Re: [Qemu-devel] [PATCH 1/2] pcie_root_port: Allow ACS to be disabled

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 30 Jul 2019 12:13:06 +0100
"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:

> * Igor Mammedov (imammedo@redhat.com) wrote:
> > On Tue, 30 Jul 2019 10:37:18 +0100
> > "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> > 
> > > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > > 
> > > ACS was added in 4.0 unconditionally, this breaks migration
> > > compatibility.
> > > Allow ACS to be disabled by adding a property that's
> > > checked by pcie_root_port.
> > > 
> > > Unfortunately pcie-root-port doesn't have any instance data,
> > > so there's no where for that flag to live, so stuff it into
> > > PCIESlot.
> > > 
> > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > ---
> > >  hw/pci-bridge/pcie_root_port.c | 3 ++-
> > >  include/hw/pci/pcie_port.h     | 2 ++
> > >  2 files changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/pci-bridge/pcie_root_port.c b/hw/pci-bridge/pcie_root_port.c
> > > index 09019ca05d..1d8a778709 100644
> > > --- a/hw/pci-bridge/pcie_root_port.c
> > > +++ b/hw/pci-bridge/pcie_root_port.c
> > > @@ -111,7 +111,7 @@ static void rp_realize(PCIDevice *d, Error **errp)
> > >      pcie_aer_root_init(d);
> > >      rp_aer_vector_update(d);
> > >  
> > > -    if (rpc->acs_offset) {
> > > +    if (rpc->acs_offset && !s->disable_acs) {
> > 
> > it's not like it would be used per instance,
> > so could we use class property and with rpc->disable_acs instead of PCIESlot?
> 
> I'm not clear I understand how class properties help;
>     object_class_property_add_bool
> takes a getter/setter that takes an Object *  parameter;
> my reading of that is that it's the instance data so has the same
> problem.

it's possible to reach class data from setter/getter,
for example s390_cpu_model_class_register_props().

But it will be a bit more code than here and considering
that it's only field in parent type which is reachable through
root port specific property only it is also ok as is as a
fix to 4.1, so if you prefer to keep it like now

Reviewed-by: Igor Mammedov <imammedo@redhat.com>


> Dave
> 
> > >          pcie_acs_init(d, rpc->acs_offset);
> > >      }
> > >      return;
> > > @@ -145,6 +145,7 @@ static void rp_exit(PCIDevice *d)
> > >  static Property rp_props[] = {
> > >      DEFINE_PROP_BIT(COMPAT_PROP_PCP, PCIDevice, cap_present,
> > >                      QEMU_PCIE_SLTCAP_PCP_BITNR, true),
> > > +    DEFINE_PROP_BOOL("disable-acs", PCIESlot, disable_acs, false),
> > >      DEFINE_PROP_END_OF_LIST()
> > >  };
> > >  
> > > diff --git a/include/hw/pci/pcie_port.h b/include/hw/pci/pcie_port.h
> > > index 09586f4641..7515430087 100644
> > > --- a/include/hw/pci/pcie_port.h
> > > +++ b/include/hw/pci/pcie_port.h
> > > @@ -53,6 +53,8 @@ struct PCIESlot {
> > >      PCIExpLinkSpeed speed;
> > >      PCIExpLinkWidth width;
> > >  
> > > +    /* Disable ACS (really for a pcie_root_port) */
> > > +    bool        disable_acs;
> > >      QLIST_ENTRY(PCIESlot) next;
> > >  };
> > >  
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK