Re: [PATCH v1 02/23] pc/q35: Apply PCI bus BSEL property for Xen PCI device hotplug

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 21 Jun 2023 13:24:42 -0400
Joel Upham <jupham125@gmail.com> wrote:

> On Wed, Jun 21, 2023 at 7:28 AM Igor Mammedov <imammedo@redhat.com> wrote:
> 
> > On Tue, 20 Jun 2023 13:24:36 -0400
> > Joel Upham <jupham125@gmail.com> wrote:
> >  
> > > On Q35 we still need to assign BSEL property to bus(es) for PCI device
> > > add/hotplug to work.
> > > Extend acpi_set_pci_info() function to support Q35 as well. This patch  
> > adds new (trivial)  
> > > function find_q35() which returns root PCIBus object on Q35, in a way
> > > similar to what find_i440fx does.  
> >
> > I think patch is mostly obsolete, q35 ACPI PCI hotplug is supported in
> > upstream QEMU.
> >
> > Also see comment below.
> >
> > I make use of the find_q35() function in later patches, but I agree now a  
> majority of this patch is a bit different.

There is likely an existing alternative already. (probably introduced by ACPI PIC hotplug for q35)
> 
> > >
> > > Signed-off-by: Alexey Gerasimenko <x1917x@xxxxxxxxx>
> > > Signed-off-by: Joel Upham <jupham125@gmail.com>
> > > ---
> > >  hw/acpi/pcihp.c      | 4 +++-
> > >  hw/pci-host/q35.c    | 9 +++++++++
> > >  include/hw/i386/pc.h | 3 +++
> > >  3 files changed, 15 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> > > index cdd6f775a1..f4e39d7a9c 100644
> > > --- a/hw/acpi/pcihp.c
> > > +++ b/hw/acpi/pcihp.c
> > > @@ -40,6 +40,7 @@
> > >  #include "qapi/error.h"
> > >  #include "qom/qom-qobject.h"
> > >  #include "trace.h"
> > > +#include "sysemu/xen.h"
> > >
> > >  #define ACPI_PCIHP_SIZE 0x0018
> > >  #define PCI_UP_BASE 0x0000
> > > @@ -84,7 +85,8 @@ static void *acpi_set_bsel(PCIBus *bus, void *opaque)
> > >      bool is_bridge = IS_PCI_BRIDGE(br);
> > >
> > >      /* hotplugged bridges can't be described in ACPI ignore them */
> > > -    if (qbus_is_hotpluggable(BUS(bus))) {  
> >  
> > > +    /* Xen requires hotplugging to the root device, even on the Q35  
> > chipset */
> > pls explain what 'root device' is.
> > Why can't you use root-ports for hotplug?
> >
> > Wording may have been incorrect.  Root port is correct. This may not be  
> needed anymore,
> and may have been left over for when I was debugging PCIe hotplugging
> problems.
> I will retest and fix patch once I know more. Xen expects the PCIe device
> to be on the root port.
> 
> I can move the function to a different patch that uses it.
> 
> > > +    if (qbus_is_hotpluggable(BUS(bus)) || xen_enabled()) {
> > >          if (!is_bridge || (!br->hotplugged &&  
> > info->has_bridge_hotplug)) {  
> > >              bus_bsel = g_malloc(sizeof *bus_bsel);
> > >
> > > diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
> > > index fd18920e7f..fe5fc0f47c 100644
> > > --- a/hw/pci-host/q35.c
> > > +++ b/hw/pci-host/q35.c
> > > @@ -259,6 +259,15 @@ static void q35_host_initfn(Object *obj)
> > >                               qdev_prop_allow_set_link_before_realize,  
> > 0);  
> > >  }
> > >
> > > +PCIBus *find_q35(void)
> > > +{
> > > +    PCIHostState *s = OBJECT_CHECK(PCIHostState,
> > > +                                   object_resolve_path("/machine/q35",  
> > NULL),  
> > > +                                   TYPE_PCI_HOST_BRIDGE);
> > > +    return s ? s->bus : NULL;
> > > +}
> > > +
> > > +
> > >  static const TypeInfo q35_host_info = {
> > >      .name       = TYPE_Q35_HOST_DEVICE,
> > >      .parent     = TYPE_PCIE_HOST_BRIDGE,
> > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > > index c661e9cc80..550f8fa221 100644
> > > --- a/include/hw/i386/pc.h
> > > +++ b/include/hw/i386/pc.h
> > > @@ -196,6 +196,9 @@ void pc_madt_cpu_entry(int uid, const CPUArchIdList  
> > *apic_ids,  
> > >  /* sgx.c */
> > >  void pc_machine_init_sgx_epc(PCMachineState *pcms);
> > >
> > > +/* q35.c */
> > > +PCIBus *find_q35(void);
> > > +
> > >  extern GlobalProperty pc_compat_8_0[];
> > >  extern const size_t pc_compat_8_0_len;
> > >  
> >
> >