Re: [PATCH v7 2/2] schemas: Add some common reserved-memory usages

[Ard Biesheuvel]

On Mon, 20 Nov 2023 at 21:12, Simon Glass <sjg@xxxxxxxxxxxx> wrote:
>
> Hi,
>
> On Mon, 13 Nov 2023 at 11:09, Chiu, Chasel <chasel.chiu@xxxxxxxxx> wrote:
> >
> >
> > Hi Ard,
> >
> > Please see my reply below inline.
> >
> > Thanks,
> > Chasel
> >
> >
> > > -----Original Message-----
> > > From: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > > Sent: Saturday, November 11, 2023 3:04 AM
> > > To: Chiu, Chasel <chasel.chiu@xxxxxxxxx>
> > > Cc: Simon Glass <sjg@xxxxxxxxxxxx>; devicetree@xxxxxxxxxxxxxxx; Mark Rutland
> > > <mark.rutland@xxxxxxx>; Rob Herring <robh@xxxxxxxxxx>; Tan, Lean Sheng
> > > <sheng.tan@xxxxxxxxxxxxx>; lkml <linux-kernel@xxxxxxxxxxxxxxx>; Dhaval
> > > Sharma <dhaval@xxxxxxxxxxxx>; Brune, Maximilian
> > > <maximilian.brune@xxxxxxxxxxxxx>; Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>;
> > > Dong, Guo <guo.dong@xxxxxxxxx>; Tom Rini <trini@xxxxxxxxxxxx>; ron minnich
> > > <rminnich@xxxxxxxxx>; Guo, Gua <gua.guo@xxxxxxxxx>; linux-
> > > acpi@xxxxxxxxxxxxxxx; U-Boot Mailing List <u-boot@xxxxxxxxxxxxx>
> > > Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory
> > > usages
> > >
> > > On Sat, 11 Nov 2023 at 04:20, Chiu, Chasel <chasel.chiu@xxxxxxxxx> wrote:
> > > >
> > > >
> > > > Just sharing some usage examples from UEFI/EDK2 scenario.
> > > > To support ACPI S4/Hibernation, memory map must be consistent before
> > > > entering and after resuming from S4, in this case payload may need to
> > > > know previous memory map from bootloader (currently generic payload
> > > > cannot access platform/bootloader specific non-volatile data, thus
> > > > could not save/restore memory map information)
> > >
> > > So how would EDK2 reconstruct the entire EFI memory map from just these
> > > unannotated /reserved-memory nodes? The EFI memory map contains much
> > > more information than that, and all of it has to match the pre-hibernate situation,
> > > right? Can you given an example?
> >
> >
> > Here we listed only typically memory types that may change cross different platforms.
> > Reserved memory type already can be handled by reserved-memory node, and rest of the types usually no need to change cross platforms thus currently we could rely on default in generic payload.
> > In the future if we see a need to add new memory types we will discuss and add it to FDT schema.
> >
> >
> >
> > >
> > > > Another usage is to support binary model which generic payload is a prebuilt
> > > binary compatible for all platforms/configurations, however the payload default
> > > memory map might not always work for all the configurations and we want to
> > > allow bootloader to override payload default memory map without recompiling.
> > > >
> > >
> > > Agreed. But can you explain how a EDK2 payload might make meaningful use of
> > > 'runtime-code' regions provided via DT  by the non-EDK2 platform init? Can you
> > > give an example?
> >
> >
> > Runtime-code/data is used by UEFI payload for booting UEFI OS which required UEFI runtime services.
> > Platform Init will select some regions from the usable memory and assign it to runtime-code/data for UPL to consume. Or assign same runtime-code/data from previous boot.
> > If UEFI OS is not supported, PlatformInit may not need to provide runtime-code/data regions to payload. (always providing runtime-code/data should be supported too)
> >
> >
> > >
> > > > Under below assumption:
> > > >         FDT OS impact has been evaluated and taken care by relevant
> > > experts/stakeholders.
> > > > Reviewed-by: Chasel Chiu <chasel.chiu@xxxxxxxxx>
> > > >
> > >
> > > I am sorry but I don't know what 'FDT OS impact' means. We are talking about a
> > > firmware-to-firmware abstraction that has the potential to leak into the OS
> > > visible interface.
> > >
> > > I am a maintainer in the Tianocore project myself, so it would help if you could
> > > explain who these relevant experts and stakeholders are. Was this discussed on
> > > the edk2-devel mailing list? If so, apologies for missing it but I may not have been
> > > cc'ed perhaps?
> >
> >
> >
> >
> > I'm not familiar with FDT OS, also I do not know if who from edk2-devel were supporting FDT OS, I think Simon might be able to connect FDT OS experts/stakeholders.
> > We are mostly focusing on payload firmware phase implementation in edk2 (and other payloads too), however, since we have aligned the payload FDT and OS FDT months ago, I'm assuming FDT OS impact must be there and we need (or already done?) FDT OS experts to support it. (again, maybe Simon could share more information about FDT OS)
> >
> > In edk2 such FDT schema is UefiPayloadPkg internal usage only and payload entry will convert FDT into HOB thus we expected the most of the edk2 generic code are no-touch/no impact, that's why we only had small group (UefiPayloadPkg) discussion.
> > Ard, if you are aware of any edk2 code that's for supporting FDT OS, please let us know and we can discuss if those code were impacted or not.
>
> We discussed this and just to clarify, 'FDT OS' is not a special OS,
> it is just Linux.
>
> So, with the above, are we all on the same page? Can the patch be
> applied, perhaps? If not, what other discussion is needed?
>

An example of how a platform-init/payload combination would make
meaningful use of such runtime-code/data regions.