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

[Simon Glass]

Hi Ilias,

On Thu, 31 Aug 2023 at 01:06, Ilias Apalodimas
<ilias.apalodimas at linaro.org> wrote:
>
> Hi Simon,
>
> On Wed, Aug 30, 2023 at 12:05:01PM -0600, Simon Glass wrote:
> > Standard passage provides for a bloblist to be passed from one firmware
> > phase to the next. That can be used to pass the devicetree along as well.
> > Add an option to support this.
> >
> > Tests for this will be added as part of the Universal Payload work.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> >  common/bloblist.c                  |  2 ++
> >  doc/develop/devicetree/control.rst |  3 ++
> >  dts/Kconfig                        |  8 ++++++
> >  include/bloblist.h                 |  5 ++++
> >  include/fdtdec.h                   |  3 +-
> >  lib/fdtdec.c                       | 44 ++++++++++++++++++++++--------
> >  6 files changed, 52 insertions(+), 13 deletions(-)
> >
> > diff --git a/common/bloblist.c b/common/bloblist.c
> > index 6f2a4577708..b07ede11cfe 100644
> > --- a/common/bloblist.c
> > +++ b/common/bloblist.c
> > @@ -48,9 +48,11 @@ static struct tag_name {
> >       { BLOBLISTT_ACPI_TABLES, "ACPI tables for x86" },
> >       { BLOBLISTT_SMBIOS_TABLES, "SMBIOS tables for x86" },
> >       { BLOBLISTT_VBOOT_CTX, "Chrome OS vboot context" },
> > +     { BLOBLISTT_CONTROL_FDT, "Control FDT" },
> >
> >       /* BLOBLISTT_PROJECT_AREA */
> >       { BLOBLISTT_U_BOOT_SPL_HANDOFF, "SPL hand-off" },
> > +     { BLOBLISTT_VBE, "VBE" },
> >       { BLOBLISTT_U_BOOT_VIDEO, "SPL video handoff" },
> >
> >       /* BLOBLISTT_VENDOR_AREA */
> > diff --git a/doc/develop/devicetree/control.rst b/doc/develop/devicetree/control.rst
> > index cbb65c9b177..56e00090166 100644
> > --- a/doc/develop/devicetree/control.rst
> > +++ b/doc/develop/devicetree/control.rst
> > @@ -108,6 +108,9 @@ If CONFIG_OF_BOARD is defined, a board-specific routine will provide the
> >  devicetree at runtime, for example if an earlier bootloader stage creates
> >  it and passes it to U-Boot.
> >
> > +If CONFIG_OF_BLOBLIST is defined, the devicetree comes from a bloblist passed
> > +from a previous stage.
> > +
>
> Is this bloblist in the format described in the firmware handoff [0] ?

Yes

>
> > +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.

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