[RFC 3/7] opensbi: add option to set big-endian mode at run-time

[Anup Patel]

On Fri, Dec 20, 2024 at 10:40 PM Ben Dooks <ben.dooks at codethink.co.uk> wrote:
>
> Add option to switch M-mode to BE at start by setting the
> MSTATUS.MBE bit early on in the initialisation code and
> ensure it stays set when hart is reinitialised.
>
> Reviewed-by: Lawrence Hunter <lawrence.hunter at codethink.co.uk>
> Reviewed-by: Roan Richmod <roan.richmond at codethink.co.uk>
> Signed-off-by: Ben Dooks <ben.dooks at codethink.co.uk>
> ---
>  Kconfig            | 4 ++++
>  firmware/fw_base.S | 8 ++++++++
>  lib/sbi/sbi_hart.c | 4 ++++
>  3 files changed, 16 insertions(+)
>
> diff --git a/Kconfig b/Kconfig
> index cc7b5bc..6c6236f 100644
> --- a/Kconfig
> +++ b/Kconfig
> @@ -7,6 +7,10 @@ config OPENSBI_BE
>         help
>           Say Y here if you like fun challenges
>
> +config OPENSBI_BE_SET
> +       bool "Set M-Mode to be big-endian in startup code"
> +       depends on OPENSBI_BE
> +
>  config OPENSBI_SRC_DIR
>         string
>         option env="OPENSBI_SRC_DIR"
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index d027e5e..f8ad6db 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -46,6 +46,14 @@
>         .globl _start
>         .globl _start_warm
>  _start:
> +#ifdef CONFIG_OPENSBI_BE_SET

Instead of kconfig option you can simply use
"#if __BYTE_ORDER == __BIG_ENDIAN"

> +#if __riscv_xlen == 64
> +       li      s0, MSTATUS_MBE
> +       csrs    CSR_MSTATUS, s0
> +#else
> +#error not done for 32bit
> +#endif
> +#endif
>         /* Find preferred boot HART id */
>         MOV_3R  s0, a0, s1, a1, s2, a2
>         call    fw_boot_hart
> diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> index 0451fcb..39311c4 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -39,6 +39,10 @@ static void mstatus_init(struct sbi_scratch *scratch)
>         uint64_t mhpmevent_init_val = 0;
>         uint64_t menvcfg_val, mstateen_val;
>
> +#ifdef CONFIG_OPENSBI_BE_SET
> +       mstatus_val |= MSTATUS_MBE;
> +#endif
> +

Same as above.

>         /* Enable FPU */
>         if (misa_extension('D') || misa_extension('F'))
>                 mstatus_val |=  MSTATUS_FS;
> --
> 2.37.2.352.g3c44437643
>
>
> --
> opensbi mailing list
> opensbi at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/opensbi

Regards,
Anup