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Date:   Sun, 31 May 2020 11:22:58 +0530
From:   Anup Patel <anup@...infault.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 4/6] clocksource/drivers/timer-riscv: Use per-CPU timer interrupt

On Sat, May 30, 2020 at 5:11 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On 2020-05-30 11:07, Anup Patel wrote:
> > Instead of directly calling RISC-V timer interrupt handler from
> > RISC-V local interrupt conntroller driver, this patch implements
> > RISC-V timer interrupt as a per-CPU interrupt using per-CPU APIs
> > of Linux IRQ subsystem.
> >
> > Signed-off-by: Anup Patel <anup.patel@....com>
> > Reviewed-by: Atish Patra <atish.patra@....com>
> > ---
> >  arch/riscv/include/asm/irq.h      |  2 --
> >  drivers/clocksource/timer-riscv.c | 41 ++++++++++++++++++++++++++++---
> >  drivers/irqchip/irq-riscv-intc.c  |  8 ------
> >  3 files changed, 38 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/irq.h
> > b/arch/riscv/include/asm/irq.h
> > index a9e5f07a7e9c..9807ad164015 100644
> > --- a/arch/riscv/include/asm/irq.h
> > +++ b/arch/riscv/include/asm/irq.h
> > @@ -10,8 +10,6 @@
> >  #include <linux/interrupt.h>
> >  #include <linux/linkage.h>
> >
> > -void riscv_timer_interrupt(void);
> > -
> >  #include <asm-generic/irq.h>
> >
> >  #endif /* _ASM_RISCV_IRQ_H */
> > diff --git a/drivers/clocksource/timer-riscv.c
> > b/drivers/clocksource/timer-riscv.c
> > index c4f15c4068c0..1fe847983f50 100644
> > --- a/drivers/clocksource/timer-riscv.c
> > +++ b/drivers/clocksource/timer-riscv.c
> > @@ -12,8 +12,11 @@
> >  #include <linux/cpu.h>
> >  #include <linux/delay.h>
> >  #include <linux/irq.h>
> > +#include <linux/irqdomain.h>
> >  #include <linux/sched_clock.h>
> >  #include <linux/io-64-nonatomic-lo-hi.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/of_irq.h>
> >  #include <asm/smp.h>
> >  #include <asm/sbi.h>
> >
> > @@ -39,6 +42,7 @@ static int riscv_clock_next_event(unsigned long
> > delta,
> >       return 0;
> >  }
> >
> > +static unsigned int riscv_clock_event_irq;
> >  static DEFINE_PER_CPU(struct clock_event_device, riscv_clock_event) =
> > {
> >       .name                   = "riscv_timer_clockevent",
> >       .features               = CLOCK_EVT_FEAT_ONESHOT,
> > @@ -74,30 +78,36 @@ static int riscv_timer_starting_cpu(unsigned int
> > cpu)
> >       struct clock_event_device *ce = per_cpu_ptr(&riscv_clock_event, cpu);
> >
> >       ce->cpumask = cpumask_of(cpu);
> > +     ce->irq = riscv_clock_event_irq;
> >       clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
> >
> > -     csr_set(CSR_IE, IE_TIE);
> > +     enable_percpu_irq(riscv_clock_event_irq,
> > +                       irq_get_trigger_type(riscv_clock_event_irq));
> >       return 0;
> >  }
> >
> >  static int riscv_timer_dying_cpu(unsigned int cpu)
> >  {
> > -     csr_clear(CSR_IE, IE_TIE);
> > +     disable_percpu_irq(riscv_clock_event_irq);
> >       return 0;
> >  }
> >
> >  /* called directly from the low-level interrupt handler */
> > -void riscv_timer_interrupt(void)
> > +static irqreturn_t riscv_timer_interrupt(int irq, void *dev_id)
> >  {
> >       struct clock_event_device *evdev = this_cpu_ptr(&riscv_clock_event);
> >
> >       csr_clear(CSR_IE, IE_TIE);
> >       evdev->event_handler(evdev);
> > +
> > +     return IRQ_HANDLED;
> >  }
> >
> >  static int __init riscv_timer_init_dt(struct device_node *n)
> >  {
> >       int cpuid, hartid, error;
> > +     struct device_node *child;
> > +     struct irq_domain *domain;
> >
> >       hartid = riscv_of_processor_hartid(n);
> >       if (hartid < 0) {
> > @@ -115,6 +125,23 @@ static int __init riscv_timer_init_dt(struct
> > device_node *n)
> >       if (cpuid != smp_processor_id())
> >               return 0;
> >
> > +     domain = NULL;
> > +     for_each_child_of_node(n, child) {
> > +             domain = irq_find_host(child);
> > +             if (domain)
> > +                     break;
> > +     }
>
> This is a bit clumsy, and probably better written as:
>
>          child = of_get_compatible(n, "riscv,cpu-intc");
>          if (!child) { error out }
>          domain = irq_find_host(child);

I thought of not hard-coding INTC compatible string here but
both RISC-V INTC and RISC-V Timer are RISC-V specific so
I guess it's simpler to use of_get_compatible() directly.

I will update.

>
> It would be even better if each CPU would have its per-CPU interrupt
> controller designated as such (with an interrupt-parent property),
> meaning that you wouldn't have to do anything at all.
>
> Too late for that anyway.

Yes, too late now.

Regards,
Anup

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