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From:   Anup Patel <anup@brainfault.org>
Date:   Thu, 13 Aug 2020 14:19:44 +0530
Message-ID: <CAAhSdy1hLAVEHohtuZ6XYxOjWgUmZPXah=tJFrb6tWoRyEiRgA@mail.gmail.com>
Subject: Re: [PATCH v2] riscv: Setup exception vector for nommu platform
To:     Qiu Wenbo <qiuwenbo@phytium.com.cn>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        Atish Patra <atishp@atishpatra.org>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <anup.patel@wdc.com>,
        Atish Patra <atish.patra@wdc.com>,
        Greentime Hu <greentime.hu@sifive.com>,
        Damien Le Moal <damien.lemoal@wdc.com>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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On Thu, Aug 13, 2020 at 9:10 AM Qiu Wenbo <qiuwenbo@phytium.com.cn> wrote:
>
> Exception vector is missing on nommu platform and that is an issue.
> This patch is tested in Sipeed Maix Bit Dev Board.
>
> Fixes: 79b1feba5455 ("RISC-V: Setup exception vector early")
> Suggested-by: Anup Patel <anup@brainfault.org>
> Suggested-by: Atish Patra <atishp@atishpatra.org>
> Signed-off-by: Qiu Wenbo <qiuwenbo@phytium.com.cn>
> ---
>  arch/riscv/kernel/head.S | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index d0c5c316e9bb..0a4e81b8dc79 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -77,16 +77,10 @@ relocate:
>         csrw CSR_SATP, a0
>  .align 2
>  1:
> -       /* Set trap vector to exception handler */
> -       la a0, handle_exception
> +       /* Set trap vector to spin forever to help debug */
> +       la a0, .Lsecondary_park
>         csrw CSR_TVEC, a0
>
> -       /*
> -        * Set sup0 scratch register to 0, indicating to exception vector that
> -        * we are presently executing in kernel.
> -        */
> -       csrw CSR_SCRATCH, zero
> -
>         /* Reload the global pointer */
>  .option push
>  .option norelax
> @@ -144,9 +138,23 @@ secondary_start_common:
>         la a0, swapper_pg_dir
>         call relocate
>  #endif
> +       call setup_trap_vector
>         tail smp_callin
>  #endif /* CONFIG_SMP */
>
> +.align 2
> +setup_trap_vector:
> +       /* Set trap vector to exception handler */
> +       la a0, handle_exception
> +       csrw CSR_TVEC, a0
> +
> +       /*
> +        * Set sup0 scratch register to 0, indicating to exception vector that
> +        * we are presently executing in kernel.
> +        */
> +       csrw CSR_SCRATCH, zero
> +       ret
> +
>  .Lsecondary_park:
>         /* We lack SMP support or have too many harts, so park this hart */
>         wfi
> @@ -240,6 +248,7 @@ clear_bss_done:
>         call relocate
>  #endif /* CONFIG_MMU */
>
> +       call setup_trap_vector
>         /* Restore C environment */
>         la tp, init_task
>         sw zero, TASK_TI_CPU(tp)
> --
> 2.28.0
>

Looks good to me.

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

Regards,
Anup