[PATCH] firmware: Simplify FDT header endianness conversion

[Anup Patel]

On Fri, Aug 30, 2024 at 1:45 AM Samuel Holland
<samuel.holland at sifive.com> wrote:
>
> Reduce the code size by using single-byte loads instead of bit
> manipulation. This method also does the right thing on (hypothetical)
> big-endian systems.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Applied this patch to the riscv/opensbi repo.

Thanks,
Anup

> ---
>
>  firmware/fw_base.S | 26 +++++---------------------
>  1 file changed, 5 insertions(+), 21 deletions(-)
>
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index b950c0b8..0b58cc42 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -242,30 +242,14 @@ _scratch_init:
>         beq     t1, a1, _fdt_reloc_done
>         /* t0 = source FDT start address */
>         add     t0, a1, zero
> -       /* t2 = source FDT size in big-endian */
> -#if __riscv_xlen > 32
> -       lwu     t2, 4(t0)
> -#else
> -       lw      t2, 4(t0)
> -#endif
> -       /* t3 = bit[15:8] of FDT size */
> -       add     t3, t2, zero
> -       srli    t3, t3, 16
> -       and     t3, t3, a4
> +       /* t2 = source FDT size (convert from big-endian) */
> +       lbu     t2, 7(t0)
> +       lbu     t3, 6(t0)
> +       lbu     t4, 5(t0)
> +       lbu     t5, 4(t0)
>         slli    t3, t3, 8
> -       /* t4 = bit[23:16] of FDT size */
> -       add     t4, t2, zero
> -       srli    t4, t4, 8
> -       and     t4, t4, a4
>         slli    t4, t4, 16
> -       /* t5 = bit[31:24] of FDT size */
> -       add     t5, t2, zero
> -       and     t5, t5, a4
>         slli    t5, t5, 24
> -       /* t2 = bit[7:0] of FDT size */
> -       srli    t2, t2, 24
> -       and     t2, t2, a4
> -       /* t2 = FDT size in little-endian */
>         or      t2, t2, t3
>         or      t2, t2, t4
>         or      t2, t2, t5
> --
> 2.45.1
>
>
> --
> opensbi mailing list
> opensbi at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/opensbi