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

[Shashi Mallela]

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; narmstr...@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 <l...@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?   /     Leif