Re: [Qemu-devel] [PATCH 3/4] hw:acpi:pcihp: assume root PCI bus if bus has no ACPI_PCIHP_PROP_BSEL property

[Igor Mammedov <imammedo@redhat.com>]

On Sun, 26 Jan 2014 12:02:23 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Jan 21, 2014 at 03:40:05PM +0100, Igor Mammedov wrote:
> > when running with machine types older than 1.7 (i.e. without ACPI
> > builtin tables), PCI bus won't have ACPI_PCIHP_PROP_BSEL property
> > set.
> > Taking in account that acpi hotplug handler in 1.7 and older
> > machines is called only for root PCI bus, to make pcihp code
> > compatible with legacy machine types assume that bus without
> > ACPI_PCIHP_PROP_BSEL property has it equal to 0 and bail out
> > if it's not root bus.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> 
> I think that's not the best way to do this.
> If bsel 0 *is* set on some bus, it should select it.
> Fallback to bus 0 only if bsel value 0 is not set anywhere.
> See e.g. how acpi_pcihp_find_hotplug_bus does it:
> 
>     if (!bsel && !find.bus) {
>         find.bus = s->root;
>     }
> 
> otherwise we introduce dependency on the logic that sets
> bsel, this makes code fragile.
Or to avoid touching PCIHP code, as an alternative
we can add BSEL property to root bus and set it to 0 when
running in compatibility mode (!use_acpi_pci_hotplug).

> 
> > ---
> >  hw/acpi/pcihp.c |   10 +++-------
> >  1 files changed, 3 insertions(+), 7 deletions(-)
> > 
> > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> > index 6d34fe9..76dce8d 100644
> > --- a/hw/acpi/pcihp.c
> > +++ b/hw/acpi/pcihp.c
> > @@ -63,14 +63,10 @@ static int acpi_pcihp_get_bsel(PCIBus *bus)
> >  {
> >      QObject *o = object_property_get_qobject(OBJECT(bus),
> >                                               ACPI_PCIHP_PROP_BSEL, NULL);
> > -    int64_t bsel = -1;
> >      if (o) {
> > -        bsel = qint_get_int(qobject_to_qint(o));
> > +        return qint_get_int(qobject_to_qint(o));
> >      }
> > -    if (bsel < 0) {
> > -        return -1;
> > -    }
> > -    return bsel;
> > +    return 0;
> >  }
> >  
> >  static void acpi_pcihp_test_hotplug_bus(PCIBus *bus, void *opaque)
> > @@ -190,7 +186,7 @@ int acpi_pcihp_device_hotplug(AcpiPciHpState *s, PCIDevice *dev,
> >  {
> >      int slot = PCI_SLOT(dev->devfn);
> >      int bsel = acpi_pcihp_get_bsel(dev->bus);
> > -    if (bsel < 0) {
> > +    if ((bsel == 0) && (dev->bus != s->root)) {
> >          return -1;
> >      }
> >  
> > -- 
> > 1.7.1