Re: [Qemu-devel] [PATCH 0/6] refactor PC machine, i440fx and piix3 to take advantage of QOM

[Anthony Liguori]

On 03/27/2012 05:31 AM, Avi Kivity wrote:
> > I think the better approach is to have a PCNorthBridge base-class that
> > contains functionality like PAM/SRAM that both I440FX and Q35 inherit
> > from.
>
> I hate to transform this into a languagey discussion, but I don't think
> inheritance is the right thing here.  While both 440fx and q35 are north
> bridges, the similar implementation of PAM/SMRAM is not part of that.
> It's just a random result of the chips' evolution.  I think the code for
> PAM/SMRAM can be reused if the specs match, but using a has-a instead of
> an is-a relationship.

The direction I was heading with the i440fx, the i440fx has-a i440fx-pmc and it 
was the pmc that actually did PAM/SMRAM.

I don't recall there being significant i440fx specific logic in the i440fx-pmc 
so it's entirely possible the the i440fx-pmc could be renamed to PCNorthBridge 
and then both the i440fx and q35 could has-a the same PCNorthBridge (possible 
with some properties to control certain behaviors.

We really need to push forward with the refactoring to find the right model 
here.

Regards,

Anthony Liguori

> As a counterexample, consider a northbridge that implements PAM/SMRAM
> differently.  You'd have to refactor PCNorthBridge into two separate
> classes.  With the other approach the new northbridge simply doesn't
> include the existing PAM/SMRAM implementation and instead implements its
> own.