Re: [PATCH 2/6] irqchip/riscv-intc: Set intc domain as the default host

From: Marc Zyngier <maz@kernel.org>
To: Anup Patel <apatel@ventanamicro.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Atish Patra <atishp@atishpatra.org>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Anup Patel <anup@brainfault.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/6] irqchip/riscv-intc: Set intc domain as the default host
Date: Tue, 25 Jan 2022 18:17:50 +0000	[thread overview]
Message-ID: <87lez37k8h.wl-maz@kernel.org> (raw)
In-Reply-To: <20220125054217.383482-3-apatel@ventanamicro.com>

On Tue, 25 Jan 2022 05:42:13 +0000,
Anup Patel <apatel@ventanamicro.com> wrote:
> 
> We have quite a few RISC-V drivers (such as RISC-V SBI IPI driver,
> RISC-V timer driver, RISC-V PMU driver, etc) which do not have a
> dedicated DT/ACPI fwnode. This patch makes intc domain as the default
> host so that these drivers can directly create local interrupt mapping
> using standardized local interrupt numbers
> 
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
>  drivers/clocksource/timer-riscv.c | 17 +----------------
>  drivers/irqchip/irq-riscv-intc.c  |  9 +++++++++
>  2 files changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> index 1767f8bf2013..dd6916ae6365 100644
> --- a/drivers/clocksource/timer-riscv.c
> +++ b/drivers/clocksource/timer-riscv.c
> @@ -102,8 +102,6 @@ static irqreturn_t riscv_timer_interrupt(int irq, void *dev_id)
>  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) {
> @@ -121,20 +119,7 @@ static int __init riscv_timer_init_dt(struct device_node *n)
>  	if (cpuid != smp_processor_id())
>  		return 0;
>  
> -	domain = NULL;
> -	child = of_get_compatible_child(n, "riscv,cpu-intc");
> -	if (!child) {
> -		pr_err("Failed to find INTC node [%pOF]\n", n);
> -		return -ENODEV;
> -	}
> -	domain = irq_find_host(child);
> -	of_node_put(child);
> -	if (!domain) {
> -		pr_err("Failed to find IRQ domain for node [%pOF]\n", n);
> -		return -ENODEV;
> -	}
> -
> -	riscv_clock_event_irq = irq_create_mapping(domain, RV_IRQ_TIMER);
> +	riscv_clock_event_irq = irq_create_mapping(NULL, RV_IRQ_TIMER);
>  	if (!riscv_clock_event_irq) {
>  		pr_err("Failed to map timer interrupt for node [%pOF]\n", n);
>  		return -ENODEV;
> diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
> index b65bd8878d4f..9f0a7a8a5c4d 100644
> --- a/drivers/irqchip/irq-riscv-intc.c
> +++ b/drivers/irqchip/irq-riscv-intc.c
> @@ -125,6 +125,15 @@ static int __init riscv_intc_init(struct device_node *node,
>  		return rc;
>  	}
>  
> +	/*
> +	 * Make INTC as the default domain which will allow drivers
> +	 * not having dedicated DT/ACPI fwnode (such as RISC-V SBI IPI
> +	 * driver, RISC-V timer driver, RISC-V PMU driver, etc) can
> +	 * directly create local interrupt mapping using standardized
> +	 * local interrupt numbers.
> +	 */
> +	irq_set_default_host(intc_domain);

No, please. This really is a bad idea. This sort of catch-all have
constantly proven to be a nuisance, because they discard all the
topology information. Eventually, you realise that you need to know
where this is coming from, but it really is too late.

I'd rather you *synthesise* a fwnode (like ACPI does) rather then do
this.

	M.

-- 
Without deviation from the norm, progress is not possible.

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