Re: [Qemu-devel] [PATCH v6 7/7] hw/pci-bridge: format SeaBIOS-compliant OFW device node for PXB

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 17, 2015 at 03:28:44PM -0400, Kevin O'Connor wrote:
> On Wed, Jun 17, 2015 at 09:15:24PM +0200, Laszlo Ersek wrote:
> > On 06/17/15 20:54, Michael S. Tsirkin wrote:
> > > Right. But what I was discussing is a different issue.  The point is
> > > that it does not make sense to have /pci@i0cf8 under two hierarchies:
> > > it's the same register.  What happens is that you access /pci@i0cf8 and
> > > then *through that* you access another pci root.  Not the other way
> > > around.  The proposal thus is to switch to /pci@i0cf8/pci-root@N in
> > > seabios,
> > 
> > For me this is still Question 1 -- 'everything in that pattern that is
> > not "N"'.
> > 
> > You seem to care about the *semantics* of that OFW device path fragment.
> > I don't. First, the relevant IEEE spec is prohibitively hard for me to
> > interpret semantically. Second, there is no known firmware that actually
> > looks at the "i0cf8" unit-address term and decides *based on that term*
> > that it has to talk PCI via 0xCF8 and 0xCFC. In other words, the current
> > second node is entirely opaque in my interpretation.
> > 
> > > unconditionally - not if (QEMU).
> > 
> > This might qualify as some kind of semantic cleanup, but it will
> > nonetheless break the SeaBIOS boot options expressed in OFW notation
> > that are already persistently stored in cbfs, on physical machines. (As
> > far as I understood.) It might not break the Coreboot-SeaBIOS interface,
> > but it might invalidate preexistent entries that exist in the prior form
> > (wherever they exist on physical hardware).
> > 
> > > And I thought Kevin agreed
> > > it's a good idea.
> > > 
> > > Kevin - is this a good summary of your opinion?
> > 
> > Kevin, please do answer.
> 
> It is true that it would "invalidate preexistent entries" for
> coreboot/seabios users that upgrade, but I think that is manageable.
> So I defer the syntax discussion and decisions to the QEMU developers
> that are doing the bulk of the work.
> 
> -Kevin

I'm fine with either /pci@i0cf8,%x or /pci-root@%x/pci@i0cf8, with a
slight preference to the later - in particular it's easier
to implement in QEMU.

It means old bios won't boot from a pxb, but I think that's
manageable - it works otherwise.

-- 
MST