Re: [Qemu-devel] [PATCH v2 3/7] ppc/pnv: Add XSCOM infrastructure

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Sep 05, 2016 at 05:11:53PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2016-09-05 at 13:39 +1000, David Gibson wrote:
> > > +static XScomDevice *xscom_find_target(XScomState *s, uint32_t
> > pcb_addr,
> > > +                                      uint32_t *range)
> > > +{
> > > +    BusChild *bc;
> > > +
> > > +    QTAILQ_FOREACH(bc, &s->bus->bus.children, sibling) {
> > > +        DeviceState *qd = bc->child;
> > > +        XScomDevice *xd = XSCOM_DEVICE(qd);
> > > +        unsigned int i;
> > > +
> > > +        for (i = 0; i < MAX_XSCOM_RANGES; i++) {
> > > +            if (xd->ranges[i].addr <= pcb_addr &&
> > > +                (xd->ranges[i].addr + xd->ranges[i].size) >
> > pcb_addr) {
> > > +                *range = i;
> > > +                return xd;
> > > +            }
> > > +        }
> > > +    }
> > 
> > Hmm.. you could set up a SCOM local address space using the
> > infrastructure in memory.c, rather than doing your own dispatch.
> 
> There are pros and cons to this approach. The memory.c stuff comes with
> quite a lot of baggage, not all of it very shinny to be honest ;-) I
> still *hate* how it forces upon us a whole 128-bit integer arithmetic
> library just so that it can represent 1_0000_0000_0000_0000 ... 

Ugh, yeah.  I tried to argue against this when it first came in, but
was overruled.

> It would be make more sense to use inclusive start/end instead and
> stick to 64-bits.
> 
> That being said, we could do that. We'd have to shift the XSCOM
> addresses left by 3 since each address is an 8 bytes reigster and
> forbid non-8-bytes accesses.

Ok.  I'm not particularly fussed either way.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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