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

[Philippe Mathieu-Daudé]

On 3/19/20 11:02 AM, Paolo Bonzini wrote:
> On 19/03/20 10:42, Philippe Mathieu-Daudé wrote:
>> 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):
> 
> Right, I should have been more verbose.  You mentioned I/O port 0xaf00
> which is CPU hotplug.  Perhaps unless you can also crash with PCI
> hotplug (0xae00-0xae0f) it's worth removing only CPU hotplug from MIPS
> machines, and keep PCI hotplug.

I am sorry I don't understand what PCI hotplug has to do with PIIX which
is a PCI-slave southbridge... If MIPS or other arch is interested in PCI
hotplug feature, that would be managed by the northbridge or another PCI
bridge.

> 
> Paolo
> 
>> 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);
>>     }
>> }
>>
>