Re: [Qemu-devel] [PATCH v1] spapr/pci: Fix primary bus number for PCI bridges

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jan 24, 2019 at 01:48:36PM +1100, Alexey Kardashevskiy wrote:
> 
> 
> On 23/01/2019 19:24, David Hildenbrand wrote:
> > While looking at the s390x implementation, looks like spapr has a
> > similar BUG when building the topology.
> > 
> > The primary bus number corresponds always to the bus number of the
> > bus the bridge is attached to.
> > 
> > Right now, if we have two bridges attached to the same bus (e.g. root
> > bus) this is however not the case. The first bridge will have primary
> > bus 0, the second bridge primary bus 1, which is wrong. Fix the assignment.
> > 
> > While at it, drop setting the PCI_SUBORDINATE_BUS temporarily to 0xff.
> > Setting it temporarily to that value (as discussed e.g. in [1]), is
> > only relevant for a running system that probes the buses. The value is
> > effectively unused for us just doing a DFS.
> 
> What is DFS?
> 
> > 
> > [1] http://www.science.unitn.it/~fiorella/guidelinux/tlk/node76.html
> > 
> > Note: Is hotplug of bridges supported? I can't find where the topology
> > is fixed up when hotplugging a PCI bridge. (e.g. bus numbers assigned
> > and PCI_SUBORDINATE_BUS of path to the root updated). But maybe we are
> > excluding bridges or this is not necessary for some reason.
> > 
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> 
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Applied, thanks.

> 
> 
> > ---
> >  hw/ppc/spapr_pci.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> > index b74f2632ec..5cdc98513d 100644
> > --- a/hw/ppc/spapr_pci.c
> > +++ b/hw/ppc/spapr_pci.c
> > @@ -2030,8 +2030,6 @@ static void spapr_phb_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
> >                                             void *opaque)
> >  {
> >      unsigned int *bus_no = opaque;
> > -    unsigned int primary = *bus_no;
> > -    unsigned int subordinate = 0xff;
> >      PCIBus *sec_bus = NULL;
> >  
> >      if ((pci_default_read_config(pdev, PCI_HEADER_TYPE, 1) !=
> > @@ -2040,7 +2038,7 @@ static void spapr_phb_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
> >      }
> >  
> >      (*bus_no)++;
> > -    pci_default_write_config(pdev, PCI_PRIMARY_BUS, primary, 1);
> > +    pci_default_write_config(pdev, PCI_PRIMARY_BUS, pci_dev_bus_num(pdev), 1);
> >      pci_default_write_config(pdev, PCI_SECONDARY_BUS, *bus_no, 1);
> >      pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, *bus_no, 1);
> >  
> > @@ -2049,7 +2047,6 @@ static void spapr_phb_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
> >          return;
> >      }
> >  
> > -    pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, subordinate, 1);
> >      pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
> >                          spapr_phb_pci_enumerate_bridge, bus_no);
> >      pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, *bus_no, 1);
> > 
> 

-- 
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

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