[PATCH 4/5] lib: sbi: Ensure coldboot HART supports next privilege mode

[Atish Patra]

On Wed, Sep 9, 2020 at 7:51 AM Anup Patel <anup.patel at wdc.com> wrote:
>
> The coldboot HART jumps to the next booting stage at the end of
> init_coldboot() so it is absolutely necessary for coldboot HART
> to support the privilege mode expected by the next booting stage.
>
> We extend the coldboot HART selection in sbi_init() to ensure that
> the selected coldboot HART always supports privilege mode specified
> in scratch space (i.e. scratch->next_mode). This will further help
> us allow E-core (without MMU) on SiFive Unleashed and PolarFire
> ICICLE boards to proceed further and wait in HSM STOPPED state.
>
> Signed-off-by: Anup Patel <anup.patel at wdc.com>
> ---
>  lib/sbi/sbi_init.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/lib/sbi/sbi_init.c b/lib/sbi/sbi_init.c
> index e1a1d96..65d81ba 100644
> --- a/lib/sbi/sbi_init.c
> +++ b/lib/sbi/sbi_init.c
> @@ -295,6 +295,7 @@ static atomic_t coldboot_lottery = ATOMIC_INITIALIZER(0);
>   */
>  void __noreturn sbi_init(struct sbi_scratch *scratch)
>  {
> +       bool next_mode_supported        = FALSE;
>         bool coldboot                   = FALSE;
>         u32 hartid                      = current_hartid();
>         const struct sbi_platform *plat = sbi_platform_ptr(scratch);
> @@ -303,7 +304,33 @@ void __noreturn sbi_init(struct sbi_scratch *scratch)
>             sbi_platform_hart_invalid(plat, hartid))
>                 sbi_hart_hang();
>
> -       if (atomic_xchg(&coldboot_lottery, 1) == 0)
> +       switch (scratch->next_mode) {
> +       case PRV_M:
> +               next_mode_supported = TRUE;
> +               break;
> +       case PRV_S:
> +               if (misa_extension('S'))
> +                       next_mode_supported = TRUE;
> +               break;
> +       case PRV_U:
> +               if (misa_extension('U'))
> +                       next_mode_supported = TRUE;
> +               break;
> +       default:
> +               sbi_hart_hang();
> +       }
> +
> +       /*
> +        * Only the HART supporting privilege mode specified in the
> +        * scratch->next_mode should be allowed to become the coldboot
> +        * HART because the coldboot HART will be directly jumping to
> +        * the next booting stage.
> +        *
> +        * We use a lottery mechanism to select coldboot HART among
> +        * HARTs which satisfy above condition.
> +        */
> +
> +       if (next_mode_supported && atomic_xchg(&coldboot_lottery, 1) == 0)
>                 coldboot = TRUE;
>
>         if (coldboot)
> --
> 2.25.1
>
>
> --
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Reviewed-by: Atish Patra <atish.patra at wdc.com>

-- 
Regards,
Atish