[PATCH 30/32] fdt: Allow the devicetree to come from a bloblist

[Ilias Apalodimas]

Hi Simon,

On Fri, 1 Sept 2023 at 18:51, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Ilias,
>
> On Fri, 1 Sept 2023 at 01:50, Ilias Apalodimas <ilias.apalodimas at linaro.org> wrote:
> >
> > [...]
> >
> > > >
> > > > > +config OF_BLOBLIST
> > > > > +     bool "DTB is provided by a bloblist"
> > > > > +     help
> > > > > +       Select this to read the devicetree from the bloblist. This allows
> > > > > +       using a bloblist to transfer the devicetree between  U-Boot phases.
> > > > > +       The devicetree is stored in the bloblist by an early phase so that
> > > > > +       U-Boot can read it.
> > > > > +
> > > >
> > > > I dont think this is a good idea.  We used to have 4-5 different options
> > > > here, which we tried to clean up and ended up with two very discrete
> > > > options.  Why do we have to reintroduce a new one?  Doesn't that bloblist
> > > > have a header of some sort?  The bloblist literally comes from a previous
> > > > stage bootloader which is what OF_BOARD is here for. So why can't we just
> > > > read the header and figure out if the magic of the bloblist matches?
> > >
> > > No, OF_BOARD is a hack to allow boards to do what they like with the FDT.
> > >
> > > This patch is a standard mechanism to pass the DT from one firmware
> > > phase to the next. We have spent quite a bit of time creating a spec
> > > for it, and we should use it.
> >
> > Where exactly am I objecting using the spec?   Can you please re-read my email?
> > I am actually pointing out we should use the spec *properly*.  So
> > instead of having a Kconfig option for the DT, which is pretty
> > pointless,  we should parse the bloblist.  If the header defined by
> > the *spec* is found, we should just search for the DT in there.
> > What you are doing here, is take the spec, pick a very specific item
> > that the list contains, and create a Kconfig option out of it.  Which
> > basically ignores the discoverable options of the bloblist.  For
> > example, that bloblist can also contain an entry to a TPM eventlog.
> > Should we start creating Kconfig options for all the firmware handoff
> > entries that are defined on that spec?
>
> OK so that is a different thing. What should it do if it expects to find a bloblist but cannot? I want it to throw an error, because I am trying to make the boot deterministic. What do you think?

That's fine by me.  You can even put that under IS_ENABLED for the
bloblist inside the existing OF_BOARD check.  So I was thinking
- If no bloblist is required in Kconfig options we do the hacks we used to
- if bloblist is selected and the config option is OF_BOARD, throw an
error and mention that the previous stage loader should hand over a DT

Is that what you had in mind?

Thanks
/Ilias
>
> >
> > Thanks
> > /Ilias
> >
> > >
> > > The patches to align bloblist with the spec have been sent, but there
> > > is a late-breaking change that we are trying to resolve. Once that is
> > > sorted out, I will send v2 of those patches.
> > >
> > > >
> > > > >  config OF_BOARD
> > > > >       bool "Provided by the board (e.g a previous loader) at runtime"
> > > > >       default y if SANDBOX || OF_HAS_PRIOR_STAGE
> > > > > diff --git a/include/bloblist.h b/include/bloblist.h
> > > > > index 080cc46a126..e16d122f4fb 100644
> > > > > --- a/include/bloblist.h
> > > > > +++ b/include/bloblist.h
> > > > > @@ -103,6 +103,11 @@ enum bloblist_tag_t {
> > > > >       BLOBLISTT_ACPI_TABLES = 0x104,  /* ACPI tables for x86 */
> > > > >       BLOBLISTT_SMBIOS_TABLES = 0x105, /* SMBIOS tables for x86 */
> > > > >       BLOBLISTT_VBOOT_CTX = 0x106,    /* Chromium OS verified boot context */
> > > > > +     /*
> > > >
> > > > [...]
> > > >
> > > > >
> > > > [0] https://github.com/FirmwareHandoff/firmware_handoff
> > >
>
> Regards,
> Simon