[RFC] Data structure for information handoff between firmware boot stages

[Simon Glass]

Hi Jose,

On Tue, 3 May 2022 at 02:26, Jose Marinho <Jose.Marinho at arm.com> wrote:
>
> Hi Simon,
>
> Thank you for reviewing the draft proposal!
>
> Would you be able to share your review comments on the PDF?
> Currently the document is not in a markup form and is yet to be hosted in a repository. That's the intent for the long term.

Yes it looks like I can do that, so will share with you when done.

Regards,
Simon

>
> Cheers,
> Jose
>
> > -----Original Message-----
> > From: Simon Glass <sjg at chromium.org>
> > Sent: 03 May 2022 08:59
> > To: Jose Marinho <Jose.Marinho at arm.com>
> > Cc: u-boot at lists.denx.de; Heinrich Schuchardt <xypron.glpk at gmx.de>; Ilias
> > Apalodimas <ilias.apalodimas at linaro.org>; Tom Rini <trini at konsulko.com>;
> > Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud at arm.com>; Manish Pandey2
> > <Manish.Pandey2 at arm.com>; nd <nd at arm.com>
> > Subject: Re: [RFC] Data structure for information handoff between firmware
> > boot stages
> >
> > Hi Jose,
> >
> > On Thu, 7 Apr 2022 at 13:23, Jose Marinho <Jose.Marinho at arm.com> wrote:
> > >
> > > Hi All,
> > >
> > > The topic of information handoff between TF-A’s BL31 and BL33 (e.g. U-boot
> > proper, EDK2) was discussed last year in the TF-A and U-boot mailing lists [1],
> > [2].
> > >
> > > Examples of information to be handed off between firmware stages are the
> > TPM log, HOB nodes, etc.
> > > Having a standard data structure which is usable/supported by every
> > community contributes to code reuse and leads to simpler codebase
> > maintenance.
> > >
> > > Some already existing data structures, such as the UEFI HOB list [3], and the
> > Bloblist from U-boot, were proposed to be employed for the handoffs.
> > > There are pros and cons with both HOBs and Bloblist.
> > > The discussion settled with a consensus that a data structure ought to be
> > defined which encapsulates the best traits of HOBs and Bloblist.
> > >
> > > Properties that the data structure should have:
> > > - node types identified by an integer,
> > > - easily relocatable,
> > >
> > > - straightforward to append new nodes,
> > > - easy to read and append to from resource constrained environments.
> > >
> > > The data structure should be suitable to pass information between different
> > firmware stages, such as:
> > > U-boot SPL -> BL31 -> U-boot
> > > BL1 -> BL2 -> BL31 -> U-boot
> > >
> > > As requested in the ML, an initial proposal was drafted [4].
> > > The document [4] is an initial proposal (at an alpha stage).
> > > The document [4] is being circulated for the purpose of gathering initial
> > feedback.
> > > This proposal is closely aligned with an ongoing effort in the u-boot mailing
> > list [5].
> > > The proposal defines 1) a set of standard nodes and 2) the registers used at
> > the handoff boundary.
> > >
> > > Standard nodes:
> > > - fdt node: HW description fdt,
> > > - HOB node,
> > > - ACPI table node: the main use-case for this node is to carry the TPM log.
> > >
> > > The document [4] accommodates an OEM range, which enables IMPDEF
> > nodes to be caried in the handoff list.
> > > By definition, the nodes in the OEM range are not standard and can be
> > defined per-platform.
> > >
> > > Note: the document [4] encapsulates the standard node definition as that is
> > the simplest approach for feedback gathering.
> > > Once there is sufficient consensus around the proposal, the standard node
> > definitions should be moved to a project independent repository. The
> > repository location is TBD.
> > > The list of standard nodes is expected to grow with community contribution.
> >
> > Thank you for the document. Is there a way to comment on it or should I just
> > send you my hand-written markup?
> >
> > Regards,
> > Simon
> >
> > >
> > > Kind Regards,
> > > Jose
> > >
> > >
> > >
> > > [1]
> > > https://lists.trustedfirmware.org/archives/list/tf-a@lists.trustedfirm
> > > ware.org/message/LUIUOVGUMVWID5RUMTYA463KGIU2EHIU/
> > >
> > > [2]
> > > https://lore.kernel.org/u-boot/CAODwPW_FwFN1E84cV1+nC1aiahiwOL-
> > TV=mP_6
> > > o8h0y9+pCNvg at mail.gmail.com/
> > >
> > > [3] https://uefi.org/sites/default/files/resources/PI_Spec_1_6.pdf
> > >
> > > [4] https://developer.arm.com/documentation/den0135/a
> > > [5]
> > > https://lore.kernel.org/u-boot/20220113022625.413990-1-sjg@chromium.or
> > > g/
> > >
> > >