Message-ID: <CAPnjgZ19-xR6QxS=fR53skz0VuAty2Z2w2vQTjP7g=tbTFpaqw@mail.gmail.com>
Date:   Tue, 31 Oct 2023 09:56:08 -0600
From:   Simon Glass <sjg@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>, devicetree@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Lean Sheng Tan <sheng.tan@...ements.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Dhaval Sharma <dhaval@...osinc.com>,
        Maximilian Brune <maximilian.brune@...ements.com>,
        Yunhui Cui <cuiyunhui@...edance.com>,
        Guo Dong <guo.dong@...el.com>, Tom Rini <trini@...sulko.com>,
        ron minnich <rminnich@...il.com>, Gua Guo <gua.guo@...el.com>,
        Chiu Chasel <chasel.chiu@...el.com>,
        linux-acpi@...r.kernel.org,
        U-Boot Mailing List <u-boot@...ts.denx.de>
Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory usages

Hi Rob,

On Mon, 16 Oct 2023 at 15:54, Simon Glass <sjg@...omium.org> wrote:
>
> Hi Rob,
>
> On Mon, 16 Oct 2023 at 10:50, Rob Herring <robh@...nel.org> wrote:
> >
> > On Fri, Oct 13, 2023 at 4:09 PM Simon Glass <sjg@...omium.org> wrote:
> > >
> > > Hi Rob,
> > >
> > > On Fri, 13 Oct 2023 at 13:42, Rob Herring <robh@...nel.org> wrote:
> > > >
> > > > On Fri, Oct 6, 2023 at 7:03 PM Simon Glass <sjg@...omium.org> wrote:
> > > > >
> > > > > Hi Ard,
> > > > >
> > > > > On Fri, 6 Oct 2023 at 17:00, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > > >
> > > > > > On Fri, 6 Oct 2023 at 20:17, Simon Glass <sjg@...omium.org> wrote:
> > > > > > >
> > > > > > > Hi Ard,
> > > > > > >
> > > > > > > On Fri, 6 Oct 2023 at 11:33, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > > > > >
> > > > > > > > On Mon, 2 Oct 2023 at 19:54, Simon Glass <sjg@...omium.org> wrote:
> > > > > > > > >
> > > > > > > > > Hi Rob,
> > > > > > > > >
> > > > > > > > > On Tue, 26 Sept 2023 at 13:42, Simon Glass <sjg@...omium.org> wrote:
> > > > > > > > > >
> > > > > > > > > > It is common to split firmware into 'Platform Init', which does the
> > > > > > > > > > initial hardware setup and a "Payload" which selects the OS to be booted.
> > > > > > > > > > Thus an handover interface is required between these two pieces.
> > > > > > > > > >
> > > > > > > > > > Where UEFI boot-time services are not available, but UEFI firmware is
> > > > > > > > > > present on either side of this interface, information about memory usage
> > > > > > > > > > and attributes must be presented to the "Payload" in some form.
> > > > > > > > > >
> > > > > > > > > > This aims to provide an small schema addition for the memory mapping
> > > > > > > > > > needed to keep these two pieces working together well.
> > > > > > > > > >
> > > > > > > > > > Signed-off-by: Simon Glass <sjg@...omium.org>
> > > > > > > > > > ---
> > > > > > > > > >
> > > > > > > > > > Changes in v7:
> > > > > > > > > > - Rename acpi-reclaim to acpi
> > > > > > > > > > - Drop individual mention of when memory can be reclaimed
> > > > > > > > > > - Rewrite the item descriptions
> > > > > > > > > > - Add back the UEFI text (with trepidation)
> > > > > > > > >
> > > > > > > > > I am again checking on this series. Can it be applied, please?
> > > > > > > > >
> > > > > > > >
> > > > > > > > Apologies for the delay in response. I have been away.
> > > > > > >
> > > > > > > OK, I hope you had a nice trip.
> > > > > > >
> > > > > >
> > > > > > Thanks, it was wonderful!
> > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > Changes in v6:
> > > > > > > > > > - Drop mention of UEFI
> > > > > > > > > > - Use compatible strings instead of node names
> > > > > > > > > >
> > > > > > > > > > Changes in v5:
> > > > > > > > > > - Drop the memory-map node (should have done that in v4)
> > > > > > > > > > - Tidy up schema a bit
> > > > > > > > > >
> > > > > > > > > > Changes in v4:
> > > > > > > > > > - Make use of the reserved-memory node instead of creating a new one
> > > > > > > > > >
> > > > > > > > > > Changes in v3:
> > > > > > > > > > - Reword commit message again
> > > > > > > > > > - cc a lot more people, from the FFI patch
> > > > > > > > > > - Split out the attributes into the /memory nodes
> > > > > > > > > >
> > > > > > > > > > Changes in v2:
> > > > > > > > > > - Reword commit message
> > > > > > > > > >
> > > > > > > > > >  .../reserved-memory/common-reserved.yaml      | 71 +++++++++++++++++++
> > > > > > > > > >  1 file changed, 71 insertions(+)
> > > > > > > > > >  create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml
> > > > > > > > > >
> > > > > > > > > > diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml
> > > > > > > > > > new file mode 100644
> > > > > > > > > > index 0000000..f7fbdfd
> > > > > > > > > > --- /dev/null
> > > > > > > > > > +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml
> > > > > > > > > > @@ -0,0 +1,71 @@
> > > > > > > > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > > > > > > > > > +%YAML 1.2
> > > > > > > > > > +---
> > > > > > > > > > +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml#
> > > > > > > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > > > > > > +
> > > > > > > > > > +title: Common memory reservations
> > > > > > > > > > +
> > > > > > > > > > +description: |
> > > > > > > > > > +  Specifies that the reserved memory region can be used for the purpose
> > > > > > > > > > +  indicated by its compatible string.
> > > > > > > > > > +
> > > > > > > > > > +  Clients may reuse this reserved memory if they understand what it is for,
> > > > > > > > > > +  subject to the notes below.
> > > > > > > > > > +
> > > > > > > > > > +maintainers:
> > > > > > > > > > +  - Simon Glass <sjg@...omium.org>
> > > > > > > > > > +
> > > > > > > > > > +allOf:
> > > > > > > > > > +  - $ref: reserved-memory.yaml
> > > > > > > > > > +
> > > > > > > > > > +properties:
> > > > > > > > > > +  compatible:
> > > > > > > > > > +    description: |
> > > > > > > > > > +      This describes some common memory reservations, with the compatible
> > > > > > > > > > +      string indicating what it is used for:
> > > > > > > > > > +
> > > > > > > > > > +         acpi: Advanced Configuration and Power Interface (ACPI) tables
> > > > > > > > > > +         acpi-nvs: ACPI Non-Volatile-Sleeping Memory (NVS). This is reserved by
> > > > > > > > > > +           the firmware for its use and is required to be saved and restored
> > > > > > > > > > +           across an NVS sleep
> > > > > > > > > > +         boot-code: Contains code used for booting which is not needed by the OS
> > > > > > > > > > +         boot-code: Contains data used for booting which is not needed by the OS
> > > > > > > > > > +         runtime-code: Contains code used for interacting with the system when
> > > > > > > > > > +           running the OS
> > > > > > > > > > +         runtime-data: Contains data used for interacting with the system when
> > > > > > > > > > +           running the OS
> > > > > > > > > > +
> > > > > > > > > > +    enum:
> > > > > > > > > > +      - acpi
> > > > > > > > > > +      - acpi-nvs
> > > > > > > > > > +      - boot-code
> > > > > > > > > > +      - boot-data
> > > > > > > > > > +      - runtime-code
> > > > > > > > > > +      - runtime-data
> > > > > > > > > > +
> > > > > > > >
> > > > > > > > As I mentioned a few times already, I don't think these compatibles
> > > > > > > > should be introduced here.
> > > > > > > >
> > > > > > > > A reserved region has a specific purpose, and the compatible should be
> > > > > > > > more descriptive than the enum above. If the consumer does not
> > > > > > > > understand this purpose, it should simply treat the memory as reserved
> > > > > > > > and not touch it. Alternatively, these regions can be referenced from
> > > > > > > > other DT nodes using phandles if needed.
> > > > > > >
> > > > > > > We still need some description of what these regions are used for, so
> > > > > > > that the payload can use the correct regions. I do not have any other
> > > > > > > solution to this problem. We are in v7 at present. At least explain
> > > > > > > where you want the compatible strings to be introduced.
> > > > > > >
> > > > > >
> > > > > > My point is really that by themselves, these regions are not usable by
> > > > > > either a payload or an OS that consumes this information. Unless there
> > > > > > is some other information being provided (via DT I imagine) that
> > > > > > describes how these things are supposed to be used, they are nothing
> > > > > > more than memory reservations that should be honored, and providing
> > > > > > this arbitrary set of labels is unnecessary.
> > > > > >
> > > > > > > What sort of extra detail are you looking for? Please be specific and
> > > > > > > preferably add some suggestions so I can close this out ASAP.
> > > > > > >
> > > > > >
> > > > > > A payload or OS can do nothing with a memory reservation called
> > > > > > 'runtime-code' it it doesn't know what is inside.
> > > >
> > > > Agreed. The question is WHAT runtime-code? The compatible needs to answer that.
> > > >
> > > > For example, we have 'ramoops' as a compatible in reserved memory.
> > > > That tells us *exactly* what's there. We know how to parse it. If we
> > > > know ramoops is not supported, then we know we can toss it out and
> > > > reclaim the memory.
> > >
> > > So if we said:
> > >
> > >    compatible = "runtime-code-efi"
> > >
> > > would that be OK? We seem to be in catch 22 here, because if I don't
> > > mention EFI unhappy, but if I do, Ard is unhappy.
> >
> > Better yes, because then it is for something specific. However, AIUI,
> > that's setup for the OS and defining that region is already defined by
> > the EFI memory map. That's Ard's issue. If there's a need outside of
> > the EFI to OS handoff,
>
> There is a need. Here is part of the commit message again. If there is
> something else you need to know, please ask.
>
> >>>>
> It is common to split firmware into 'Platform Init', which does the
> initial hardware setup and a "Payload" which selects the OS to be booted.
> Thus an handover interface is required between these two pieces.
>
> Where UEFI boot-time services are not available, but UEFI firmware is
> present on either side of this interface, information about memory usage
> and attributes must be presented to the "Payload" in some form.
> <<<
>
> > then you need to define what that usecase looks
> > like. Describe the problem rather than present your solution.
> >
> > If this is all specific to EDK2 then it should say that rather than
> > 'efi'. I imagine Ard would be happier with something tied to EDK2 than
> > *all* UEFI. Though maybe the problem could be any implementation? IDK.
> > Maybe it's TF-A that needs to define where the EFI runtime services
> > region is and that needs to be passed all the way thru to the EFI
> > implementation? So again, define the problem.
>
> It is not specific to EDK2. Imagine this boot sequence:
>
> - Platform Init (U-Boot) starts up
> - U-Boot uses its platform knowledge to sets some ACPI tables and put
> various things in memory
> - U-Boot sets up some runtime code and data for the OS
> - U-Boot jumps to the Tianocore payload **
> - Payload (Tianocore) wants to know where the ACPI tables are, for example
> - Tianocore needs to provide boot services to the OS, so needs to know
> the memory map, etc.
>
> ** At this point we want to use DT to pass the required information.
>
> Of course, Platform Init could be coreboot or Tianocore or some
> strange private binary. Payload could be U-Boot or something else.
> That is the point of this effort, to build interoperability.
>
> >
> > > What about the boottime code....you want to know which project it is from?
> >
> > I think it is the same.
> >
> > >
> > > +      - acpi
> > > +      - acpi-nvs
> > >
> > > Those two should be enough info, right?
> >
> > I think so. NVS is not a term I've heard in relation to ACPI, but that
> > may just be my limited ACPI knowledge.
>
> Perhaps it is only an Intel thing. It stands for Non-Volatile-Sleeping
> Memory and it has various platform settings in a binary format that is
> normally SoC-specific.
>
> >
> > > +      - boot-code
> > > +      - boot-data
> > >
> > > For these, they don't pertain to the OS, so perhaps they are OK?
> >
> > Hard to tell that just from the name... 'boot' could be any component
> > involved in booting including the OS.
>
>  suggested that 'boot' should mean booting the OS. If the OS does lots
> of fixup stuff at the start of it, I don't know what that is called.
>
> So if boot-code is no good, what do you suggest?
>
> Alternatively I could remove these for now, if it will help make progress.
>
> >
> > > In
> > > any case, using a generic term like this makes some sense to me. We
> > > can always add a new compatible like "efi-boottime-services" later. It
> > > may be that the boottime services would be handled by the payload, so
> > > not needed in all cases.
> >
> > Why later? You have a specific use in mind and I imagine Ard has
> > thoughts on that.
>
> Because we don't need it right away, and just want to make some progress.
>
> Perhaps the problem here is that Linux has tied itself up in knots
> with its EFI stuff and DT fixups and what-not. But this is not that.
> It is a simple handoff between two pieces of firmware, Platform Init
> and Payload. It has nothing to do with the OS. With Tianocore they are
> typically combined, but with this usage they are split, and we can
> swap out one project for another on either side of the DT interface.
>
> I do have views on the 'EFI' opt-out with reserved-memory, if you are
> interested, but that relates to the OS. If you are wanting to place
> some constraints on /reserved-memory and /memory we could do that
> e.g. that the DT and the map returned by EFI boot services must be
> consistent. But as it is, the nodes are ignored by the OS when booting
> with EFI, aren't they?

Can this be applied, please? If there are further comments, please let me know.

Regards,
Simon

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