Re: [Qemu-ppc] [PATCH v2 1/2] ppc/pnv: Add model for Power8 PHB3 PCIe Host bridge

[Benjamin Herrenschmidt]

On Mon, 2018-07-23 at 14:16 +1000, David Gibson wrote:
> > 
> > Now, this is an ICS subclass, so why shouldn't it directly poke at the
> > target ICP ?
> 
> That's ok in theory, but causing it to expose the icp interface to a
> new module isn't great.
> 
> > It's an alternate to the normal ICS since it behaves a bit
> > differently (PQ bits & all).
> 
> AFAICT the PQ bits are effectively another filtering layer on top of
> the same ICS logic as elsewhere.  I think it's better if we can share
> that shared logic, rather than replicating it.

I don't know, is there much shared logic ? And the shared bits are the
subclassing, that's handled that way...

This is really a different piece of HW, a separate ICS implementation,
that has its own quirks, is configured via different registers, does
EOI differently etc...

Even the resend stuff is done differently, the resend bitmap is
actually SW visible via an IODA table.

I mean, we could (maybe we do these days not sure) have an ICS
superclass wrapper on the actual icp_irq() but that's really all there
is to it I think.

Cheers,
Ben.