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

[Andrew Jones]

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.

Thanks,
drew