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

[Rick Chen]

> 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.

BTW,  riscv_ipi_init_secondary_hart() shall be enclosed by #if
CONFIG_IS_ENABLED(SMP),
or there will occur a warning when some other configs compiling:

arch/riscv/cpu/cpu.c:80:13: warning: 'riscv_ipi_init_secondary_hart'
defined but not used [-Wunused-function]
 static void riscv_ipi_init_secondary_hart(ulong hart, ulong arg0, ulong arg1)
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks,
Rick

>
> > 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
> >>
>