Re: [patch RFC 26/38] x86/xen: Wrap XEN MSI management into irqdomain

[Thomas Gleixner]

On Mon, Aug 24 2020 at 08:21, Jürgen Groß wrote:
> On 21.08.20 02:24, Thomas Gleixner wrote:
>
> Looking into https://www.kernel.org/doc/Documentation/IRQ-domain.txt (is
> this still valid?)

It's halfways correct. Emphasis on halfways.

> I believe Xen should be able to use the "No Map" approach, as Xen only
> ever uses software IRQs (at least those are the only ones visible to
> any driver). The (virtualized) hardware interrupts are Xen events
> after all.
>
> So maybe morphing Xen into supporting irqdomains in a sane way isn't
> that complicated. Maybe I'm missing the main complexities, though.

The wrapper domain I did is pretty much that, but with the extra
functionality required by hierarchical irq domains. So, yes it's
functionally correct, but it's only utilizing the alloc/free interface
and not any of the other mechanisms provided by irqdomains. The latter
should make the overall code simpler but that obviously needs some
thought.

Thanks,

        tglx