Re: [RFC 0/3] acpi: cphp: add CPHP_GET_CPU_ID_CMD command to cpu hotplug MMIO interface

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Oct 09, 2019 at 09:22:49AM -0400, Igor Mammedov wrote:
> As an alternative to passing to firmware topology info via new fwcfg files
> so it could recreate APIC IDs based on it and order CPUs are enumerated,
> 
> extend CPU hotplug interface to return APIC ID as response to the new command
> CPHP_GET_CPU_ID_CMD.

One big piece missing here is motivation:
Who's going to use this interface?

So far CPU hotplug was used by the ACPI, so we didn't
really commit to a fixed interface too strongly.

Is this a replacement to Laszlo's fw cfg interface?
If yes is the idea that OVMF going to depend on CPU hotplug directly then?
It does not depend on it now, does it?

If answers to all of the above is yes, then I don't really like it: it
is better to keep all paravirt stuff in one place, namely in fw cfg.



> 
> CC: Laszlo Ersek <lersek@redhat.com>
> CC: Eduardo Habkost <ehabkost@redhat.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Gerd Hoffmann <kraxel@redhat.com>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Philippe Mathieu-Daudé <philmd@redhat.com>
> CC: Richard Henderson <rth@twiddle.net>
>  
> Igor Mammedov (3):
>   acpi: cpuhp: fix 'Command data' description is spec
>   acpi: cpuhp: add typical usecases into spec
>   acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command
> 
>  docs/specs/acpi_cpu_hotplug.txt | 37 ++++++++++++++++++++++++++++++---
>  hw/acpi/cpu.c                   | 15 +++++++++++++
>  hw/acpi/trace-events            |  1 +
>  3 files changed, 50 insertions(+), 3 deletions(-)
> 
> -- 
> 2.18.1