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From:   Atish Patra <atishp@atishpatra.org>
Date:   Wed, 12 Aug 2020 23:45:09 -0700
Message-ID: <CAOnJCUJTR_FEmjvs+L1KV6UJNbsZKrrVr7noWHUi8gG6qoWHxA@mail.gmail.com>
Subject: Re: [PATCH v2] riscv: Setup exception vector for nommu platform
To:     Damien Le Moal <Damien.LeMoal@wdc.com>
Cc:     Qiu Wenbo <qiuwenbo@phytium.com.cn>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        Anup Patel <anup@brainfault.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>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Wed, Aug 12, 2020 at 10:44 PM Damien Le Moal <Damien.LeMoal@wdc.com> wrote:
>
> On 2020/08/13 12:40, Qiu Wenbo 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>
>
> Please add a cc stable #5.8 tag. Kendryte support is in 5.8 stable.
>

That won't be necessary as the patch that broke nommu (79b1feba5455) was
part of the 1st PR sent towards 5.9-rc1.


> > ---
> >  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)
> >
>
>
> --
> Damien Le Moal
> Western Digital Research


--
Regards,
Atish