Re: [PATCH 1/5] RISC-V: Add mechanism to provide custom IPI operations

[Anup Patel]

On Fri, Jun 5, 2020 at 2:10 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
>
> On Thu, 21 May 2020 06:45:40 PDT (-0700), Anup Patel wrote:
> > We add mechanism to set custom IPI operations so that CLINT driver
> > from drivers directory can provide custom IPI operations.
> >
> > Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> > ---
> >  arch/riscv/include/asm/smp.h | 11 ++++++++
> >  arch/riscv/kernel/smp.c      | 52 ++++++++++++++++++++++++------------
> >  arch/riscv/kernel/smpboot.c  |  3 +--
> >  3 files changed, 47 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> > index 40bb1c15a731..ad0601260cb1 100644
> > --- a/arch/riscv/include/asm/smp.h
> > +++ b/arch/riscv/include/asm/smp.h
> > @@ -40,6 +40,17 @@ void arch_send_call_function_single_ipi(int cpu);
> >  int riscv_hartid_to_cpuid(int hartid);
> >  void riscv_cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask *out);
> >
> > +struct riscv_ipi_ops {
> > +     void (*ipi_inject)(const unsigned long *hart_mask);
> > +     void (*ipi_clear)(void);
> > +};
> > +
> > +/* Set custom IPI operations */
> > +void riscv_set_ipi_ops(struct riscv_ipi_ops *ops);
> > +
> > +/* Clear IPI for current CPU */
> > +void riscv_clear_ipi(void);
> > +
> >  /*
> >   * Obtains the hart ID of the currently executing task.  This relies on
> >   * THREAD_INFO_IN_TASK, but we define that unconditionally.
> > diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> > index b1d4f452f843..8375cc5970f6 100644
> > --- a/arch/riscv/kernel/smp.c
> > +++ b/arch/riscv/kernel/smp.c
> > @@ -84,6 +84,35 @@ static void ipi_stop(void)
> >               wait_for_interrupt();
> >  }
> >
> > +#if IS_ENABLED(CONFIG_RISCV_SBI)
> > +static void clear_ipi(void)
> > +{
> > +     csr_clear(CSR_IP, IE_SIE);
> > +}
> > +
> > +static struct riscv_ipi_ops sbi_ipi_ops = {
> > +     .ipi_inject = sbi_send_ipi,
> > +     .ipi_clear = clear_ipi,
> > +};
> > +
> > +static struct riscv_ipi_ops *ipi_ops = &sbi_ipi_ops;
> > +#else
> > +static struct riscv_ipi_ops *ipi_ops;
> > +#endif
> > +
> > +void riscv_set_ipi_ops(struct riscv_ipi_ops *ops)
> > +{
> > +     ipi_ops = ops;
> > +}
> > +EXPORT_SYMBOL_GPL(riscv_set_ipi_ops);
> > +
> > +void riscv_clear_ipi(void)
> > +{
> > +     if (ipi_ops)
> > +             ipi_ops->ipi_clear();
> > +}
> > +EXPORT_SYMBOL_GPL(riscv_clear_ipi);
>
> There should at least be a warning on SMP systems when an ipi_ops hasn't been
> set, as otherwise the system will just hang.

Sure, I will add pr_warn() here.

>
> > +
> >  static void send_ipi_mask(const struct cpumask *mask, enum ipi_message_type op)
> >  {
> >       struct cpumask hartid_mask;
> > @@ -95,10 +124,9 @@ static void send_ipi_mask(const struct cpumask *mask, enum ipi_message_type op)
> >       smp_mb__after_atomic();
> >
> >       riscv_cpuid_to_hartid_mask(mask, &hartid_mask);
> > -     if (IS_ENABLED(CONFIG_RISCV_SBI))
> > -             sbi_send_ipi(cpumask_bits(&hartid_mask));
> > -     else
> > -             clint_send_ipi_mask(mask);
> > +
> > +     if (ipi_ops)
> > +             ipi_ops->ipi_inject(cpumask_bits(&hartid_mask));
> >  }
> >
> >  static void send_ipi_single(int cpu, enum ipi_message_type op)
> > @@ -109,18 +137,8 @@ static void send_ipi_single(int cpu, enum ipi_message_type op)
> >       set_bit(op, &ipi_data[cpu].bits);
> >       smp_mb__after_atomic();
> >
> > -     if (IS_ENABLED(CONFIG_RISCV_SBI))
> > -             sbi_send_ipi(cpumask_bits(cpumask_of(hartid)));
> > -     else
> > -             clint_send_ipi_single(hartid);
> > -}
> > -
> > -static inline void clear_ipi(void)
> > -{
> > -     if (IS_ENABLED(CONFIG_RISCV_SBI))
> > -             csr_clear(CSR_IP, IE_SIE);
> > -     else
> > -             clint_clear_ipi(cpuid_to_hartid_map(smp_processor_id()));
> > +     if (ipi_ops)
> > +             ipi_ops->ipi_inject(cpumask_bits(cpumask_of(hartid)));
> >  }
> >
> >  void handle_IPI(struct pt_regs *regs)
> > @@ -131,7 +149,7 @@ void handle_IPI(struct pt_regs *regs)
> >
> >       irq_enter();
> >
> > -     clear_ipi();
> > +     riscv_clear_ipi();
> >
> >       while (true) {
> >               unsigned long ops;
> > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > index 4e9922790f6e..5fe849791bf0 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -147,8 +147,7 @@ asmlinkage __visible void smp_callin(void)
> >  {
> >       struct mm_struct *mm = &init_mm;
> >
> > -     if (!IS_ENABLED(CONFIG_RISCV_SBI))
> > -             clint_clear_ipi(cpuid_to_hartid_map(smp_processor_id()));
> > +     riscv_clear_ipi();
> >
> >       /* All kernel threads share the same mm context.  */
> >       mmgrab(mm);

Regards,
Anup