[PATCH] fw_base.S: Fix boot hart status synchronization

[Anup Patel]

On Thu, Oct 19, 2023 at 2:57 PM <guoren at kernel.org> wrote:
>
> From: Guo Ren <guoren at linux.alibaba.com>
>
> It's wrong to put the fence after setting the boot status flag because
> all relocation operations must be finished before setting the status
> flag. So, this fence must be put before the setting status flag, and
> there is no use in putting a fence between _start_warm and setting
> status flag.
>
> Also, nop can't delay other harts too much, so use div instead, just
> like Linux cpu_relax. Current opensbi force enables “M” Standard
> Extension, and mul instructions have been used in the fw_base.S.
>
> After the above two fixes, the boot hart index param of the
> fw_dynamic_info could be guaranteed properly for all platforms.
>
> Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren at kernel.org>

Looks good to me.

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

Applied this patch to the riscv/opensbi repo.

Thanks,
Anup

> ---
>  firmware/fw_base.S | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index 42b03fe890f0..f7763f4d9e56 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -399,8 +399,8 @@ _fdt_reloc_done:
>         /* mark boot hart done */
>         li      t0, BOOT_STATUS_BOOT_HART_DONE
>         lla     t1, _boot_status
> -       REG_S   t0, 0(t1)
>         fence   rw, rw
> +       REG_S   t0, 0(t1)
>         j       _start_warm
>
>         /* waiting for boot hart to be done (_boot_status == 2) */
> @@ -409,9 +409,9 @@ _wait_for_boot_hart:
>         lla     t1, _boot_status
>         REG_L   t1, 0(t1)
>         /* Reduce the bus traffic so that boot hart may proceed faster */
> -       nop
> -       nop
> -       nop
> +       div     t2, t2, zero
> +       div     t2, t2, zero
> +       div     t2, t2, zero
>         bne     t0, t1, _wait_for_boot_hart
>
>  _start_warm:
> --
> 2.36.1
>