linux-kernel - Re: [PATCH v6 4/6] clocksource/drivers/timer-riscv: Use per-CPU timer interrupt

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Message-ID: <e9a832ec748671b4daef398ecf784db2@kernel.org>
Date:   Sat, 30 May 2020 12:41:22 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Anup Patel <anup.patel@....com>
Cc:     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>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 4/6] clocksource/drivers/timer-riscv: Use per-CPU timer
 interrupt

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);

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.

         M.
-- 
Jazz is not dead. It just smells funny...