Re: [edk2-devel] [PATCH edk2-platforms v6 2/7] Platform/SbsaQemu: read amount of cpus during init

["Ard Biesheuvel" <ardb@kernel.org>]

On Tue, 19 Mar 2024 at 11:25, Marcin Juszkiewicz
<marcin.juszkiewicz@linaro.org> wrote:
>
> W dniu 15.03.2024 o 12:49, Marcin Juszkiewicz pisze:
> > W dniu 14.03.2024 o 16:13, Ard Biesheuvel pisze:
>
> >> How is it guaranteed that other components will only see the correct
> >> core count? DXE dispatch is ordered using a dependency graph, so all
> >> users of this PCD should never execute before this driver.
> >
> > SbsaQemuPlatformDxe is a DXE, right? So it is called on platform init.
> >
> > At the end of initialization it calls SbsaQemuGetCpuCount() from
> > SbsaQemuHardwareInfoLib to SET this PCD. It does not use it during
> > platform init cause it does not require this information. But calls
> > function to make sure that amount of cpus is known to whatever will be
> > called later.
> >
> > Sure, maybe SbsaQemuHardwareInfoLib should be something else (DXE,
> > Protocol or other EDK2 magic thing) but it is set of functions to be
> > called from other places of EDK2.
>
> EDK2 starts and one of the first DXE called is SbsaQemuPlatformDxe one:
>

How is this guaranteed? DXE are generally dispatched in the order in
which they appear in the FDF, but only if all DEPEX dependencies are
satisfied. DEPEXes are compiled from the DXE .inf along with all its
[recursive] library dependencies, so upstream changes could affect the
DEPEX of SbsaQemuPlatformDxe, and therefore where it appears in the
dispatch order.

None of the below is relevant, really. If you want to rely on dynamic
PCDs in DXE, the only safe way to set them is from the PEI phase.


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#116891): https://edk2.groups.io/g/devel/message/116891
Mute This Topic: https://groups.io/mt/104763764/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-