Re: [Qemu-devel] [PATCH 6/8] pci: Simpler implementation of primary PCI bus

[David Gibson]

On Wed, May 29, 2013 at 12:55:53PM +0300, Michael S. Tsirkin wrote:
> On Wed, May 29, 2013 at 07:43:41PM +1000, David Gibson wrote:
> > On Thu, May 23, 2013 at 10:16:27PM +1000, David Gibson wrote:
> > > On Thu, May 23, 2013 at 02:22:30PM +0300, Michael S. Tsirkin wrote:
> > > > On Thu, May 09, 2013 at 10:31:10AM +1000, David Gibson wrote:
> > > > > Currently pci_get_primary_bus() searches the list of root buses for 
> > > > > one
> > > > > with domain 0.  But since host buses are always registered with 
> > > > > domain 0,
> > > > > this just amounts to finding the only PCI host bus.
> > > > > 
> > > > > This simplifies the implementation by defining the primary PCI bus to
> > > > > be the first one registered, using a global variable to track it.
> > > > > 
> > > > > Signed-off-by: David Gibson <address@hidden>
> > > > 
> > > > Or better: can we just fail if there is more than
> > > > one root?
> > > 
> > > That might work, I'll look into doing that.
> > 
> > So, the difficulty with this is that then any machine with multiple
> > PCI bridges could not use pci_nic_init(), since it calls
> > pci_get_bus_devfn() which calls pci_find_primary_bus() which would
> > always fail.  And using pci_nic_init() is more or less mandatory in
> > the machine_init function to support old-style nic configuration.
> > 
> > Suggestions?
> 
> You mean multiple PCI roots?
> Well, there are no legacy machines with multiple roots to support, are
> there?  So why do we need to support legacy flags for these new
> configurations?

Because people expect them.  Plus on spapr we already support the
legacy nic options; it would be very strange for them to suddenly
break when we add a second host bridge.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

signature.asc
Description: Digital signature