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

[Palmer Dabbelt]

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

Thanks, this is on fixes.