[PATCH v3] platform: generic: Keep some empty space in FDT passed to next stage

[Anup Patel]

On Tue, Dec 16, 2025 at 9:25 PM Samuel Holland
<samuel.holland at sifive.com> wrote:
>
> Anup,
>
> On 2025-12-16 8:45 AM, Anup Patel wrote:
> > On Tue, Dec 9, 2025 at 11:01 AM Anup Patel <apatel at ventanamicro.com> 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>
> >
> > Applied this patch to the riscv/opensbi repo.
>
> Again, this patch reintroduces the bug that was fixed by the "Fixes:" commit.
> You can't just say "somebody will add the memset() somewhere later" and ignore
> the bug you are introducing. You need to add the memset() *now* along with the
> fdt_open_into() call.

Yes, but that fix broke U-boot booting.
The original fix itself was incomplete. Adding memset() to
fdt_open_into() is a separate change. Feel free to send
patch for it.

Regards,
Anup

>
> Regards,
> Samuel
>
> >> ---
> >> Changes since v2:
> >> - Fix comments in generic_final_init()
> >> Changes since v1:
> >> - Add Kconfig option for amount of empty space in FDT with default
> >>   value as 4KB
> >> ---
> >>  platform/generic/Kconfig    | 5 +++++
> >>  platform/generic/platform.c | 3 +++
> >>  2 files changed, 8 insertions(+)
> >>
> >> diff --git a/platform/generic/Kconfig b/platform/generic/Kconfig
> >> index 25b8886b..b1808012 100644
> >> --- a/platform/generic/Kconfig
> >> +++ b/platform/generic/Kconfig
> >> @@ -23,6 +23,11 @@ config PLATFORM_GENERIC_MINOR_VER
> >>         range 0 65535
> >>         default 1
> >>
> >> +config PLATFORM_GENERIC_FDT_EMPTY_SPACE
> >> +       int "Platform FDT empty space (KB)"
> >> +       range 0 1024
> >> +       default 4
> >> +
> >>  config PLATFORM_ALLWINNER_D1
> >>         bool "Allwinner D1 support"
> >>         depends on FDT_IRQCHIP_PLIC
> >> diff --git a/platform/generic/platform.c b/platform/generic/platform.c
> >> index e66f99fa..01fa03e0 100644
> >> --- a/platform/generic/platform.c
> >> +++ b/platform/generic/platform.c
> >> @@ -245,7 +245,10 @@ int generic_final_init(bool cold_boot)
> >>         fdt_fixups(fdt);
> >>         fdt_domain_fixup(fdt);
> >>
> >> +       /* Set the empty space in FDT based on kconfig option */
> >>         fdt_pack(fdt);
> >> +       fdt_open_into(fdt, fdt, fdt_totalsize(fdt) +
> >> +                     CONFIG_PLATFORM_GENERIC_FDT_EMPTY_SPACE * 1024);
> >>
> >>         return 0;
> >>  }
> >> --
> >> 2.43.0
> >>
> >
>