Those 
are all easily handled (patches 35, 36, 38).

> I hadn't got as far as patch 29, but
> looking at it now that looks like a pretty strong indication
> that this is the wrong way to go. It creates 3 extra
> cortex-m33 CPU classes, and if we find another thing that
> ought to be a CPU property then we'll be up to 8;

If we find another thing that needs to be different between cpus, you mean?

> and it becomes visible in user-facing command line stuff.

No it doesn't -- command line is *not* affected, because both before and after, all 
properties are applied identically to all objects.

QMP is affected, which is where I stopped and started asking questions about what QMP is 
actually trying to do.


> I think our object model pretty strongly wants "create object;
> set properties on it that only affect this object you created;
> realize it", and having one particular subset of objects that
> doesn't work the same way is going to be very confusing.

Eh, I didn't think it's particularly confusing as a concept.
The code is rough, buy what one might expect from an RFC.

We really ought to have *some* solution to not repeating property + feature + isar 
interpretation on a per-cpu basis.  I'd be delighted to hear alternatives.


r~