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

[Philippe Mathieu-Daudé]

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-
> > philippe@linaro.org; Jonathan Cameron <jonathan.cameron@huawei.com>;
> > lpieralisi@kernel.org; peter.maydell@linaro.org;
> > richard.henderson@linaro.org; imammedo@redhat.com; andrew.jones@linux.dev;
> > david@redhat.com; philmd@linaro.org; eric.auger@redhat.com;
> > oliver.upton@linux.dev; pbonzini@redhat.com; mst@redhat.com;
> > will@kernel.org; gshan@redhat.com; rafael@kernel.org;
> > linux@armlinux.org.uk; darren@os.amperecomputing.com;
> > ilkka@os.amperecomputing.com; vishnu@os.amperecomputing.com;
> > karl.heubaum@oracle.com; miguel.luis@oracle.com; salil.mehta@opnsrc.net;
> > zhukeqian <zhukeqian1@huawei.com>; wangxiongfeng (C)
> > <wangxiongfeng2@huawei.com>; wangyanan (Y) <wangyanan55@huawei.com>;
> > jiakernel2@gmail.com; maobibo@loongson.cn; lixianglai@loongson.cn; Linuxarm
> > <linuxarm@huawei.com>
> > 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(+)