[SeaBIOS] [PATCH 2/2] fw/pci: map memory and IO regions for multiple pci root buses

[Kevin O'Connor]

On Mon, Nov 24, 2014 at 09:38:38PM +0200, Marcel Apfelbaum wrote:
> On Mon, 2014-11-24 at 13:01 -0500, Kevin O'Connor wrote:
> > On Mon, Nov 24, 2014 at 12:21:31PM -0500, Kevin O'Connor wrote:
> > > On Mon, Nov 24, 2014 at 03:28:52PM +0100, Gerd Hoffmann wrote:
> > > > I think I would try to reuse the existing code which does the same for
> > > > bridges.  Reuse "struct pci_bus" to add one more level (and maybe rename
> > > > the struct), then have the resource propagation code in
> > > > pci_bios_check_devices() do the job.
> > > > 
> > > > That will need some reorganization, because the simple "struct pci_bus
> > > > *busses" array indexed by bus number will not work any more.
> > > 
> > > Why not just pretend that the extra root PCI buses are children of bus
> > > zero (for resource sizing and mapping purposes).
> > 
> > Thinking about this further, an even easier route may be to just place
> > all devices on the extra root PCI buses in busses[0].  If I understand
> > it correctly, when a system has more than one PCI root bus, all the
> > root buses snoop all mem and io accesses, so there isn't a requirement
> > for the io/mem regions to be continuous for that bus.
> While from the host bridges perspective you are right,
> from the OS point of view we have a problem, at least for APCI based ones.
> They want disjoint IO/mem ranges for each primary root bus.
> (See: http://www.acpi.info/acpi_faq.htm)
> 
> I have a POC on a private branch with a working version and especially Windows
> needs the disjoint regions.
> 
> However, we can do the above and broke the _CRS into little pieces, one for each device.
> This will work, but maybe is not elegant and we may end with a lot of problems on QEMU side.
> What do you think?

If it's better to group the allocations for a given root bus together,
then I'd just go with my first email - pretend each extra root bus is
a child of bus zero for allocation purposes, and then audit the code
so that it works with bus->bus_dev == NULL.

I do wonder why it's better to have extra PCI root buses instead of
using PCI-to-PCI buses, but I guess I'll find out when I read your
RFC.

-Kevin