Re: [PATCH v8 07/10] hw/arm/sbsa-ref: add ITS support in SBSA GIC

[Leif Lindholm <leif@nuviainc.com>]

On Thu, Nov 11, 2021 at 16:55:09 +0000, Peter Maydell wrote:
> On Tue, 9 Nov 2021 at 22:52, Leif Lindholm <leif@nuviainc.com> wrote:
> >
> > On Tue, Nov 09, 2021 at 21:21:46 +0000, Peter Maydell wrote:
> > > The other thing we should nail down is how the user is going to
> > > select which flavour of machine they want to provide. Three
> > > options:
> > >  (1) no control, QEMU just emulates whatever the newest flavour is.
> > > User needs to go find a firmware image new enough to cope.
> > >  (2) different flavours exposed as different machine types
> > > (analogous to how we have musca-a and musca-b1, or raspi3ap and
> > > raspi3b, for instance). Old user command lines keep working
> > > because -M sbsa-ref doesn't change; the new stuff would be
> > > available via -M sbsa-ref-2 or whatever.
> > >  (3) different flavours exposed via a property
> > > (so you would have -M sbsa-ref,machine-revision=2 or something).
> > > If the revision defaults to 1 then old user setups still work
> > > but everybody starts to have to cart around an extra command
> > > line argument. If it defaults to "newest we know about" you
> > > get the opposite set of tradeoffs.
> >
> > I'm leaning towards (1), at least while working towards a "complete"
> > platform (when we may still add/change features, but not how those
> > features are communicated to the firmware).
> 
> That's certainly the easiest on the QEMU side; you know the
> userbase so would know whether that kind of compat break is
> going to be OK with them.
> 
> Q1: who is going to write the code for this?

Me, my team, and perhaps a little bit of help from Shashi where it
intersects his code.

> Q2: do we want to try to land "ITS in sbsa-ref" in 6.2? Given
> we're in freeze we're quite short of time even if we handwave
> the fact it's a new feature, not a bugfix, so I would lean
> towards 'no'...

Shashi - what is your feeling?
If we could make ITS support depend on the platform version being
communicated through TF-A, we could simplify the transition a lot.
But that would definitely mean missing 6.2.

Peter - could we sneak in an "add version node to DT" into 6.2?

/
    Leif