[PATCH v2 4/7] riscv: Clear pending IPIs on initialization

[Sean Anderson]

On 9/15/20 5:15 AM, Rick Chen wrote:
>> Even though we no longer call smp_function if an IPI was not sent by
>> U-Boot, we still need to clear any IPIs which were pending from the
>> execution environment. Otherwise, secondary harts will busy-wait in
>> secondary_hart_loop, instead of relaxing.
>>
>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
>> Reviewed-by: Bin Meng <bin.meng at windriver.com>
>>
>> ---
>>
>> Changes in v2:
>> - Make riscv_ipi_init_secondary_hart static
>>
>>  arch/riscv/cpu/cpu.c | 18 ++++++++++++++++++
>>  1 file changed, 18 insertions(+)
>>
>> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
>> index bfa2d4a426..ab08af5a33 100644
>> --- a/arch/riscv/cpu/cpu.c
>> +++ b/arch/riscv/cpu/cpu.c
>> @@ -72,6 +72,15 @@ static int riscv_cpu_probe(void)
>>         return 0;
>>  }
>>
>> +/*
>> + * This is called on secondary harts just after the IPI is init'd. Currently
>> + * there's nothing to do, since we just need to clear any existing IPIs, and
>> + * that is handled by the sending of an ipi itself.
> 
> Can we call this function as dummy_pending_ipi_clear() or

Sure that sounds good.

> prior_stage_pending_ipi_clear(), since the it is the IPIs which does
> not be clear
> from prior stage bootloader and it is not a general case. It is
> special case to deal with.
> 
> Also move the descriptions "On the K210, the prior stage bootloader
> does not clear IPIs. This presents a problem,..."
> in [PATCH v2 0/7] riscv: Correctly handle IPIs already pending upon
> boot here or commit of patch [1/7].
> Because it will not show in git log history any more.
> 
> With the history description, it will help to understand and readable
> about the SMP enhance flow for the later joiner.

Ok, I will expand the description of those patches.

> 
> Thanks,
> Rick
> 
>> + */
>> +static void riscv_ipi_init_secondary_hart(ulong hart, ulong arg0, ulong arg1)
>> +{
>> +}
>> +
>>  int arch_cpu_init_dm(void)
>>  {
>>         int ret;
>> @@ -111,6 +120,15 @@ int arch_cpu_init_dm(void)
>>         ret = riscv_init_ipi();
>>         if (ret)
>>                 return ret;
>> +
>> +       /*
>> +        * Clear all pending IPIs on secondary harts. We don't do anything on
>> +        * the boot hart, since we never send an IPI to ourselves, and no
>> +        * interrupts are enabled
>> +        */
>> +       ret = smp_call_function((ulong)riscv_ipi_init_secondary_hart, 0, 0, 0);
>> +       if (ret)
>> +               return ret;
>>  #endif
>>
>>         return 0;
>> --
>> 2.28.0
>>