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

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

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On Wed, Jun 27, 2018 at 11:38:17AM +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2018-06-27 at 03:35 +0300, Michael S. Tsirkin wrote:
> > 
> > > +
> > > +/* Extract field fname from val */
> > > +#define GETFIELD(fname, val)                    \
> > > +        (((val) & fname##_MASK) >> fname##_LSH)
> > > +
> > > +/* Set field fname of oval to fval
> > > + * NOTE: oval isn't modified, the combined result is returned
> > > + */
> > > +#define SETFIELD(fname, oval, fval)                     \
> > > +        (((oval) & ~fname##_MASK) | \
> > > +         ((((typeof(oval))(fval)) << fname##_LSH) & fname##_MASK))
> > > +
> > 
> > Pls don't make up macros like these. We can't have each device do it.
> 
> So what ? We move the macros in a generic place ? These are MUCH better
> than open-coding the masks & shifts and much less error prone.

There are already deposit32 and deposit64() functions which I think
would cover this.

> 
> > > @@ -1031,6 +1110,7 @@ static Property pnv_chip_properties[] = {
> > >      DEFINE_PROP_UINT64("ram-size", PnvChip, ram_size, 0),
> > >      DEFINE_PROP_UINT32("nr-cores", PnvChip, nr_cores, 1),
> > >      DEFINE_PROP_UINT64("cores-mask", PnvChip, cores_mask, 0x0),
> > > +    DEFINE_PROP_UINT32("num-phbs", PnvChip, num_phbs, 1),
> > >      DEFINE_PROP_END_OF_LIST(),
> > >  };
> > 
> > How about instanciating each extra phb using -device?
> > Seems better than teaching everyone about platform-specific
> > options.
> 
> It's about which PHBs are enabled, not which are instanciated, if I
> understand Cedric changes ...
> 
> This aims are implementing the POWER8 chip correctly, it has a fixed
> number of PHBs per-chip at very specific XSCOM addresses, that the
> firwmare knows about.

Yeah, this is a recurring design conflict, which I'm not sure how to
address.  Usually instantiating things with -device works better, but
when do we do when that allows more flexibility with hardware
arrangement than is actually possible in the hardware.

-- 
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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