Re: [PATCH v2] riscv: Setup exception vector for nommu platform

[Palmer Dabbelt]

On Thu, 13 Aug 2020 01:49:44 PDT (-0700), anup@xxxxxxxxxxxxxx wrote:
> On Thu, Aug 13, 2020 at 9:10 AM Qiu Wenbo <qiuwenbo@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > Suggested-by: Atish Patra <atishp@xxxxxxxxxxxxxx>
> > Signed-off-by: Qiu Wenbo <qiuwenbo@xxxxxxxxxxxxxx>
> > ---
> >  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@xxxxxxxxxxxxxx>
>
> Regards,
> Anup

Thanks, this is on fixes.