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

From: Shashi Mallela
Subject: RE: [PATCH v8 07/10] hw/arm/sbsa-ref: add ITS support in SBSA GIC
Date: Thu, 11 Nov 2021 14:04:48 -0500

From: Leif Lindholm
Sent: November 11, 2021 1:21 PM
To: Peter Maydell
Cc: Shashi Mallela; Radoslaw Biernacki; Michael S. Tsirkin; Igor Mammedov; qemu-arm; QEMU Developers; Eric Auger; narmstrong@baylibre.com; Alex Bennée; Marcin Juszkiewicz
Subject: Re: [PATCH v8 07/10] hw/arm/sbsa-ref: add ITS support in SBSA GIC


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.


Sounds okay to me too.


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





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