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

[Simon Glass]

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?

>
> 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