linux-kernel - Re: [PATCH v3 2/6] irqchip/riscv-intc: Allow drivers to directly discover INTC hwnode

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Message-ID: <CAAhSdy2abxjz2GAF7dTbxDa32244wEJeYBCeuY2Ag84HK_FXow@mail.gmail.com>
Date:   Mon, 21 Feb 2022 15:25:05 +0530
From:   Anup Patel <anup@...infault.org>
To:     Marc Zyngier <maz@...nel.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>,
        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 v3 2/6] irqchip/riscv-intc: Allow drivers to directly
 discover INTC hwnode

On Mon, Feb 21, 2022 at 3:21 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Sun, 20 Feb 2022 05:08:50 +0000,
> Anup Patel <apatel@...tanamicro.com> wrote:
> >
> > Various RISC-V drivers (such as SBI IPI, SBI Timer, SBI PMU, and
> > KVM RISC-V) don't have associated DT node but these drivers need
> > standard per-CPU (local) interrupts defined by the RISC-V privileged
> > specification.
> >
> > We add riscv_get_intc_hwnode() in arch/riscv which allows RISC-V
> > drivers not having DT node to discover INTC hwnode which in-turn
> > helps these drivers to map per-CPU (local) interrupts provided
> > by the INTC driver.
> >
> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > ---
> >  arch/riscv/include/asm/irq.h     |  4 ++++
> >  arch/riscv/kernel/irq.c          | 19 +++++++++++++++++++
> >  drivers/irqchip/irq-riscv-intc.c |  7 +++++++
> >  3 files changed, 30 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/irq.h b/arch/riscv/include/asm/irq.h
> > index e4c435509983..43b9ebfbd943 100644
> > --- a/arch/riscv/include/asm/irq.h
> > +++ b/arch/riscv/include/asm/irq.h
> > @@ -12,6 +12,10 @@
> >
> >  #include <asm-generic/irq.h>
> >
> > +void riscv_set_intc_hwnode_fn(struct fwnode_handle *(*fn)(void));
> > +
> > +struct fwnode_handle *riscv_get_intc_hwnode(void);
> > +
> >  extern void __init init_IRQ(void);
> >
> >  #endif /* _ASM_RISCV_IRQ_H */
> > diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> > index 7207fa08d78f..ead92432df8c 100644
> > --- a/arch/riscv/kernel/irq.c
> > +++ b/arch/riscv/kernel/irq.c
> > @@ -7,9 +7,28 @@
> >
> >  #include <linux/interrupt.h>
> >  #include <linux/irqchip.h>
> > +#include <linux/irqdomain.h>
> > +#include <linux/module.h>
> >  #include <linux/seq_file.h>
> >  #include <asm/smp.h>
> >
> > +static struct fwnode_handle *(*__get_intc_node)(void);
> > +
> > +void riscv_set_intc_hwnode_fn(struct fwnode_handle *(*fn)(void))
> > +{
> > +     __get_intc_node = fn;
> > +}
> > +EXPORT_SYMBOL_GPL(riscv_set_intc_hwnode_fn);
>
> We're talking about the root interrupt controller here. How can this
> ever be implemented as a module?

Okay, I will drop the EXPORT() from here.

>
> > +
> > +struct fwnode_handle *riscv_get_intc_hwnode(void)
> > +{
> > +     if (__get_intc_node)
> > +             return __get_intc_node();
> > +
> > +     return NULL;
> > +}
> > +EXPORT_SYMBOL_GPL(riscv_get_intc_hwnode);
> > +
> >  int arch_show_interrupts(struct seq_file *p, int prec)
> >  {
> >       show_ipi_stats(p, prec);
> > diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
> > index b65bd8878d4f..fa24ecd01d39 100644
> > --- a/drivers/irqchip/irq-riscv-intc.c
> > +++ b/drivers/irqchip/irq-riscv-intc.c
> > @@ -92,6 +92,11 @@ static const struct irq_domain_ops riscv_intc_domain_ops = {
> >       .xlate  = irq_domain_xlate_onecell,
> >  };
> >
> > +static struct fwnode_handle *riscv_intc_hwnode(void)
> > +{
> > +     return (intc_domain) ? intc_domain->fwnode : NULL;
> > +}
>
> This makes no sense. Either you have found the interrupt controller
> and allocated the domain, or you haven't. But you don't register a
> callback without having found it.

We are registering this callback after creating the INTC domain.

>
> And you have totally ignored my previous comments about the multitude
> of irq domains for the INTC. Either you get rid of all but one and you
> can register a single fwnode, or you stay with what you have today,

Only the INTC DT nodes are per-CPU but we are creating only one
INTC domain to manage per-CPU IRQs across all CPUs.

Regards,
Anup

>
> You can't have it both ways.
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.