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

[Peter Maydell]

On Thu, 2 Sept 2021 at 13:43, Leif Lindholm <leif@nuviainc.com> wrote:
> Hmm. I mean, you're absolutely right about the complexity and need for
> discussion. My concern is that we cannot insert the ITS block in the
> memory map where it would be in an ARM GIC implementation without
> changing the memory map (pushing the redistributor further down).
>
> It is also true that simply versioning sbsa-ref does not mean we end
> up with a properly aligned with ARM IP register frame layout. Some
> additional logic is required for that.
>
> If we assume that we don't want to further complicate this set by
> adding the additional logic *now*, I see three options:
> - Implement memory map versioning for sbsa-ref for this set, placing
>   the ITS (if enabled) directly after the DIST for sbsa-ref-6.2.
> - In this set, place the ITS frames in a different location relative
>   to the REDIST frames than it will end up once the further logic is
>   implemented.
> - Drop the sbsa-ref ITS support from this set, and bring it in with
>   the set implementing the additional logic.
>
> Typing that, I'm getting the feeling that if I was the maintainer,
> the third option would be my preference...

So, we took that third option just to get the initial ITS support
into QEMU, and it has now landed. Where do we want to go with
the sbsa-ref support ?

There doesn't seem like there's much coding required on the QEMU
side, it's probably about an afternoon at most to update this patch
to match whatever we decide we need to do. But it's very unclear
to me what it is we should be doing.

Leif, what's your plan/preferences here ?

Presumably somebody also needs to do the system-software side
of things to handle the ITS being present and the redistributor
frames moving...

thanks
-- PMM