[SeaBIOS] [RFC v3] pciinit: setup mcfg for pxb-pcie to support multiple pci domains

[Zihan Yang]

Kevin O'Connor <kevin at koconnor.net> 于2018年9月28日周五 上午6:30写道：
>
> On Thu, Sep 27, 2018 at 11:05:13PM +0800, Zihan Yang wrote:
> > Laszlo Ersek <lersek at redhat.com> 于2018年9月26日周三 上午1:17写道：
> > > First, I fail to see the use case where ~256 PCI bus numbers aren't
> > > enough. If I strain myself, perhaps I can imagine using ~200 PCIe root
> > > ports on Q35 (each of which requires a separate bus number), so that we
> > > can independently hot-plug 200 devices then. And that's supposedly not
> > > enough, because we want... 300? 400? A thousand? Doesn't sound realistic
> > > to me. (This is not meant to be a strawman argument, I really have no
> > > idea what the feature would be useful for.)
> >
> > It might not be very intuitive, but it indeed exists. The very
> > beginning discussion
> > about 4 months ago has mentioned a possible use case, and I paste it here
> [...]
> > Things might change in the future if we can figure out a better solution, and I
> > hope we can have an easier and more elegant solution in OVMF. But now
> > we are just trying to give a possible solution as a poc.
>
> Thanks.  I wasn't aware this was a proof of concept.  (Nor have I been
> following the discussions on the qemu list.)  I don't think it makes
> sense to merge this into the main SeaBIOS repository.  The
> QEMU/firmware interface is already complex and I don't think we should
> complicate it further without a more concrete use case.  In
> particular, it seems unclear if 256 buses is enough or if 1024 buses
> is too little.

Yes, 1024 is indeed an ambiguous bound for now, but can you elaborate how
concrete should the use case be? For example, do we need to know what
they are going to do with so many network/storage devices? Because I
think normal users rarely need so many devices, but those who really want
devices might not always be willing to tell us their internal project status.

Thanks
Zihan

> -Kevin