[PATCH 1/2] bloblist: fix the overriding of fdt from bloblist

[Raymond Mao]

Hi Caleb,

On Fri, 28 Mar 2025 at 08:27, Caleb Connolly <caleb.connolly at linaro.org> wrote:
>
>
>
> On 3/28/25 11:44, Caleb Connolly wrote:
> > Hi Raymond,
> >
> > On 3/28/25 00:13, Raymond Mao wrote:
> >> When a bloblist is valid and contains fdt, it explicitly means
> >> a previous boot stage is passing transfer list compliant with
> >> Firmware Handoff specification, thus the fdt from bloblist should
> >> not be overridden with the ones from board or env variables.
>
> Actually, I'm a little confused here. Can you point to the documentation
> that says an FDT from a bloblist should always take priority?
>
> I can see why this makes sense to lock down, but clarification would be
> good regardless.
>

All the adaptations on bloblist are in order to make it compliant with
the Firmware Handoff spec [1].
In the spec, all data being handed over between boot stages should be
within a transfer list (aka. bloblist in U-Boot).
So the logic is clear to me, when the bloblist contains a valid fdt,
that explicitly means the previous boot stages are passing arguments
following the Firmware Handoff spec, and U-Boot should follow the same
way to pass them to the next stage - kernel.

[1]: https://github.com/FirmwareHandoff/firmware_handoff

Regards,
Raymond

> Kind regards,
> >>
> >> Fixes: 70fe23859437 ("fdt: Allow the devicetree to come from a bloblist")
> >> Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
> >
> > Reviewed-by: Caleb Connolly <caleb.connolly at linaro.org>
> >> ---
> >>   lib/fdtdec.c | 3 ++-
> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/lib/fdtdec.c b/lib/fdtdec.c
> >> index f09c9926a7a..c38738b48c7 100644
> >> --- a/lib/fdtdec.c
> >> +++ b/lib/fdtdec.c
> >> @@ -1708,7 +1708,7 @@ int fdtdec_setup(void)
> >>                   gd->fdt_src = FDTSRC_BLOBLIST;
> >>                   log_debug("Devicetree is in bloblist at %p\n",
> >>                         gd->fdt_blob);
> >> -                ret = 0;
> >> +                goto setup_fdt;
> >>               } else {
> >>                   log_debug("No FDT found in bloblist\n");
> >>                   ret = -ENOENT;
> >> @@ -1752,6 +1752,7 @@ int fdtdec_setup(void)
> >>           }
> >>       }
> >> +setup_fdt:
> >>       if (CONFIG_IS_ENABLED(MULTI_DTB_FIT))
> >>           setup_multi_dtb_fit();
> >
>
> --
> Caleb (they/them)
>