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

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

On 3/19/20 10:36 AM, Paolo Bonzini wrote:
> On 18/03/20 23:15, Philippe Mathieu-Daudé wrote:
>> 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.
> 
> Yes, all hotplug stuff (PCI/memory/CPU) are custom additions by QEMU.
> 
>> +    DEFINE_PROP_BOOL("system-hotplug-support", PIIX4PMState,
>> +                     use_acpi_system_hotplug, true),
> 
> Why not cpu-hotplug-support?

Because I have no idea what this code is about, and it seems more than 
cpu (pci, memory):

static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
                                            PCIBus *bus, PIIX4PMState *s)
{
     memory_region_init_io(&s->io_gpe, OBJECT(s), &piix4_gpe_ops, s,
                           "acpi-gpe0", GPE_LEN);
     memory_region_add_subregion(parent, GPE_BASE, &s->io_gpe);

     acpi_pcihp_init(OBJECT(s), &s->acpi_pci_hotplug, bus, parent,
                     s->use_acpi_pci_hotplug);

     s->cpu_hotplug_legacy = true;
     object_property_add_bool(OBJECT(s), "cpu-hotplug-legacy",
                              piix4_get_cpu_hotplug_legacy,
                              piix4_set_cpu_hotplug_legacy,
                              NULL);
     legacy_acpi_cpu_hotplug_init(parent, OBJECT(s), &s->gpe_cpu,
                                  PIIX4_CPU_HOTPLUG_IO_BASE);

     if (s->acpi_memory_hotplug.is_enabled) {
         acpi_memory_hotplug_init(parent, OBJECT(s), 
&s->acpi_memory_hotplug,
                                  ACPI_MEMORY_HOTPLUG_BASE);
     }
}