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

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Message-ID: <87ilu67tvw.wl-maz@kernel.org>
Date:   Wed, 26 Jan 2022 09:01:39 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Anup Patel <apatel@...tanamicro.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Atish Patra <atishp@...shpatra.org>,
        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 2/6] irqchip/riscv-intc: Set intc domain as the default host

On Wed, 26 Jan 2022 03:16:55 +0000,
Anup Patel <anup@...infault.org> wrote:
> 
> On Tue, Jan 25, 2022 at 11:47 PM Marc Zyngier <maz@...nel.org> wrote:
> >
> > On Tue, 25 Jan 2022 05:42:13 +0000,
> > Anup Patel <apatel@...tanamicro.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@...tanamicro.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.
> 
> In absence of INTC as the default domain, currently we have various
> drivers looking up INTC irq_domain from DT (or ACPI). This is quite a
> bit of duplicate code across various drivers.
>
> How about having a irq_domain lookup routine (riscv_intc_find_irq_domain())
> exported by the RISC-V INTC driver or arch/riscv ?
> OR
> Do you have an alternative suggestion ?

But *why* don't you provide an interrupt controller node for DT? I
really don't think that's outlandish to require.

For ACPI, we already have an interface that allows a fwnode to be
registered (acpi_set_irq_model) and interrupts mapped
(acpi_register_gsi).

You should already have all the required tools you need.

	M.

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