pc: piix4_pm: init legacy PCI hotplug when running on Xen

If user starts QEMU with "-machine pc,accel=xen", then
compat property in xenfv won't work and it would cause error:
"Unsupported bus. Bus doesn't have property 'acpi-pcihp-bsel' set"
when PCI device is added with -device on QEMU CLI.

From: Igor Mammedov <imammedo@redhat.com>

In case of Xen instead of using compat property, just use the fact
that xen doesn't use QEMU's fw_cfg/acpi tables to switch piix4_pm
into legacy PCI hotplug mode when Xen is enabled.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Li Liang <liang.z.li@intel.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>

hw/acpi/piix4.c

@@ -36,6 +36,7 @@
 #include "hw/mem/pc-dimm.h"
 #include "hw/acpi/memory_hotplug.h"
 #include "hw/acpi/acpi_dev_interface.h"
+#include "hw/xen/xen.h"
 
 //#define DEBUG
 
@@ -501,6 +502,9 @@ I2CBus *piix4_pm_init(PCIBus *bus, int devfn, uint32_t smb_io_base,
     s->irq = sci_irq;
     s->smi_irq = smi_irq;
     s->kvm_enabled = kvm_enabled;
+    if (xen_enabled()) {
+        s->use_acpi_pci_hotplug = false;
+    }
 
     qdev_init_nofail(dev);
 

hw/i386/pc_piix.c

@@ -916,17 +916,6 @@ static QEMUMachine xenfv_machine = {
     .max_cpus = HVM_MAX_VCPUS,
     .default_machine_opts = "accel=xen",
     .hot_add_cpu = pc_hot_add_cpu,
-    .compat_props = (GlobalProperty[]) {
-        /* xenfv has no fwcfg and so does not load acpi from QEMU.
-         * as such new acpi features don't work.
-         */
-        {
-            .driver   = "PIIX4_PM",
-            .property = "acpi-pci-hotplug-with-bridge-support",
-            .value    = "off",
-        },
-        { /* end of list */ }
-    },
 };
 #endif