Re: [Patch v4 12/16] x86, irq, ACPI: Implement interface to support ACPI based IOAPIC hot-addition

Jiang Liu
2014-09-11T06:08:32Z

On 2014/9/11 4:06, Thomas Gleixner wrote:
> On Wed, 10 Sep 2014, Jiang Liu wrote:
>>>> int mp_register_ioapic(int id, u32 address, u32 gsi_base,
>>>> @@ -3867,8 +3873,15 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
>>>> }
>>>> for_each_ioapic(ioapic)
>>>> if (ioapics[ioapic].mp_config.apicaddr == address) {
>>>> - pr_warn("address 0x%x conflicts with IOAPIC%d\n",
>>>> - address, ioapic);
>>>> + /*
>>>> + * IOAPIC unit may also be visible in PCI scope.
>>>> + * When ioapic PCI driver's probe() is called,
>>>> + * the IOAPIC unit may have already been initialized
>>>> + * at boot time.
>>>> + */
>>>> + if (!ioapic_initialized)
>>>> + pr_warn("address 0x%x conflicts with IOAPIC%d\n",
>>>> + address, ioapic);
>>>
>>> Hmm. This smells fishy. Why do we allow multiple initializations of
>>> the same IOAPIC in the first place. Either it's done via ACPI or via
>>> PCI, but not both.
>> The ACPI subsystem will register and initialize all IOAPICs when walking
>> ACPI MADT table during boot, before initializing PCI subsystem.
>> Later when binding ioapic PCI driver to IOAPIC PCI device, it will try
>> to register the IOAPIC device again.
>>
>> After this patchset is applied, we could remove the !ioapic_initialized
>> check. We check acpi_ioapic_register() before calling
>> acpi_register_ioapic(). So the check becomes redundant.
>> Or we could remove the temporary code from this patch.
>
> How about removing the disfunctional ioapic PCI driver first and then
> implementing the whole thing cleanly?
>
>>>
>>>> return -EEXIST;
>>>> }
>>>>
>>>> @@ -3918,6 +3931,14 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
>>>> ioapics[idx].irqdomain = NULL;
>>>> ioapics[idx].irqdomain_cfg = *cfg;
>>>>
>>>> + if (ioapic_initialized) {
>>>
>>> I have a hard time to understand this conditional. Why can't we do
>>> that unconditionally?
>> How about following comments?
>> /*
>> * If mp_register_ioapic() is called during early boot stage when
>> * walking ACPI/SFI/DT tables, it's too early to create irqdomain,
>> * we are still using bootmem allocator. So delay it to setup_IO_APIC().
>> */
>
> Fine, but then the "if (ioapic_initialized)" conditional still does
> not make sense. We surely have some global non ioapic specific
> indicator that bootmem is done and the proper memory allocator is
> available, right?
Maybe a good name helps here. How about
bool hotplug = !!ioapic_initialized;

if (hotplug)
mp_irqdomain_create(idx);

Regards!
Gerry

>
> Aside of that is there a point to walk those tables before we actually
> can make any use of their content?
>
> Thanks,
>
> tglx
>