Re: [PATCH 3/9] hw/acpi: Add ACPI CPU hotplug init stub

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Salil,

On 29/9/23 17:47, Salil Mehta wrote:
>> From: Alex Bennée <alex.bennee@linaro.org>
>> Sent: Friday, September 29, 2023 3:27 PM
>> To: Salil Mehta <salil.mehta@huawei.com>
>> Cc: qemu-devel@nongnu.org; qemu-arm@nongnu.org; maz@kernel.org; jean-
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>> Subject: Re: [PATCH 3/9] hw/acpi: Add ACPI CPU hotplug init stub
>>
>>
>> Salil Mehta <salil.mehta@huawei.com> writes:
>>
>>> ACPI CPU hotplug related initialization should only happen if ACPI_CPU_HOTPLUG
>>> support has been enabled for particular architecture. Add cpu_hotplug_hw_init()
>>> stub to avoid compilation break.
>>
>> When does the compilation break? It's usually ok to include stubs with
>> that commit.
> 
> 
> To be specific. it is not a compilation break but linking error.
> 
> Support of ACPI_CPU_HOTPLUG is optional. This flag is defined in architecture
> specific Kconfig. Function cpu_hotplug_hw_init() is part of the hw/acpi/cpu.c
> which gets compiled only when a particular architecture defines ACPI_CPU_HOTPLUG
> flag.
> 
> ACPI GED framework support for CPU Hotplug is not specific to any architecture.
> acpi_ged_initfn() calls cpu_hotplug_hw_init() when GED device gets created.
> This functions gets called irrespective of the fact CPU Hotplug is supported or
> not. If ACPI_CPU_HOTPLUG is not enabled then presence of cpu_hotplug_hw_init()
> will cause linking error without the presence of stub.

We can extract the common pattern in both
- ich9_pm_set_cpu_hotplug_legacy()
- piix4_set_cpu_hotplug_legacy()
to take (AcpiCpuHotplug, CPUHotplugState) params,
then guard the cpu_hotplug_hw_init() call within
CONFIG_ACPI_CPU_HOTPLUG ifdef'ry. Doing so we can
also remove the acpi_switch_to_modern_cphp() stub.

Regards,

Phil.

>>> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
>>> ---
>>>   hw/acpi/acpi-cpu-hotplug-stub.c | 6 ++++++
>>>   1 file changed, 6 insertions(+)