RE: [edk2-devel] [PATCH 0/1] OvmfPkg/Bhyve: QemuFwCfg support

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From: Corvin Köhne <C.Koehne_at_beckhoff.com>
Date: Tue, 29 Mar 2022 09:57:40 UTC

Hi Gerd,

> There is FW_CFG_NB_CPUS + FW_CFG_MAX_CPUS.  ovmf uses different names,
> see OvmfPkg/Include/IndustryStandard/QemuFwCfg.h
>
> PlatformPei for qemu uses QemuFwCfgItemSmpCpuCount aka FW_CFG_NB_CPUS,
> which is the number of cpus which are online.
>
> I think FW_CFG_MAX_CPUS is basically unused these days.  It played a
> role back when seabios created the acpi tables for cpu hotplug as
> described in the comment above.  In qemu 2.0 & newer the acpi tables are
> generated by qemu instead.  The firmware just downloads them from fw_cfg
> and installs them for the OS, it doesn't need to know virtual machine
> configuration details any more.

The FwCfgItem of this patch is used by bhyve to build the MADT. So, it's
similar to the use case of FW_CFG_MAX_CPUS. At the moment, I'm using
an additional bhyve specific FwCfgItem. I just want to ask, if it makes sense
to use FW_CFG_MAX_CPUS to avoid two items for the same purpose or to
keep it as is.


Best regards
Corvin


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