[PATCH 2/4] fdt: Introduce OF_BLOBLIST

[Simon Glass]

Hi Raymond,

On Fri, 4 Apr 2025 at 04:34, Raymond Mao <raymond.mao at linaro.org> wrote:
>
> Hi Simon,
>
> On Fri, 28 Mar 2025 at 11:44, Simon Glass <sjg at chromium.org> wrote:
> >
> > Add an option which indicates that the devicetree comes from the
> > bloblist.
> >
> > After discussions with Tom, it seems we are comfortable with introducing
> > this option, ensuring of course that the transfer list is properly
> > supported.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> >  doc/develop/devicetree/control.rst |  3 ++
> >  dts/Kconfig                        |  8 ++++
> >  lib/fdtdec.c                       | 66 ++++++++++++------------------
> >  3 files changed, 38 insertions(+), 39 deletions(-)
> >
> > diff --git a/doc/develop/devicetree/control.rst b/doc/develop/devicetree/control.rst
> > index 0233945f8b6..d80f4d420a9 100644
> > --- a/doc/develop/devicetree/control.rst
> > +++ b/doc/develop/devicetree/control.rst
> > @@ -137,6 +137,9 @@ If `OF_BOARD` is selected by Kconfig, 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 `OF_BLOBLIST` is defined, the devicetree comes from a bloblist passed
> > +from a previous stage.
> > +
> >  If `BLOBLIST` is selected by Kconfig, the devicetree may come from a bloblist
> >  passed from a previous stage, if present.
> >
> > diff --git a/dts/Kconfig b/dts/Kconfig
> > index 6a5141b56e9..04359a4d7b2 100644
> > --- a/dts/Kconfig
> > +++ b/dts/Kconfig
> > @@ -167,6 +167,14 @@ config OF_INITIAL_DTB_READONLY
> >           If initial DTB for DT control is read-only (e.g. points to
> >           memory-mapped flash memory), then set this option.
> >
> > +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 earlier phase so that
> > +         U-Boot can read it.
> > +
> >  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/lib/fdtdec.c b/lib/fdtdec.c
> > index f09c9926a7a..833f8aca3ce 100644
> > --- a/lib/fdtdec.c
> > +++ b/lib/fdtdec.c
> > @@ -1689,55 +1689,43 @@ void fdtdec_setup_embed(void)
> >
> >  int fdtdec_setup(void)
>
> I think a better idea is to use BLOBLIST_PASSAGE_MANDATORY, see below
> pseudo code:
>
> ```
> if (IS_ENABLED(CONFIG_OF_BOARD)) {
>     /* get fdt from board */
> }
>
> /* allow fdtcontroladdr to override it */
>
> if (CONFIG_IS_ENABLED(BLOBLIST) && ... ) {
>     /* try to find fdt from bloblist */
>
>     if (CONFIG_IS_ENABLED(BLOBLIST_PASSAGE_MANDATORY) {
>         if (no_fdt_in_bloblist)
>             return ERROR;
>
>         /* override fdt with the one from bloblist */
>     }
> }
> ```

See my other email on this. With OF_BLOBLIST we actually don't need
BLOBLIST_PASSAGE_MANDATORY so we can drop it.

Regards,
Simon