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

[Michael S. Tsirkin]

On Wed, Jun 17, 2015 at 09:44:07PM +0200, Laszlo Ersek wrote:
> On 06/17/15 21:32, Michael S. Tsirkin wrote:
> > 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 /address@hidden under two 
> >>>> hierarchies:
> >>>> it's the same register.  What happens is that you access /address@hidden 
> >>>> and
> >>>> then *through that* you access another pci root.  Not the other way
> >>>> around.  The proposal thus is to switch to 
> >>>> /address@hidden/address@hidden 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 /address@hidden,%x or /address@hidden/address@hidden, 
> > 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.
> 
> I don't understand -- the second option you named
> ("/address@hidden/address@hidden") is what this patch implements, and "old" 
> (ie.
> current) SeaBIOS does boot from it.
> 
> Laszlo

Ouch. I meant /address@hidden//address@hidden
As you see, it's confusing.