Re: [SeaBIOS] Fwd: [RFC 0/2] (Ongoing)Support multiple pci domains in pci_device

[Kevin O'Connor]

On Thu, Aug 09, 2018 at 07:44:22AM +0800, Zihan Yang wrote:
> Kevin O'Connor <[e-mail]> 于2018年8月8日周三 下午10:14写道：
> > On Thu, Aug 02, 2018 at 10:39:13AM +0800, Zihan Yang wrote:
> > > NOTE: This patch set is still ongoing and does not fully function
> > > as its goal. But it involves some API changes, therefore I post them for
> > > comments before moving on to make sure I'm on the right path.
> > >
> > > The corresponding qemu part can be found at
> > > https://gitlab.com/WhoisZihan/qemu-pci-domain/tree/master/qemu
> > > I will submit it to qemu list later.
> > >
> > > Currently seabios assumes there is only one pci domain(0), and almost
> > > everything operates on pci domain 0 by default. This patch aims to add
> > > multiple pci domain support for pci_device, while reserve the original
> > > API for compatibility.
> >
> > Thanks.  I understand the desire to support multiple PCI domains in
> > QEMU and the guest OS.  However, what is the high level reason for
> > wanting the BIOS to be able to interact with the secondary PCI
> > domains?
>
> The pxb-pcie host bus is put into a separated domain, so are the devices
> under the pxb host bus. I think we should also initialize busses in other
> domains and probe those devices during bios initialization. But currently
> qemu only binds port 0xcf8 and 0xcfc to q35 host's conf_mem and data_mem,
> if we want to read the config space of pxb host, we should use another port.
> I use port range 0x1000 and 0x1004 for a temporary workaround because they
> seem to be 'free' now.

The patchset is quite large and touches a large amount of code in
different parts of SeaBIOS.  I'd like to understand the high-level,
user-visible, reason for making the change.  What important
capabilities will a user be unable to accomplish if we don't make this
change?

As far as I know, there is no standard for accessing PCI besides the
main one at cf8/cfc - so I'm not sure there is a good solution to this
problem.  Perhaps it would be easier for users to always put their
boot devices on the main PCI.

Thanks,
-Kevin