linux-kernel - Re: [PATCH] riscv: fix scratch register clearing in M-mode.

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Date:   Thu, 19 Dec 2019 12:24:37 +0530
From:   Anup Patel <anup@...infault.org>
To:     Greentime Hu <greentime.hu@...ive.com>
Cc:     Greentime Hu <green.hu@...il.com>, greentime@...nel.org,
        Christoph Hellwig <hch@....de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: fix scratch register clearing in M-mode.

On Thu, Dec 19, 2019 at 12:15 PM Greentime Hu <greentime.hu@...ive.com> wrote:
>
> This patch fixes that the sscratch register clearing in M-mode. It cleared
> sscratch register in M-mode, but it should clear mscratch register. That will
> cause kernel trap if the CPU core doesn't support S-mode when trying to access
> sscratch.
>
> Fixes: 9e80635619b5 ("riscv: clear the instruction cache and all registers when booting")
> Signed-off-by: Greentime Hu <greentime.hu@...ive.com>

In any case, we should always prefer accessing CSRs using CSR_xyz defines.

Looks good to me.

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

Regards,
Anup

> ---
>  arch/riscv/kernel/head.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 84a6f0a4b120..797802c73dee 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -246,7 +246,7 @@ ENTRY(reset_regs)
>         li      t4, 0
>         li      t5, 0
>         li      t6, 0
> -       csrw    sscratch, 0
> +       csrw    CSR_SCRATCH, 0
>
>  #ifdef CONFIG_FPU
>         csrr    t0, CSR_MISA
> --
> 2.17.1
>
>