[PATCH 2/3] fdt: Allow expanding the devicetree during relocation

[Simon Glass]

Hi Tom,

On Fri, 6 Dec 2024 at 07:13, Tom Rini <trini at konsulko.com> wrote:
>
> On Fri, Dec 06, 2024 at 06:11:12AM -0700, Simon Glass wrote:
>
> [snip]
> > A comment in that function says that we assume there is space after the
> > existing fdt to use for padding, with the padding size set to
> > CONFIG_SYS_FDT_PAD
> >
> > However, there is no guarantee that this space is available. If using
> > the control FDT, then global_data is immediately above it, so expanding
> > the FDT and adding FDT properties will cause U-Boot to fail.
>
> This sounds like a generic issue and should be fixed outside of a "Pi"
> series.

Yes and I know you keep asking for multiple smaller series, but I've
explained that keeping track of all that for months at a time is too
challenging for me.

>
> > diff --git a/dts/Kconfig b/dts/Kconfig
> > index 41a758e83a6..360611edd01 100644
> > --- a/dts/Kconfig
> > +++ b/dts/Kconfig
> > @@ -219,6 +219,17 @@ config OF_OMIT_DTB
> >         This is used for boards which normally provide a devicetree via a
> >         runtime mechanism (such as OF_BOARD), to avoid confusion.
> >
> > +config OF_EXPAND
> > +     hex # "Amount to allow the control FDT to expand"
>
> No "# ..." because the help explains what to do here, if needed.

OK

>
> > +     default SYS_FDT_PAD if OF_LIBFDT
> > +     default 0
>
> A "default 0" is almost always wrong.

In this case it is correct, since it means not to add any extra space
for the FDT.

>
> > +     help
> > +       Some boards make use of the control FDT to boot an OS, thus when
> > +       image_setup_libfdt() adds extra things to the end of the FDT, there
> > +       needs to be enough space.
> > +
> > +       Set this to the number of bytes of extra space required for the FDT.
>
> We should just use SYS_FDT_PAD directly and not add a new option.

I thought I read somewhere that fdt_high == -1 should not be used. So
for most boards, this padding is not needed?

Regards,
Simon