[PATCH-for-5.0 1/2] hw/acpi/piix4: Add 'system-hotplug-support' property

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

The I/O ranges registered by the piix4_acpi_system_hot_add_init()
function are not documented in the PIIX4 datasheet.
This appears to be a PC-only feature added in commit 5e3cb5347e
("initialize hot add system / acpi gpe") which was then moved
to the PIIX4 device model in commit 9d5e77a22f ("make
qemu_system_device_hot_add piix independent")
Add a property (default enabled, to not modify the current
behavior) to allow machines wanting to model a simple PIIX4
to disable this feature.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
Should I squash this with the next patch and start with
default=false, which is closer to the hardware model?
---
 hw/acpi/piix4.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
index 964d6f5990..9c970336ac 100644
--- a/hw/acpi/piix4.c
+++ b/hw/acpi/piix4.c
@@ -78,6 +78,7 @@ typedef struct PIIX4PMState {
 
     AcpiPciHpState acpi_pci_hotplug;
     bool use_acpi_pci_hotplug;
+    bool use_acpi_system_hotplug;
 
     uint8_t disable_s3;
     uint8_t disable_s4;
@@ -503,8 +504,10 @@ static void piix4_pm_realize(PCIDevice *dev, Error **errp)
     s->machine_ready.notify = piix4_pm_machine_ready;
     qemu_add_machine_init_done_notifier(&s->machine_ready);
 
-    piix4_acpi_system_hot_add_init(pci_address_space_io(dev),
-                                   pci_get_bus(dev), s);
+    if (s->use_acpi_system_hotplug) {
+        piix4_acpi_system_hot_add_init(pci_address_space_io(dev),
+                                       pci_get_bus(dev), s);
+    }
     qbus_set_hotplug_handler(BUS(pci_get_bus(dev)), OBJECT(s), &error_abort);
 
     piix4_pm_add_propeties(s);
@@ -635,6 +638,8 @@ static Property piix4_pm_properties[] = {
                      use_acpi_pci_hotplug, true),
     DEFINE_PROP_BOOL("memory-hotplug-support", PIIX4PMState,
                      acpi_memory_hotplug.is_enabled, true),
+    DEFINE_PROP_BOOL("system-hotplug-support", PIIX4PMState,
+                     use_acpi_system_hotplug, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
-- 
2.21.1