RE: [PATCH RFC V2 10/37] arm/acpi: Enable ACPI support for vcpu hotplug

[Salil Mehta]

Hi Gavin,

> From: Gavin Shan <gshan@redhat.com>
> Sent: Thursday, September 28, 2023 1:26 AM
> To: Salil Mehta <salil.mehta@huawei.com>; qemu-devel@nongnu.org; 
> qemu-arm@nongnu.org
> Cc: 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; will@kernel.org; ardb@kernel.org;
> oliver.upton@linux.dev; pbonzini@redhat.com; mst@redhat.com;
> rafael@kernel.org; borntraeger@linux.ibm.com; alex.bennee@linaro.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
> Subject: Re: [PATCH RFC V2 10/37] arm/acpi: Enable ACPI support for vcpu
> hotplug
> 
> Hi Salil,
> 
> On 9/26/23 20:04, Salil Mehta wrote:
> > ACPI is required to interface QEMU with the guest. Roughly falls into below
> > cases,
> >
> > 1. Convey the possible vcpus config at the machine init time to the guest
> >     using various DSDT tables like MADT etc.
> > 2. Convey vcpu hotplug events to guest(using GED)
> > 3. Assist in evaluation of various ACPI methods(like _EVT, _STA, _OST, _EJ0,
> >     _MAT etc.)
> > 4. Provides ACPI cpu hotplug state and 12 Byte memory mapped cpu hotplug
> >     control register interface to the OSPM/guest corresponding to each 
> > possible
> >     vcpu. The register interface consists of various R/W fields and their
> >     handling operations. These are called whenever register fields or memory
> >     regions are accessed(i.e. read or written) by OSPM when ever it 
> > evaluates
> >     various ACPI methods.
> >
> > Note: lot of this framework code is inherited from the changes already done 
> > for
> >        x86 but still some minor changes are required to make it compatible 
> > with
> >        ARM64.)
> >
> > This patch enables the ACPI support for virtual cpu hotplug. ACPI changes
> > required will follow in subsequent patches.
> >
> > Co-developed-by: Salil Mehta <salil.mehta@huawei.com>
> > Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> > Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> > Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> > ---
> >   hw/arm/Kconfig | 1 +
> >   1 file changed, 1 insertion(+)
> >
> 
> I assume this patch needs to be moved around to last one, until vCPU hotplug
> is supported in the code base.

In that case subsequent patches will not get compiled till this
switch is not enabled. git-bisect wont work correctly in case of
compilation failure is observed in previous patches when this
switch gets compiled eventually.

With the current order every subsequent patch is getting compiled.
And in fact in this case you can even bring up the system. Later
was not a requirement though.

Also, this patch cannot be beyond the patch where functions defined
in the patches subsequent to this will get called. For example,
build_cpus_aml() i.e. [Patch RFC V2 17/37]

Thanks
Salil.