[PATCH] platform: generic: Keep some empty space in FDT passed to next stage

[Anup Patel]

On Wed, Nov 5, 2025 at 9:44 PM Andrew Jones <ajones at ventanamicro.com> wrote:
>
> On Wed, Nov 05, 2025 at 09:31:45PM +0530, Anup Patel wrote:
> > Leaving no empty space in the FDT passed to the next booting stage
> > causes the following U-Boot crash on Ventana internal platforms:
> >
> > Unhandled exception: Load access fault
> > EPC: 00000000fffa6372 RA: 00000000fffa7418 TVAL: 0001746174730068
> > EPC: 0000000080245372 RA: 0000000080246418 reloc adjusted
> >
> > SP:  00000000fef38440 GP:  00000000fef40e60 TP:  0000000000000000
> > T0:  00000000fef40a70 T1:  000000000000ff00 T2:  0000000000000000
> > S0:  00000000fffc17a8 S1:  00000000fef38d40 A0:  7375746174730068
> > A1:  00000000fffc17a8 A2:  0000000000000010 A3:  0000000000000010
> > A4:  0000000000000000 A5:  00000000fffc17b8 A6:  0000000000ff0000
> > A7:  000000000000b100 S2:  0000000000000000 S3:  0000000000000001
> > S4:  00000000fef38d40 S5:  7375746174730068 S6:  0000000000000000
> > S7:  00000000fef4eef0 S8:  00000000fef4ef90 S9:  0000000000000000
> > S10: 0000000000000000 S11: 00000000fef4efc0 T3:  00000000fef40ea8
> > T4:  0000000000ff0000 T5:  00000000fef40a60 T6:  00000000fef40a6c
> >
> > To address the above issue, keep some minimal empty space in the
> > FDT instead of no empty space.
> >
> > Fixes: bbe9a23060e9 ("platform: generic: Pack the FDT after applying fixups")
> > Signed-off-by: Anup Patel <apatel at ventanamicro.com>
> > ---
> >  platform/generic/platform.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/platform/generic/platform.c b/platform/generic/platform.c
> > index e66f99fa..ea44676b 100644
> > --- a/platform/generic/platform.c
> > +++ b/platform/generic/platform.c
> > @@ -245,7 +245,9 @@ int generic_final_init(bool cold_boot)
> >       fdt_fixups(fdt);
> >       fdt_domain_fixup(fdt);
> >
> > +     /* Minimize the empty space in FDT to 4KB */
> >       fdt_pack(fdt);
> > +     fdt_open_into(fdt, fdt, fdt_totalsize(fdt) + 4096);
> >
> >       return 0;
> >  }
> > --
> > 2.43.0
> >
>
> I agree opensbi needs to workaround uboot issues in order to ensure it
> doesn't break current configurations, but maybe we should make the
> extra space added be a Kconfig managed define, rather than a hard 4096.
> The main reason would be to enable setting it to zero so issues with
> second stage loaders like this one can be flushed out and fixed.
>

Adding a Kconfig option for the amount of extra space should be fine,
I will update and send v2.

Thanks,
Anup