Re: [PATCH v3 1/4] ArmPkg: Replace CoreId and ClusterId with Mpidr in ARM_CORE_INFO struct

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

On Sun, 30 Jan 2022 at 11:44, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> Hello Rebecca,
>
> On Thu, 16 Dec 2021 at 04:46, Rebecca Cran <rebecca@nuviainc.com> wrote:
> >
> > Remove the ClusterId and CoreId fields in the ARM_CORE_INFO structure in
> > favor of a new Mpidr field. Update code in
> > ArmPlatformPkg/PrePeiCore/MainMPCore and ArmPlatformPkg/PrePi/MainMPCore.c
> > to use the new field and call new macros GET_MPIDR_AFF0 and GET_MPIDR_AFF1
> > instead.
> >
> > Signed-off-by: Rebecca Cran <rebecca@nuviainc.com>
>
> I am going to merge this patch into EDK2 in isolation, along with the
> edk2-platforms changes to keep things working.
>
> For the remainder of the series, there are two issues that I think
> should be resolved. Apologies for not mentioning this before.
>
> 1) Can we make the MP protocol a separate driver? That would be
> cleaner in terms of breakage of other platforms re MpInitLib, and it
> would also help with the next point.
>
> 2) I don't see any management of coherency between the BSP and the APs
> (unless I am missing something). I think it would be best to treat APs
> as non-coherent masters (given that they boot with the MMU disabled),
> which means that every variable in memory that is used to pass
> information between BSP and AP needs to be DMA mapped and unmapped
> appropriately, and follow the ownership rules of DMA mappings.
>
> On platforms where none of this is needed, the DmaLib dependency can
> be satisfied by CoherentDmaLib, whereas other platforms can use the
> non-coherent version instead, which does all the tedious cache
> maintenance.
>
> Given that library dependencies can be specified per-driver in .DSC
> file, using a separate driver permits us to pick the right DmaLib
> without forcing it upon other parts of the code. It should also
> prevent circular dependency issues for DmaLib implementations that
> DEPEX on the CPU arch protocol produced by CpuDxe.
>

I've had a stab at refactoring this code. Branch can be found here:
https://github.com/ardbiesheuvel/edk2/tree/armpkg-mpservicesdxe-refactor

This still needs the coherency management changes, I'll have a go at
that later this week unless anyone else beats me to it.