Re: [Qemu-ppc] [PATCH 12/12] pseries: Generate unique LIOBNs for PCI host bridges

[David Gibson]

On Fri, Nov 23, 2012 at 04:01:58PM +0200, Michael S. Tsirkin wrote:
> On Fri, Nov 23, 2012 at 02:44:15PM +0100, Alexander Graf wrote:
> > 
> > On 23.11.2012, at 14:44, Michael S. Tsirkin wrote:
> > 
> > > On Fri, Nov 23, 2012 at 11:59:51PM +1100, David Gibson wrote:
> > >>> Look, even if solution using a required property is less elegant for CLI
> > >>> use, it will work, won't it?
> > >>> So how about we merge it so that things work, and then we can discuss a
> > >>> patch on top that auto-generates this property?
> > >> 
> > >> Well, there you have a point.  And actually I've realised there are
> > >> other things we need to assign uniquely for each PHB and don't yet (IO
> > >> window addresses).  So I need to look at a wider rework of this, which
> > >> I'll start on next week.
> > > 
> > > Fine. Basically my point is it's typically a mistake to
> > > make some userspace visible parameter depend on order
> > > of initialization of devices in qemu. I don't insist
> > > on making users fully specify such parameters but it
> > > is one way to do this.
> > 
> > I think it's reasonable to require to be able to specify it. If you
> > don't, it's fine to base on device order IMHO.
> 
> Let me clarify why it's not fine.  My understanding is these addresses
> do not change across reboots on real hardware.

Well, the BUID would be expected to remain the same.  The others
probably remain stable across reboots in practice, but I don't think
there's any reason they need to - the kernel will get the LIOBN and
window addresses from the device tree afresh on every boot.

-- 
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